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Eye-ing the body electric

Posted by , on 20 December 2011

How do you make an eye? One early trigger for eye formation in Xenopus, as a new Development paper from Michael Levin’s lab shows, is a small change in bioelectric signals. In fact, that trigger alone is enough to induce eye development in other parts of the body.

In an experiment that measured regions of hyperpolerization in the developing Xenopus embryo, the researchers found two small hyperpolarized spots in the anterior neural field – exactly where the eyes are later formed. Was this change in transmembrane potential (Vmem) related to eye development? To find out, the group carried out a series of experiments to show that the hyperpolarized cells were indeed the same cells that later formed the eye. Not only that, but depolarizing these cells disrupted eye development, suggesting that the transmembrane potential is part of a required signalling mechanism for eye formation.

Eye development involves the formation of an “eye field” from a region of the anterior neural field. This is regulated by eye field transcription factors (EFTFs) such as Pax6 and Rx1. Levin and his colleagues demonstrated that the transmembrane potential in the eye field regulates expression of these EFTFs. When they depolarized the hyperpolarized cells in the eye field, expression levels of Pax6 and Rx1 went down, which explains why eye development was affected upon depolarization.

But what happens if you alter the Vmem not just in the region where eyes are normally formed, but in other parts of the body? To test this, the researchers globally disrupted the Vmem by introducing dominant negative potassium channel subunits into all four blastomeres of four-cell embryos. Within the eye region, the results were as before: many of the embryos did not form functional eyes in the eye region when the Vmem was disrupted. And outside of the eye region? After just changing the transmembrane potential, eyes started to pop up in different parts of the body! Several of the embryos now developed eye tissue in the gut area, and these ectopic eyes have morphological characteristics very similar to regular, functional, eyes.

Ectopic eye, with lens, formed on a tadpole’s gut.

Eye formation caused by a change in transmembrane potential outside of the eye region was also associated with an upregulation of the expression of eye field transcription factors Pax6 and Rx1, suggesting that a bioelectric signal alone is sufficient to initiate the molecular mechanisms required for eye development.

So why don’t we have eyes everywhere? In the discussion section of the paper, the authors hypothesize that a narrow, specific, range of Vmem is associated with the development of particular tissues. This suggests that the eye region is the only area where the Vmem is at the optimal level to upregulate the required transcription factors at the right moment in development to form an eye.

Bioelectric signals also control other physiological processes, such as cell migration and wound healing, but this is the first study that shows a role of bioelectric parameters in eye development.

Development is more than gene regulation alone, and we’re slowly starting to find out all the mechanisms and processes that work together to form organs and organisms.

ResearchBlogging.orgPai, V., Aw, S., Shomrat, T., Lemire, J., & Levin, M. (2011). Transmembrane voltage potential controls embryonic eye patterning in Xenopus laevis Development DOI: 10.1242/dev.073759

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In Development this week (Vol. 139, Issue 2)

Posted by , on 20 December 2011

Here are the highlights from the current issue of Development:

 

Balanced ephrin/Eph signals drive topographic mapping

During development of the retinotectal axonal projection, which connects the retina to the optic tectum in the midbrain, the axons of neighbouring retinal ganglion cells project to neighbouring positions in the optic tectum (topographical mapping). However, although retinal fibres rigidly target their destinations in some experimental circumstances, in others they adapt to grossly diverse targets. Here (see p. 335), Franco Weth and colleagues present a surprisingly simple model that explains these hitherto puzzling discrepancies. In this model, topographical axonal mapping relies solely on the balance of forward and reverse signalling by the ephrin/Eph family of guidance molecules. To test their model, the researchers develop a novel ephrin/Eph (double-cue) stripe assay and show experimentally that the simultaneous presence of forward and reverse ephrin/Eph signalling is indeed sufficient for appropriate topographic growth decisions in chick embryonic nerve fibres. Moreover, using computer simulations, they show that their new model is capable of reproducing the discrepant data collected over the years on topographic mapping by the retinotectal axonal projection.

