Meiotic Recognition of Evolutionarily Diverged Homologs: Chromosomal Hybrid Sterility Revisited

Abstract

Hybrid sterility (HS) is an early postzygotic reproductive isolation mechanism observed in all sexually reproducing species. Infertility of hybrids prevents gene flow between incipient species and leads to speciation. While Drosophila studies have focused almost exclusively on the genic control of HS, two other model species, Mus musculus and budding yeast provided the first experimental evidence of hybrid sterility governed by the nongenic effects of DNA sequence divergence. Here, we propose that the nongenic effect of increasing DNA divergence between closely related species may impair mutual recognition of homologous chromosomes and disrupt their synapsis. Unsynapsed or mispaired homologs can induce early meiotic arrest, or their random segregation can cause aneuploidy of spermatids and sperm cells. Impaired recognition of homologs may thus act as a universal chromosomal checkpoint contributing to the complexity of genetic control of HS. Chromosomal HS controlled by the Prdm9 gene in mice and HS driven by the mismatch repair machinery in yeast are currently the most advanced examples of chromosomal homology search-based HS. More focus on the cellular and molecular phenotypes of meiosis will be needed to further validate the role of homolog recognition in hybrid sterility and speciation.

Natural variation in the zinc-finger-encoding exon of Prdm9 affects hybrid sterility phenotypes in mice

“…Given that all F 1 -hybrid males were either completely fertile or showed only reduced fertility, we tested whether they displayed chromosomal asynapsis, a hallmark characteristic of Prdm9 -dependent hybrid sterility ( Forejt and Jansa 2023 ). We immunostained spermatocyte spreads of F 1 hybrids that inherited alleles msc10 , msc11 , and msc12 , as well as hybrids that inherited the mmt1 allele in combination with both DOM and MUS t -haplotypes.…”

Microgeographic population structuring in a genus of California trapdoor spiders and discovery of an enigmatic new species (Euctenizidae: Promyrmekiaphila korematsui sp. nov.)

“…Selective pressure for prezygotic isolating mechanisms is likely less severe for allopatric species than for species found in sympatry, where mating could result in low fitness offspring (Servedio & Noor, 2003). In allopatry, postzygotic incompatibility may build up through other mechanisms, such as Dobzhansky-Muller incompatibilities from genetic drift, or hybrid inviability or sterility resulting from chromosome incompatibility (Forejt & Jansa, 2023;Orr & Turelli, 2001). this species and other low-vagility species in this region (Bryson et al, 2016;Hedin et al, 2013;Howard, 1979;Kuchta et al, 2009;Leavitt et al, 2015).…”