Synaptonemal complexes and XY behavior in two species of argentinian armadillos: Chaetophractus villosus and Dasypus hybridus (Xenarthra, Dasypodidae)

Spermatocytes from the two armadillo species, C. villosus and D. hybridus were studied in microspreads for synaptonemal complexes (SCs) and in thin sections for electron microscopy (EM). The complete se karyotype generally agrees with previous reports on mitotic chromosomes, except for the sex chromosomes. The X chromosome is submetacentric in both species and the Y is the shortest one in C. villosus and the second shortest in D. hybridus, and an extremely acrocentric one. A SC is formed along the total length of the Y chromosome, and this SC persists along all the pachytene substages. A single recombi-nation nodule (RN) is located in the region of the se nearest to the attachment to the nuclear envelope. The lateral element (LE) of the X axis in the SC shows a wavy aspect in most of the se length distant from the nuclear envelope. Nucleoli are attached to acrocentric or submetacentric bivalents, are visibly double in some cells , and in thin sections show an elaborate nucleolonema. Some differences in the XY are species-specific, as the higher degree of tangling and stronger heteropycnosis in D. hybridus. The effective, single crossover of the XY pair is highly localized, despite the permanence of a long tract of SC

Changes in crossover distribution along a quadrivalent in aman carrier of a reciprocal translocation t(11; 14)

A testicu1ar biopsy from an infertile man carrying a heterozygous chromosome translocation t(ll; 14) was studied with synaptonemal complex analysis and immunolocalization of the protein MLH 1 for crossover detection. A full blockage of spermatogenesis at the spermatocyte stage was related to the presence of the translocation quadrivalents at pachytene. Only 2% of the quadrivalents showed full synapsis. Most of the spermatocytes showed asynaptic free ends that frequently mingled with the XY pair. The average number of crossovers per cell was diminished from a mean of 52.7 in controls to a mean of 48 in the patient. The difference between the number of crossovers in the quadrivalent and the normal bivalents was highly significant. The distribution of crossovers over the segment of the quadrivalent corresponding to bivalent #14 was also very different from that ofthe control. It is concluded that in this translocation, the pattern of crossovers is changed, mainly due to a synaptic hindrance in the quadrivalent, and that the spermatogenesis arrest is mainly due to the quadrivalents that interact with the XY pair