Iain Martyn & Tatiane Kanno share their experiences of the discovery of the human organizer
“It’s alive!” Iain’s first impressions
“Hybrid human chicken embryos: HALF HUMAN – HALF CHICKEN abomination created in US lab” was my favourite headline reporting on our work1. While the headline and accompanying article managed to miss the science completely, the author may have been surprised to know how close he or she came to capturing mood of that first, Frankenstein-like moment of discovery of the “abomination”.
For starters, it really was a dark and stormy night. The lab, high on the seventh floor of a sheer, grey, impenetrable tower, was deserted and silent. Only the intermittent odd hum and hiss of an incubator or the sound of rain and wind lashing on the windows broke the stillness and betrayed the presence of something living and growing in its confines. Far below, next to the seething, storm-overloaded river, a hunched figure made its way hurriedly across a narrow bridge towards the tower.
That would of course be me, making the dash from my apartment to the lab foolishly without a rain-jacket and trying not to get soaked. Almost exactly 24 hours previously I had grafted human embryonic stem cells into a developing chicken embryo, a long-shot search for the never-before-seen human organizer, and now it was time to check the result. What exactly was I going to see? What would it look like? A monster? Some sort of bird-human chimera? Despite the gothic atmosphere I thought to myself it was more likely that all I was going to see was a mess of dead or dying cells. This was after all my first attempt and I was a novice at chick embryology. The only reason I was here at this midnight hour in the first place was because I had run late the night before, taking over six hours to set up what any half-competent chick embryologist could do in two. Still, as I made my way into the darkened lab, took the grafts from the incubator, and loaded them onto the microscope, I could not help the apprehension rise within me.
In the first dish the cells were indeed dead or dying, torn apart by a clumsy error made during the grafting. In the second dish the graft was alive, but relatively unchanged from last night, undisturbed by the developing host chick and not disturbing it in turn. In the third dish…well three really is a lucky number: in the third dish was a little “abomination”. There, besides the normally developing host chick, the fluorescently tagged human cells had grown, expanded their area, and fused with the host tissue. More dramatically, they had also coalesced and grown into a long thin rod-like structure, emanating from the center of the graft and pointing like a dismembered finger towards the host. This is the point where lightning should have struck, thunder should have boomed, and I should have stood up and shouted “it’s alive!”, but I was more concerned with gathering evidence and recording what I saw. In fact, I think I only released the breath I’d been holding when I was sure I had taken two good pictures with the microscope’s camera and saw that they were each safely stored on the computer.
Good thing that I did as well, for none of the remaining grafts showed anything so remotely as dramatic. And when I returned to the successful graft the following morning to see if it had grown into anything even more remarkable I found only dead or dying cells. Those pictures and the memory of the previous night were all that remained, and if it were not for them, and not for that one successful graft, I might have given up and gone back to my co-PIs Ericand Alito report that it was a total failure. As it were, I became convinced that if it happened once it would happen again. The way forward to fully studying and proving the existence of the human organizer was still long and difficult, and it required teaming up with a bona fide chick embryologist, but after that night I was sure we could get there.
Iain and Tati conducting graft experiments
“…but what is it?” The striking moment for Tati
My story in the Brivanlou lab begins before I join the team as a postdoc, not so very long ago. At that time, I was a PhD student visiting the lab to learn and perform some experiments with embryonic stem cells. When I finished my internship, I returned to Brazil to defend my thesis. Few months went by and there I was, coming back to New York.
It was my first day back as an official lab member when I first came across this project. I remember being in the conference room, feeling that mixture of excitement and anxiety for starting a new chapter in my career when I heard “Hey, welcome back! Can I show you something cool?” That was the moment when I was introduced to lucky embryo number 3. As an embryology enthusiast, I got thrilled with those pictures! Some ideas had already started to pop up in my mind. We teamed up to optimize the chick experiments and that was just the beginning of our long journey in search for the human organizer.
The first set of grafting took longer than I expected: even being very familiar with chick embryo manipulation, it was my first time trying to generate a chimera. It was late, I was exhausted and hungry crossing the narrow bridge back home, but I was also feeling an excitement and eagerness for the daybreak to see the results. As it turned out, our first grafted embryos looked more like a Picasso painting. I still think MoMa museum would love to exhibit our nightmarish sci-fi art. But a tweak here and there and we managed to keep the embryos alive and looking more… normal-ish! After that, it was a marathon. Besides the long hours in lab grafting, swayed by Brazilian forró songs and replenishing ATP with Iain’s hidden snacks, we also had to go through endless washing steps for in situ and long confocal imaging sessions.
And then, finally there it was! In the elongated structure emanating from the human cells we found expression of SOX2!! How awesome that could be?! To me, that was the mind-blowing moment, but of course I still had to hold my horses and wait for the in situ results of SOX3 probe to confirm our findings. SOX2 and SOX 3 were ectopically induced in chick cells that surrounded the human cells!! We had generated our very first chick-human chimera, our “Chuman”! Our results bring valuable insights into early human development.
