The function of the broad-complex during Drosophila melanogaster oogenesis

The Broad-Complex (BR-C) is an early ecdysone response gene that functions during metamorphosis and encodes a family of zinc-finger transcription fact ors. It is expressed in a dynamic pattern during oogenesis. Its late expres sion in the lateral-dorsal-anterior follicle cells is related to the morpho genesis of the chorionic appendages. All four zinc-finger isoforms are expr essed in oogenesis, which is consistent with the abnormal appendage phenoty pes resulting from their ectopic expression. We investigated die mechanism by which the BR-C affects chorion deposition by using BrdU to follow the ef fects of BR-C misexpression on DNA replication and in situ hybridization to ovarian mRNA to evaluate chorion gene expression. Ectopic BR-C expression leads to prolonged endoreplication and to additional amplification of genes , besides the chorion genes, at other sites in the genome. The pattern of c horion gene expression is not affected along die anterior-posterior axis, b ut the follicle cells at tilt anterior of che oocyte fail to migrate correc tly ill an anterior direction when BR-C is misexpressed. We conclude that t he target genes of the BA-C in oogenesis include a protein essential for en doreplication and chorion gene amplification. This may provide a link betwe en steroid hormones and the control of DNA replication during oogenesis.