Detection of nondisjunction and recombination in meiotic and postmeiotic cells from XYSxr [XY,Tp(Y)1Ct] mice using multicolor fluorescence in situ hybridization.

Abstract

Current meiotic dogma holds that synapsis is required for recombination and that recombination is required for proper disjunction. The mouse chromosome aberration XYsxr [sex reversal; redesignated XY,Tp(Y)lCt] appears to challenge this assumption, for although chromosomes X and Y often fail to synapse and recombine, there is no dramatic increase in aneuploid progeny. An explanation of this conundrum might be that X-Y univalent spermatocytes do not survive. The phenotype of sex reversal is generated by the "obligatory" crossover between the X and Y chromosomes, which always occurs proximal to a duplicated copy of the testis-determining gene Sry and transfers one copy from one chromatid of the Y chromosome to one chromatid of the X.Animals that inherit an X chromosome with the Sry gene are chromosomaily female but phenotypically male. We have used fluorescence in situ hybridization (FISH) to visualize probes for the X and Y chromosomes and for the Siy sequence and chromosome 8 to track the fate of both recombinant and nonrecombinant chromosomes through metaphases I and II into spermatids and sperm. In the 219 gametes examined by multicolor FISH, the frequency of aneuploid products (XY or "0") was low (3.7%) despite a high frequency (66%) of X-Y separation at metaphase I. In balanced gametes, X and Y recombinant chromosomes slightly exceeded nonrecombinants. Both of these observations support the earlier proposal that asynapsis and nondisjunction in primary spermatocytes lead to their developmental arrest and degeneration.Aneuploidy arising from meiotic missegregation is the primary cause of numerical chromosome abnormalities. Two general approaches have been developed to directly measure frequency of aneuploidy in spermatozoa: (i) cytogenetic analysis of the sperm's whole chromosome complement following penetration of sperm from a xenotropic species into zona-free hamster oocytes (1-4) and (ii) in situ hybridization to sperm cells (5). The first technique is tedious, technically difficult, and limited by the number of hamster oocytes that can be fertilized for any single analysis. Until now, in situ hybridization studies, whether isotopic (6) or nonisotopic (5, 7), have been limited to the detection of one or at most two chromosome markers, thus severely limiting utility of this procedure. However, the recent introduction of multicolor in situ hybridization methods (8, 9) has greatly increased the potential usefulness of in situ hybridization for studying aneuploidy in spermatozoa.Meiotic synapsis is generally considered necessary to bring homologous DNA into close enough register for recombination to occur. Normal disjunction at anaphase I depends upon the production of at least one chiasma (the cytologicalThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.consequence of meiotic recombination) per bivalent (pair of synapsed chromosomes) to facilitate...

Reduced MAD2 levels dampen the apoptotic response to non-exchange sex chromosomes and lead to sperm aneuploidy

“…This indicates that, in the presence of a normally functioning SAC, spermatocytes with non-exchange sex chromosomes are efficiently eliminated by the apoptotic response, in agreement with earlier studies (Burgoyne et al, 1992;Odorisio et al, 1998). However, the high elimination stringency appears to be at least partially dependent on strain background: in XY Sxr mice (with a mixed genetic background of C3H/HeH and 101/H strains) with 64% of X-Y achiasmy, 3.7% of sperm were X-Y aneuploid (Ashley et al, 1994). This indicates some leakiness of the (wildtype) SAC in this setting, and contrasts with our current observations in the C57BL/6-129/Sv background of 50% X-Y achiasmy and 0% aneuploidy.…”

Meiotic failure in male mice lacking an X-linked factor

“…4D-F). The presence of univalents could lead to chromosomal segregation defects at the subsequent anaphase I stage, and aberrant chromosome attachment to the spindle or chromosome nondisjunction could trigger the spindle checkpoint and induce apoptosis (Ashley et al 1994;Li and Nicklas 1995;Odorisio et al 1998;Eaker et al 2002). We detected both defective chromosome segregation in Tex11 −/Y anaphase spermatocytes (Fig.…”

Alternative dominance of the parental genomes in hybrid cells generated through the fusion of mouse embryonic stem cells with fibroblasts

“…Xist RNA detection on X-chromosomes was performed as previously described 48 . Mouse X and Y repeats used in DNA FISH analysis were prepared as previously described 49 . IF and FISH slides were analyzed on a Nikon Ni-E microscope using NIS-elements software.…”