Genome-wide chromatin occupancy of BRDT and gene expression analysis suggest transcriptional partners and specific epigenetic landscapes that regulate gene expression during spermatogenesis.

BRDT, a member of the BET family of double bromodomain-containing proteins, is essential for spermatogenesis in the mouse and has been postulated to be a key regulator of transcription in meiotic and post-meiotic cells. To understand the function of BRDT in these processes, we first characterized the genome-wide distribution of the BRDT binding sites, in particular within gene units, by ChIP-Seq analysis of enriched fractions of pachytene spermatocytes and round spermatids. In both cell types, BRDT binding sites were mainly located in promoters, first exons, and introns of genes.

Alternative 3' UTRs act as scaffolds to regulate membrane protein localization.

About half of human genes use alternative cleavage and polyadenylation (ApA) to generate messenger RNA transcripts that differ in the length of their 3' untranslated regions (3' UTRs) while producing the same protein. Here we show in human cell lines that alternative 3' UTRs differentially regulate the localization of membrane proteins. The long 3' UTR of CD47 enables efficient cell surface expression of CD47 protein, whereas the short 3' UTR primarily localizes CD47 protein to the endoplasmic reticulum.

The role of the double bromodomain-containing BET genes during mammalian spermatogenesis.

The double bromodomain-containing BET (bromodomain and extra terminal) family of proteins is highly conserved from yeast to humans and consists not just of transcriptional regulators but also histone-interacting chromatin remodelers. The four mammalian BET genes are each expressed at unique times during spermatogenesis, and the testis-specific gene Brdt is essential for spermatogenesis. Loss of the first bromodomain of BRDT results in improper/incomplete spermatid elongation and severely morphologically defective sperm.

The testis-specific double bromodomain-containing protein BRDT forms a complex with multiple spliceosome components and is required for mRNA splicing and 3'-UTR truncation in round spermatids.

Members of the BET (bromodomain and extra terminal motif) family of proteins have been shown to be chromatin-interacting regulators of transcription. We previously generated a mutation in the testis-specific mammalian BET gene Brdt (bromodomain, testis-specific) that yields protein lacking the first bromodomain (BRDT(ΔBD1)) and observed disrupted spermiogenesis and male sterility. To determine whether BRDT(ΔBD1) protein results in altered transcription, we analyzed the transcriptomes of control versus Brdt(ΔBD1/ΔBD1) round spermatids.

The first bromodomain of the testis-specific double bromodomain protein Brdt is required for chromocenter organization that is modulated by genetic background.

Mice homozygous for a mutation (Brdt(∆BD1/∆BD1)) lacking the first bromodomain of Brdt, a testis-specific member of the BET family of double-bromodomain containing proteins, are sterile and exhibit profound defects in chromatin remodeling during spermiogenesis. We have now observed that a prominent feature of the aberrant spermatid nuclei is a fragmented chromocenter, a structure comprised of peri-centromeric heterochromatin. There was a concomitant increase in the levels of heterochromatin protein 1 alpha (Hp1α), suggesting that the presence of multiple chromocenters was correlated with a spread of heterochromatin beyond the normal centromeric region.