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BackgroundSpatially restricted morphogen expression drives many patterning and regeneration processes, but how is the pattern of morphogen expression established and maintained? Patterning of Drosophila leg imaginal discs requires expression of the DPP morphogen dorsally and the wingless (WG) morphogen ventrally. We have shown that these mutually exclusive patterns of expression are controlled by a self-organizing system of feedback loops that involve WG and DPP, but whether the feedback is direct or indirect is not known.Methods/findingsBy analyzing expression patterns of regulatory DNA driving reporter genes in different genetic backgrounds, we identify a key component of this system by showing that WG directly represses transcription of the dpp gene in the ventral leg disc. Repression of dpp requires a tri-partite complex of the WG mediators armadillo (ARM) and dTCF, and the co-repressor Brinker, (BRK), wherein ARM.dTCF and BRK bind to independent sites within the dpp locus.Conclusions/significanceMany examples of dTCF repression in the absence of WNT signaling have been described, but few examples of signal-driven repression requiring both ARM and dTCF binding have been reported. Thus, our findings represent a new mode of WG mediated repression and demonstrate that direct regulation between morphogen signaling pathways can contribute to a robust self-organizing system capable of dynamically maintaining territories of morphogen expression.

Bone morphogenetic protein (BMP) signalling regulates embryonic dorsal-ventral cell fate decisions in flies, frogs and fish. BMP activity is controlled by several secreted factors including the antagonists chordin and short gastrulation (SOG). Here we show that a second secreted protein, Twisted gastrulation (Tsg), enhances the antagonistic activity of Sog/chordin. In Drosophila, visualization of BMP signalling using anti-phospho-Smad staining shows that the tsg and sog loss-of-function phenotypes are very similar. In S2 cells and imaginal discs, TSG and SOG together make a more effective inhibitor of BMP signalling than either of them alone. Blocking Tsg function in zebrafish with morpholino oligonucleotides causes ventralization similar to that produced by chordin mutants. Co-injection of sub-inhibitory levels of morpholines directed against both Tsg and chordin synergistically enhances the penetrance of the ventralized phenotype. We show that Tsgs from different species are functionally equivalent, and conclude that Tsg is a conserved protein that functions with SOG/chordin to antagonize BMP signalling.

Treacher Collins syndrome (TCS) is a congenital disorder of craniofacial development arising from mutations in TCOF1, which encodes the nucleolar phosphoprotein Treacle. Haploinsufficiency of Tcof1 perturbs mature ribosome biogenesis, resulting in stabilization of p53 and the cyclin G1-mediated cell-cycle arrest that underpins the specificity of neuroepithelial apoptosis and neural crest cell hypoplasia characteristic of TCS. Here we show that inhibition of p53 prevents cyclin G1-driven apoptotic elimination of neural crest cells while rescuing the craniofacial abnormalities associated with mutations in Tcof1 and extending life span. These improvements, however, occur independently of the effects on ribosome biogenesis; thus suggesting that it is p53-dependent neuroepithelial apoptosis that is the primary mechanism underlying the pathogenesis of TCS. Our work further implies that neuroepithelial and neural crest cells are particularly sensitive to cellular stress during embryogenesis and that suppression of p53 function provides an attractive avenue for possible clinical prevention of TCS craniofacial birth defects and possibly those of other neurocristopathies., Treacher Collins syndrome (Online Mendelian Inheritance in Man (OMIM) number 154500) is an autosomal dominant disorder of facial morphogenesis. The clinical features of TCS include abnormalities of the external ears [...]

Opitz G/BBB syndrome is associated with mutations in the MID1 protein's carboxyl-terminal domain. This domain appears to play a significant role in midline development during blastogenesis. The MID1 gene is located on Xp22. The complete structure of the MID1 gene has been determined and mutational analysis performed for all nine exons in 40 unrelated patients with Opitz G/BBB syndrome. Six new mutations have been identified in addition to three previously known ones.

Background: Astyanax mexicanus is a well‐established fish model system for evolutionary and developmental biology research. These fish exist as surface forms that inhabit rivers and 30 different populations of cavefish. Despite important progress in the deployment of new technologies, deep mechanistic insights into the genetic basis of evolution, development, and behavior have been limited by a lack of transgenic lines commonly used in genetic model systems. Results: Here, we expand the toolkit of transgenesis by characterizing two novel stable transgenic lines that were generated using the highly efficient Tol2 system, commonly used to generate transgenic zebrafish. A stable transgenic line consisting of the zebrafish ubiquitin promoter expresses enhanced green fluorescent protein ubiquitously throughout development in a surface population of Astyanax. To define specific cell‐types, a Cntnap2‐mCherry construct labels lateral line mechanosensory neurons in zebrafish. Strikingly, both constructs appear to label the predicted cell types, suggesting many genetic tools and defined promoter regions in zebrafish are directly transferrable to cavefish. Conclusion: The lines provide proof‐of‐principle for the application of Tol2 transgenic technology in A. mexicanus. Expansion on these initial transgenic lines will provide a platform to address broadly important problems in the quest to bridge the genotype‐phenotype gap. Key Findings: We have generated two new stable transgenic lines in Astyanax mexicanus using the Tol2 transposase system.We characterize in detail both lines, one expresses ubiquitously GFP and the other expresses mCherry cell‐type specific in the lateral line and the brain.We purposely used previously published zebrafish constructs in order to validate cross‐reactivity between the evolutionary divergent promoters. [ABSTRACT FROM AUTHOR]

