Meeting Abstract

P3.116  Tuesday, Jan. 6  A preneuronal serotonergic system drives morphogenesis in sea urchin embryos CARROLL, K.N.*; SCULLY, T.A.; BROWN, K.M.; CHENG, Y.; MATEER, E.; DZIRLO-AYVAZ, M.; ANITOLE-MISLEH, K.; The George Washington University

In the sea urchin embryo, pharmacological studies in our lab and others have suggested that serotonin may initiate cell movement processes during gastrulation. To further investigate the role of a serotonergic system in embryogenesis, we measured levels of serotonin and its precursor and metabolites, as well as mRNA levels and enzyme activity of the serotonin synthetic enzyme, tryptophan hydroxylase, in Lytechinus pictus blastula- and gastrula-stage embryos and larvae. Serotonin levels peak in mesenchyme blastula embryos, immediately prior to gastrulation, and at mid gastrula and late pluteus larva stages. Alterations in serotonin levels mostly follow the measured fluctuations in serotonin synthesis and metabolism. Preliminary studies suggest that preneural embryos may utilize a different enzyme, phenylalanine hydroxylase/tryptophan hydroxylase (PAH/TPH), than that used in larval neurons (TPH) to hydroxylate tryptophan. The gastrulation process is most sensitive to inhibitors of mammalian types 1, 2, and 7 serotonin receptors. These antagonists blocked the initial invagination of the vegetal plate, whereas lower concentrations delayed the initiation of the secondary phase of gastrulation with little effect on subsequent development. Serotonin or dibutyryl cyclic AMP, coincubated with ritanserin or chlorpromazine, type 2 and 7 receptor antagonists, at least partially rescued embryos from gastrulation inhibition. Homology searches of the sea urchin genome identified types 1, 2 and 7 receptors, but only 2 and 7 are linked to an increase in cyclic AMP following activation by serotonin. In sum, sea urchin embryos contain a serotonergic system that may regulate the early gastrulation process through types 2 and/or 7 serotonin receptors.