Here are the research highlights from the current issue of Development:

Evolution of mesoderm induction

Fibroblast growth factors (FGFs) are essential for mesoderm induction in vertebrates and for early mesoderm formation in invertebrate chordates. However, functional studies to date do not support a role for FGF signalling in mesoderm induction in other deuterostomes (animals in which the first embryonic opening forms the anus), such as sea urchins. Thus, the ancestral role of FGF signalling during mesoderm specification in deuterostomes is unclear. On p. 1024, Christopher Lowe and co-workers examine the role of FGF signalling during the early development of the hemichordate Saccoglossus kowalevskii. The researchers report that the FGF ligand fgf8/17/18 is expressed in the ectoderm overlying sites of mesoderm specification within this marine worm’s archenteron (primitive gut) endomesoderm. Mesoderm induction, they show, requires contact between the ectoderm and the endomesoderm. Moreover, loss-of-function experiments indicate that FGF ligand and receptor are both necessary for mesoderm specification. These and other results indicate that FGF signalling is required throughout mesoderm specification in hemichordates and support an ancestral role for FGF signalling in mesoderm formation in deuterostomes.

Histone demethylase builds testis niche

In adult stem cell niches, crosstalk between extrinsic cues (such as signals from neighbouring cells) and intrinsic cues (such as chromatin structure) regulates stem cell identity and activity. Now, on p. 1014, Xin Chen and colleagues report that the histone demethylase dUTX regulates crosstalk among the germline stem cells (GSCs), hub cells and cyst stem cells (CySCs) of the Drosophila testis niche. The researchers show that dUTX acts in CySCs to maintain hub cell identity by activating transcription of the Socs36E gene (which encodes an inhibitor of the JAK-STAT signalling pathway that is required for GSC identity and activity) via removal of a repressive histone modification near its transcription start site. dUTX also acts in GSCs, they report, to maintain hub structure through regulation of DE-cadherin, the Drosophila homologue of vertebrate cadherins. These results show how an epigenetic factor regulates crosstalk among different cell types within an adult stem cell niche and provide important information about the in vivo function of a histone demethylase.

Novel Wnt inhibitors identified

Members of the Eaf gene family are involved in tumour suppression and in embryogenesis but what are the molecular mechanisms that underlie these activities? Here (p. 1067), Wuhan Xiao and colleagues report that eaf1 and eaf2 modulate mesodermal and neural patterning in zebrafish embryos through inhibition of canonical Wnt/β-catenin signalling. They show that ectopic expression of eaf1 and eaf2 in zebrafish embryos and in cultured cells blocks β-catenin reporter activity. Furthermore, they show that Eaf1 and Eaf2 bind to the Armadillo repeat region and C-terminus of β-catenin, and to other β-catenin transcription complex proteins. Both the N- and C-terminus of Eaf1 and Eaf2 must be intact for their suppressive activity, they report. Finally, they show that the biological activities of Eaf family proteins are conserved across species. Together, these results identify a novel role for Eaf1 and Eaf2 in the inhibition of canonical Wnt/β-catenin signalling that might provide the mechanistic basis for the tumour suppressor activity of Eaf family proteins.

Linking planar polarity to junctional remodelling

During morphogenesis, the elongation of polarised tissues involves cells within epithelial sheets and tubes making and breaking intercellular contacts in an oriented manner. How cells remodel their junctional contacts is poorly understood but growing evidence suggests that localised endocytic trafficking of E-cadherin might modulate cell adhesion. Now, Samantha Warrington and co-workers (p. 1045) report that the Frizzled-dependent core planar polarity pathway, which has been implicated in the regulation of cell adhesion through E-cadherin trafficking, promotes polarised cell rearrangements in Drosophila. The researchers report that the core planar polarity pathway promotes cell intercalation during tracheal tube morphogenesis by promoting E-cadherin turnover at junctions through local recruitment and regulation of the guanine exchange factor RhoGEF2. Core planar polarity pathway activity also leads to planar-polarised recruitment of RhoGEF2 and E-cadherin in the epidermis of the embryonic germband and the pupal wing. Thus, the researchers suggest, local promotion of E-cadherin endocytosis through recruitment of RhoGEF2 is a general mechanism by which the core planar polarity pathway promotes polarised cell rearrangements.

