Detection of PACH1, a nuclear factor implicated in the transcriptional regulation of meiotic and early haploid stages of spermatogenesis

Abstract

Spermatogenesis occurs in a series of well-defined stages and serves as an excellent model for lineage-specific cell development. Yet, little is known regarding the transcriptional mechanisms responsible for cell- and stage-dependent gene regulation in the male germ line. The rat and mouse proenkephalin genes are expressed from an alternative, spermatogenic cell-specific promoter specifically in meiotically-active pachytene spermatocytes and early post-meiotic spermatids. This promoter thus serves as an excellent model for defining transcriptional regulators involved in germ line-specific gene expression in meiotic cells. Previous transgenic studies identified a proximal, 51 bp 5'-flanking sequence containing two direct repeat elements that are absolutely required for in vivo proenkephalin promoter activity in spermatocytes and spermatids. Here, footprinting analyses were used to further delineate the specific interactions of a spermatogenic cell nuclear factor with the repeat elements within the proximal promoter region. This repeat-binding factor was also shown to be developmentally upregulated specifically in pachytene spermatocytes. Using Southwestern analysis, we have identified a unique nuclear protein enriched in pachytene spermatocytes that specifically recognizes the repeat elements within the proximal 5'-flanking sequence. We propose that this DNA binding factor, termed PACH1, is a key transcriptional regulator of the proenkephalin and potentially other gene promoters, uniquely expressed during meiosis in the male germ line.