👤 John J Eppig

B lymphopoiesis requires that immunoglobulin genes be accessible to RAG1-RAG2 recombinase. However, the RAG proteins bind widely to open chromatin, which suggests that additional mechanisms must restrict RAG-mediated DNA cleavage. Here we show that developmental downregulation of interleukin 7 (IL-7)-receptor signaling in small pre-B cells induced expression of the bromodomain-family member BRWD1, which was recruited to a specific epigenetic landscape at Igk dictated by pre-B cell receptor (pre-BCR)-dependent Erk activation. BRWD1 enhanced RAG recruitment, increased gene accessibility and positioned nucleosomes 5' to each Jκ recombination signal sequence. BRWD1 thus targets recombination to Igk and places recombination within the context of signaling cascades that control B cell development. Our findings represent a paradigm in which, at any particular antigen-receptor locus, specialized mechanisms enforce lineage- and stage-specific recombination. Show less

Postmeiotic gene expression is essential for development and maturation of sperm and eggs. We report that the dual bromodomain-containing protein BRWD1, which is essential for both male and female fertility, promotes haploid spermatid-specific transcription but has distinct roles in oocyte meiotic progression. Brwd1 deficiency caused down-regulation of ∼300 mostly spermatid-specific transcripts in testis, including nearly complete elimination of those encoding the protamines and transition proteins, but was not associated with global epigenetic changes in chromatin, which suggests that BRWD1 acts selectively. In females, Brwd1 ablation caused severe chromosome condensation and structural defects associated with abnormal telomere structure but only minor changes in gene expression at the germinal vesicle stage, including more than twofold overexpression of the histone methyltransferase MLL5 and LINE-1 elements transposons. Thus, loss of BRWD1 function interferes with the completion of oogenesis and spermatogenesis through sexually dimorphic mechanisms: it is essential in females for epigenetic control of meiotic chromosome stability and in males for haploid gene transcription during postmeiotic sperm differentiation. Show less

A novel mutation, repro5, was isolated in a forward genetic screen for infertility mutations induced by ENU mutagenesis. Homozygous mutant mice were phenotypically normal but were infertile. Oocytes from mutant females appeared normal, but were severely maturation-defective in that they had reduced ability to progress to metaphase II (MII), and those reaching MII were unable to progress beyond the two pronuclei stage following in vitro fertilization (IVF). Mutant males exhibited defective spermiogenesis, resulting in oligoasthenoteratospermia. Genetic mapping, positional cloning, and complementation studies with a disruption allele led to the identification of a mutation in Brwd1 (Bromodomain and WD repeat domain containing 1) as the causative lesion. Bromodomain-containing proteins typically interact with regions of chromatin containing histones hyperacetylated at lysine residues, a characteristic of chromatin in early spermiogenesis before eventual replacement of histones by the protamines. Previous data indicated that Brwd1 is broadly expressed, encoding a putative transcriptional regulator that is believed to act on chromatin through interactions with the Brg1-dependent SWI/SNF chromatin-remodeling pathway. Brwd1 represents one of a small number of genes whose elimination disrupts gametogenesis in both sexes after the major events of meiotic prophase I have been completed. Show less