Complex dance of eye morphogenesis unveiled

Optic cup morphogenesis (OCM), which generates the basic structure of the vertebrate eye, is usually depicted as a series of epithelial sheet folding events but experimental evidence to support this stepwise model is lacking. Now, Kristen Kwan, Chi-Bin Chien and colleagues investigate the cellular dynamics of OCM in zebrafish by combining four-dimensional time-lapse imaging and cell tracking (see p. 359). The researchers show that OCM depends on a complex set of sometimes unanticipated cell movements that are coordinated between the prospective neural retina, retinal pigmented epithelium and lens, the tissues that comprise the mature optic cup. Using their cell tracking data, the researchers construct subdomain fate maps for these three tissues that might provide clues to developmental signalling events. Finally, they show that similar movements occur during chick eye morphogenesis, which suggests that the complex choreography of cell movements that shape the vertebrate eye is conserved. These new insights into eye development could, therefore, help to improve our understanding of human eye defects.

Shedding light on Rho kinase signalling

Small-molecule inhibitors can be used as loss-of-function tools to investigate the molecular mechanisms of development but, although exposure to these inhibitors can be temporally controlled, their effects are not spatially restricted. Now, Nanette Nascone-Yoder and colleagues have generated a pharmacological agent that allows for photoactivatable, and hence spatiotemporally limited, inhibition of Rho kinase (see p. 437). Rho signalling is involved in many morphogenetic events, including primitive gut elongation in Xenopus embryos. The researchers install a photolabile ‘caging’ group on Rockout, a small-molecule inhibitor of Rho kinase, and show that caged Rockout (cRO) can permeate Xenopus embryonic tissues. When cultured in the dark, cRO-treated embryos develop normally, but UV irradiation of the right side of these embryos produces animals with a unilaterally shortened gut. Finally, the use of cRO reveals a differential requirement for Rho signalling on the left and right sides of the gut during intestinal rotation. Photocaging pharmacological inhibitors, the researchers conclude, might be a generalisable technique for producing loss-of-function reagents for use in multiple developmental contexts.

The eyes have it: bioelectric induction

Endogenous steady-state ion currents, voltage gradients and electric fields produced by ion channels and pumps regulate patterning and have been implicated in adult eye wound healing. So might they play a role in eye development? On p. 313 Michael Levin and co-workers report that transmembrane voltage potential (Vmem) is an important component of the eye induction cascade in Xenopus. The researchers identify a hyperpolarised cluster of cells in the anterior neural field of Xenopus embryos and show that depolarisation of the lineages from which these cells are derived results in malformed eyes. Remarkably, given our understanding of lineage restrictions and plasticity, manipulation of Vmem in non-eye cells induces ectopic eye formation far outside the anterior neural field. Other experiments show that a Ca2+ channel-dependent pathway transduces the Vmem signal and regulates the pattern of eye field transcription factor expression. This new information on the roles of voltage gradients as mediators of patterning during embryogenesis might have implications for the development of regenerative approaches to ocular diseases. (See also this post on the Node.)

Heads up for neural specification

During mouse embryogenesis, the anterior ectoderm develops into neural derivatives (the forebrain) and non-neural derivatives (the cephalic non-neural ectoderm). On p. 423, Kirstie Lawson, Anne Camus and co-workers use single-cell labelling and gene expression analysis to provide new insights into this cell fate choice. At late gastrulation, they report, the expression patterns of anterior ectoderm genes overlap significantly and correlate with areas of prospective fate but do not define lineages. They show that the rostral limit to forebrain contribution is more distal than previously reported. Finally, they report that some precursors of the anterior neural ridge, a signalling centre that is involved in forebrain development and patterning, are clonally related to neural ectoderm and are dispersed over a broad area of the anterior ectoderm where neural precursors also reside. Together, these results suggest that, although the segregation of neural and non-neural cells in the anterior ectoderm is incomplete at the gastrulation stage, there are elements of regionalisation in this tissue that preconfigure the organisation of the head.