Signals for melanocyte stem cells

Adult stem cells are crucial for the growth, homeostasis and regeneration of adult tissues. Melanocyte (melanophore) stem cells (MSCs), which give rise to pigment cells in vertebrates, are an attractive model for studying the regulation of adult stem cells. In this issue, two papers provide new information about the involvement of signalling by the receptor tyrosine kinases Kit and ErbB in the establishment of MSCs in zebrafish.

On p. 1003, Christiane Nüsslein-Volhard and colleagues investigate the embryonic origin of the melanophores that emerge during juvenile development and that contribute to the striking colour patterns of adult zebrafish. The researchers identify a small set of melanophore progenitors (MPs) that are established early in embryonic development and that are associated with the segmentally reiterated dorsal root ganglia in the fish. They use lineage analysis and four-dimensional in vivo imaging to show that the progeny of these embryonic MPs spread segmentally and give rise to the melanophores that create the adult melanophore stripes. Other experiments indicate that the MPs require zebrafish kit ligand a (kitlga, also known as slk) to function as MSCs, and that MP establishment depends on ErbB signalling during early embryonic development. Based on their results, the researchers propose that dorsal root ganglia provide a niche for MSCs and suggest that Kit signalling might attract and maintain MSCs in this niche.

On p. 996, Thomas O’Reilly-Pol and Stephen Johnson use clonal analysis to investigate which stages of melanocyte regeneration – establishment of MSCs, recruitment of MSCs to produce committed daughter cells, or the proliferation, differentiation and survival of these daughter cells – are affected by Kit signalling deficits; previous work had shown that a reduction in Kit signalling results in dose-dependent reductions of melanocytes during larval regeneration. The researchers show that the reduction in melanocytes in kita mutants is due to a defect in MSC establishment. By contrast, the other stages of melanocyte regeneration are unaffected. Additional analyses indicate that the MSC establishment defect in kita mutants arises from inappropriate differentiation of the MSC lineage, a finding that confirms and extends the results presented by Nüsslein-Volhard and colleagues.

PLUS…

Rooting plant development

In 1993, Liam Dolan, Ben Scheres and colleagues published a paper in Development detailing the anatomical structure of the Arabidopsis root. As part of the Development Classics series, Ben Scheres discusses how this work underpinned subsequent research on root developmental biology and sparked a detailed molecular analysis of how stem cell groups are positioned and maintained in plants. See the Spotlight article on p. 939

Auxin metabolism and homeostasis during plant development

Auxin plays important roles during the entire life span of a plant. Auxin metabolism is not well understood but recent discoveries, reviewed by Karin Ljung, have started to shed light on the processes that regulate the synthesis and degradation of this important plant hormone. See the Primer article on p. 943

Specialized progenitors and regeneration

Regeneration in planarians requires a population of cells known as neoblasts. Recent data, discussed by Peter Reddien, indicate that some neoblasts express lineage-specific factors during regeneration and in uninjured animals, suggesting that an important early step in planarian regeneration is neoblast specialization. See the Hypothesis article on p. 951

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Last year, Matter launched, after a successful  Kickstarter campaign, as a magazine that publishes only long, well-written articles related to “science, technology and the ideas shaping our future”. Each issue is one article, which costs $0.99 to access. (On my iPad, they ‘re categorized as books, and are each about 40 pages long, which I think justifies both the price and the fact that I’m filing this under “book review”.)

The latest issue is of Matter is about online scammers, but the one before that was about developmental biology! Or rather, “Electric Shock”, written by Cynthia Graber, is about a biologist. It profiles the life of Michael Levin and his work in understanding the role of bioelectricity in organ regeneration.

Matter’s audience is broad, and most of them are not biologists, so when Graber describes Levin’s work, she also has to explain the basics of developmental biology: “One cell divides into two, two into four, four into eight, continuing until there are dozens, thousands, millions of them. In the process, some cells transform into blood, others into bone; some into tissue, others into tendon.”

The specific work described in the article is a study published in Communicative and Integrative Biology last month, as an addendum to an earlier paper from the Levin lab in The Journal of Neuroscience.  Their earlier work had shown that tadpole tails can regenerate in response to regulated ion transport, and that bioelectric signals can induce ectopic eyes in tadpoles, but now they also achieved regeneration in (older) developing frogs’ legs!

