CTCF-mediated 3D chromatin predetermines the gene expression program in the male germline (Hi-C)
Spermatogenesis is a unidirectional differentiation process to produce haploid sperm. However, it remains largely unknown how the gene expression program is determined to direct a unidirectional differentiation. Here we unveil the high-resolution 3D chromatin architecture of male germ cells and show that CTCF-mediated 3D chromatin predetermines the gene expression program required for spermatogenesis. At the mitosis-to-meiosis transition, the germline-specific Polycomb protein SCML2 resolves chromatin loops specific to mitotic spermatogonia. On autosomes, CTCF-mediated 3D chromatin manifests the structural feature of meiosis-specific super-enhancer (meiotic SE) loci already in undifferentiated spermatogonia. In meiotic spermatocytes, the master transcription factor A-MYB is recruited to these meiotic SE loci to strengthen their 3D contacts to instruct the burst of meiotic gene expression. Further, SCML2 and A-MYB establish unique 3D chromatin of the sex chromosomes in meiotic sex chromosome inactivation. We propose that CTCF-mediated 3D chromatin underlines epigenetic priming to direct unidirectional differentiation, thereby determining the cellular identity of the male germline. Overall design: Determination of 3D chromatin structures of THY1+ and KIT+ spermatogonia, pachytene spermatocytes and round spermatids by Hi-C analyses.