Aneuploidy in late‐step spermatids of mice detected by two‐chromosome fluorescence in situ hybridization

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Abstract
A multicolor procedure employing fluorescence in situ hybridization is described for detecting chromosomal domains and germinal aneuploidy in late‐step spermatids in mice using DNA probes specific for repetitive sequences near the centromeres of chromosomes 8 and X. These probes were nick‐translated with biotin‐ or digoxigenin‐labeled nucleotides, and were detected with FITC or rhodamine. Probe and hybridization specificities were confirmed using metaphase chromosomes from spleen and bone marrow cells as well as from primary and secondary spermatocytes. Late‐step spermatids, identified in testicular preparations by their hooked shape, yielded compact fluorescence domains in ∼ 50% and > 99% of cells when hybridized with probes for chromosomes X and 8, respectively. In a survey of > 80,000 late‐step spermatids from 8 healthy young adult C57BL/6 or B6C3F1 mice, ∼ 3/10,000 spermatids had fluorescence phenotypes indicative of X‐X or 8–8 hyperhaploidy. These frequencies are consistent with published frequencies of aneuploidy in meiotic metaphase II and first cleavage metaphases of the mouse, providing preliminary validation of sperm hybridization for the detection of aneuploidy. No significant animal or strain differences were observed. In addition, the hyperhaploidy frequencies for murine spermatids were indistinguishable for those for sperm from healthy men obtained by a similar hybridization procedure. These procedures for detecting aneuploid male gametes are examples of “bridging biomarkers” between human and animal studies. They have promising applications for investigations of the genetic, reproductive, and toxicological factors leading to abnormal reproductive outcomes of paternal origin.

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