ORAL-ABORAL AXIS SPECIFICATION IN THE SEA URCHIN EMBRYO

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Coffman Lab has used its INBRE support (startup funds awarded to James Coffman, PI) to carry out research on the mechanism underlying developmental specification of the oral-aboral (OA) axis of the sea urchin larva. Axis specification is the initial symmetry breaking event in development that sets up the spatial coordinates for the body plan of an organism. Based on previous work, we have hypothesized that the OA axis of the sea urchin larva is initially specified by a redox gradient established by asymmetric distribution of mitochondria in the egg and early embryo, with the side of the embryo inheriting the highest density of mitochondria being pre-disposed to activate expression of the TGF-beta signaling molecule Nodal and thence develop as oral ectoderm. We further hypothesize that the specification of OA polarity involves mitochondrial H2O2-mediated activation of p38-MAPK, which others have shown to be required for Nodal expression. During this funding period we have begun to test this hypothesis, using a p38-GFP fusion protein to monitor p38 activity and mitochondrially-targeted catalase to block emission of mitochondrial H2O2 in live embryos. We have found that the relationship between p38-MAPK activity and Nodal expression is not as simple as we initially hypothesized. Although p38 is clearly required for the initiation of Nodal expression, our data suggest that p38 activity is spatially isotropic in the early embryo at the time of nodal activation in Strongylocentrotus purpuratus (in contrast to the situation previously reported for a different species of sea urchin, Lytechinus variegatus). Nonetheless, preliminary data indicate that blockade of mitochondrial H2O2 does perturb specification of the OA axis via nodal expression. This INBRE-supported work provided preliminary data that helped us obtain (and is now being extended in) a NIEHS R01 research grant entitled "Redox-sensitive developmental pathways and gene regulatory networks" (ES016722).