Unpaired chromosomes at meiosis: cause or effect of gametogenic insufficiency?

Abstract

Pairing failure at meiosis has been postulated as a cause of gametogenic arrest in both heterozygous translocation carriers and males whose spermatocytes exhibit univalent X and Y chromosomes. The present investigation is a survey of pachytene translocation configurations, at the electron microscopic level, in six stocks of mice, comprising a total of 464 spermatocytes and 343 oocytes. Univalence of the X and Y chromosomes was studied in the same stocks, as well as in three additional homozygous translocation stocks. Fully paired as well as asynaptic configurations were found in all translocation stocks, and the proportions of each configuration differed considerably between spermatocytes and oocytes of mice carrying the same translocation. In both spermatocytes and oocytes, other pairing anomalies were more frequent in cells with asynapsed than with fully synapsed configurations, and spermatocytes with univalent sex chromosomes had a higher proportion of autosomal anomalies than did spermatocytes with XY bivalents. It is concluded that pairing failure at meiosis is primarily a symptom, rather than a cause, of gametogenic arrest, and that chromosome rearrangements, even if they appear to be balanced, may affect the rate of atresia by interfering with the normal rate of meiotic progression. Once pairing failure is established, it could secondarily increase the probability of gametogenic failure.

An analysis of meiotic pairing in trisomy 21 oocytes using fluorescent in situ hybridization

“…Clearly, the observations of asynapsis in both trisomy 18 (Cheng et al, 1995a) and trisomy 21 reported here implicates the aneuploid state in predisposing to pairing failure, not only for the trisomic chromosome, but for other chromosomes as well. Our observation of increased asynapsis in chromosomes other than the trisomic one is similar to the result of Mittwoch and Mahadevaiah (1992) who observed that murine gametes with inherited rearrangements were likely to experience asynapsis of other chromosomes. It is possible that the imbalance of genetic information or the absence of an effective pairing partner may disrupt the mechanism of homologous pairing through excessive unsuccessful nonhomologous pairing trials.…”

Spermatogenesis in common shrews, <i>Sorex araneus</i>, from a hybrid zone with extensive Robertsonian polymorphism

“…Thus, the Abisko and Sidensjö races are expected to have a different genetic background. High levels of germ cell death without pairing abnormalities has been observed in Robertsonian homozygotes in the house mouse (Mittwoch and Mahadevaiah, 1992;Everett et al, 1996). Also, Said et al (1993) concluded that the degree of disorder in the process of spermatogenesis might be due to genetic incompatibilities and not to chromosomal heterozygosity per se.…”

Meiotic recombination and male infertility: from basic science to clinical reality?

“…28 This clearly has important clinical ramifications as asynapsis in pachytene may arise from a primary meiotic defect that could result in an increased probability of atresia. [29][30][31][32] High frequencies of asynapsed regions in pachytene, likely prevent the normal progression of meiotic prophase substages. Asynapsed regions may trigger a checkpoint that leads to partial or complete spermatogenic arrest as a result of severe meiotic defects and hence results in the NOA phenotype.…”