Citation: Erkenbrack, E. M., Petsios, E. (2017). A conserved role for VEGF signaling in specification of homologous mesenchymal cell types positioned at spatially distinct developmental addresses in early development of sea urchins. J Exp Zool (Mol Dev Evol) 328(5): 423-432.
Notch-mediated lateral inhibition is an evolutionarily conserved mechanism patterning the ectoderm of echinoids
Notch signaling is a crucial cog in early development of euechinoid sea urchins, specifying both non-skeletogenic mesodermal lineages and serotonergic neurons in the apical neuroectoderm. Here, the spatial distributions and function of delta, gcm, and hesc, three genes critical to these processes in euechinoids, are examined in the distantly related cidaroid sea urchin Eucidaris tribuloides. Spatial distribution and experimental perturbation of delta and hesc suggest that the function of Notch signaling in ectodermal patterning in early development of E. tribuloides is consistent with canonical lateral inhibition. Delta transcripts were observed in the archenteron, apical ectoderm, and lateral ectoderm in gastrulating embryos of E. tribuloides. Perturbation of Notch signaling by either delta morpholino or treatment of DAPT downregulated hesc and upregulated delta and gcm, resulting in ectopic expression of delta and gcm. Similarly, hesc perturbation mirrored the effects of delta perturbation. Interestingly, perturbation of delta or hesc resulted in more cells expressing gcm and supernumerary pigment cells, suggesting that pigment cell proliferation is regulated by Notch in E. tribuloides. These results are consistent with an evolutionary scenario whereby, in the echinoid ancestor, Notch signaling was deployed in the ectoderm to specify neurogenic progenitors and controlled pigment cell proliferation in the dorsal ectoderm.
Animals consist of a wide variety of cells that serve different functions depending on their location in the body. Cells with similar functions, or cell types, in different animal species are related both by an evolutionary line of descentÐsimilar to the relatedness of species themselvesÐand by a developmental line of descent in the embryo. Networks of interacting genes, or gene regulatory networks, control gene expression in the cell, thereby specifying cell type identity. Understanding how new cell types arise by changing gene regulatory networks is critical both to comprehending fundamental aspects of human biology and to manipulating cell types in the laboratory. We approached this question by studying endometrial stromal fibroblast (ESF) cells from the uterus of humans and opossums, two distantly related mammals. We showed that the distantly related cell type in opossum expresses a similar set of regulatory genes as the human cell, but in response to pregnancy-related signals, the opossum cells induce a stress response. In the human cells, these signals induce differentiation into decidual cells, a specialized cell type present in humans and closely related mammals. These results suggest that a gene regulatory network that modulated an ancestral, pregnancy-related stress response was hijacked and repurposed to function in differentiation and specification of the decidual cell type.
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