Serotonin involvement in Drosophila gastrulation process. B. Schaerlinger¹, J.M. Launay², L. Maroteaux¹. 1) IGBMC, Illkirch, France; 2) Hopital Lariboisiere, Paris, France.

   Drosophila gastrulation is a brief transitory period that presents the first morphological manifestation of cell fate and differentiation programs. After a diversity of cell movements (invagination, convergent extension, folding and epiboly), the gastrulation provides the embryo with a body plan into three germ layer : ectoderm, mesoderm and endoderm. The serotonin and its G protein coupled receptor 5-HT2Dro present a peak of expression in the presumptive ectoderm at the onset of the gastrulation, before cell differentiation. Defects in either serotonin synthesis or 5-HT2Dro expression leads to gastrulation defects and an embryonic lethality. In this work, we investigated the phenotype of a novel point mutant in the 5-HT2Dro receptor gene called M51 which is embryonic lethal. The point mutation localised in the N-terminal domain of the receptor increases the affinity of the serotonin for the receptor. In contrast to deficiency in 5-HT2Dro locus, M51 strain did not present any cuticular phenotype. As the deficient strain for 5-HT2Dro presented gastrulation defects, we investigated potential gastrulation defects in M51 strain. We analysed cell movement in wild-type and homozygotes mutant embryos. Time lapse video showed that homozygous mutants embryos exhibit delays in gastrulation movements. In drosophila, serotonin seems required for gastrulation timing through G protein coupled receptor activation. The mechanisms involved in this process are still unknown but characterisation of M51 mutant and the finding of direct interactant proteins with 5-HT2Dro receptor by a two hybrid analysis are ongoing and should give us some clues to understand the role of serotonin in gastrulation processes.