Maternal and zygotic control of serotonin biosynthesis are both necessary for Drosophila germband extension

In the accompanying paper, we report that Drosophila gastrulae genetically depleted for the 5-HT2Dro serotonin receptor or for serotonin show abnormal germband extension. In wild-type gastrulae, peaks of both the 5-HT2Dro rec eptor and serotonin coincide precisely with the onset of germband extension . Here, we assessed the genetic requirement for this peak of serotonin. We report the characterisation of the serotonin content of individual Drosophi la embryos, progeny from flies heterozygous for mutations in genes that are involved in the serotonin synthesis pathway and include the GTP-cyclohydro lase, tryptophan hydroxylase and DOPA decarboxylase loci. The peak of serot onin synthesis at the beginning of germband extension appears strictly depe ndent upon the maternal deposition of biopterins, products of GTP-cyclohydr olase and cofactors of tryptophan hydroxylase and upon the zygotic synthesi s of both tryptophan hydroxylase and DOPA decarboxylase enzymes. Mutant emb ryos with an impairment in this peak of serotonin synthesis die with a cuti cular organisation which is also observed in embryos deficient for the 5-HT 2Dro receptor. This characteristic cuticular phenotype is thus the hallmark of desynchronisation of the morphogenetic movements during gastrulation. T ogether, these findings provide additional support for the notion that sero tonin, acting through the 5-HT2Dro receptor, is necessary for proper gastru lation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.