RT Journal Article SR Electronic T1 Dynamics of Meiotic Sex Chromosome Inactivation and Pachytene Activation in Mice Spermatogenesis JF bioRxiv FD Cold Spring Harbor Laboratory SP 665372 DO 10.1101/665372 A1 Ábel Vértesy A1 Javier Frias-Aldeguer A1 Zeliha Sahin A1 Nicolas Rivron A1 Alexander van Oudenaarden A1 Niels Geijsen YR 2019 UL http://biorxiv.org/content/early/2019/06/10/665372.abstract AB During germ cell development, cells undergo a drastic switch from mitosis to meiosis to form haploid germ cells. Sequencing and computational technologies now allow studying development at the single-cell level. Here we developed a multiplexed trajectory reconstruction to create a high-resolution developmental map of spermatogonia and prophase-I spermatocytes from testes of a Dazl-GFP reporter mouse. We identified three main transitions in the meiotic prophase-I: meiotic entry, the meiotic sex chromosome inactivation (MSCI), and concomitant pachytene activation. We validated the key features of these transitions in vivo using single molecule FISH. Focusing on MSCI, we found that 34% of sex chromosomal genes are induced shortly before MSCI, that silencing time is diverse and correlates with specific gene functions. These highlight a previously underappreciated level of regulation of MSCI. Finally, we found that spermatozoal genes in pachytene are activated in a temporal pattern reflecting the future anatomic and functional order of the sperm cell. Altogether we highlighted how precise and sequential changes in gene expression regulate cellular states in meiotic prophase-I.