ROCK solid epithelial organisation

The basement membrane is essential for epithelial tissue organisation and function but what restricts the basement membrane to the basal periphery of epithelial tissues and what are the basement membrane-mediated signals that regulate coordinated tissue organisation? On p. 411, Melinda Larsen and colleagues use cultures of embryonic mouse submandibular salivary glands to investigate these questions. They show that inhibition of the Rho kinase ROCK in these cultures results in basement membrane accumulation throughout the epithelial compartment. ROCK-mediated control of Par-1b localisation in the outer basal epithelial cell layer (which produces basement membrane) is responsible for normal basal basement membrane positioning, they report. Moreover, inhibition of Par-1b kinase activity prevents basement membrane deposition and disrupts tissue organisation. Conversely, overexpression of Par-1b drives ectopic basement membrane production. These and other results suggest that Par-1b is a master regulator of basement membrane deposition in developing salivary glands and that ROCK control of Par-1b function is essential for normal epithelial integrity and organisation.

PLUS…

When cell cycle meets development

The recent Company of Biologists workshop ‘Growth, Division and Differentiation: Understanding Developmental Control’, which was held in September 2011 at Wiston House, West Sussex, UK. Kaldis and Richardson   review the common themes that emerged from the meeting, highlighting novel insights into the interplay between regulators of cell proliferation and differentiation during development.

See the Meeting Review on p. 225

Palatogenesis: morphogenetic and molecular mechanisms of secondary palate development

Mammalian palatogenesis is a highly regulated morphogenetic process, the complexity of which is reflected by the common occurrence of cleft palate in humans. Here, Bush and Jiang review major advances in our understanding of the mechanisms that control secondary palate development.

 See the Review Article on p. 231

Shaping sound in space: the regulation of inner ear patterning

Groves and Fekete review recent studies of inner ear development and patterning, which reveal that multiple stages of ear development are orchestrated by gradients of signaling molecules.

See the Review Article on p. 245

 

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Book review: An introduction to mathematical biology

Posted by , on 15 December 2011

This book review originally appeared in Development. Lance Davidson reviews “Mathematical Models of Biological Systems” (by Hugo van den Berg).

Book info:
Mathematical Models of Biological Systems By Hugo van den Berg Oxford University Press (2010) 256 pages ISBN 978-0-19-958218-1 (paperback), 978-0-19-958219-8 (hardback) £27.50/$49.50 (paperback), £65/$117 (hardback)

One of the key goals of modern cell and developmental biology is to expose the underlying principles that drive cell differentiation and to elucidate how organisms construct functional multicellular structures. Thanks to advances in sequencing, high throughput screens and sophisticated imaging technologies, these fields are now awash with quantitative descriptions of gene transcription, cell signaling and cell mechanics. However, extracting key principles from the flood of new data is a major challenge for researchers and a central obstacle to fundamental progress in cell and developmental biology. The tools required to interpret this vast amount of biological data and to test hypotheses based on these studies can be found in quantitative analysis and mathematical modeling. With the book Mathematical Models of Biological Systems, Hugo van den Berg aims to contribute to the training of a new generation of biologists and mathematicians and to provide them with an introduction to the methods that are now available to quantitatively analyze biological data.

Like many quantitative biologists, my first exposure to mathematical modeling was not in the context of cell biology or developmental biology, but came through examples from physical chemistry, physiology and population ecology. In these fields, simple problems can be formulated using ordinary differential equations (ODEs) with complete statements of the state variables, such as initial conditions. As students, we learned to write ‘word-models’ and to translate these into sets of ODEs. Word models are narrative passages intended to translate the details of a biological problem such that biologists and mathematicians alike can understand the problem in a way that allows equations to be written which capture those details. For instance, we can distil the interactions between predators and prey by stating the rules that govern their populations. Rules that govern the population of prey might include sources of population growth, such as birth or migration, and losses to the population due to predation or disease. The precise statement of these rules should be complete enough to govern the mathematical formulation of the model. Given a well-defined word model, the mathematical biologist can then write a series of ODEs; for example, with variables that represent the number of predators and prey and equations to describe how populations of predators and prey change. As students, we sometimes discovered that there were closed form solutions of these ODEs, in which changes in variables can be predicted explicitly by equations. But more often we found that we could only evaluate the general dynamic behavior of the variables; for instance, whether populations of predators and prey are stable or not. The insights and training that these model-building exercises gave us were instrumental in becoming fluent in the basic skills of mathematical modeling. The processes of formulating a model and relating fundamental principles to the mathematics and experimental outcomes were often more informative than the solution itself. However, after marveling at the awesome power of ODEs, we soon realized that the solution of some, or indeed most sets of, ODEs was intractable, that there was no way to capture relevant details of complex biology with continuous variables, or that model predictions could not be tested experimentally. As such, the tool kit of ODEs used to learn the skills of mathematical modeling is less useful for developing the quantitative models that are needed to describe problems in cell and developmental biology.

