Aneuploidy in spermatids of Robertsonian (Rb) chromosome heterozygous mice

Abstract

Rb translocations are chromosomal rearrangements frequently found in natural populations of the house mouse Mus musculus domesticus. The standard diploid karyotype of the house mouse consisting of 40 telocentric chromosomes may be reduced by the emergence of metacentric Rb chromosomes. Multiple simple Rb heterozygotes form trivalents exhibiting higher anaphase nondisjunction frequency and consequently higher number of unbalanced gametes than in normal males. This work will attempt to establish whether frequencies of aneuploidy observed in heterozygote spermatids of the house mouse M. musculus domesticus show differences in chromosomes derived from different trivalents. Towards this goal, the number and distribution frequency of aneuploidy was assessed via FISH staining of specific chromosomes of spermatids derived from 2n = 32 individuals. Our results showed that for a given set of target chromosomes, 90 % of the gametes were balanced, resulting from alternate segregation, and that there were no differences (approx. 10 %) in aneuploidy frequencies in chromosomes derived from different trivalents. These observations suggest that segregation effectiveness does not depend on the type of chromosomes involved in trivalents. As a consequence of the trivalent’s configuration, joint segregation of the telocentric chromosomes occurs thus favoring their appearance together in early spermatids. Our data suggest that Rb chromosomes and their telocentric homologs are subject to architectural constraints placing them close to each other. This proximity may ultimately facilitate fusion between them, hence contributing to a prevalence of Rb metacentric chromosomes.

Chromosomal Polymorphism and Speciation: The Case of the Genus Mazama (Cetartiodactyla; Cervidae)

“…Because of this, we decided to perform the technique of sperm-FISH to estimate the proportion of normal/balanced and unbalanced spermatozoa in bucks with heterozygous rearrangements and animals from crossbreeding between cytotypes of the same lineage in MAM. The proportion of meiotic products from adjacent segregation modes in RT carriers analyzed in this study is consistent with reports for domestic species such as bulls, boars and mice (2.58–5.42%, 3.16%, and 8–11.5%, respectively) [ 64 , 65 , 66 , 67 ]. These findings may suggest a low negative effect on the reproductive fitness of heterozygous carriers of RT reported here for MAM, unlike that reported for several RT in humans where there is a wide variation in reproductive impact (0.2–49.1% of adjacent segregation products) [ 68 ].…”

Analysis of Meiotic Segregation Pattern and Interchromosomal Effects in a Bull Heterozygous for a 3/16 Robertsonian Translocation

“…The high rates of genetically normal/balanced gametes observed in our study (94.13%, when occulting ICE) as well as in other human and murine studies [Ogur et al, 2006;Manieu et al, 2014;Wang et al, 2017] could be explained by a preferential cis-pairing configuration of the trivalent during the pachytene stage, favoring alternate segregation [Vidal et al, 1982;Switoński et al, 1987].…”

How much, if anything, do we know about sperm chromosomes of Robertsonian translocation carriers?

“…These alterations in the internuclear sperm organization can be attributed to changes in the expression profile of paternal alleles in the embryo, which may suggest that the disturbed topology of sperm chromosomes could be an additional factor in reproductive failure. The key to understanding this issue would undoubtedly be to clarify whether chromosome positional variations in infertile carriers are the cause or the consequence of impaired spermatogenesis [92,[94][95][96][97].…”