In “Electric Shock”, Graber describes not just the work itself, but the context. Why did Levin become interested in bioelectricity? What was he like as a child? How does he spend his time outside of the lab? We learn that Levin takes his parents to Florida each year, for a few weeks in March. He brings along a lot of reading material on those trips, to think about his work from new angles, and discusses it with his family.  “…at night, he explains his thoughts to his father over dinner. “If I can’t explain my ideas to a very smart non-expert then I haven’t really fleshed them out properly anyway,” he says.””

I love reading profiles of researchers that go beyond what’s in the scientific literature. In this case, I was especially amused because the very week that this issue of Matter came out, we also published one of Levin’s papers in Development, so he was suddenly everywhere! His most recent Development paper was about planarian regeneration, which wasn’t covered in the Matter piece, but we also published the frog ectopic eye work last year, and it was great to get a glimpse into the lab where the work was done.

Read the original article:
Electric Shock – by Cynthia Graber

Papers mentioned in this review:
Tseng A. & Levin M. (2013). Cracking the bioelectric code: Probing endogenous ionic controls of pattern formation, Communicative & Integrative Biology, 6 (1) e22595. DOI: 10.4161/cib.22595
Tseng A.S., Beane W.S., Lemire J.M., Masi A. & Levin M. (2010). Induction of Vertebrate Regeneration by a Transient Sodium Current, Journal of Neuroscience, 30 (39) 13192-13200. DOI: 10.1523/JNEUROSCI.3315-10.2010
Beane W.S., Morokuma J., Lemire J.M. & Levin M. (2013). Bioelectric signaling regulates head and organ size during planarian regeneration, Development, 140 (2) 313-322. DOI: 10.1242/dev.086900
Pai V.P., Aw S., Shomrat T., Lemire J.M. & Levin M. (2012). Transmembrane voltage potential controls embryonic eye patterning in Xenopus laevis, Development, 139 (2) 313-323. DOI: 10.1242/dev.073759

(Disclaimer: I contributed to the Matter Kickstarter campaign and as a result I am on their massive editorial board and get to be part of crowdsourced topic suggestions for the magazine. However, I was not involved in commissioning this piece, and was as pleasantly surprised as anyone to suddenly find a profile of a developmental biologist in a broader media publication!)

(7 votes)

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The annual Science Online conference is currently underway in North Carolina. It attracts mainly scientists and science writers who use the internet to advance science communication. Everyone at the conference is extremely Twitter-savvy, and it’s impossible to keep up with the #scio13 hashtag, but I’ve created a Storify below that includes some of the tweets from some of the sessions that you might be interested in. From the first day I included sessions about first person narrative in talking about your research, about using visual metaphors, about outreach, about electronic notebooks, and about peer review. The Storify will be updated over the weekend to include more sessions as they happen.

If you’re not at the conference, you might still be able to join one of the affiliated Watch Parties that are taking place across the world to allow others to view some of the sessions. I’m co-hosting the London Watch Party tomorrow. (Feel free to join if you’re nearby!)

Storify:
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Many salamanders can regenerate limbs, and even a seven-year-old child appreciates exactly the reasons why this feat is so remarkable.  How can an animal that has been living its life, using its leg full of muscles and bones and tendons and nerves every single day, suddenly grow a new one at some random time?  When the leg first grew on the same salamander when it was just a tiny animal, we can imagine it followed a prescribed developmental program for its instructions and used a prescribed pool of progenitor cells for its construction.  Once the limb tissues are already working, the cells are differentiated and doing their jobs, so how do they go back in time and create tissues anew?  Scientific understanding of how limbs develop has progressed immensely over the last several decades, but understanding of how limbs can regenerate and why some animals do it better than others has remained elusive.  This lag in understanding vertebrate limb regeneration on a molecular level stems from the fact that the two model systems with the most sophisticated tools for studying limb development—chick and mouse—do not naturally regenerate entire limbs as adults.  Figuring out what the regenerative roadblocks are in chick, mouse, and human will be imperative for improving regeneration in species that do not do it well.  However, it will be equally important—and perhaps fundamental for elucidating these roadblocks—to understand how animals that regenerate limbs remarkably well do it.  This is why we are developing tools that allow for more precise molecular genetic and cell biological inquiry into axolotl limb regeneration.

EGFP expression in a live animal. This axolotl hindlimb was amputated mid-femur. The blastema that formed was infected with EGFP-encoding retrovirus two weeks post-amputation, and the limb was allowed to fully regenerate. Cells descended from infected blastema cells express EGFP. Since the injection was limited to the blastema, cells proximal to the amputation plane do not express EGFP.