This work was one of those “high risk, high reward” kinds of project. It could lead to an amazing discovery or could give us nothing. Gladly, with a wonderful teamwork, we got the reward!
Welcome to our monthly trawl for developmental biology (and other related) preprints!
This month we found a tranche of preprints getting deep into the mechanics of fly development, a clutch on organoids (retinal, cerebral, cortical!), an investigation into the role of gender in scientific collaboration, and a veritable zoo in our evo-devo section – from ladybirds to placozoans via pufferfish, hydra and choanoflagellates.
The preprints were hosted on bioRxiv, PeerJ, andarXiv. Let us know if we missed anything, and use these links to get to the section you want:
Amot regulates neuronal dendritic tree through Yap1
Katarzyna O. Rojek, Joanna Krzemien, Hubert Dolezyczek, Pawel M. Boguszewski, Leszek Kaczmarek, Witold Konopka, Marcin Rylski, Jacek Jaworski, Lars Holmgren, Tomasz J. Proszynski
Morphogen-Lineage Selector Interactions During Surface Epithelial Commitment
Sandra P Melo, Jillian M Pattison, Samantha N Piekos, Jessica L Torkelson, Elizaveta Bashkirova, Maxwell R Mumbach, Charlotte Rajasingh, Hanson Hui Zhen, Lingjie Li, Eric Liaw, Daniel Alber, Adam J Rubin, Gautam Shankar, Howard Y Chang, Paul A Khavari, Anthony E Oro
Francesconi, et al.’s transdifferentiation/reprogramming schema
Active fluctuations modulate gene expression in mouse oocytes
Maria Almonacid, Stephany El-Hayek, Alice Othmani, Isabelle Queguiner, Fanny Coulpier, Sophie Lemoine, Leïla Bastianelli, Christophe Klein, Tristan Piolot, Philippe Mailly, Raphaël Voituriez, Auguste Genovesio, Marie-Hélène Verlhac
Genome-scale oscillations in DNA methylation during exit from pluripotency
Steffen Rulands, Heather J Lee, Stephen J Clark, Christof Angermueller, Sebastien A Smallwood, Felix Krueger, Hisham Mohammed, Wendy Dean, Jennifer Nichols, Peter Rugg-Gunn, Gavin Kelsey, Oliver Stegle, Benjamin D Simons, Wolf Reik
How ladybirds get their spots, from Gautier, et al.’s preprint
The genomic basis of colour pattern polymorphism in the harlequin ladybird
Mathieu Gautier, Junichi Yamaguchi, Julien Foucaud, Anne Loiseau, Aurelien Ausset, Benoit Facon, Bernhard Gschloessl, Jacques Lagnel, Etienne Loire, Hugues Parrinello, Danny Severac, Celine Lopez-Roques, Cecile Donnadieu, Maxime Manno, Helene Berges, Karim Gharbi, Lori Lawson-Handley, Lian-Sheng Zang, Heiko Vogel, Arnaud Estoup, Benjamin Prud’homme
Transcriptomic atlas of mushroom development highlights an independent origin of complex multicellularity
Krisztina Krizsan, Eva Almasi, Zsolt Merenyi, Neha Sahu, Mate Viragh, Tamas Koszo, Stephen Mondo, Brigitta Kiss, Balazs Balint, Ursula Kues, Kerrie Barry, Judit Cseklye, Botond Hegedus, Bernard Henrissat, Jenifer Johnson, Anna Lipzen, Robin A. Ohm, Istvan Nagy, Jasmyn Pangilinan, Juying Yan, Yi Xiong, Igor V. Grigoriev, David S. Hibbett, Laszlo G. Nagy
Systematic Characterization of RhoGEF/RhoGAP Regulatory Proteins Reveals Organization Principles of Rho GTPase Signaling
Paul Markus Mueller, Juliane Rademacher, Richard D Bagshaw, Keziban Merve Alp, Girolamo Giudice, Loise E Heinrich, Carolin Barth, Rebecca L Eccles, Marta Sanchez-Castro, Lennart Brandenburg, Geraldine Mbamalu, Monika Tucholska, Lisa Spatt, Celina Wortmann, Maciej T Czajkowski, Robert William Welke, Sunqu Zhang, Vivian Nguyen, Trendelina Rrustemi, Philipp Trnka, Kiara Freitag, Brett Larsen, Oliver Popp, Philipp Mertins, Chris Bakal, Anne-Claude Gingras, Olivier Pertz, Frederick P Roth, Karen Colwill, Tony Pawson, Evangelia Petsalaki, Oliver Rocks
Kilohertz frame-rate two-photon tomography
Abbas Kazemipour, Ondrej Novak, Daniel Flickinger, Jonathan S Marvin, Jonathan King, Philip Borden, Shaul Druckmann, Karel Svoboda, Loren L Looger, Kaspar Podgorski
Precise tuning of gene expression output levels in mammalian cells
Yale S. Michaels, Mike B Barnkob, Hector Barbosa, Toni A Baeumler, Mary K Thompson, Violaine Andre, Huw Colin-York, Marco Fritzsche, Uzi Gileadi, Hilary M Sheppard, David JHF Knapp, Thomas A Milne, Vincenzo Cerundolo, Tudor A Fulga
Reproducible big data science: A case study in continuous FAIRness
Ravi K Madduri, Kyle Chard, Mike D’Arcy, Segun C Jung, Alexis Rodriguez, Dinanath Sulakhe, Eric W Deutsch, Cory Funk, Ben Heavner, Matthew Richards, Paul Shannon, Gustavo Glusman, Nathan Price, Carl Kesselman, Ian Foster
Applications are invited for a four-year funded PhD studentship to conduct research in developmental neurobiology under the supervision of Dr Alexander Fletcher and Prof. Marysia Placzek at the University of Sheffield.
