Maternal function of a retroviral-type zinc-finger protein is essential for Drosophila development

Previous studies have shown that zygotic expression of the Drosophila lark gene, which encodes an RNA-binding protein, is essential for embryogenesis. We now show that lark mRNA is abundant in preblastoderm (0-2 h) embryos, prior to zygotic transcription, indicative of maternal inheritance. Lark can also be detected within the nurse cells of developing egg chambers, suggesting a function for the protein during oogenesis. To test the hypothesis that the maternal inheritance of lark is required for oogenesis or early development, we employed the "FLP-DFS" technique to eliminate the lark maternal component within the germ line. Unfertilized and fertilized eggs lacking the lark maternal component exhibit a "fragile" phenotype, indicating that the protein functions during oogenesis. Furthermore, differentiation of the fertilized eggs is abnormal-most embryos arrest prior to blastoderm formation and exhibit morphological phenotypes that might reflect underlying defects in syncytial nuclear cycling or cellularization. Mutational analysis of a retroviral-type zinc finger within the lark protein indicates that it is required for the maternal function of the protein: females are completely sterile when their only source of lark protein contains a zinc-finger mutation. The aggregate of our studies shows that the germ-line expression of lark is essential for development, and suggests that the retroviral-type zinc finger mediates important RNA-binding functions during oogenesis and/or early development.