Two things a researcher might want to do when studying how salamanders regenerate limbs are tracking cells during regeneration and expressing introduced genetic elements to analyze their effects.  In the past, labeling methods such as heavy isotopes, dyes, and electroporation of plasmid DNA have been used in regenerating salamander limbs.  Electroporation of plasmid DNA has also been used to mis-express genetic elements.  While studies using these methods provided key insights into, for example, which cells become mitotically active following amputation, all three of these methods suffer a similar drawback:  the element gets diluted with each successive cell division, and in a regenerating limb, lots of cell division occurs.  It was impossible to follow cells from the stump, through the blastema (group of relatively dedifferentiated cells that forms at the tip of the stump and will give rise to internal limb tissues in the regenerate), and into the new limb.  Transplantation studies using tissues from permanently marked donors, such as animals induced to have a different ploidy or transgenic animals, have aimed to bypass these caveats, but transplantation is not ideal in many situations (for example, some tissues cannot be cleanly separated, and the procedure itself is obviously invasive and best done well before limb regeneration will be studied).  Furthermore, donor tissue is relatively limited at this point to just a few genetic lines of axolotls constitutively expressing a fluorophore, and generation of novel animals by transgenesis is a lengthy and labor-intensive process.  Expression studies using electroporated plasmid DNA were limited because even good electroporations may not lead to enough sustained expression to detect an effect.  In our Development paper, we showed that retroviruses can infect regenerating axolotl limbs.  These retroviruses are simply injected into limb tissue, and they can infect any mitotically active cell they encounter.  Since the retroviral genomes integrate into host cells, they can be used to permanently express a label such as GFP, which allows for tracking cells during regeneration, opening the door to many future studies.  Expression from the retroviral vectors is robust and using retroviruses might be a powerful way to finally address the consequences of misexpressing candidate genes during limb regeneration.  Additionally, we showed that retroviral infections can in principle be targeted to specific cell types by targeting infections to vascular endothelial cells.  This works by borrowing technology exploited by other researchers in the mouse.  Axolotl and mouse cells do not make the receptor for a particular coat protein found on the surface of certain bird viruses.  However, if axolotls or mice are made to express that receptor, they can become infected by viruses with these coats, and expression of the receptor can be confined to particular cell types by the researcher provided genetic elements for doing so (for example, a cell-type-specific promoter) exist.  Hence, the retroviruses can also someday be targeted to a whole battery of different specific cell types in regenerating axolotl limbs once cell-type-specific promoters are found.  These tools will allow for more precise control of labels and introduced gene expression during regeneration.

Figuring out how salamanders regenerate limbs won’t just satisfy the curiosity of the seven-year-old in us all, it also stands to someday dramatically improve the lives of the millions of people living with the consequences of limb amputation.  With key risk factors such as diabetes and peripheral artery disease on the rise, limb loss is unfortunately becoming an even more common problem in places like the United States, giving scientists a call to arms when it comes to unraveling the mystery of limb regeneration.

(10 votes)

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Let’s start this monthly summary with two fantastic posts that were left out of last month’s roundup due to the holiday period (and scheduled posts).

Idoia Quintana studies shark brain development in Spain, and travelled to Scotland recently to learn how to work with mouse brains, so she could do some cross-species comparison.

“At the beginning was tricky, working with mice was a big challenge for me; but at the same time was amazing to do research in a species in which several optimized techniques are available. Particularly I enjoyed learning slice culture techniques and I hope to have time to implement them in shark embryos and perform some axon guidance experiments upon my return.”

Benjamin Coyac attended the UPMC/Curie Institute International Course in Developmental Biology, and described what it was like to study in Paris for several weeks with students from around the world.

“The intensity of the program enabled us to get to know each other very quickly. Little talks about science or our lives as international students began to build a common experience in our shared interest in developmental biology. By the end of the program, not only we had acquired scientific skills in theory, methods and practicals, but also we became friends and started to build a strong network of future developmental scientists.”

And now on to the January posts.

Mouse development
Stephanie Vanderweide travelled from California to Montreal in the middle of the Canadian winter to learn how to microinject 2-cell and 8-cell mouse embryos in Yojiro Yamanaka’s lab, as part of a project to study the molecular mechanisms involved in the first lineage decision of the developing mouse embryo.

