Developmental Biology (Dev Biol)

Publications in this journal

• Article: The G alpha subunit Gα8 inhibits proliferation, promotes adhesion and regulates cell differentiation.

  Yuantai Wu, Chris Janetopoulos
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  ABSTRACT: Heterotrimeric G protein-mediated signal transduction plays a pivotal role in both vegetative and developmental stages in the eukaryote Dictyostelium discoideum. Here we describe novel functions of the G protein alpha subunit Gα8 during vegetative and development stages. Gα8 is expressed at low levels during vegetative growth. Loss of Gα8 promotes cell proliferation, whereas excess Gα8 expression dramatically inhibits growth and induces aberrant cytokinesis on substrates in a Gβ-dependent manner. Overexpression of Gα8 also leads to increased cell-cell cohesion and cell-substrate adhesion. We demonstrate that the increased cell-cell cohesion is mainly caused by induced CadA expression, and the induced cell-substrate adhesion is responsible for the cytokinesis defects. However, the expression of several putative constitutively active mutants of Gα8 does not augment the phenotypes caused by intact Gα8. Gα8 is strongly induced after starvation, and loss of Gα8 results in decreased expression of certain adhesion molecules including CsA and tgrC1. Interestingly, Gα8 is preferentially distributed in the upper and lower cup of the fruiting body. Lack of Gα8 decreases the expression of the specific marker of the anterior-like cells, suggesting that Gα8 is required for anterior-like cell differentiation.
  Developmental Biology 05/2013;
• Article: A temporal mechanism that produces neuronal diversity in the Drosophila visual center.

  Takumi Suzuki, Masako Kaido, Rie Takayama, Makoto Sato
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  ABSTRACT: The brain consists of various types of neurons that are generated from neural stem cells; however, the mechanisms underlying neuronal diversity remain uncertain. A recent study demonstrated that the medulla, the largest component of the Drosophila optic lobe, is a suitable model system for brain development because it shares structural features with the mammalian brain and consists of a moderate number and various types of neurons. The concentric zones in the medulla primordium that are characterized by the expression of four transcription factors, including Homothorax (Hth), Brain-specific homeobox (Bsh), Runt (Run), and Drifter (Drf), correspond to types of medulla neurons. Here, we examine the mechanisms that temporally determine the neuronal types in the medulla primordium. For this purpose, we searched for transcription factors that are transiently expressed in a subset of medulla neuroblasts (NBs, neuronal stem cell-like neural precursor cells) and identified five candidates (Hth, Klumpfuss (Klu), Eyeless (Ey), Sloppy paired (Slp), and Dichaete (D)). The results of genetic experiments at least explain the temporal transition of the transcription factor expression in NBs in the order of Ey, Slp and D. Our results also suggest that expression of Hth, Klu and Ey in NBs trigger the production of Hth/Bsh-, Run- and Drf-positive neurons, respectively. These results suggest that medulla neuron types are specified in a birth order-dependent manner by the action of temporal transcription factors that are sequentially expressed in NBs.
  Developmental Biology 05/2013;
• Article: A distant, cis-acting enhancer drives induction of Arf by Tgfβ in the developing eye.

  Yanbin Zheng, Caitlin Devitt, Jing Liu, Jie Mei, Stephen X Skapek
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  ABSTRACT: The Arf tumor suppressor represents one of several genes encoded at the Cdkn2a and Cdkn2b loci in the mouse. Beyond its role blunting the growth of incipient cancer cells, the Arf gene also plays an essential role in development: Its gene product, p19(Arf), is induced by Tgfβ2 in the developing eye to dampen proliferative signals from Pdgfrβ, which effect ultimately fosters the vascular remodeling required for normal vision in the mouse. Mechanisms underlying Arf induction by Tgfβ2 are not fully understood. Using the chr4(Δ70kb/Δ70kb) mouse, we now show that deletion of the coronary artery disease (CAD) risk interval lying upstream of the Cdkn2a/b locus represses developmentally-timed induction of Arf resulting in eye disease mimicking the persistent hyperplastic primary vitreous (PHPV) found in Arf-null mice and in children. Using mouse embryo fibroblasts, we demonstrate that Arf induction by Tgfβ is blocked in cis to the 70kb deletion, but Arf induction by activated RAS and cell culture "shock" is not. Finally, we show that Arf induction by Tgfβ is derailed by preventing RNA polymerase II recruitment following Smad 2/3 binding to the promoter. These findings provide the first evidence that the CAD risk interval, located at a distance from Arf, acts as a cis enhancer of Tgfβ2-driven induction of Arf during development.
  Developmental Biology 05/2013;
• Article: Real-time in vivo monitoring of circadian E-box enhancer activity: A robust and sensitive zebrafish reporter line for developmental, chemical and neural biology of the circadian clock.

