The role of easter, an apparent serine protease, in organizing the dorsal-ventral pattern of the Drosophila embryo.

The maternally transcribed product of the Drosophila easter gene is essential for the establishment of a normal dorsal-ventral pattern in embryos. Loss-of-function mutations in easter result in a dorsalization of the embryonic pattern, while dominant gain-of-function mutations ventralize the embryonic pattern. P element insertion alleles of easter were isolated and used to identify genomic and cDNA clones that include the easter gene. Injection of in vitro-synthesized transcripts of the cDNA into embryos from easter mutant females completely rescued the mutant phenotype, allowing normal development. This result confirmed that the cDNA encodes easter and that the easter product is only required after fertilization. The sequence of the cDNA suggests that the product of the easter gene is an extracytoplasmic serine protease. The implications of the dominant alleles of this putative protease for the mechanism of dorsal-ventral pattern formation are discussed.