This project is on the development of the hypothalamus, a brain structure with very similar anatomy across vertebrate species. We know that the hypothalamus is very important for mediating physiological homeostasis, yet its development remains poorly understood. This project will address this through a combination of gain-and loss-of function studies in vivo and ex vivo 3D culture with computational modelling.
This project is a great opportunity for a student interested in developmental neurobiology, who is keen to tackle new techniques and work in a truly interdisciplinary environment, acquiring programming and modelling skills and gaining expertise in tissue culture and imaging.
A four-year fully-funded EPSRC studentship is available to home students (British or EU nationality based in the UK) starting in October 2018. Please get in touch with Alexander Fletcher (a.g.fletcher@sheffield.ac.uk) for more details.
We are at the National Institute of Child Health and Human Development (NICHD) at NIH. Our lab is interested in understanding cell lineage differentiation, gene regulation and how non-coding DNA elements and the 3D architecture of chromosomes contribute to these processes during early mouse development.
Fully-funded postdoc positions for multiple years including health benefits
Opportunity to start your own research program or lead ongoing projects
The NIH research community is unparalleled in its size, diversity and resources
Possibility of living in a diverse, liberal and vibrant city: Washington DC
Or living in a calm residential area with great schools and good affordable housing , Bethesda and Rockville
Who you are:
You share our enthusiasm for epigenetics, gene regulation, nuclear organization and mouse development.
You have PhD-experience in one or more of the following: mouse development, mouse genetics, epigenetics, massively-parallel sequencing techniques or computational biology.
Apply: Send the following to gsrunit@gmail.com:
2 paragraph cover letter explaining your scientific trajectory and why you would like to join us.
CV and email contacts for 3 references.
The NIH is dedicated to building a diverse community in its training and employment programs.
An engineer position in cell biology and biomaterials is available starting from September 2018 in the group of André Le Bivic, at the Institute of Biology of Development of Marseille (IBDM), France. The project aims at understanding the impact of extracellular matrix stiffness on the development of human colon organoids, and in particular on the crosstalk between the matrix and the polarity complexes. The initial contract will be made for 12 months, with possible extension to up to 2 years.
We are seeking for a highly motivated candidate who will use a wide range of methods to support this interdisciplinary research project on the impact of extracellular matrix stiffness on epithelial morphogenesis. The main tasks of the engineer will be the preparation of organoid cultures in 3D from human colon samples and the development / optimization of different types of biocompatible matrices (collagen, BME, PEG or PAA etc.). Specifically, the job requires expert knowledge in the synthesis of biocompatible polymers. Some knowledge in cell biology (cell culture, transfection and immunostaining) and imaging (confocal microscopy, image analysis) would be a plus. The working language in the laboratory is English. Candidates are expected to be able to communicate in English.
A cover letter, a CV and the names of two referents must be sent to the following addresses: Elsa Bazellières: elsa.bazellieres@univ-amu.fr and André Le Bivic: andre.le-bivic@univ-amu.fr
The story behind melanocyte BACE2, posted by Yan Zhang and Richard White. You can read our recently published full article at Developmental Cell using this link.
Our story began six years ago when my mentor, Dr. Richard White, opened the zebrafish facility and showed me those swimming creatures. He pointed to one type with pigmented stripes and told me those are wild-type fish named AB. He caught one fish with a net and that fish very quickly jumped out of the net and escaped to a water reservoir, before I could have a closer look at her. I did not know that after that day, I would officially join a fish lab and have days and nights to observe those free swimming, free jumping animals.
That escaped fish has a stunning array of pigment patterns which is composed of three types of pigment cells: black melanophores, yellow or orange xanthophores and silvery iridophores (Parichy, 2003). While the tank next to it is filled with a transparent version, casper, where the black melanophores and the silvery iridophores are absent (White et al., 2008), some of the other fish have fuzzy pigmentation with a black tumor on the back. Those are melanomas due to uncontrolled growth of melanophores (Patton et al., 2005). I was fascinated by how diverse a pigment pattern can look like and why animals evolve them.
Animals do this for a reason. Dolphins and marlin have a darker upper surface and a white lower belly. They countershade themselves so that when seen from the top, the dark dorsal matches with deep water darkness and when seen from the bottom, the light colored belly mixes into a sunlit water above. This is one example of camouflage in front of predators. Female guppies prefer male guppies with more orange coloration, possibly because males fed on high-carotenoid diet could better reject interspecific allografts of scales and resist parasite infection, suggesting they have better immune function (Houde, 1997) – a nice example of how guppies use pigment color as a honest signal for health during sexual selection.