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Dates for your calendar

Posted by , on 9 December 2011

Dates for your calendar
This is a selection of upcoming dates of interest, but it’s by no means an exhaustive list. We’ll try to do these once in a while, but don’t hesitate to write your own posts to let people know about similar deadlines, or leave a comment below. Also make sure to check eligibility before applying.

Conference Registration now open:
ISSCR meeting (June 13-16, 2012)
BSDB meeting (April 15-18, 2012)
LASDB meeting (April 26-29, 2012) – early deadline closes December 12!
-Keystone: The Life of a Stem Cell: From Birth to Death (Mar 11-16, 2012) – early deadline closes January 11, Abstract deadline closes December 13.
-Keystone: Non-Coding RNAs with Eukaryotic Transcription (Mar 31-Apr 5, 2012) – early deadline closes January 30, Abstract deadline closes January 5
-EMBO: Plant development and environmental interactions (27 – 30 May, 2012) – registration and abstract submission closes February 15.
-EMBO: 30 Years of Wnt Signaling (27 June – 1 July, 2012) – Pre-registration & abstract submission deadline: 29 February 2012

Courses:
-SDB-LASDB 4th PASI short course A Systems Biology Approach to Understanding Mechanisms of Organismal Evolution
April 16-25, 2012 in Montevideo, Uruguay (Note, this is right before the LASDB conference at the same location.)
Application deadline is December 15, 2011
-EMBO Practical Course in Advanced Optical Microscopy (March 21-31, 2012) – General application deadline Friday 20 January 2012. Deadline for visa-dependent students 31 December 2011
-EMBO Laboratory Management Courses for postdocs and for independent group leaders. Held at various times during the year in the UK and Germany. Still spots left at some of the courses.
-For those of you in or near the UK, the Royal Society is hosting several Media and Communication Skills Courses for scientists.

Travel fellowships:
-The next round of The Company of Biologists travel fellowships closes December 31st. The funds can be used for a short research exchange in another lab. Postdocs and PhD students (from all countries) can apply.

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Wellcome PhD – Lab 3: Pigs that fly

Posted by , on 8 December 2011

This is my personal report on the last of three laboratory projects which I have undertaken during the rotation year of my 4-year Wellcome Trust PhD. I studied how flies depend on Pigs to fly.

A Drosophila wing disc, the structure in the larva that will form the adult wings, showing normal cells (green) and cells without Pigs (dark), stained for surface markers (Notch intracellular domain, blue) and actin cytoskeleton (Phalloidin, red).

It is vital that the cells that make up your body’s tissues are correctly organised. If cells can’t differentiate between up and down (or inside and outside) they can’t possibly organise themselves into the complex structures we need to function. For the final rotation in the first year of my 4-year Wellcome Trust PhD I joined Dr Katja Röper’s lab to work with fruit flies (Drosophila melanogaster), investigating the complex and unusual nature of an organiser protein – the brilliantly titled ‘Pickled eggs’ (Pigs for short).

As I have discussed in some of my previous posts, cells contain a network of internal scaffolding known as the cytoskeleton, which helps to control cell shape and movement. It also provides transport routes to help move molecules and organise everything within a cell. Different parts of the cytoskeleton perform different functions, differentiated by the size of the structures they form and the proteins they are made of. The thinnest are microfilaments, made of actin, responsible for cell shape (they also allow muscles to work). The thickest are microtubules, made of tubulin, which form the major transport routes within a cell. Other animals (but not flies) contain further intermediate filaments that have primarily structural roles.