  Meltem Weger, Benjamin D Weger, Nicolas Diotel, Sepand Rastegar, Tsuyoshi Hirota, Steve A Kay, Uwe Strähle, Thomas Dickmeis
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  ABSTRACT: The circadian clock co-ordinates physiology and behavior with the day/night cycle. It consists of a transcriptional-translational feedback loop that generates self-sustained oscillations in transcriptional activity with a roughly 24h period via E-box enhancer elements. Numerous in vivo aspects of core clock feedback loop function are still incompletely understood, including its maturation during development, tissue-specific activity and perturbation in disease states. Zebrafish are promising models for biomedical research due to their high regenerative capacity and suitability for in vivo drug screens, and transgenic zebrafish lines are valuable tools to study transcriptional activity in vivo during development. To monitor the activity of the core clock feedback loop in vivo, we created a transgenic zebrafish line expressing a luciferase reporter gene under the regulation of a minimal promoter and four E-boxes. This Tg(4xE-box:Luc) line shows robust oscillating reporter gene expression both under light-dark cycles and upon release into constant darkness. Luciferase activity starts to oscillate during the first days of development, indicating that the core clock loop is already functional at an early stage. To test whether the Tg(4xE-box:Luc) line could be used in drug screens aimed at identifying compounds that target the circadian clock in vivo, we examined drug effects on circadian period. We were readily able to detect period changes as low as 0.7h upon treatment with the period-lengthening drugs lithium chloride and longdaysin in an assay set-up suitable for large-scale screens. Reporter gene mRNA expression is also detected in the adult brain and reveals differential clock activity across the brain, overlapping with endogenous clock gene expression. Notably, core clock activity is strongly correlated with brain regions where neurogenesis takes place and can be detected in several types of neural progenitors. Our results demonstrate that the Tg(4xE-box:Luc) line is an excellent tool for studying the regulation of the circadian clock and its maturation in vivo and in real-time. Furthermore, it is highly suitable for in vivo screens targeting the core clock mechanism that take into account the complexity of an intact organism. Finally, it allows mapping of clock activity in the brain of a vertebrate model organism with prominent adult neurogenesis and high regeneration capacity.
  Developmental Biology 05/2013;
• Article: Evolution of the Insect Terminal Patterning System - Insights from the Milkweed Bug, Oncopeltus fasciatus.

  Anat Weisbrod, Mira Cohen, Ariel D Chipman
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  ABSTRACT: The anterior and posterior ends of the insect embryo are patterned through the terminal patterning system, which is best known from the fruitfly Drosophila melanogaster. In Drosophila, the RTK receptor Torso, and its presumed co-activator Torso-like, initiate a signaling cascade, which activates two terminal gap genes, tailless and huckebein. These in turn interact with various patterning genes to define terminal structures. Work on other insect species has shown that this system is poorly conserved, and not all of its components have been found in all cases studied. We place the variability of the system within a broader phylogenetic framework. We describe the expression and knock-down phenotypes of the homologues of terminal patterning genes in the hemimetabolous Oncopeltus fasciatus. We have examined the interactions among these genes and between them and other patterning genes. We demonstrate that all of these genes have different roles in Oncopeltus relative to Drosophila; torso-like is expressed in follicle cells during oogenesis and is involved in the invagination of the blastoderm to form the germ band, and possibly also in defining the growth zone; tailless is regulated by orthodenticle and has a role only in anterior determination; huckebein is expressed only in the middle of the blastoderm; finally, torso was not found in Oncopeltus and its role in terminal patterning seems novel within holometabolous insects. We then use our data, together with published data on other insects, to reconstruct the evolution of the terminal patterning gene network in insects. We suggest that the Drosophila terminal patterning network evolved recently in the lineage leading to the Diptera, and represents an example of evolutionary "tinkering", where pre-existing pathways are co-opted for a new function.
  Developmental Biology 05/2013;
• Article: Zebrafish Zic2a and Zic2b regulate neural crest and craniofacial development.

