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, p rior to zygotic transcription, indicative of maternal inheritance. lark can also be detected within the nurse cells of developing egg chambers, sugges ting a function for the protein during oogenesis. To test the hypothesis th at the maternal inheritance of lark is required for oogenesis or early deve lopment, we employed the "FLP-DFS" technique to eliminate the lark maternal component within the germ line. Unfertilized and fertilized eggs lacking t he lark(+) maternal component exhibit a "fragile" phenotype, indicating tha t the protein functions during oogenesis. Furthermore, differentiation of t he fertilized eggs is abnormal - most embryos arrest prior to blastoderm fo rmation and exhibit morphological phenotypes that might reflect underlying defects in syncytial nuclear cycling or cellularization. Mutational analysi s of a retroviral-type zinc finger within the lark protein indicates that i i is required for the maternal function of the protein. females are complet ely sterile when their only source of lark protein contains a zinc-finger m utation. The aggregate of our studies shows that the germ-line expression o f lark is essential for development, and suggests that the retroviral-type zinc finger mediates important RNA-binding functions during oogenesis and/o r early development. Dev. Genet. 25:387-306, 1999. (C) 1999 Wiley-Liss, Inc .