Evidence for meiotic spindle checkpoint from analysis of spermatocytes from Robertsonian-chromosome heterozygous mice

Mice heterozygous for Robertsonian centric fusion chromosomal translocation s frequently produce aneuploid sperm. In this study RBJ/Dn x C57BL/6J F-1 m ales, heterozygous for four Robertsonian translocations (2N=36), were analy zed to determine effects on germ cells of error during meiosis. Analysis of sperm by three color fluorescence in situ hybridization revealed significa ntly elevated aneuploidy, thus validating Robertsonian heterozygous mice as a model for production of chromosomally abnormal gametes. Primary spermato cytes from heterozygous males exhibited abnormalities of chromosome pairing in meiotic prophase and metaphase. In spite of prophase abnormalities, the prophase/metaphase transition occurred. However, an increased frequency of cells with misaligned condensed chromosomes was observed. Cytological anal ysis of both young and adult heterozygous mice revealed increased apoptosis in spermatocytes during meiotic metaphase I. Metaphase spermatocytes with misaligned chromosomes accounted for a significant proportion of the apopto tic spermatocytes, suggesting that a checkpoint process identifies aberrant meioses. Immunofluorescence staining revealed that kinetochores of chromos omes that failed to align on the spindle stained more intensely for kinetoc hore antigens CENP-E and CENP-F than did aligned chromosomes. Taken togethe r, these observations are consistent with detection of malattached chromoso mes by a meiotic spindle checkpoint mechanism that monitors attachment and/ or congression of homologous chromosome pairs. However, the relatively high frequency of gametic aneuploidy suggests that the checkpoint mechanism doe s not efficiently eliminate all germ cells with chromosomal abnormalities.