Our interests into Bace2 started when Dr. Richard White found out this gene is highly enriched in human melanoma, suggestive of oncogenic effects. We thought knocking it out would make melanomas less aggressive. But when we got zebrafish Bace2 mutants from the Sanger Center, the melanophores looked a lot “more” aggressive, an initially counterintuitive observation. It turned out this pigment mutant has super elongated melanophore cell projections, a structure named the dendrite. In mammals, melanocytes use these long dendrites to transfer melanin to neighboring keratinocytes, a process involved in tanning response to protect keratinocytes from UV-induced damage (Yamaguchi et al., 2007). Unlike mammals, zebrafish melanophores do not transfer melanin across cells, but instead traffic melanin intracellularly to modulate fish appearance (Logan et al., 2006). When melanin is aggregated around the nucleus, the fish looks lighter, and this typically occurs when fish are raised in a daylight environment. When the fish is raised in dark, melanin tends to be dispersed so that melanin covers more area and fish can match their dark-looking color with the environment. Even though zebrafish no longer use dendrites as a channel for melanin delivery, their melanophores can still be very dendritic especially when young melanophores are still actively developing. They likely use these dendrites for patterning and other ways of communicating with their neighbors. Mature melanophores lose those dendrites for unknown reasons, but not for the bace2 mutant, where their melanophores keep dendricity from embryos to adults (Figure 1).
(A) Brightfield imaging shows that the bace2-/- melanophores are hyperdendritic compared with WT fish (arrowhead) in the tail fin at 72 hpf. Labeling of the melanophore cell membranes (bottom panel) using the Tg(tyrp1b: membrane-mCherry) line demonstrates that this is due to a change in cell morphology rather than a redistribution of melanin.Figure 1. The zebrafish bace2-/- mutant has hyperdendritic melanophores. (B) These hyperdendritic melanophores are maintained into adulthood, and yield irregular stripe boundaries (arrowhead). Scale bars: (A, B middle and bottom) 100 μm; (B top) 0.5 cm.
We were intrigued by this out of control problem and sought to study why. We showed that Bace2 works during melanophore maturation, a time frame when melanophores turn on pigment genes and gain melanin. The question was how does it work? Bace2 is a cell-intrinsic sheddase which modulated cell morphology inside the melanophore lineage. We further sought to find out which protein is cleaved by Bace2 to exhibit all those phenotypes. We had no luck in the beginning. Pmel and Gpnmb are the two initial guesses as both of them are involved in melanin production and PMEL can be cut by BACE2 in mice (Rochin et al., 2013; Shimshek et al., 2016). But we soon found out those two substrates could not explain the melanophore dendricity. The research was stuck for a while. When I was even trying to grab everything I could find in our chemical room and threw them into fish to have a try, Dr. White came to me and said, why don’t we try an unbiased chemical screen?
The breakthrough came with a change in methodology. The chemical screen gave us an unexpected but fruitful hit. We found four chemicals able to convert bace2 mutant melanophores into normal looking ones, all of which converge on the same pathway-one that contains insulin, PI3K and mTOR. We realized this is something never studied before, a new PI3K/mTOR regulator that has a melanophore-specific consequence. All of the pieces came together. It turned out Bace2 itself cleaves the insulin receptor and this cleavage modulates how many functional insulin receptors are left on the cell membrane. In the mutant fish, Bace2 no longer cleaves it and melanophores have hyperactivated insulin/PI3K/mTOR which drives this uncontrolled dendricity. The driving force came from long distance, as we found that a brain-derived insulin peptide (insb) is the stimulating ligand that feeds into insulin receptor in this context.
There are other consequence associated with uncontrolled dendricity: those bace2 mutant melanophores are actively differentiating, actively dividing and wandering around to ectopic locations (Figure 2). We decided to name this bace2 mutant wanderlust as those melanophores like to explore the world, travel to new sites and are free of constraints.
Figure 2. bace2-/- mutants develop melanophores outside of the stripe during metamorphosis at 24 days post fertilization (dpf) (arrowhead). Scale bars: 100 μm.
One thing that emerged from this research is the power of unbiased approaches to a problem. We were stuck for a while, but the screen turned out to be the most efficient and rapid way to get to the answer. It’s one of the greatest things about the zebrafish, and has allowed us to connect things – insulin and melanophores – that would have been hard to guess otherwise.
Neurogenesis is understood as the process by which neural stem cells (NSCs) produce new neurons. In the adult mammalian brain, this process is known to persist in two restricted locations- the dentate gyrus (DG) region of the hippocampus (see figure below) and the lateral walls of the subventricular zone (Ming and Song, 2011). Neurogenesis has been reported to occur at a high pace during embryonic development, decrease rapidly during growth and maturity, and persist in the adult brain at very low levels. New born neurons in the mature brain have been affiliated with important functions including learning, memory and damage repair.
Dendrite development of newborn neurons (green) in the dentate gyrus. Red = cell nuclei marker. Adapted from published article.
