Dynamics of Delta/Notch signaling on endomesoderm segregation in the sea urchin embryo.

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Endomesoderm is the common progenitor of endoderm and mesoderm early in the development of many animals. In the sea urchin embryo, the Delta/Notch pathway is necessary for the diversification of this tissue, as are two early transcription factors, Gcm and FoxA, which are expressed in mesoderm and endoderm, respectively. Here, we provide a detailed lineage analysis of the cleavages leading to endomesoderm segregation, and examine the expression patterns and the regulatory relationships of three known regulators of this cell fate dichotomy in the context of the lineages. We observed that endomesoderm segregation first occurs at hatched blastula stage. Prior to this stage, Gcm and FoxA are co-expressed in the same cells, whereas at hatching these genes are detected in two distinct cell populations. Gcm remains expressed in the most vegetal endomesoderm descendant cells, while FoxA is downregulated in those cells and activated in the above neighboring cells. Initially, Delta is expressed exclusively in the micromeres, where it is necessary for the most vegetal endomesoderm cell descendants to express Gcm and become mesoderm. Our experiments show a requirement for a continuous Delta input for more than two cleavages (or about 2.5 hours) before Gcm expression continues in those cells independently of further Delta input. Thus, this study provides new insights into the timing mechanisms and the molecular dynamics of endomesoderm segregation during sea urchin embryogenesis and into the mode of action of the Delta/Notch pathway in mediating mesoderm fate.





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Croce, Jenifer C, and David R McClay (2010). Dynamics of Delta/Notch signaling on endomesoderm segregation in the sea urchin embryo. Development, 137(1). pp. 83–91. 10.1242/dev.044149 Retrieved from https://hdl.handle.net/10161/4173.

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David R. McClay

Arthur S. Pearse Distinguished Professor of Biology

We ask how the embryo works. Prior to morphogenesis the embryo specifies each cell through transcriptional regulation and signaling. Our research builds gene regulatory networks to understand how that early specification works. We then ask how this specification programs cells for their morphogenetic movements at gastrulation, and how the cells deploy patterning information.
Current projects examine 1) novel signal transduction mechanisms that establish and maintain embryonic boundaries
mold the embryo at gastrulation; 2) specification of primary mesenchyme cells in such a way that they are prepared to execute an epithelial-mesenchymal transition, and then study mechanistically the regulation of that transition; 3) the specification of endoderm necessary for invagination of the archenteron; 4) formation of the oral/aboral ectoderm and the means by which patterning information is distributed three dimensionally around the embryo. That information is necessary for patterning and inducing skeletogenesis.
Other projects examine neural tube folding with the goal of identifying genes associated with neural tube defects. Finally, a large current effort in systems biology is being expended with the goal of enlarging our knowledge of early networks and how they interact.

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