  Jessica J Teslaa, Abigail N Keller, Molly K Nyholm, Yevgenya Grinblat
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  ABSTRACT: Holoprosencephaly (HPE), the most common malformation of the human forebrain, is associated with defects of the craniofacial skeleton. ZIC2, a zinc-finger transcription factor, is strongly linked to HPE and to a characteristic set of dysmorphic facial features in humans. We have previously identified important functions for zebrafish Zic2 in the developing forebrain. Here, we demonstrate that ZIC2 orthologs zic2a and zic2b also regulate the forming zebrafish craniofacial skeleton, including the jaw and neurocranial cartilages, and use the zebrafish to study Zic2-regulated processes that may contribute to the complex etiology of HPE. Using temporally controlled Zic2a overexpression, we show that the developing craniofacial cartilages are sensitive to Zic2 elevation prior to 24hpf. This window of sensitivity overlaps the critical expansion and migration of the neural crest (NC) cells, which migrate from the developing neural tube to populate vertebrate craniofacial structures. We demonstrate that zic2b influences the induction of NC at the neural plate border, while both zic2a and zic2b regulate NC migratory onset and strongly contribute to chromatophore development. Both Zic2 depletion and early ectopic Zic2 expression cause moderate, incompletely penetrant mispatterning of the NC-derived jaw precursors at 24hpf, yet by 2dpf these changes in Zic2 expression result in profoundly mispatterned chondrogenic condensations. We attribute this discrepancy to an additional role for Zic2a and Zic2b in patterning the forebrain primordium, an important signaling source during craniofacial development. This hypothesis is supported by evidence that transplanted Zic2-deficient cells can contribute to craniofacial cartilages in a wild-type background. Collectively, these data suggest that zebrafish Zic2 plays a dual role during craniofacial development, contributing to two disparate aspects of craniofacial morphogenesis: (1) Neural crest induction and migration, and (2) early patterning of tissues adjacent to craniofacial chondrogenic condensations.
  Developmental Biology 05/2013;
• Article: PI3K regulates branch initiation and extension of cultured mammary epithelia, via Akt and Rac1 respectively.

  Wenting Zhu, Celeste M Nelson
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  ABSTRACT: The tree-like architecture of the mammary gland is generated by branching morphogenesis, which is regulated by many signals from the microenvironment. Here we examined how signaling downstream of phosphoinositide 3-kinase (PI3K) regulates different steps of mammary branching using three-dimensional culture models of the mammary epithelial duct. We found that PI3K was required for both branch initiation and elongation. Activated Akt was enhanced at branch initiation sites where its negative regulator, PTEN, was blocked by signaling via Sprouty2 (SPRY2); inhibiting Akt prevented branch initiation. The pattern of SPRY2 expression, and thus of Akt activation and branch initiation, was controlled by mechanical signaling from endogenous cytoskeletal contractility. In contrast, activated GTP-bound Rac1 localized to the leading edge of nascent branches and was required for branch elongation. These data suggest that the PI3K network integrates mechanical and biochemical signaling to control branching morphogenesis of mammary epithelial cells.
  Developmental Biology 05/2013;
• Article: Differential stage-dependent regulation of prostatic epithelial morphogenesis by Hedgehog signaling.

