Kaiso, a critical regulator of spermatogenesis

Spermatogenesis is a highly coordinated process by which diploid spermatogonia (2n) differentiate into mature haploid (1n) spermatozoa in the seminiferous epithelium. Here, we show that Kaiso (Zbtb33) is critical to spermatogenesis, via binding to KBEs (Kaiso-binding elements) in the 5' upstream regulatory regions of Gdnf and Plzf to repress their expression, promoting the differentiation of spermatogonial stem cells (SSCs). In Kaiso-/Y mice, Plzf and Gdnf were derepressed in both SSCs and Sertoli cells, explaining the increased number of SSCs observed in these abnormal mice. We also found that Bcl6, an antiapoptotic spermatocyte survival factor, represses the Crem pathway genes. In particular, Kaiso represses Bcl6 by binding two KBEs in the Bcl6 5' upstream regulatory region and first intron, thus indirectly derepressing Crem and Crem pathway genes. In Kaiso-/Y mice, Bcl6 is overexpressed, and these mice lack differentiated post-mitotic cells and consequently, are infertile. Interestingly, epigenetic “marks,” histone post-translational modifications such as lysine methylation, within histone H3 (H3K27me3), of the promoters of Kaiso target genes, were found transgenerationally heritable, prior to “wash out” during generations 1-3 in Kaiso-/Y mice, thus impacting Kaiso target gene expression. Consequently, Kaiso, by repressing Plzf, Gdnf, and Bcl6, indirectly upregulates Crem, and thereby plays a critical role not only in SSC differentiation, but also in post-meiotic events during spermatogenesis. Overall design: Methylated genomic DNA was isolated from fragmented whole genomic DNA using the methyl-CpG binding domain of mouse MBD2 protein coupled to paramagnetic Dynabeads® labeled with M-280 streptavidin, via a biotin linker. Isolated Methylated DNA sequence was analyzed by NGS technology.