Although these different parts of the cytoskeleton have been studied independently for many years, it has only recently been discovered that they often work together. It turns out that there are many components needed to make these interactions possible. One of these components in fruit flies is the protein Pigs, a ‘GAS2-like protein’ related to four known human proteins. Pigs is thought to interact with both microfilaments and microtubules, forming a bridge that holds the different structures together.

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Book review: A molecular view of the life and time of RNA

Posted by , on 8 December 2011

This book review originally appeared in Development. Ilan Davis reviews “Molecular Biology of RNA” (by David Elliot and Michael Ladomery).

Book info:
Molecular Biology of RNA By David Elliot, Michael Ladomery Oxford University Press (2010) 460 pages ISBN 978-0-19-928837-3 £34.99/$55 (paperback)

Following the discovery of the structure of DNA and during the early days of molecular biology, RNA was considered to be a less interesting cellular component to study than DNA. This was primarily because RNA was thought to be simply a molecular photocopy of the genetic blue print stored in DNA. But how things have changed! Since those early days, our understanding of the cellular roles of RNA has changed radically. RNA is now considered to be of central importance to both molecular biology and cellular function. Far from only containing genetic information, RNA is now regarded to have credible catalytic properties through the availability of its 2′-OH, a reactive group that replaces a non-reactive ‘O’ atom in DNA. Moreover, its catalytic roles include key functions in the most important molecular machines of the cell, such as the spliceosome and ribosome. In hindsight, it would perhaps not be so surprising if the RNA world hypothesis turned out to be correct. This hypothesis states that the first life forms on our planet were RNA-based simple cells in the pre-biotic soup. RNA is certainly a better candidate than either DNA or proteins for a self-replicating molecule that acts both as a template for, and that has the necessary catalytic machinery to perform, its own replication. Moreover, the discovery that most mRNAs are spliced, and the gradual uncovering of a breathtaking number of ways in which gene expression is regulated post-transcriptionally, have meant that the field of RNA has undergone rapid growth in the past few decades. This rapid growth has recently increased even further because of the discovery of RNA interference (RNAi), as well as the discovery that small RNAs, distinct from tRNA and snRNA, undergo processing to fulfil a range of cellular functions. These include the regulation of transposable element transposition by piRNAs, regulation of translation by microRNAs and still poorly explored large non-coding RNAs (ncRNA). Many of these ncRNAs have turned out to have important roles in development and during disease processes, such as cancer. Therefore, it is clear that all aspects of RNA molecular biology have now become central to our understanding of cell and developmental biology.

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Repulsive signals: bad breath, rude manners, and ephrin ligands

Posted by , on 7 December 2011

Satellite cells are muscle stem cells that regenerate injured muscle (remember this earlier post?).  They are highly motile cells that may be able to travel in order to repair injured muscle far away, and a recent paper in Development describes the role of Eph/ephrin signaling in satellite cell motility and patterning.

One of the most well-understood guidance pathways is the Eph/ephrin pathway, which has major roles in cell migration and axon guidance throughout development.  In this pathway, Eph receptors on one cell interact with ephrin ligands bound to another cell’s membrane.  This interaction typically causes rapid changes in the Eph-expressing cell’s adhesion and cytoskeletal organization, and frequently causes the cells to repel each other.  A recent paper describes the role of Eph/ephrin signaling in satellite cell motility and patterning.  Stark and colleagues showed that ephrin ligands are differentially localized to healthy and regenerating muscle tissue, and used a well-established “stripe assay” to show that ephrins can repel mouse satellite cells.  As seen in the images above (increasing magnification from left to right), stripes of ephrin-B1 ligand (bottom row, blue stripes) repulsed the satellite cells, compared to the distribution of cells on control stripes (top row).  In addition, Stark and colleagues explanted mouse satellite cells into the hindbrain of developing quail embryos, from which neural crest cells emigrate using Eph/ephrin signaling.  Some satellite cells migrated along with the neural crest cells and conformed to the same boundaries.

For a more general description of this image, see my imaging blog within EuroStemCell, the European stem cell portal.