Heather writes about a technique developed in the Niswander lab, where she’s a student. The lab set up a confocal-based live imaging system to visualize mouse embryo development in real time.

“We have been using this system to study neural tube closure, but there are many other tissues and organs that develop during these time periods (E8.5-E10.5) that are amenable to imaging including the heart, face, limbs and neural crest. By using tissue-specific Cre- recombinase reporter strains, the behavior of individual cell types can now be observed in real time in the early mammalian embryo.”

Woods Hole Embryology course
The application period for the 2013 Woods Hole Embryology Course has been extended to February 8. If you’re accepted to the course, we may see your images on the Node in the future: this is the course that produces the gorgeous images that Node readers have selected for Development covers. Speaking of which, the first round of images from the 2012 course are now up!

Publishing discussions
Finally, we’ve covered two very different discussions related to scientific publishing: peer review and the secrets behind methods sections.
-Katherine Brown wrote a post responding to an earlier discussion, about the future of peer review – both in general and in the specific case of Development.
-Eva followed the #overlyhonestmethods hashtag on Twitter, where within a few days hundreds of scientists shared the true stories behind their methods sections.

Also on the Node
-Lots of new job ads
–Hope for Huntington’s
–Top posts of 2012

(1 votes)

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A two-year post-doctoral positionis available in the group of Guillaume Balavoine and Michel Vervoort (http://www.ijm.fr/en/ijm/research/research-groups/metazoaires/) at the Institut Jacques Monod (IJM) in Paris (France). The IJM is a leading French biological research institute, comprising about 25 interactive research groups and high-quality technological facilities, including a cutting-edge imaging platform.

The primary research focus of the group is to reconstruct the early stages of animal evolution, by comparing the genetic networks that regulate the developmental patterning of key aspects of the body plan across metazoans. The main model studied by the group is the annelid worm Platynereis dumerilii, an emerging model species. Platynereis is a member of the Spiralian/Lophotrochozoan branch of the bilaterian tree and is hypothesized to be as close to a “bilaterian living fossil” as a bilaterian can be, both in terms of genome organization and body plan.

The post-doc project aims at understanding and modelling cell movements and cell shape changes that direct CNS and segment morphogenesis in Platynereis, as well as determining the roles of the Planar Cell Polarity (PCP) and Rho/ROCK/MyoII pathways in these behaviours. The project will be centered on the use of live imaging, molecular and modelling tools.

Candidates should have a strong background in developmental and/or evolutionary biology. Expertise in live imaging would also be welcome. Candidates must hold a Ph.D. degree in developmental or evolutionary biology and have at least one first author publication in a peer-reviewed journal.

Potential candidates should send their application by mail to Guillaume Balavoine (balavoine.guillaume[at]ijm.univ-paris-diderot.fr) and Michel Vervoort (vervoort.michel[at]ijm.univ-paris-diderot.fr) with a statement of interest, a Curriculum Vitae and contact informations for two referees.

The position will remain open until filled; however applications received by March 15^th 2013 will be given priority. The starting date is flexible (in 2013), with an early date preferred.

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Each year, students of the Woods Hole Embryology course produce some amazing images. Last year, readers of the Node selected four images from the 2011 course to appear on the cover of Development.

Now it’s time to do the same with the images from the 2012 course. Here’s the first batch of four images. Please vote in the poll below the images for the one you would like to see on the cover of Development. (Click any of the images to see a bigger version.) Poll closes on February 19, noon GMT.

1. Chick ectopic limb. An FGF-4-soaked bead was implanted at stage 14. The embryo was fixed four days later, and stained with alcian blue to reveal the developing cartilage of the skeleton. An ectopic limb can be seen developing next to the normal forelimb, and the bead is still present in the body wall. This image was taken by Elsie Place (MRC National Institute of Medical Research).

2. Two day old Xenopus embryo epidermis, highlighting multiciliated cells. The embryo had been injected with mRNAs encoding membrane blue fluorescent protein, Centrin GFP, and Clamp RFP at the 4-cell stage and imaged as a live mount by confocal microscopy. This image was taken by Andrew Mathewson (Fred Hutchinson Cancer Research Center).

