Regulation of shark gene expression during embryonic development of Drosophila melanogaster

Abstract

The non-receptor S&barbelow;rc-h&barbelow;omology 2 (SH2) domain, a&barbelow;nkyrin r&barbelow;epeat tyrosine k&barbelow;inase, Shark (Ferrante et al., 1995), is required for the process of embryonic dorsal closure in Drosophila melanogaster (Fernandez et al., 2000). While this is the earliest process that requires shark, it is unknown whether it is the only one. Previous studies have indicated that shark is expressed maternally and zygotically in ectodermally derived epithelium (Fernandez et al., 2000). The aims of the present study were to carry out a more detailed analysis of the embryonic expression pattern of shark in order to gain further insight into potential additional roles of shark during embryogenesis and to define regions of the shark promoter required for this expression. Novel findings include the co-expression of shark mRNA and protein in the ventral and cephalic furrow of the gastrulating embryo, the amnioproctodeal invagination, anterior and posterior midgut primordia, both the endoderm and visceral mesoderm layers of the midgut, and in the midgut constrictions. shark1/shark1 germline clone embryos were examined for defects in the development of midgut constrictions in stage 15--16 embryos, and none were detected. A minimal promoter region necessary for wild type expression was defined that contained an evolutionarily conserved 29 base pair motif with three TAAT repeats, which are core DNA binding sites for several homeodomain transcription factors. This motif was not necessary for wild type shark expression. However, Shark expression was altered in stage 17 embryos bearing homozygous null mutations in the genes encoding the homeodomain transcription factors Sex combs reduced, Antennapedia, and Ultrabithorax.