  Min Yu, Wade Bushman
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  ABSTRACT: Published studies of Hh (Hedgehog) signaling in the developing prostate have reported varying and discrepant effects on epithelial proliferation, ductal morphogenesis and growth. We report here that these differing observations accrue from stage-specific effects of Hh signaling in the developing prostate. Using in vitro organ culture of the E16 UGS and P1 prostate, we show that ectopic Hh pathway activation stimulates epithelial proliferation prenatally, but inhibits epithelial proliferation postanatally. Extrapolating from previously published observations that Hh target gene expression is altered in the reactive stroma of prostate cancer, we examined and found discordant regulation of a subset of target genes by Hh signaling in the prenatal and postnatal prostate. Cell based studies and recombination assays show that these changes are not simply attributable to the age of the mesenchyme or the epithelium, but more likely reflect a complex regulation by the cellular microenvironment. To determine the in vivo relevance of these observations, we examined the effect of transgenic activation of Hh signaling on epithelial proliferation in the prenatal and postnatal prostate and confirmed the operation of stage-specific effects. These observations demonstrate stage-specific differences in the effect of Hh signaling on epithelial proliferation in the developing prostate and suggest that these are a product of complex interactions determined by the cellular microenvironment.
  Developmental Biology 05/2013;
• Article: ESET histone methyltransferase is essential to hypertrophic differentiation of growth plate chondrocytes and formation of epiphyseal plates.

  Liu Yang, Kevin A Lawson, Colin J Teteak, Junhui Zou, Jacques Hacquebord, David Patterson, Andrew C Ghatan, Qi Mei, Anna Zielinska-Kwiatkowska, Steven D Bain, Russell J Fernandes, Howard A Chansky
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  ABSTRACT: The ESET (also called SETDB1) protein contains an N-terminal tudor domain that mediates protein-protein interactions and a C-terminal SET domain that catalyzes methylation of histone H3 at lysine 9. We report here that ESET protein is transiently upregulated in prehypertrophic chondrocytes in newborn mice. To investigate the in vivo effects of ESET on chondrocyte differentiation, we generated conditional knockout mice to specifically eliminate the catalytic SET domain of ESET protein only in mesenchymal cells. Such deletion of the ESET gene caused acceleration of chondrocyte hypertrophy in both embryos and young animals, depleting chondrocytes that are otherwise available to form epiphyseal plates for endochondral bone growth. ESET-deficient mice are thus characterized by defective long bone growth and trabecular bone formation. To understand the underlying mechanism for ESET regulation of chondrocytes, we carried out co-expression experiments and found that ESET associates with histone deacetylase 4 to bind and inhibit the activity of Runx2, a hypertrophy-promoting transcription factor. Repression of Runx2-mediated gene transactivation by ESET is dependent on its H3-K9 methyltransferase activity as well as its associated histone deacetylase activity. In addition, knockout of ESET is associated with repression of Indian hedgehog gene in pre- and early hypertrophic chondrocytes. Together, these results provide clear evidence that ESET controls hypertrophic differentiation of growth plate chondrocytes and endochondral ossification during embryogenesis and postnatal development.
  Developmental Biology 05/2013;
• Article: Primordial germ cells in an oligochaete annelid are specified according to the birth rank order in the mesodermal teloblast lineage.