3. Confocal image (extended focus Z stack) of an E10.5 day mouse embryo (lateral view; thorax) immunostained with antibodies against PECAM (endothelial factor present in the vasculature; red), beta-III-tubulin (neurons; green) and DAPI (cell nuclei; blue). This image was taken by Joyce Pieretti (University of Chicago), Manuela Truebano (Plymouth University), Saori Tani (Kobe University) and Daniela Di Bella (Fundacion Instituto Leloir)

4. Mouse embryo, day E9.5. Widefield fluorescence image showing immunostaining with anti-Tuj1 (orange) and anti-glucagon (green), counterstained with DAPI (cyan). This image was taken by Eduardo Zattara (University of Maryland, College Park).

(7 votes)

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Here are the highlights from the current issue of Development:

Pancreatic injury unlocks cell potential

Identifying methods by which pancreatic β-cells can be produced is of major therapeutic importance. Whether there are adult pancreatic cells with the potential to make new β-cells is a matter of much debate. During embryonic development, the transcription factor Ptf1a initially marks multipotent progenitors, before becoming restricted to acinar cells. Here (p. 751), Christopher Wright and colleagues test whether mature Ptf1a-expressing cells can regain multipotentiality upon injury by labelling Ptf1a-positive acinar cells in mice and following their fate after pancreatic duct ligation. Remarkably, not only do new duct cells arise from the labelled cells, but some labelled cells start to express endocrine markers and display the hallmarks of mature β-cells, suggesting transdifferentiation of acinar cells into β-cells. This process is inefficient and slow, but can be enhanced by prior ablation of endogenous β-cells. Thus, pancreatic injury appears to induce reactivation of a more embryonic-like multipotent state in Ptf1a-expressing cells, from which endocrine cells can differentiate, possibly opening up new avenues for generating β-cells.

Lipid leads the way in wound healing

During epithelial wound healing, actin assembles at the leading edge of cells that border the wound, forming dynamic protrusions and, in some cases, an actomyosin cable. Together, these actin-rich structures are essential for wound closure. The process of dorsal closure in Drosophila shares many characteristics with wound healing and is a convenient system for cell biological analysis. Building on earlier results showing that the apical polarity determinant Par3/Bazooka (Baz) is lost from the leading edge of cells during dorsal closure, Tom Millard and colleagues (p. 800) now uncover a molecular mechanism by which Baz localisation regulates actin dynamics. Baz is known to bind the lipid phosphatase Pten, and the authors find that loss of Baz from the leading edge causes Pten redistribution. This, in turn, leads to an accumulation of the lipid PIP3 at the leading edge, which promotes formation of actin protrusions that are required for closure. This pathway is conserved during both dorsal closure and wound healing, offering a mechanistic basis for actin assembly during epithelial closure.

Mapping the neural crest

Neural crest (NC) cells arise in the neural tube (NT), undergo an epithelial-mesenchymal transition, and migrate away along defined routes, differentiating into multiple lineages. Precisely how NC cells exit the NT, and whether their fate is predetermined by their initial position within the NT, has been controversial. To address these issues, the Kulesa and Bronner laboratories performed a collaborative study (p. 820). Using a combination of photoactivation and two-photon time-lapse microscopy, they precisely marked individual or small groups of NC precursors in vivo in the chick embryonic NT and followed their fate. They found that most NC cells exit the NT at the dorsal midline, and that some precursors remain resident in the dorsal midline, producing an unordered emigration of cells. Moreover, they showed that differentiation potential is not defined by initial position within the NT, as has previously been suggested, although time of NT exit did influence fate. Together, these results suggest a more plastic and dynamic behaviour for NC cell emigration than previously appreciated.

X inactivation: the great escape

X-chromosome inactivation (XCI) enables dosage compensation between XX females and XY males, and its absence causes lethality, owing to defects in extra-embryonic tissues. However, it has also been shown that some genes are able to escape XCI in these tissues. Here, Catherine Corbel, Edith Heard and colleagues reconcile these findings and show that the inactive X (Xi) in one particular extra-embryonic cell type – trophoblast giant cells (TGCs) – has an unusual chromatin status (p. 861). Using RNA FISH on sections of postimplantation mouse embryos, they show that XCI is maintained in embryonic lineages, whereas TGCs show a high level of escape from XCI. Partial re-expression of most X-linked genes analysed, with the exception of the G6pd housekeeping gene, was observed in TGCs. In addition, the Xi in TGCs possesses an unusual organization and chromatin status, exhibiting both active and inactive chromatin marks. The authors propose that this apparent ‘bivalence’ of the Xi might account for its instability in TGCs and suggest that additional mechanisms maintain silencing at key loci.