Currently, researchers are focused on dissecting the mechanisms of neurogenesis in the adult brain to understand its unique self-repair strategies, which in turn have the potential to combat a variety of challenging neurodegenerative disorders. But do we know enough? Realistically, this is just the start of a new era in regenerative medicine, and the ‘Adult Neurogenesis 2018’ conference had just taken us a couple steps forward by showcasing cutting-edge research progress in this field.
Adult Neurogenesis 2018 was organised by Gerd Kempermann in collaboration with Abcam in the beautiful city of Dresden. The meeting was held in at the Center for Regenerative Therapies Dresden (CRTD) (see figure below) which currently hosts eighteen core groups in a network of 87 principal investigators from diverse research institutes on the Dresden campus, with expertise in biomedical fields extending from the biology of cells and tissues to biomaterials to nanoengineering. Gerd welcomed us all and initiated the meeting with a refreshing narrative, briefing us about what history has taught us, where we are headed, and the reason behind the field of adult neurogenesis.
Center for Regenerative Therapies Dresden (CRTD). Adapted from website
That adult neurogenesis occurs throughout life in mammals including humans has been confirmed by multiple studies and regularly published articles following Joseph Altman and Gopal Das’s original discovery over 50 years ago (Altman and Das, 1965). However, from Santiago Ramón y Cajal’s 90 year old harsh decree of adult brain being devoid of any neurogenesis (Cajal, 1991) to Arturo Alverez-Buylla and colleagues’ 2018 description of undetectable levels of neurogenesis in the adult human hippocampus (Sorrells et al., 2018), the field of adult neurogenesis has faced its fair share of obstacles (Kempermann et al., 2018).
There is a growing need not only to unravel the mystery behind adult neurogenesis, but also to develop technology that can provide universal and undeniable proof of its very nature, including its existence and features. Kempermann used these key facts to redefine the impact, importance and purpose of adult neurogenesis.
The Adult Neurogenesis 2018 meeting brought together some of the most influential and inspiring minds in the field of neurogenesis including, but not limited to, F. Gage, S. Jessberger, B. Berninger, S. Thuret, A. Schinder, L. Barry-Cuif, F. Calegari and M. Brand. It hosted a total of 24 talks and showcased 98 posters (see figure below) which allowed researchers from various parts of the world to share and connect with each other.
Poster presentation event during Adult Neurogenesis 2018 at CRTD, Dresden, Germany
The meeting provided excellent networking opportunities allowing interdisciplinary collaboration which will ultimately lead to increase in pace and quality of scientific research. Therefore, the very existence of the meeting itself, paved a path towards finding the answer to when and how are we going to able to understand and uncover the potential of adult neurogenesis. In this report, I have managed to highlight some of my personal favourites, which undoubtedly does not cover the entirety of topics covered in the meeting.
Heterogeneity: Similar but not identical
The beauty of adult neurogenesis lies in its complex diversity. Our brain contains different types and subtypes of neuronal and glial cells all with unique functions. Moreover, depending upon factors including temporal intracellular gradients, time of birth, localisation and differences in synaptic connections, cells expressing identical protein markers in the brain can show significantly varied functions. Fortunately, recent discoveries highlighting the in-depth heterogenic nature of the immature cells involved in adult neurogenesis have begun to elucidate some of the most challenging questions regarding complexity.
Vijay Adusumilli highlighted the heterogeneity within nestin expressing NSCs of the hippocampus at a given time. Nestin is a prominent NSC marker in vivo as well in vitro. Interestingly, nestin positive DG NSCs can themselves be split into groups based on their intracellular reactive oxygen species (ROS) content. His observations emphasised how intricate differences between NSCs can produce functional diversity of neurogenesis in our brain.
Jason Snyder provided us with details on differences and relationships between adult-born and developmentally-born neurons in the hippocampus. Snyder found that changes in adult neurogenesis were inversely proportional to the activity of developmentally-born neurons. He hypothesized that the interplay between adult and developmentally-born neurons plays an important role in the acquisition and turnover of information in the hippocampus.
Alejandro Schinder gave a refreshing introduction to the intricate neuronal connections of granule cells (GCs) in the DG of the hippocampus. His lab had previously demonstrated that immature GCs of DG undergo biased neuronal activation compared to mature neurons (Marín-Burgin et al., 2012), in contrast to other regions of the hippocampus and neocortex. This functional heterogeneity between mature and immature GCs provides insights into their possible role as pattern integrators and differential decoders of information in the DG.
Together, these talks gave us an idea of how heterogeneity within NSCs, and between NSCs and new born neurons, are key factors to consider during future research in translational neuroscience.
Control or to be controlled?
Expanded research in adult neurogenesis has not only helped us provide an unprecedented surveillance of brain development but has also given us a chance to repair brain damage. Since NSCs are known to be the fundamental units of brain regeneration, recent studies have focused on modulating their behaviour and thereby developing possible therapeutic strategies for neurodegenerative disorders. This meeting was able to showcase some of the important and newly discovered modulators of adult neurogenesis.
How is it controlled?