  Yukie Kato, Ayaki Nakamoto, Inori Shiomi, Hajime Nakao, Takashi Shimizu
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  ABSTRACT: The primordial germ cells (PGCs) in the oligochaete annelid Tubifex tubifex are descentants of the mesodermal (M) teloblast and are located in the two midbody segments X and XI in which they serve as germline precursors forming the testicular gonad and the ovarian gonad, respectively. During embryogenesis, vasa-expressing cells (termed presumptive PGCs or pre-PGCs) emerge in a variable set of midbody segments including the genital segments (X and XI); at the end of embryogenesis, pre-PGCs are confined to the genital segments, where they become PGCs in the juvenile. Here, using live imaging of pre-PGCs, we have demonstrated that during Tubifex embryogenesis, pre-PGCs (defined by Vasa expression) stay in segments where they have emerged, suggesting that it is unlikely that pre-PGCs move intersegmentally during embryogenesis. Thus, it is apparent that pre-PGCs derived from the 10th and 11th M teloblast-derived primary m blast cells (designated m10 and m11) that give rise, respectively, to segments X and XI are specified in situ as PGCs and that those born in other segments become undetectable at the end of embryogenesis. To address the mechanisms for this segment-specific development of PGCs, we have performed a set of cell-transplantation experiments as well as cell-ablation experiments. When m10 and m11 that are normally located in the mid region of the embryo were placed in positions near the anterior end of the host embryo, these cells formed two consecutive segments, which exhibited Vasa-positive PGC-like cells at early juvenile stage. This suggests that in terms of PGC generation, the fates of m10 and m11 remain unchanged even if they are placed in ectopic positions along the anteroposterior axis. Nor was the fate of m10 and m11 changed even if mesodermal blast cell chains preceding or succeeding m10 and m11 were absent. In a previous study, it was shown that PGC development in segments X and XI occurs normally in the absence of the overlying ectoderm. All this strongly suggests that irrespective of their surrounding cellular environments, m10 and m11 autonomously generate PGCs. We propose that m10 and m11 are exclusively specified as precursors of PGCs at the time of their birth from the M teloblast and that the M teloblast possesses a developmental program through which the sequence of mesodermal blast cell identities is determined.
  Developmental Biology 05/2013;
• Article: The LIM-Homeodomain Transcription factor Islet-1 is required for the development of sympathetic neurons and adrenal chromaffin cells.

  Katrin Huber, Priyanka Narasinham, Stella Shtukmaster, Dietmar Pfeifer, Sylvia M Evans, Yunfu Sun
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  ABSTRACT: Islet-1 is a Lim-Homeodomain transcription factor with important functions for the development of distinct neuronal and non-neuronal cell populations. We show here that Islet-1 acts genetically downstream of Phox2B in cells of the sympathoadrenal cell lineage and that the development of sympathetic neurons and chromaffin cells is impaired in mouse embryos with a conditional deletion of Islet-1 controlled by the wnt1 promotor. Islet-1 is not essential for the initial differentiation of sympathoadrenal cells, as indicated by the correct expression of pan-neuronal and catecholaminergic subtype specific genes in primary sympathetic ganglia of Islet-1 deficient mouse embryos. However, our data indicate that the subsequent survival of sympathetic neuron precursors and their differentiation towards TrkA expressing neurons depends on Islet-1 function. In contrast to spinal sensory neurons, sympathetic neurons of Islet-1 deficient mice did not display ectopic expression of genes normally present in the CNS. In Islet-1 deficient mouse embryos the numbers of chromaffin cells were only mildly reduced, in contrast to that of sympathetic neurons, but the initiation of the adrenaline synthesizing enzyme PNMT was abrogated and the expression level of chromogranin A was diminished. Microarray analysis revealed that developing chromaffin cells of Islet-1 deficient mice displayed normal expression levels of TH, DBH and the transcription factors Phox2B, Mash-1, Hand2, Gata3 and Insm1, but the expression levels of the transcription factors Gata2 and Hand1, and AP-2ß were significantly reduced. Together our data indicate that Islet-1 is not essentially required for the initial differentiation of sympathoadrenal cells, but has an important function for the correct subsequent development of sympathetic neurons and chromaffin cells.
  Developmental Biology 05/2013;
• Article: The widely used Wnt1-Cre transgene causes developmental phenotypes by ectopic activation of Wnt signaling.