HNF1β controls nephron development

The nephron is a highly specialised unit of the kidney. It arises by mesenchymal-to-epithelium transitions. After epithelialization, a polarized renal vesicle forms, and this further differentiates into a comma-shaped body and a S-shaped body (SSB), in which the future nephron segments are mapped into proximal, intermediate and distal domains. How SSBs are patterned and subsequently differentiate during kidney morphogenesis is poorly defined. Here, two papers use complementary approaches to show that hepatocyte nuclear factor 1β (HNF1β), which is known to be required for the earliest steps of metanephric kidney development and is implicated in developmental renal pathologies, controls this early patterning.

On p. 873, Silvia Cereghini and co-workers show that conditional inactivation of Hnf1b in murine nephron progenitors causes abnormal SSB regionalisation and morphology. In particular, Hnf1b deficiency leads to the absence of a proximal-medial SSB subdomain. This defect correlates with a downregulation of Notch pathway components and of Iroquois transcription factors, and perturbs the subsequent differentiation and morphogenesis of SSBs. Using parallel studies in Xenopus embryos, the researchers show that Hnf1b is required for the acquisition of proximal and intermediate tubule fate, acting again through the Notch pathway and Iroqouis genes. Together, these results show that HNF1B is required for the acquisition of a proximal-medial segment fate in vertebrates and uncover a previously unappreciated function of a novel SSB subdomain.
Using a similar gene targeting approach, Evelyne Fischer and colleagues (p. 886) demonstrate that Hnf1b inactivation in the murine metanephric mesenchyme (MM), which gives rise to nephron progenitors, leads to drastic tubular defects. The researchers report that mutant embryos show significant alterations to SSB structure: the typical bulge of epithelial cells between the intermediate and distal SSB segments is absent in mutant embryos. The lack of Hnf1b correlates with decreased expression of several genes, including the Notch ligand Delta-like 1, and results in impaired tubular expansion and differentiation. Finally, the researchers show that the nephron defects observed in Hnf1b-deficient mice resemble those observed in human foetuses carrying HNF1B mutations. The authors conclude that HNF1β plays an essential role in controlling the formation of a specific SSB sub-compartment by activating a set of crucial kidney development genes.

PLUS…

Stem cells living with a Notch

Freddy Radtke and colleagues review the role of Notch signaling in stem cells, comparing insights from flies, fish and mice to highlight similarities, as well as differences, between species, tissues and stem cell compartments. See the Review article on p. 689

Human pluripotent stem cells: an emerging model in developmental biology

Zhu and Huangfu discuss how studies of human pluripotent stem cells (hPSCs) can complement classic approaches using model organisms, and how hPSCs can be used to recapitulate aspects of human embryonic development ‘in a dish’. See the Review on p. 705

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Happy 2013 everyone! I hope you’re all settling into the year nicely.We sent out our EuroStemCell January newsletter last week and I thought some of you might be interested in our latest schools activities and fact sheets on stem cell research.

Highlights this month include a new lesson for 12-14 year olds on Stem cell treatments and ethics and a blog from Cambridge Stem Cell Institute researchers about their successful school visit using our CSI: Cell science investigators lesson.

Our collection of fact sheets is always growing: the latest additions are on (1) Umbilical cord blood and stem cells and (2) the role of commercial organisations in developing stem cell treatments. We’ve also added more fact sheet translations – most recently into French, Spanish and Italian.

Remember: you can stay in touch inbetween newsletters by following @eurostemcell on Twitter or liking us on Facebook. Your feedback is always very welcome – via these channels or use our contact form to get in touch.

(2 votes)

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The Woods Hole image voting posts are some of the most popular posts on the Node (and yes, there will be a new one up VERY soon!). These images are all made by students of the Woods Hole Embryology course, and you still have a chance to be part of the 2013 class!

The application deadline for all Woods Hole summer courses, including this one, has been extended to February 8th. The course itself runs from June 1 to July 14, and is open to graduate students, postdocs, and junior faculty.

Scholarships are available for accepted students, so don’t let money be an issue in your decision to apply.

For more information, see the course website. Good luck! We hope to see some of your images and posts on the Node in the coming year…

(1 votes)

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