Meiotic Chromosome Contacts as a Plausible Prelude for Robertsonian Translocations

Abstract

Robertsonian translocations are common chromosomal alterations. Chromosome variability affects human health and natural evolution. Despite the significance of such mutations, no mechanisms explaining the emergence of such translocations have yet been demonstrated. Several models have explored possible changes in interphase nuclei. Evidence for non-homologous chromosomes end joining in meiosis is scarce, and is often limited to uncovering mechanisms in damaged cells only. This study presents a primarily qualitative analysis of contacts of non-homologous chromosomes by short arms, during meiotic prophase I in the mole vole, Ellobius alaicus, a species with a variable karyotype, due to Robertsonian translocations. Immunocytochemical staining of spermatocytes demonstrated the presence of four contact types for non-homologous chromosomes in meiotic prophase I: (1) proximity, (2) touching, (3) anchoring/tethering, and (4) fusion. Our results suggest distinct mechanisms for chromosomal interactions in meiosis. Thus, we propose to change the translocation mechanism model from ‘contact first’ to ‘contact first in meiosis’.

Meiotic Nuclear Architecture in Distinct Mole Vole Hybrids with Robertsonian Translocations: Chromosome Chains, Stretched Centromeres, and Distorted Recombination

“…We assume that the inertness of chromosome #7 in meiosis may be due to the absence or extremely low content of constitutive heterochromatin. This was confirmed using antibodies to histone H3K9me3, a marker of constitutive heterochromatin, both in bivalent #7 in E. tancrei (unpublished) and in a sibling species E. alaicus [ 109 ].…”

“…However, chromocenters in all mole voles were usually not detected by DAPI staining. Nevertheless, we found that acrocentric chromosomes were grouped by their pericentromeric regions around the H3K9me3 domains in the sibling species E. alaicus [ 109 ]. We saw a similar grouped position of acrocentrics in E. talpinus ( Figure 2 A).…”

Kinase CDK2 in Mammalian Meiotic Prophase I: Screening for Hetero- and Homomorphic Sex Chromosomes

“…In addition to CDK2 antibodies to identify this kinase, we used antibodies to proteins RAD51 and MLH1 (a mismatch repair protein) as markers for DNA double-strand breaks and recombination [ 23 , 24 ]. We studied seven rodent species from four subfamilies and three families with various sex chromosome systems, reflecting different evolutionary stages ( Table S1 , Figure S1 ): The Norwegian rat Rattus norvegicus (Muridae), with XX-XY and PAR, the common vole Microtus arvalis with XX, achiasmatic XY and no PAR; the lesser mole rat Nannospalax leucodon (Spalacidae), with XX-XY and PAR; the gray dwarf hamster Cricetulus migratorius (Cricetidae), with XX-XY, PAR and equal-length heteromorphic chromosomes; and three species with isomorphic (homomorphic) sex chromosomes for both sexes: The northern mole vole Ellobius talpinus , the eastern mole vole E. tancrei , and the Alay mole vole Ellobius alaicus (male XX with broad central asynaptic zone [ 25 , 26 ] and female XX with delayed synapsis [ 27 ]). The primary focus was on the classical system XX-XY (rat) and the deviant XX-XX (the northern mole voles).…”

Incomplete Sterility of Chromosomal Hybrids: Implications for Karyotype Evolution and Homoploid Hybrid Speciation

“…In this context, the question arises whether this model is applicable to monocentric organisms. The data available in literature show that, although to a lesser extent, organisms with monocentric chromosomes can also be tolerant to heterozygosity for multiple chromosomal fusions and fissions (e.g., Nachman and Myers, 1989;Nunes et al, 2011;Matveevsky et al, 2020). This indicates the potential of the discussed mechanism for karyotype evolution and speciation in monocentric organisms.…”