  Ace E Lewis, Harish N Vasudevan, Audrey K O'Neill, Philippe Soriano, Jeffrey O Bush
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  ABSTRACT: The Wnt1-Cre transgenic mouse line is extensively used in the study of the development of the neural crest and its derivatives and the midbrain. The Wnt1 gene has important developmental roles in formation of the midbrain-hindbrain boundary, regulation of midbrain size, and neurogenesis of ventral midbrain dopaminergic (mDA) neurons. Here, we report that Wnt1-Cre transgenic mice exhibit phenotypes in multiple aspects of midbrain development. Significant expansion of the midbrain and increased proliferation in the developing inferior colliculus is associated with ectopic expression of Wnt1. Marked elevation of Wnt1 expression in the ventral midbrain is correlated with disruption of the differentiation program of ventral mDA neurons. We find that these phenotypes can be attributed to ectopic expression of Wnt1 from the Wnt1-Cre transgene leading to the ectopic activation of canonical Wnt/β-catenin signaling. Since these caveats could complicate the utility of Wnt1-Cre in some developmental circumstances, we report a new Wnt1-Cre2 transgenic mouse line that can serve the same purposes as the original without the associated phenotypic complications. These studies reveal an important caveat to a widely-used reagent, provide an improved version of this reagent, and indicate that the original Wnt1-Cre transgenic mouse line may be useful as a gain of function model for interrogating Wnt signaling mechanisms in multiple aspects of midbrain development.
  Developmental Biology 05/2013;
• Article: The role of SOX10 during enteric nervous system development.

  Nadege Bondurand, Mai Har Sham
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  ABSTRACT: The SOX10 transcription factor is a characteristic marker for migratory multipotent neural crest (NC) progenitors as well as several of their differentiated derivatives. The involvement of SOX10 in Waardenburg-Hirschsprung disease (pigmentation defects, deafness and intestinal aganglionosis) and studies of mutant animal models have contributed significantly to the understanding of its function in neural crest cells (NCC) in general and in the melanocytes and enteric nervous system (ENS) in particular. Cell-based studies have further demonstrated the important roles of this transcription factor in maintaining the NC progenitor cell number and in determining glial cell fate. Phenotypic variability observed among patients presenting with SOX10 mutations is in agreement with molecular genetics and animal model studies, which revealed that SOX10 cooperates with different partner factors; a number of genetic modifiers of SOX10 have been identified. This study reviews the expression, regulation, and function of SOX10 in normal development of the ENS and in disease conditions, as well as the genetic and molecular interactions of SOX10 with other ENS genes/factors. We also discuss future research areas. Further understanding of SOX10 function will benefit from genomic and cell biological studies that integrate the cell-intrinsic molecular mechanisms and the interactions of the enteric NCC with the niche environment.
  Developmental Biology 05/2013;
• Article: Mouse limbs expressing only the Gli3 repressor resemble those of Sonic Hedgehog mutants.

  Ting Cao, Chengbing Wang, Mei Yang, Chuanqing Wu, Baolin Wang
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  ABSTRACT: Anterioposterior vertebrate limb patterning is controlled by opposing action between Sonic Hedgehog (Shh) and the Gli3 transcriptional repressor. Unexpectedly, Gli3(Δ699) mutant mice, which are thought to express only a Gli3 repressor and not the full-length activator, exhibit limb phenotypes inconsistent with those of Shh mutant mice. Therefore, it remains debatable whether Shh patterns the anterioposterior limb primarily by inhibiting generation of the Gli3 repressor. However, one caveat is that Gli3(Δ699) may not be as potent as the natural form of Gli3 repressor because of the nature of the mutant allele. In the present study, we created a conditional Gli3 mutant allele that exclusively expresses Gli3 repressor in the presence of Cre recombinase. Using this mutant, we show that the phenotypes of mouse limbs expressing only the Gli3 repressor exhibit no or single digit, resembling those of Shh mutant limbs. Consistent with the limb phenotypes, the expression of genes dependent on Shh signaling is also inhibited in both mutants. This inhibition by the Gli3 repressor is independent of Shh. Thus, our study clarifies the current controversy and provides important genetic evidence to support the hypothesis that Shh patterns the anterioposterior limb primarily through the inhibition of Gli3 repressor formation.
  Developmental Biology 05/2013;
• Article: The mechanisms of planar cell polarity, growth and the Hippo pathway: Some known unknowns.

