Dispersive forces and resisting spot welds by alternative homolog conjunction govern chromosome shape in Drosophila spermatocytes during prophase I

PLoS Genet. 2022 Jul 27;18(7):e1010327. doi: 10.1371/journal.pgen.1010327. eCollection 2022 Jul.

Abstract

The bivalent chromosomes that are generated during prophase of meiosis I comprise a pair of homologous chromosomes. Homolog pairing during prophase I must include mechanisms that avoid or eliminate entanglements between non-homologous chromosomes. In Drosophila spermatocytes, non-homologous associations are disrupted by chromosome territory formation, while linkages between homologous chromosomes are maintained by special conjunction proteins. These proteins function as alternative for crossovers that link homologs during canonical meiosis but are absent during the achiasmate Drosophila male meiosis. How and where within bivalents the alternative homolog conjunction proteins function is still poorly understood. To clarify the rules that govern territory formation and alternative homolog conjunction, we have analyzed spermatocytes with chromosomal aberrations. We examined territory formation after acute chromosome cleavage by Cas9, targeted to the dodeca satellite adjacent to the centromere of chromosome 3 specifically in spermatocytes. Moreover, we studied territory organization, as well as the eventual orientation of chromosomes during meiosis I, in spermatocytes with stable structural aberrations, including heterozygous reciprocal autosomal translocations. Our observations indicate that alternative homolog conjunction is applied in a spatially confined manner. Comparable to crossovers, only a single conjunction spot per chromosome arm appears to be applied usually. These conjunction spots resist separation by the dispersing forces that drive apart homologous pericentromeric heterochromatin and embedded centromeres within territories, as well as the distinct chromosomal entities into peripheral, maximally separated territories within the spermatocyte nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Centromere / genetics
  • Chromosome Pairing / genetics
  • Chromosome Segregation / genetics
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / metabolism
  • Drosophila* / genetics
  • Male
  • Meiosis / genetics
  • Meiotic Prophase I / genetics
  • Prophase
  • Spermatocytes* / metabolism

Grants and funding

The research was supported by funds obtained from the Swiss National Science Foundation (www.snf.ch), grant number 31003A_179433 (CFL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.