The forkhead transcription factor UNC-130/FOXD integrates both BMP and Notch signaling to regulate dorsoventral patterning of the C. elegans postembryonic mesoderm

Agouti and BMP signaling drive a naturally occurring fate conversion of melanophores to leucophores in zebrafish

The often-distinctive pigment patterns of vertebrates are varied in form and function and depend on several types of pigment cells derived from embryonic neural crest or latent stem cells of neural crest origin. These cells and the patterns they produce have been useful for uncovering features of differentiation and morphogenesis that underlie adult phenotypes, and they offer opportunities to discover how patterns and the cell types themselves have diversified. In zebrafish, a body pattern of stripes arises by self-organizing interactions among three types of pigment cells. Yet these fish also exhibit white ornamentation on their fins that depends on the transdifferentiation of black melanophores to white cells, "melanoleucophores." To identify mechanisms underlying this conversion we used ultrastructural, transcriptomic, mutational, and other approaches. We show that melanophore-melanoleucophore transition depends on regional BMP signals transduced through noncanonical receptors (Rgmb-Neo1a-Lrig2) as well as BMP-dependent signaling by Agouti genes, asip1 and asip2b. These signals lead to expression of transcription factor genes including foxd3 and runx3 that are necessary to induce loss of melanin, curtail new melanin production, and deploy a pathway for accumulating guanine crystals that, together, confer a white phenotype. These analyses uncover an important role for positional information in specifying ornamentation in zebrafish and show how tissue environmental cues and an altered gene regulatory program have allowed terminal addition of a distinct phenotype to a preexisting cell type.

Highly conserved and extremely evolvable: BMP signalling in secondary axis patterning of Cnidaria and Bilateria

Bilateria encompass the vast majority of the animal phyla. As the name states, they are bilaterally symmetric, that is with a morphologically clear main body axis connecting their anterior and posterior ends, a second axis running between their dorsal and ventral surfaces, and with a left side being roughly a mirror image of their right side. Bone morphogenetic protein (BMP) signalling has widely conserved functions in the formation and patterning of the second, dorso-ventral (DV) body axis, albeit to different extents in different bilaterian species. Whilst initial findings in the fruit fly Drosophila and the frog Xenopus highlighted similarities amongst these evolutionarily very distant species, more recent analyses featuring other models revealed considerable diversity in the mechanisms underlying dorsoventral patterning. In fact, as phylogenetic sampling becomes broader, we find that this axis patterning system is so evolvable that even its core components can be deployed differently or lost in different model organisms. In this review, we will try to highlight the diversity of ways by which BMP signalling controls bilaterality in different animals, some of which do not belong to Bilateria. Future research combining functional analyses and modelling is bound to give us some understanding as to where the limits to the extent of the evolvability of BMP-dependent axial patterning may lie.

Mechanisms of lineage specification in Caenorhabditis elegans

The studies of cell fate and lineage specification are fundamental to our understanding of the development of multicellular organisms. Caenorhabditis elegans has been one of the premiere systems for studying cell fate specification mechanisms at single cell resolution, due to its transparent nature, the invariant cell lineage, and fixed number of somatic cells. We discuss the general themes and regulatory mechanisms that have emerged from these studies, with a focus on somatic lineages and cell fates. We next review the key factors and pathways that regulate the specification of discrete cells and lineages during embryogenesis and postembryonic development; we focus on transcription factors and include numerous lineage diagrams that depict the expression of key factors that specify embryonic founder cells and postembryonic blast cells, and the diverse somatic cell fates they generate. We end by discussing some future perspectives in cell and lineage specification.

A comprehensive study of arthropod and onychophoran Fox gene expression patterns

Fox genes represent an evolutionary old class of transcription factor encoding genes that evolved in the last common ancestor of fungi and animals. They represent key-components of multiple gene regulatory networks (GRNs) that are essential for embryonic development. Most of our knowledge about the function of Fox genes comes from vertebrate research, and for arthropods the only comprehensive gene expression analysis is that of the fly Drosophila melanogaster. For other arthropods, only selected Fox genes have been investigated. In this study, we provide the first comprehensive gene expression analysis of arthropod Fox genes including representative species of all main groups of arthropods, Pancrustacea, Myriapoda and Chelicerata. We also provide the first comprehensive analysis of Fox gene expression in an onychophoran species. Our data show that many of the Fox genes likely retained their function during panarthropod evolution highlighting their importance in development. Comparison with published data from other groups of animals shows that this high degree of evolutionary conservation often dates back beyond the last common ancestor of Panarthropoda.

Crosstalk between BMP and Notch Induces Sox2 in Cerebral Endothelial Cells

Bone morphogenetic protein (BMP) and Notch signaling are critical for endothelial cell (EC) differentiation in vascular development. Recent studies have shown that excess BMP activity induces Notch signaling in cerebral ECs resulting in arteriovenous malformation (AVMs). However, it is unclear how the crosstalk between BMP and Notch signaling affects cerebral EC differentiation at the gene regulatory level. Here, we report that BMP6 activates the activin receptor-like kinase (ALK) 3, a BMP type 1 receptor, to induce Notch1 receptor and Jagged1 and Jagged2 ligands. We show that increased expression of the Notch components alters the transcriptional regulatory complex in the SRY-Box 2 (Sox2) promoter region so as to induce its expression in cerebral ECs. Together, our results identify Sox2 as a direct target of BMP and Notch signaling and provide information on how altered BMP and Notch signaling affects the endothelial transcriptional landscape.

A large transcribed enhancer region regulates C. elegans bed-3 and the development of egg laying muscles

Gene expression is regulated by the interaction of the RNA polymerase with various transcription factors at promoter and enhancer elements. Transcriptome analyses found that many non-protein-coding regions are transcribed to produce long non-coding RNAs and enhancer-associated RNAs. Production of these transcripts is associated with activation of nearby protein-coding genes, and at least in some cases, the transcripts themselves mediate this activation. Non-coding transcripts are also reported from large enhancers or clusters of enhancers. However, not much is known about the function of large transcribed enhancer regions during organismal development. Here we investigated a transcribed 10.6 kb intergenic region located upstream of the C. elegans bed-3 gene. We found that parts of this region exhibit tissue-specific promoter and enhancer activities. Deletion of the region disrupts egg laying, a phenotype also observed in bed-3 mutants, but with the severity correlating with the size of the deletion. This phenotype is not caused by overall reduction in bed-3 expression. Rather, deletions reduce bed-3 expression specifically in the mesoderm lineage. We found that bed-3 has a previously unknown function in the generation of sex myoblast (SM) cells from the M lineage, and deletions cause loss of SM cells leading to loss of vulval muscles required for egg laying. Furthermore, injection of dsRNA targeting non-coding transcripts from this region disrupted egg laying in the wild type but not in RNAi-defective mutants. Therefore, the region upstream of bed-3 is required for robust expression of bed-3 in a specific tissue, and non-coding transcripts may mediate this interaction.