These 2 factors can directly bind each other and form heterotrimers regulating the basal level of transcription of target genes.[17,18] But both structural and mechanistic insights into HSF1–HSF2 heterotrimerization are very limited.[19–21] Their double knockout results in meiosis arrest, spermatocyte apoptosis, and male infertility. This evidence concerns the gene HSF1 and male infertility.