Background: Roberts syndrome (RBS) is a human developmental disorder caused by mutations in the cohesin acetyltransferase ESCO2. We previously reported that mTORC1 signaling was depressed and overall translation was reduced in RBS cells and zebrafish models for RBS. Treatment of RBS cells and zebrafish RBS models with L-leucine partially rescued mTOR function and protein synthesis, correlating with increased cell division and improved development. Results: In this study, we use RBS cells to model mTORC1 repression and analyze transcription and translation with ribosome profiling to determine gene-level effects of L-leucine. L-leucine treatment partially rescued translational efficiency of ribosomal subunits, translation initiation factors, snoRNA production, and mitochondrial function in RBS cells, consistent with these processes being mTORC1 controlled. In contrast, other genes are differentially expressed independent of L-leucine treatment, including imprinted genes such as H19 and GTL2, miRNAs regulated by GTL2, HOX genes, and genes in nucleolar associated domains. Conclusions: Our study distinguishes between gene expression changes in RBS cells that are TOR dependent and those that are independent. Some of the TOR independent gene expression changes likely reflect the architectural role of cohesin in chromatin looping and gene expression. This study reveals the dramatic rescue effects of L-leucine stimulation of mTORC1 in RBS cells and supports that normal gene expression and translation requires ESCO2 function. [ABSTRACT FROM AUTHOR]

The piRNA pathway plays an important role in maintaining genome stability in the germ line by silencing transposable elements (TEs) from fly to mammals. As a highly conserved piRNA pathway component, Piwi is widely expressed in both germ cells and somatic cells in the Drosophila ovary and is required for piRNA production in both cell types. In addition to its known role in somatic cap cells to maintain germline stem cells (GSCs), this study has demonstrated that Piwi has novel functions in somatic cells and germ cells of the Drosophila ovary to promote germ cell differentiation. Piwi knockdown in escort cells causes a reduction in escort cell (EC) number and accumulation of undifferentiated germ cells, some of which show active BMP signaling, indicating that Piwi is required to maintain ECs and promote germ cell differentiation. Simultaneous knockdown of dpp, encoding a BMP, in ECs can partially rescue the germ cell differentiation defect, indicating that Piwi is required in ECs to repress dpp. Consistent with its key role in piRNA production, TE transcripts increase significantly and DNA damage is also elevated in the piwi knockdown somatic cells. Germ cell-specific knockdown of piwi surprisingly causes depletion of germ cells before adulthood, suggesting that Piwi might control primordial germ cell maintenance or GSC establishment. Finally, Piwi inactivation in the germ line of the adult ovary leads to gradual GSC loss and germ cell differentiation defects, indicating the intrinsic role of Piwi in adult GSC maintenance and differentiation. This study has revealed new germline requirement of Piwi in controlling GSC maintenance and lineage differentiation as well as its new somatic function in promoting germ cell differentiation. Therefore, Piwi is required in multiple cell types to control GSC lineage development in the Drosophila ovary. [ABSTRACT FROM AUTHOR]

The ciliary body (CB) of the mammalian eye is responsible for secreting aqueous humor to maintain intraocular pressure, which is elevated in the eyes of glaucoma patients. It contains a folded two-layered epithelial structure comprising the nonpigmented inner ciliary epithelium (ICE), the pigmented outer ciliary epithelium (OCE), and the underlying stroma. Although the CB has an important function in the eye, its morphogenesis remains poorly studied. In this study, we show that conditional inactivation of the Jagged 1 (Jag1)-Notch2 signaling pathway in the developing CB abolishes its morphogenesis. Notch2 is expressed in the OCE of the CB, whereas Jag1 is expressed in the ICE. Conditional inactivation of Jag1 in the ICE or Notch2 in the OCE disrupts CB morphogenesis, but neither affects the specification of the CB region. Notch2 signaling in the OCE is required for promoting cell proliferation and maintaining bone morphogenetic protein (BMP) signaling, both of which have been suggested to be important for CB morphogenesis. Although Notch and BMP signaling pathways are known to cross-talk via the interaction between their downstream transcriptional factors, this study suggests that Notch2 maintains BMP signaling in the OCE possibly by repressing expression of secreted BMP inhibitors. Based on our findings, we propose that Jag1-Notch2 signaling controls CB morphogenesis at least in part by regulating cell proliferation and BMP signaling. [ABSTRACT FROM AUTHOR]

The optic fissure (OF) is a transient opening on the ventral side of the developing vertebrate eye that closes before nearly all retinal progenitor cell differentiation has occurred. Failure to close the OF results in coloboma, a congenital disease that is a major cause of childhood blindness. Although human genetic studies and animal models have linked a number of genes to coloboma, the cellular and molecular mechanisms driving the closure of the OF are still largely unclear. In this study, we used Cre-LoxP-mediated conditional removal of fibroblast growth factor (FGF) receptors, Fgfr1 and Fgfr2, from the developing optic cup (OC) to show that FGF signaling regulates the closing of the OF. Our molecular, cellular and transcriptome analyses of Fgfr1 and Fgfr2 double conditional knockout OCs suggest that FGF signaling controls the OF closure through modulation of retinal progenitor cell proliferation, fate specification and morphological changes. Furthermore, Fgfr1 and Fgfr2 double conditional mutant retinal progenitor cells fail to initiate retinal ganglion cell (RGC) genesis. Taken together, our mouse genetic studies reveal that FGF signaling is essential for OF morphogenesis and RGC development. [ABSTRACT FROM AUTHOR]