Testing the function of widespread transcription of the testis

In many organisms including Drosophila and mammals, male germ cells, particularly spermatocytes, have one of the most complex transcriptomes, where a large fraction of the genome including noncoding DNA are transcribed. However, significance of this widespread transcription remains enigmatic. Through the study of satellite DNA transcription in Drosophila spermatocytes as a representational model for widespread transcription, we propose that transcription is required to remodel chromatin in preparation for sperm DNA packaging. We identified HP2, a known heterochromatin protein, as being required for transcription of AAGAG satellite DNA. HP2 depletion led to retention of heterochromatin marks in post-meiotic spermatids and subsequent failure in histone-to-protamine transition. Strikingly, spermatids with less AAGAG satellite DNA can develop normally even when AAGAG transcription is perturbed by HP2 depletion. Together, we propose that spermatocytes’ widespread transcription serves as a mechanism to facilitate remodeling of chromatin to prepare for sperm DNA packaging.