PLU-1, a transcriptional repressor and putative testis-cancer antigen, has a specific expression and localisation...

PLU-1, a large multi-domain nuclear protein with strong transcriptional repression activity, is a member of the ARID family of DNA binding proteins. In previous studies, high levels of expression of Plu-1 mRNA and PLU-1 protein were detected in breast cancers, while expression in normal adult tissues was detected only in the testis, ovary and transiently in the mammary gland of the pregnant female. Due to its high levels of expression in the testis and to its specific relationship to cancer, PLU-1 has been proposed to belong to the family of testis-cancer antigens. In this study we attempted to determine putative functions for PLU-1 during spermatogenesis. To address this, we analysed the pattern of expression and localisation of this protein in mouse testicular cells during postnatal development and adulthood. Using in situ hybridisation and immunostaining of testis sections we show that Plu-1 mRNA and PLU-1 protein are both highly expressed in the mitotic spermatogonia. Expression is reduced dramatically in the early prophase I stages (zygotene, leptotene), but reappears at pachytene and is still detectable in diplotene cells. We also found that PLU-1 localises diffusely over the nucleus, which indicates a potential chromatin binding ability of this protein. Consistent with this notion, we found that PLU-1 is present in the chromatin fraction in biochemical cell fractionation experiments using both somatic and meiotic cells. Our data point to a role for PLU-1 in meiotic transcription, which may be restricted to certain meiotic stages and may be mediated by the ability of this protein to associate with the chromatin.