Autophagy is an intracellular degradation system for cytosolic proteins and organelles, which is critical for cellular homeostasis (Nixon, 2013). Iris Schäffner and her colleagues investigated the FoxO family of transcription factors with respect to regulation of autophagy in adult hippocampal neurogenesis. Schäffner hypothesized a novel pathway connecting FoxO-dependent autophagic flux to development of adult hippocampal neurons.
Tara Walker talked about how the number of new born DG neurons are kept in check. Regulation of DG neurogenesis involves the death of the majority of new born neurons. She hypothesized that a population of early hippocampal precursor cells die due to ferroptosis, an alternative form of cell death, and thus identified an additional mechanism by which adult hippocampal neurogenesis could be controlled.
Sandra Wendler was able to identify distinct roles of mitochondrial fusion dynamics in the lineage of adult NSCs in the hippocampus. Wendler was able to show that although mitochondrial fusion was dispensable for the proliferative steps of NSCs, this process becomes essential for the maturation and survival of neurons later on.
Sebastian Jessberger shared his discoveries on molecular mechanisms underlying neurogenesis with respect to lipid metabolism. He showed that Fasn, a key enzyme in de novo lipogenesis, was highly active in NSCs (see figure below) (Knobloch et al., 2013). His results provided functional coupling between regulation of lipid metabolism and adult NSC proliferation.
Fasn protein (red) is expressed in neural stem cells (green) in the hippocampus. Insets show high-power views of Fasn-expressing cells with 49,6-diamidino-2-phenylindole (DAPI; grey = cell nuclei). GCL – Granule cell layer. Adapted from published article.
Taken together, these talks provided some key examples of how adult neurogenesis is controlled in the brain. A complete picture of the intricate mechanisms underlying neurogenesis are still unknown. However, piece by piece, we have started understanding the secrets of how new born neurons are created and regulated.
How can we control it?
Georg Kuhn introduced physical exercise and enriched environment as modulators of adult neurogenesis. Kuhn explained how cardiovascular fitness and exercise are particularly important for prevention, delayed-onset or amelioration of CNS diseases including stroke and dementia (Åberg et al., 2009; Naylor et al., 2008). In parallel, Nora Abrous showed that spatial learning remodels not only new dentate neurons but also creates short term new networks within the hippocampus and long term new networks that extend beyond the hippocampus itself.
Moving deeper in a biological perspective, David Petrik showed how cells regulating adult neurogenesis are responsive to mechanical forces at the tissue level. Increased fluid flow along the walls of the lateral ventricle increased the proliferation of NSCs and this ability was dependent on Epithelial Sodium Channel (ENaC) (Petrik et al., 2018). The flow also controlled calcium oscillations in NSCs on the lateral wall, but not at a deeper niche depth, depicting specific spatial control of neurogenesis by fluid flow.
Federico Calegari took it to the cellular level, exploring whether or not cognitive impairment could be reversed in old age or compensated throughout life by extrinsically exploiting endogenous NSCs. His lab had previously developed a system that allowed temporal control of cdk4–cyclinD1 overexpression to control the number of neurons produced in vivo (Artegiani et al., 2011). This showed, for the first time, that neurogenesis can be controlled in an acute spatio-temporal manner that allowed to elucidate and control adult neurogenesis.
Taken together, these talks provided examples of how control can be imposed upon neurogenesis in the mammalian brain, both extrinsically and intrinsically. Following on, recent studies have started screening for factors that act as master regulators of NSC homeostasis to understand the extent to which we can control neurogenesis.
The truth to be told
The ultimate objective for unfolding the mysteries and unlocking the potential of adult neurogenesis is to provide a better quality of human life. However, due to the restricted localisation and diluted potential of adult neurogenesis in mammals, not to mention to the lack of human subjects, cellular regenerative therapies for the human brain is proceeding at a considerably slow pace. The conference addressed this issue by showcasing novel technological developments and innovative adaptations of pre-existing biomedical tools which can directly increase the speed and quality of discovery with respect to clinical translation.
Studying the properties of neurogenesis can have significant indirect benefits to clinical medicine. Sandrine Thuret talked about how differential neurogenesis can be used as a biomarker to detect the fate of disease pathology in humans. Her lab showed that differential response of NSCs to patient specific serum can be extended to predict conversion of mildly cognitive impaired patients to Alzheimer’s disease (AD) (Maruszak et al., 2017)
Identification of neurogenic regulators in disease models can serve as key players in restoring healthy physiology in patients with neurodegenerative disorders. Claire Rampon talked about how manipulating mitochondrial properties of new neurons can improve altered cellular properties of an AD mouse brain model and may open new avenues for far-reaching therapeutic strategies for cognitive impairment (Richetin et al., 2017).
Different animal models can have significantly varied neurogenic properties compared to humans which can be particularly useful in developing innovative strategies for human brain repair. Michael Brand talked about how zebrafish is not only an easier model for experimentation, but also provides an excellent source to study adult brain regeneration (Grandel et al., 2006; Kroehne et al., 2011). Brand discussed how zebrafish can be used to study thyroid regulation of adult neurogenesis, emphasising that the genetic factors underlying extensive regeneration in adult zebrafish may be a crucial key to unlock adult brain regeneration in humans.
