(14) TAF7L and TAF7L2 are testis-specific dosage-dependent transcription factors and essential for male fertility

TAF7L and TAF7L2 are testis-specific dosage-dependent transcription factors and essential for male fertility

Zhenlong Kang, N. Adrian Leu, P. Jeremy Wang*

Department of Biomedical Sciences, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA

Abstract Text:

TATA-binding protein (TBP)-associated factor 7L (TAF7L; a paralogue of TAF7) is an X-encoded testis-specific component of the core transcription factor IID (TFIID) complex required for transcription of protein-coding genes by RNA polymerase II. We previously reported that Taf7l knockout (Taf7l^-/Y) mice exhibit structurally abnormal sperm, reduced sperm count, weakened motility, and compromised fertility. Here we find that Taf7l2 is a novel testis-specific paralogue of Taf7. Taf7l2 with only one exon is a retrogene originated from Taf7l. Taf7l2 is autosomal (Chr 10) and shares 60% amino acid identity with TAF7L. In contrast with the ubiquitous expression pattern of TAF7, both TAF7L and TAF7L2 are only expressed in testis. We have generated Taf7l2 single knockout (Taf7l2^-/-), Taf7l^-/Y-Taf7l2^-/- double knockout, and various Taf7l-Taf7l2 mutant mice. Taf7l2^-/- mice had a 50% reduction in sperm count. Interestingly, Taf7l2^+/- mice also had reduced sperm count. Taf7l^-/Y-Taf7l2^+/- mice had an 80% reduction in sperm count. Strikingly, Taf7l^-/Y-Taf7l2^-/- double knockout (DKO) mice lacked mature sperm in the cauda epididymis and were infertile. Histological and immunofluorescence analysis showed that many middle and late-stage spermatocytes were abnormal, and round spermatids could not transition to elongating spermatids in the double knockout mice. These genetic studies demonstrate that TAF7L/TAF7L have overlapping functions but together is essential for spermiogenesis. RNA-seq analysis of pachytene spermatocytes (PS) and round spermatids (RS) sorted from wild type and Taf7l-Taf7l2 DKO testes revealed massively dysregulated gene expression in Taf7l-Taf7l2 deficient germ cells. GO analysis showed that up-regulated genes were mainly related to regulation of transcription by RNA polymerase II, while down-regulated genes were mainly involved in flagellated sperm motility and spermatogenic processes, in both PS and RS from DKO male mice. Our future plan is to combine RNA-seq and CUT&RUN to reveal the target genes regulated by TAF7L and TAF7L2. Our findings have identified a dosage-dependent mechanism of transcriptional regulation in spermatogenesis. Furthermore, TA7L and TAF7L2 constitute a novel testis-specific TFIID complex that function in meiotic and postmeiotic male germ cells.