ResearchBlogging.orgStark, D., Karvas, R., Siegel, A., & Cornelison, D. (2011). Eph/ephrin interactions modulate muscle satellite cell motility and patterning Development, 138 (24), 5279-5289 DOI: 10.1242/dev.068411

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In Development this week (Vol. 139, Issue 1)

Posted by , on 6 December 2011

Here are the highlights from the current issue of Development:

Notching up pancreas development

According to the lateral inhibition model, during early pancreas development, Neurog3 expression in multipotent progenitor cells (MPCs) initiates endocrine differentiation and activates expression of the Notch ligand Dll1. Dll1 then activates Notch receptors in neighbouring cells, which turns on Hes1 expression. Finally, Hes1 inhibits Neurog3 expression in these neighbouring cells, thereby preventing excessive endocrine differentiation. On p. 33, Palle Serup and colleagues challenge this model by showing that Dll1, Hes1 and Dll1/Hes1 mutant phenotypes diverge at key points of mouse pancreas development. Moreover, pancreatic hypoplasia in Dll1 mutants is independent of endocrine development and is not, therefore, caused by excessive endocrine differentiation and progenitor depletion, as previously believed. Instead, the researchers report, reduced MPC proliferation is responsible for this hypoplasia. Other results indicate that Ptf1a (pancreas transcription factor 1 subunit α) activates Dll1 expression and that Hes1 sustains Ptf1a expression and Dll1 expression in early MPCs. Thus, Ptf1a-mediated control of Dll1 expression, rather than a lateral inhibition mechanism, is crucial for Notch-mediated control of early pancreas development.

Modelling stem cell population dynamics

Many tissues and organs are maintained by stem cell populations. Anatomical constraints, cell proliferation dynamics and cell fate specification all affect stem cell behaviour, but their relative effects are difficult to examine in vivo. E. Jane Albert Hubbard, Hillel Kugler and colleagues now use available data to build a computational model of germline development in C. elegans (see p. 47). In this model, germline cells move, divide, respond to signals, progress through mitosis and meiosis, and differentiate according to various local rules. Simulations driven by the model recapitulate C. elegans germline development and the effects of various genetic manipulations. Moreover, the model can be used to make new predictions about stem cell population dynamics. For example, it predicts that early cell cycle defects may later influence maintenance of the progenitor cell population, an unexpected prediction that the researchers validate in vivo. This general modelling approach could, therefore, prove to be a powerful tool for increasing our understanding of stem cell population dynamics.

Time and place generate neuronal diversity

The spinal cord contains many distinct interneuron cell types that have specialised roles in somatosensory perception and motor control. How this neuronal diversity is generated from multipotent progenitor cells is unclear. Here (p. 179), Martyn Goulding and colleagues investigate the differentiation of Renshaw cells, one of the spinal interneuron subtypes that arises from the spatially defined V1 class of interneurons. They show that the first-born postmitotic V1 interneurons are committed to the Renshaw cell fate. This fate, they report, is determined by a temporal transcriptional program that involves selective activation of the Oc1 and Oc2 transcription factors during the first wave of V1 interneuron neurogenesis, broader expression of the Foxd3 transcription factor in postmitotic V1 interneurons, and later expression of the MafB transcription factor. Importantly, Renshaw cell specification and differentiation proceeds normally in the absence of neuronal activity. Overall, these results suggest that a combination of spatial and temporal determinants might be the major mechanism for generating neuronal diversity in the spinal cord.

Topsy-turvy cilia precede neural progenitor delamination

During the development of the mammalian cerebral cortex, basal progenitor cells delaminate from the apical adherens junction belt of the neuroepithelium. But what are the cell biological processes that precede the delamination of these neural progenitors? On p. 95, Wieland Huttner and co-workers identify a new pre-delamination state of neuroepithelial cells in the mouse embryonic neocortex. Using electron microscopy, the researchers show that, in a subpopulation of neuroepithelial cells, the re-establishment of the primary cilium after mitosis occurs at the basolateral rather than at the apical plasma membrane. Neuroepithelial cells carrying basolateral cilia selectively express the basal progenitor marker Tbr2, they report, and delaminate from the apical adherens junction belt to become basal progenitors. Notably, overexpression of insulinoma-associated 1, a transcription factor that promotes the generation of basal progenitors, increases the proportion of neuroepithelial cells with basolateral cilia. Together, these results suggest that the re-establishment of a basolateral primary cilium is a cell biological feature that precedes neural progenitor delamination.