  Peter A Lawrence, José Casal
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  ABSTRACT: Planar cell polarity (PCP) is a small but important area of research. In this review we discuss a limited number of topics within the PCP field, chosen because they are difficult, unsolved, controversial or just because we find them interesting. Because Drosophila is the best studied and technically most amenable system we have concentrated on it, but also consider some examples from work on vertebrates. Topics discussed include the number of genetic pathways involved in PCP, as well as the causal relationship between embryonic axes, gradients of morphogens and PCP itself. We consider the vexed question of the roles of the Wnt genes in PCP in both vertebrates and Drosophila. We discuss whether the proteins involved in PCP need to be localised asymmetrically in cells in order to function. We criticise the way the Hippo pathway is described in the literature and ask what its wildtype function is. We explore afresh how the Hippo pathway might be linked both to growth and to PCP through the gigantic cadherin molecule Fat. We offer some new ways of making sense of published results, particularly those relating to the Frizzled/Starry night and Dachsous/Fat systems of PCP.
  Developmental Biology 05/2013; 377(1):1-8.
• Article: Differential BMP signaling controls formation and differentiation of multipotent preplacodal ectoderm progenitors from human embryonic stem cells.

  Alan W Leung, D Kent Morest, James Y H Li
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  ABSTRACT: Sensory and endoneurocrine tissues as diverse as the lens, the olfactory epithelium, the inner ear, the cranial sensory ganglia, and the anterior pituitary arise from a common pool of progenitors in the preplacodal ectoderm (PPE). Around late gastrulation, the PPE forms at the border surrounding the anterior neural plate, and expresses a unique set of evolutionarily conserved transcription regulators including Six1, Eya 1 and Eya2. Here, we describe the first report to generate and characterize the SIX1(+) PPE cells from human ES cells by adherent differentiation. Before forming PPE cells, differentiating cultures first expressed the non-neural ectoderm specific transcriptional factors TFAP2A, GATA2, GATA3, DLX3, and DLX5, which are crucial in establishing the PPE competence. We demonstrated that bone morphogenetic protein (BMP) activity plays a transient but essential role in inducing expression of these PPE competence factors and eventually the PPE cells. Interestingly, we found that attenuating BMP signaling after establishing the competence state induces anterior placode precursors. By manipulating BMP and hedgehog signaling pathways, we further differentiate these precursors into restricted lineages including the lens placode and the oral ectoderm (pituitary precursor) cells. Finally, we also show that sensory neurons can be generated from human PPE cells, demonstrating the multipotency of the human ES-derived PPE cells.
  Developmental Biology 04/2013;
• Article: Myf5 expression during fetal myogenesis defines the developmental progenitors of adult satellite cells.

  Stefano Biressi, Christopher R R Bjornson, Poppy M M Carlig, Koichi Nishijo, Charles Keller, Thomas A Rando
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  ABSTRACT: Myf5 is a member of the muscle-specific determination genes and plays a critical role in skeletal muscle development. Whereas the expression of Myf5 during embryonic and fetal myogenesis has been extensively studied, its expression in progenitors that will ultimately give rise to adult satellite cells, the stem cells responsible for muscle repair, is still largely unexplored. To investigate this aspect, we have generated a mouse strain carrying a CreER coding sequence in the Myf5 locus. In this strain, Tamoxifen-inducible Cre activity parallels endogenous Myf5 expression. Combining Myf5(CreER) and Cre reporter alleles, we were able to evaluate the contribution of cells expressing Myf5 at distinct developmental stages to the pool of satellite cells in adult hindlimb muscles. Although it was possible to trace back the origin of some rare satellite cells to a subpopulation of Myf5(+ve) progenitors in the limb buds at the late embryonic stage (∼E12), a significant number of satellite cells arise from cells which expressed Myf5 for the first time at the fetal stage (∼E15). These studies provide direct evidence that adult satellite cells derive from progenitors that first express the myogenic determination gene Myf5 during fetal stages of myogenesis.
  Developmental Biology 04/2013;
• Article: A multipotent transit-amplifying neuroblast lineage in the central brain gives rise to optic lobe glial cells in Drosophila.

