Dynamic sex chromosome expression in Drosophila male germ cells

Nat Commun. 2021 Feb 9;12(1):892. doi: 10.1038/s41467-021-20897-y.


Given their copy number differences and unique modes of inheritance, the evolved gene content and expression of sex chromosomes is unusual. In many organisms the X and Y chromosomes are inactivated in spermatocytes, possibly as a defense mechanism against insertions into unpaired chromatin. In addition to current sex chromosomes, Drosophila has a small gene-poor X-chromosome relic (4th) that re-acquired autosomal status. Here we use single cell RNA-Seq on fly larvae to demonstrate that the single X and pair of 4th chromosomes are specifically inactivated in primary spermatocytes, based on measuring all genes or a set of broadly expressed genes in testis we identified. In contrast, genes on the single Y chromosome become maximally active in primary spermatocytes. Reduced X transcript levels are due to failed activation of RNA-Polymerase-II by phosphorylation of Serine 2 and 5.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Drosophila / genetics*
  • Drosophila / growth & development
  • Gene Expression Regulation
  • Genes, X-Linked / genetics
  • Genes, Y-Linked / genetics
  • Larva / genetics
  • Larva / growth & development
  • Male
  • Organ Specificity
  • RNA Polymerase II / metabolism
  • Sex Chromosomes / genetics*
  • Sex Chromosomes / metabolism
  • Spermatocytes / metabolism*
  • Spermatogenesis / genetics
  • Testis / cytology
  • Testis / metabolism
  • Transcription, Genetic


  • RNA Polymerase II