Digging into Polycomb repression

Polycomb group proteins control diverse developmental processes by repressing the transcription of developmental regulator genes through chromatin modification. The Drosophila Polycomb repressive complex 1 (PRC1), which contains the four core subunits Sce (Sex combs extra), Psc (Posterior sex combs), Ph (Polyhomeotic) and Pc (Polycomb), exhibits two chromatin-modifying activities – H2A monoubiquitylation and chromatin compaction. Here (p. 117), Jürg Müller and co-workers provide new insights into PRC1-mediated transcriptional repression. The researchers show that Sce is the major H2A ubiquitylase in Drosophila and identify the genes that are bound by PRC1. Then, by analysing mutants that lack individual PRC1 subunits, they identify two classes of PRC1 target genes. Repression of class I genes requires all four PRC1 core subunits whereas repression of class II genes requires only Psc and Ph. The researchers suggest, therefore, that H2A monoubiquitylation is crucial for the repression of a subset of PRC1 target genes but that chromatin compaction mediated by Psc and Ph may be the major mechanism by which PRC1 represses other target genes.

Gβγ signals polarise primordial germ cells

Directed cell migration occurs many times during embryogenesis. For example, in many species, primordial germ cells (PGCs) migrate after specification to the site of the future gonad. This migration involves PGC polarisation and PGC responsiveness to external guidance cues. In zebrafish, the chemokine Cxcl12a regulates directed migration, whereas the Rho GTPase Rac1 regulates polarisation. But what controls Rac activity? Fang Lin and co-workers now report that signalling mediated by the G protein subunits Gβ and Gγ (Gβγ) regulates Rac activity in zebrafish PGCs (see p. 57). The researchers show that PGCs defective for Gβγ signalling, like those with reduced Rac activity, fail to polarise and fail to migrate actively in response to directional cues. They also show that PGCs require Gβγ signalling for polarised activation of Rac and for maintenance of their overall Rac levels. These and other results suggest that, during PGC migration in zebrafish, Gβγ signalling regulates Rac activity to control the cell polarity that is needed for PGC responsiveness to chemokine signalling.

Plus…

 

Cell fate decisions and axis determination in the early mouse embryo

The mouse embryo generates multiple cell lineages, as well as its future body axes in the early phase of its development. Here, Takaoka and Hamada address the timing of the first cell fate decisions and of the establishment of embryonic polarity, and ask how far back one can trace their origins.

See the Review article on p. 3

Epigenetic reprogramming in mouse pre-implantation development and primordial germ cells

During mouse development, the epigenetic states of pre-implantation embryos and primordial germ cells undergo extensive reprogramming. Recent studies of DNA demethylation dynamics, reviewed by Saitou, Kagiwada and Kurimoto, provide new insights into the regulation of these epigenetic states. See the Review article on p. 15

 

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Let’s make a developmental biology bingo game!

Posted by , on 5 December 2011

Ever noticed how each field has its own jargon?

Benchfly, a site with free video protocols and other resources for researchers, has created “Group Meeting Bingo”. The site generates bingo cards with the particular phrases common to various fields of research. They have cards for biochemistry, cell biology, and various other fields, but no developmental biology…yet!

So, let’s make a developmental biology bingo game!

Over the next few weeks (until we have enough words), you can leave a comment below (no registration required) with your suggestions for typical words that regularly show up in developmental biology talks. Benchfly will then turn our suggestions into a playable bingo game!

They suggest taking out the cards during meetings, but I’ve enjoyed just refreshing the existing cards on the site and marveling at all the field-specific words.


Section of one of the cell biology bingo cards. Of course some of the words from other fields can appear on the developmental biology cards as well!

Looking forward to see what you all come up with for the developmental biology game!

NB: The Node does not endorse playing bingo at the expense of paying attention to talks. Personally I’ve played a similar game at a conference where the meeting organizers handed out the cards, and encouraged everyone to play. I found it very easy to pay attention to the talks there, take notes, learn things, and still win the game. It’s actually easier to spot the words if you are paying attention!

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