p38 MAPK activation is required for Paracentrotus lividus skeletogenesis

We investigated the p38 MAPK role during sea urchin, Paracentrotus lividus, development. We found that at the morula stage, before the onset of skeletogenesis, p38 MAPK shows a peak of activity, and we tested whether p38 MAPK activity has any effect on skeletogenesis. By immunohistochemistry on whole-mount embryos we show the preferential localization of the active p38 form both in the presumptive PMCs and bilateral spiculogenesis centers in control embryos, and in the radialized supernumerary spiculogenesis centers induced by NiCl(2) treatment. By using SB203580, a p38 MAPK specific inhibitor, we show that p38 activity is required both for the initial triradiate spicule rudiments formation and for their correct elongation.