Strategies for meiotic sex chromosome dynamics and telomeric elongation in Marsupials

PLoS Genet. 2022 Feb 7;18(2):e1010040. doi: 10.1371/journal.pgen.1010040. eCollection 2022 Feb.

Abstract

During meiotic prophase I, homologous chromosomes pair, synapse and recombine in a tightly regulated process that ensures the generation of genetically variable haploid gametes. Although the mechanisms underlying meiotic cell division have been well studied in model species, our understanding of the dynamics of meiotic prophase I in non-traditional model mammals remains in its infancy. Here, we reveal key meiotic features in previously uncharacterised marsupial species (the tammar wallaby and the fat-tailed dunnart), plus the fat-tailed mouse opossum, with a focus on sex chromosome pairing strategies, recombination and meiotic telomere homeostasis. We uncovered differences between phylogroups with important functional and evolutionary implications. First, sex chromosomes, which lack a pseudo-autosomal region in marsupials, had species specific pairing and silencing strategies, with implications for sex chromosome evolution. Second, we detected two waves of γH2AX accumulation during prophase I. The first wave was accompanied by low γH2AX levels on autosomes, which correlated with the low recombination rates that distinguish marsupials from eutherian mammals. In the second wave, γH2AX was restricted to sex chromosomes in all three species, which correlated with transcription from the X in tammar wallaby. This suggests non-canonical functions of γH2AX on meiotic sex chromosomes. Finally, we uncover evidence for telomere elongation in primary spermatocytes of the fat-tailed dunnart, a unique strategy within mammals. Our results provide new insights into meiotic progression and telomere homeostasis in marsupials, highlighting the importance of capturing the diversity of meiotic strategies within mammals.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromosome Pairing / physiology*
  • Macropodidae / genetics
  • Marsupialia / genetics
  • Meiosis / genetics
  • Meiosis / physiology
  • Meiotic Prophase I / physiology
  • Opossums / genetics
  • Sex Chromosomes / genetics
  • Sex Chromosomes / physiology*
  • Telomere / genetics
  • Telomere / physiology*
  • X Chromosome / genetics
  • Y Chromosome / genetics

Grants and funding

This work was supported by the Ministry of Economy, Industry and Competitiveness (CGL2017-83802-P to A.R-H. and CGL2014-53106-P to J.P.), the Spanish Ministry of Science and Innovation (PID2020-112557GB-I00 to A.R-H.) and the Agència de Gestió d'Ajuts Universitaris i de Recerca, AGAUR (SGR1215 to A.R-H.). L.M.-G. and C.V. were supported by a FPU predoctoral fellowship from the Ministry of Science, Innovation and University (FPU18/03867) and by a FPI predoctoral fellowship from the Ministry of Economy, Industry and Competitiveness (BES-2015-072924), respectively. P.D.W. is supported by Australian Research Council Discovery Projects (DP170101147, DP180100931 and DP210103512). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.