Essential Requirement for Both hsf1 and hsf2 Transcriptional Activity in Spermatogenesis and Male Fertility

Heat shock factors (Hsfs) are major transactivators of heat shock proteins but are also involved in regulation of other genes active in embryonic development. High expression levels of Hsfs in mouse testis during development suggest a role for these factors in spermatogenesis, a cyclic process of spermatogonia cell-differentiation into mature spermatozoa. In contrast to hsf1^-/- mice, which exhibit normal spermatogenesis, targeted disruption of hsf2 results in reduced testicular size but only a small impairment in male fertility. We show here that disruption of both hsf1 and hsf2 results in a more severe phenotype associated with male sterility due to severe defects in spermatogenesis. Earliest defects observed are the reduced number of germ cells in juvenile mice and germ cells that enter the meiotic prophase fail to progress beyond the pachytene stage. This was associated with a reduction or absence of transcription of genes critically involved in spermatogenesis. The findings suggest that additive or synergistic transcriptional activity of both hsf1 and hsf2 is required for normal mammalian spermatogenesis and male fertility.