Files and links (1)
Free to read and download, Open Access
The Drosophila Suppressor of Hairy-wing [Su(Hw)] protein is a multi-zinc finger DNA binding factor required for the gypsy insulator function. At the gypsy element, Su(Hw) recruits partners Centrosomal Protein of 190 kD (CP190) and Modifier of mdg4 67.2 kD isoform (Mod67.2), which facilitate the enhancer blocking and barrier functions of the insulator. Our genome-wide studies have identified thousands of endogenous non-gypsy Su(Hw) binding sites (SBSs) in Drosophila genome, constitutively occupied throughout development. Yet, only a third of SBSs associate with CP190 and Mod67.2, suggesting that the endogenous function of Su(Hw) may not necessarily involve formation of a gypsy-like chromatin insulator.
To understand the function of endogenous SBSs, we investigated the requirement for Su(Hw) during female germline development. To this end, we performed genome-wide transcriptional analyses in su(Hw) mutant ovaries coupled with the genome-wide definition of ovary SBSs. We identified 49 direct targets of Su(Hw) regulation in the ovary, with 80% of these genes showing increased RNA accumulation when Su(Hw) is lost. Derepressed Su(Hw) targets are normally highly expressed in central nervous system, suggesting that Su(Hw) has a critical role in silencing neural genes in the non-neural tissues. We find that a single upregulated target gene is largely responsible for the female sterility of the su(Hw) mutants. This gene encodes an elav family factor RNA binding protein 9 (Rbp9), and Su(Hw)-mediated repression of Rbp9 is required at a specific stage of germline development. Decreasing the levels of Rbp9 restores female fertility of su(Hw) null mutants. Further, we demonstrate that Su(Hw) is required for transcriptional activation of pointed, gene involved in eggshell patterning during late embryogenesis. Importantly, both CP190 and Mod67.2 are dispensable for Rbp9 regulation, indicating that mechanism of Rbp9 repression is independent of the insulator function of Su(Hw).
Our studies extend the known transcriptional activities of Su(Hw), indicating that it can function as an insulator, activator and repressor, the latter function being essential for oogenesis. These findings highlight that insulator proteins are versatile transcriptional regulators, suggesting that tissue specific contributions to transcription result from direct regulation of individual genes.