Direct reprogramming of adult cells to neurons is an emerging technology which holds great promise for cell-based brain repair. Benedikt Berninger’s lab had identified resident pericytes (a non-neural cell type in the mature brain) to have the potential to be directly converted into neurons (see figure below) (Karow et al., 2012). Berninger talked about the nature of intermediate states taken up by reprogrammed pericytes towards neurogenesis. He showed that as they reprogram, cells pass through a neural stem cell-like state, and that this state is of functional importance for the reprogramming success (Karow et al., 2018-in press). This knowledge may provide new ways for further improving direct reprogramming and in turn, help overcome the scarcity of neurogenesis in the adult mammalian brain.
Time-lapse imaging of a brain pericyte reprogramming into a neuron. Mash-1 and Sox2 are the two transcription factors used for reprogramming. Blue arrow showing the cell of interest. Adapted from published article.
‘Real-time’ or ‘live’ imaging microscopes allow scientists to observe biological functions of cells and tissues in action. Using an intra-vital imaging procedure, Laure Bally-Cuif showed that her lab was able to dynamically image and track a full population of adult NSCs at a single cell resolution within their niche. This provided the power to deduce live aspects of stem cell behaviour over several weeks in vivo (Dray et al., 2015). Jessberger showed how clonal population derived from neurogenic events can be monitored in vivo using 2-photon microscopy (see figure below) (Pilz et al., 2018). He focused on the importance of using technically straightforward measures to study properties of neurogenesis in its native state.
Selected imaging time points for two radial-glia like neural stem cells (respectively indicated with open and filled arrowheads) over the course of 2 months, showing the emergence of two neuronal clones. Adapted from published article.
Fred Gage briefed us about our journey through adult neurogenesis, 2-photon microscopical advances and brain organoids. He showed how human brain organoids can be implanted into mice and observed while it integrates into the rodent CNS (see figure below) (Mansour et al., 2018). The motivation was to find a way to vascularize the human organoid to improve the survival and maturation of these 3-Dimensional human brain tissues to better understand human brain development and study human brain disorders.
Intracerebral grafting of human brain organoids into mouse brain. Red outlined grey tissue marks the whole mouse brain. Bright green tissue marks the implanted human brain organoid. Zoomed in box shows neurite outgrowth of implant into host mouse brain. Adapted from published article.
Taken together, these talks have emphasised how ground-breaking discoveries coupled with the outstanding development in biomedical technologies has allowed remarkable progress in this field, and provided us with a glimpse into the future and promise of adult neurogenesis.
Conclusion
In light of the recent developments in the field of adult neurogenesis, it is an exhilarating era to exist in. The ‘Adult Neurogenesis 2018’ meeting highlighted many inspiring and pioneering discoveries including insights into neurogenic heterogeneity, control of neurogenesis, and recent technological developments. Neurodegenerative disorders are extremely challenging and expensive to treat. The very discovery of neurogenesis to persist adult mammals including humans has filled us with hope. Given the pace of scientific research, the next few decades might just witness a major leap that humanity can take towards clinical neuroscience.
‘’If I were not in this field today, I would have joined after this conference’’-
We had some wonderful entries from across the field, and are delighted today to announce the winner: Antonio Barral Gil, a PhD student in Miguel Manzanares’ Lab at CNIC (The Spanish Center for Cardiac Research) in Madrid. Entrants were tasked with writing a short piece on the state of the field, and Antonio’s piece impressed the judges (the Node’s Community Manager Aidan Maartens and Development’s Executive Editor Katherine Brown) for its energy and excitement, as well as its style and content.
Congratulations Antonio!
Antonio obtained his Degree in Biotechnology in 2015 from the Universidad Pablo de Olavide (Sevilla). He then moved to Madrid, where in 2017 he got his Master’s in Molecular Biomedicine at the Universidad Autónoma de Madrid thanks to a CNIC scholarship. He carried out his Master’s thesis in Miguel Manzanares’ lab, focusing on characterizing the role of the transcription factor NANOG during gastrulation. He has recently started his PhD at the same lab, this time focusing on heart regeneration and development.
The meeting will be held in September; look out for Antonio’s report soon after!
The López-Schier laboratory at the Helmholtz Zentrum Munich in Germany is seeking creative and highly motivated PhD students or postdoctoral scholars to work within our group of 9 graduate students and postdoctoral fellows. The working language of the laboratory is English.
Our group focuses on understanding the development, regeneration and function of sensory systems. We use the zebrafish as experimental model, and integrate molecular, cellular, behavioural and clinical data. We also have developed new technical approaches to understand organogenesis, including cell-fate acquisition after regeneration from tissue-resident progenitor cells. Mutations in many of the genes that we have identified are responsible for neurological diseases and cancer.
We currently have a fully funded opening for the following projects:
Cellular and genetic bases of organogenesis, including cell packing and tissue remodelling. This project combines single-cell transcriptional profiling, genome engineering using CRISPR/Cas9 and quantitative live imaging data by light-sheet microscopy. Preference will be given to candidates with theoretical or practical knowledge in cell biology or biophysics.
