The XY pair of the mink (Mustela vision) during different periods of testicular activity

Analysis of the synaptonemal complex of the nine-banded armadillo, Dasypus novemcinctus

The synaptonemal complex (SC) of three specimens of the nine-banded armadillo (Dasypus novemcinctus) was analyzed. Thirty-two bivalents (2n = 64) were observed, 31 of them being autosomes and one an XY sexual bivalent. Chromosome synapsis processes and nucleolus structure changes were analyzed in zygotene and pachytene cells, allowing a detailed description of the beginning of meiotic prophase in this species. There was complete synapsis of X and Y chromosomes. Some abnormalities in SC were observed in cells during zygotene and at the beginning of pachytene, but not in cells in the middle and late pachytene, suggesting the occurrence of synaptic adjustments in their SC.

Meiosis and apoptosis in germ cells of X-autosome translocation carrier boars

Meiotic features and fate of germ cells were studied using electron microscopy on surface spread spermatocytes and in situ tests for apoptosis on testicular tissues of normal boars and X-autosome translocation (X-AT) carrier boars. Histological sections of the translocation t(Xp+; 14q-) carrier boars showed accumulation of degenerating germ cells including binucleate and multinucleate cells, as well as pyknosis and nuclear fragmentation characteristic of apoptosis. Synaptonemal complex analysis of X-AT carrier boars revealed 19 bivalents including a large complex made up of the altered X (Xp+) and normal chromosome 14, and a smaller element representing the Y chromosome in synapsis with the derived chromosome 14 (14q-) in most (89.3%) of the germ cells. In situ tests for apoptotic DNA fragmentation revealed positive signals exclusively among early spermatocytes and degenerating germ cells. These findings and the absence of stages beyond pachytene suggest that the meiocytes are arrested at pachytene and eliminated through apoptotic process in spite of the complete synapsis displayed by the chromosomes involved in this translocation. Failure of meiotic progress in our X-AT carriers would appear to be the result of the disruption of gene sequence (or function) caused by the involvement of the X chromosome in this rearrangement, rather than the deleterious consequences of abnormal segregation anticipated in reciprocal translocation carriers. We hypothesize that this disruption could have affected the induction of stage-specific gene products in meiosis such as heat shock proteins and caused the excessive release of endonucleases normally produced by early prophase meiocytes, leading to their apoptosis in our X-autosome translocation carrier boars.