Expression and potential role of Fsrg1, a murine bromodomain-containing homologue of the Drosophila gene female sterile homeotic.

We have isolated a cDNA which is a murine homologue of the Drosophila gene female sterile homeotic (fsh). This homologue, which we have designated Fsrg1*, contains two bromodomains and an ET motif characteristic of the Fsh sub-class of bromodomain-containing proteins. Northern blot hybridization analysis of adult tissues revealed that Fsrg1 was expressed at low levels rather ubiquitously, but most abundantly in the testis and ovary. Polyclonal antibodies raised against an Fsrg1 fusion protein were used to characterize the Fsrg1 gene product in tissues. Constructs were also generated in which the Fsrg1 cDNA was tagged with epitopes for hemaglutinin and used in transfection experiments. Immunoblot analysis revealed that the Fsrg1 protein migrates with a relative molecular mass of approximately 110 kDa, although the cDNA sequence would predict a protein of approximately 88 kDa. The migration at approximately 110 kDa was observed for both in vivo protein and protein produced in cultured cells. The Fsrg1 protein was localized to the nucleus when expressed in cultured cells, consistent with the presence of a nuclear localization signal motif in the Fsrg1 sequence. No kinase activity was detected for this nuclear protein as assessed in either autokinase or specific substrate assays. In situ hybridization analysis revealed strikingly high expression of Fsrg1 in granulosa cells of growing follicles in the adult ovary and suggested its possible involvement in folliculogenesis. Additional clues to its potential function were provided by the demonstration of its high level of expression in epithelia of tissues which undergo hormonally-modulated remodeling.