The engrailed locus of D. melanogaster provides an essential zygotic function in precellular embryos

Early embryonic development in Drosophila depends on genes expressed during oogenesis or after zygote formation. We show that the engrailed gene is needed for the processes that organize the embryo during the nuclear divisions that precede cellularization. During the precellular blastoderm stages engrailed mutant embryos show several notable anomalies: the pole cells form at a position slightly displaced from the posterior pole; yolk nuclei continue to divide after the tenth nuclear division cycle, when wild-type yolk nuclei have stopped dividing mitotically; and somatic nuclei are not positioned uniformly along the embryo periphery and do not undergo mitotic divisions in regular waves. This early requirement for engrailed does not appear to be a maternal function, and only genetically engrailed embryos displayed these precellular phenotypes. Synthesis of a 2.7 kb poly(A)⁺ transcript of the engrailed region was found in precellular embryos.