  Gudrun Viktorin, Nadia Riebli, Heinrich Reichert
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  ABSTRACT: The neurons and glial cells of the Drosophila brain are generated by neural stem cell-like progenitors during two developmental phases, one short embryonic phase and one more prolonged postembryonic phase. Like the bulk of the adult-specific neurons, most of glial cells found in the adult central brain are generated postembryonically. Five of the neural stem cell-like progenitors that give rise to glial cells during postembryonic brain development have been identified as type II neuroglioblasts that generate neural and glial progeny through transient amplifying INPs. Here we identify DL1 as a novel multipotent neuroglial progenitor in the central brain and show that this type II neuroblast not only gives rise to neurons that innervate the central complex but also to glial cells that contribute exclusively to the optic lobe. Immediately following their generation in the central brain during the second half of larval development, these DL1 lineage-derived glia migrate into the developing optic lobe, where they differentiate into three identified types of optic lobe glial cells, inner chiasm glia, outer chiasm glia and cortex glia. Taken together, these findings reveal an unexpected central brain origin of optic lobe glial cells and central complex interneurons from one and the same type II neuroglioblast.
  Developmental Biology 04/2013;
• Article: Embryonic founders of adult muscle stem cells are primed by the determination gene Mrf4.

  Ramkumar Sambasivan, Glenda Comai, Isabelle Le Roux, Danielle Gomès, Julie Konge, Gérard Dumas, Clémire Cimper, Shahragim Tajbakhsh
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  ABSTRACT: Skeletal muscle satellite cells play a critical role during muscle growth, homeostasis and regeneration. Selective induction of the muscle determination genes Myf5, Myod and Mrf4 during prenatal development can potentially impact on the reported functional heterogeneity of adult satellite cells. Accordingly, expression of Myf5 was reported to diminish the self-renewal potential of the majority of satellite cells. In contrast, virtually all adult satellite cells showed antecedence of Myod activity. Here we examine the priming of myogenic cells by Mrf4 throughout development. Using a Cre-lox based genetic strategy and novel highly sensitive Pax7 reporter alleles compared to the ubiquitous Rosa26-based reporters, we show that all adult satellite cells, independently of their anatomical location or embryonic origin, have been primed for Mrf4 expression. Given that Mrf4(Cre) and Mrf4(nlacZ) are active exclusively in progenitors during embryogenesis, whereas later expression is restricted to differentiated myogenic cells, our findings suggest that adult satellite cells emerge from embryonic founder cells in which the Mrf4 locus was activated. Therefore, this level of myogenic priming by induction of Mrf4, does not compromise the potential of the founder cells to assume an upstream muscle stem cell state. We propose that embryonic myogenic cells and the majority of adult muscle stem cells form a lineage continuum.
  Developmental Biology 04/2013;
• Article: Foxg1 is required to limit the formation of ciliary margin tissue and Wnt/β-catenin signalling in the developing nasal retina of the mouse.

  Vassiliki Fotaki, Rowena Smith, Thomas Pratt, David J Price
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  ABSTRACT: The ciliary margin (CM) develops in the peripheral retina and gives rise to the iris and the ciliary body. The Wnt/β-catenin signalling pathway has been implicated in ciliary margin development. Here, we tested the hypothesis that in the developing mouse retina Foxg1 is responsible for suppressing the Wnt/β-catenin pathway and restricting CM development. We showed that there is excess CM tissue in Foxg1(-/-) null embryos and this expansion is more pronounced in the nasal retina where Foxg1 normally shows its highest expression levels. Results on expression of a reporter allele for Wnt/β-catenin signalling and of Lef1, a target of Wnt/β-catenin signalling, displayed significant upregulation of this pathway in Foxg1(-/-) nulls at embryonic days (E) 12.5 and E14.5. Interestingly, this upregulation was observed specifically in the nasal retina, where normally very few Wnt-responsive cells are observed. These results indicate a suppressive role of Foxg1 on this signalling pathway. Our results reveal a new role of Foxg1 in limiting CM development in the nasal peripheral retina and add a new molecular player in the developmental network involved in CM specification.
  Developmental Biology 04/2013;