fusilli, an essential gene with a maternal role in Drosophila embryonic dorsal-ventral patterning

The Drosophila fusilli (fus) gene was identified in a genetic screen for do minant maternal enhancers of an unusual dorsalizing mutation in the cactus gene, cact(E10). While females that are heterozygous for the cact(E10) alle le produce embryos with wild-type dorsal-ventral patterning, more than 90% of the embryos produced by females that are heterozygous for both cact(E10) and the fus(1) mutation are weakly dorsalized, Loss of fusilli activity ca uses lethality during embryogenesis but not dorsal-ventral patterning defec ts, indicating that fusilli is important in more than one developmental pro cess. The fusilli gene encodes a protein with RNA binding motifs related to those in mammalian hnRNP F and H, which play roles in regulated RNA splici ng. The fusilli RNA is not present in the oocyte or early embryo, and germ- line clones of fusilli mutations have no maternal effect on dorsal-ventral patterning, indicating that the fusilli maternal effect does not depend on germ-line expression of the gene. Because the fusilli RNA is present in ova rian follicle cells, we propose that fusilli acts downstream of the Drosoph ila EGF receptor to control the biogenesis of follicle cell transcripts tha t control the initial dorsal-ventral asymmetry of the embryo. (C) 2001 Acad emic Press.