Control of cell number, organ size and proportions. Using state of the art high-resolution cell tracking, optogenetics, genome engineering and machine learning, we attempt to understand how cells self-organize and to predict cellular behavior during the regenerative response after tissue injury. This project is ideal for a candidate with a background in physics or engineering and a good command of computer programming.
Qualifications & skills
– University studies in biology-related sciences, physics, engineering or computer science (PhD)
– Ideally having recently completed or about to complete a PhD (Postdoctoral)
– Having published or likely to publish at least one first-author paper in a
first/second tier journal (Postdoctoral)
– Candidates for all position should have a strong inner drive, independence, and willingness to work in a highly interdisciplinary team
– A good command of the English language is essential
Laboratory
The team’s projects are interdisciplinary, and are aimed at understanding the basic rules that allow sensory systems to develop, regenerate and function. We use confocal, spinning-disc and light-sheet microscopy imaging, biochemistry, genome engineering by CRISPR/Cas9, laser nanosurgery, optogenetics, and machine learning.
Environment
The Helmholtz Zentrum in an innovative, well-equipped and scientifically stimulating élite research centre located in the outskirts of Munich, one of the most attractive and innovative major cities in Germany. Situated at the foothills of the Alps, Munich is a cosmopolitan city that has ranked among those with the highest quality of life in Europe.
Contact
Please, apply via electronic mail only, including a cover letter with a short statement of research interests and motivation, a Curriculum Vitae including a list of names and email-addresses for two/three academic references, to:
Dr. Hernán López-Schier
Research Unit Sensory Biology & Organogenesis
Helmholtz Zentrum München
Ingolstädter Landstrasse 1
85764 Neuherberg – Munich, Germany
In early June, a group of 30 world-leading experts came together thanks to an invitation by the Company of Biologists to Wiston House (Sussex, UK) to discuss our current understanding about evolutionary and molecular mechanisms that contributed to developing the specific qualities of our human brains.
Fortunately, the Company of Biologists offers fully funded participation for up to ten young career scientists to attend these workshops, and I had the honor to take part in this extraordinary event. The workshop excelled at what many conferences strive for, but only few achieve: open discussion of unpublished data and the big outstanding questions in the field. What I as a youngster appreciated most about the experience was the accepting atmosphere during discussions on- and offline, which was aided by the young participants being offered the same amount of time to present their work in talks as the senior scientists. This even playing field fueled optimism and inspiration for future cross-disciplinary collaborations. This was further facilitated by the workshop bringing together people working on many different aspects of human brain evolution and development: geneticists, to molecular and cellular biologists, behavioralists, anthropologists, mathematicians and engineers. All were united in the goal of understanding how our brain turned out to be so strikingly different, but also in some aspects so similar, when compared to other mammalian species.
I much appreciated the interspersed discussion sessions led by the three organizers, Arnold Kriegstein, Victor Borrell and Wieland Huttner, which pushed the leading edge of the field to inspire creative thoughts about new directions to take. The participants scratched their heads and engaged in lively discussions concerning some of the big new findings in the field and how to integrate those across scales of investigation from genetics to biophysical models and behavioral outcomes. For instance, we discussed the origin and implications of having a folded cortex with gyri and sulci, their variability and inheritance, whether or not cortical folding is “simply” an epiphenomenon that is only mechanically induced, and what the temporal relationship between folding and connectivity may be. Participants presented interesting data on model systems to approach these questions, including exciting work on brain diseases related to folding and ferrets as a suitable and tractable animal model of a folded brain. Relatedly, when it comes to recent technological advances concerning model systems for human brain development, organoids, three-dimensional cellular networks derived from human ES or induced pluripotent stem cells, are a highly intriguing opportunity that allows for genetic accessibility and experimental control recapitulating many of the early steps of in vivocortical development. It is certainly an exciting time for this technology, which has the potential to fruitfully contribute to our understanding of genetic and cellular events that shape early circuit formation in human neuronal networks.
Throughout the course of the workshop, a lot of emphasis was put on the unique proliferative events that allow for the human brain to accumulate its staggering number of neurons. In the closing discussion session, it was discussed that on top of the sheer number of neurons, it will be important to further our understanding of how different cell types with human-specific molecular signatures contribute to certain traits of the human brain. Relatedly, understanding how synapses and neuronal connectivity may have been shaped differently during human evolution will help our understanding of functional consequences of early developmental events thought to be unique to humans.
Altogether, I am tremendously grateful for having been given the opportunity to attend this workshop and follow the inspiring discussions that certainly broadened my perspective and gave a sense of where the field will move to in the years to come. Wiston House is an amazing place for an event like this, peaceful and remote, in a beautiful landscape that cannot help but inspire creative thinking and groundbreaking new collaborations through thought-sharing. I cannot thank the Company of Biologists, and Wiston House staff enough for providing this unexampled setting to answer unique questions about the mysteries of the past and present existence of our elusive human brains.
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