Sex chromosome aneuploidy in sperm-derived pronuclei, motile sperm and unselected sperm, scored by three-color FISH

Nuclear DNA fragmentation negatively affects zona binding competence of Y bearing mouse spermatozoa

PURPOSE

To investigate the influence of sperm DNA integrity on the zona binding ability of mouse spermatozoa in relation to their sex chromosomal constitution.

METHOD(S)

In this prospective experimental study, the sperm DNA fragmentation was induced by exposing testicular area of Swiss Albino mice (Mus musculus) to different doses of γ-radiation (0, 2.5, 5.0 and 10.0 Gy). Sperm DNA fragmentation was quantified by single cell gel electrophoresis (comet assay). In vitro sperm zona binding assay was performed and the numbers of zona bound X and Y bearing spermatozoa were determined using fluorescence in situ hybridization (FISH).

RESULT(S)

The assessment of zona pellucida bound X and Y-bearing spermatozoa using fluorescence in situ hybridization has revealed a unique binding pattern. The number of zona bound Y-spermatozoa declined significantly (P < 0.01 to 0.0001) with increase in the DNA damage. The skewed binding pattern of X and Y-bearing sperm was strongly correlated with the extent of sperm DNA damage.

CONCLUSION(S)

The zona pellucida may have a role in preventing DNA damaged mouse sperm binding especially towards Y-bearing sperm. However, the exact mechanism behind this observation needs to be elucidated further.

Incidence of aneuploid spermatozoa from subfertile men: selected with motility versus hemizona-bound

Spermatozoa-zona pellucida binding selects for human spermatozoa with progressive motility, normal morphology and functional competency. We postulated that this gamete interaction would also act to select against spermatozoa with chromosomal numerical aberrations. Spermatozoa from 41 men participating in the intracytoplasmic sperm injection (ICSI) programme were evaluated for the incidence of aneuploidy of chromosomes 18, X and Y. The hemizona assay was utilized to determine whether zona-bound spermatozoa from these patients have a reduced incidence of aneuploidy compared with those selected by motility only in a standard swim-up procedure. Using multicolour fluorescence in-situ hybridization (FISH) with DNA probes specific for chromosomes 18, X and Y, the disomy rates for chromosomes 18, X, Y and XY were found to be 0.31, 0.27, 0.29 and 0. 14% respectively in the swim-up motile fraction, and 0.31, 0.33, 0. 32 and 0.19% respectively in the pellet fraction. Analysing the zona-bound spermatozoa, the disomy rates for chromosome 18, X, Y and XY were found to be 0.02, 0.15, 0.12 and 0.07% respectively. The zona-bound spermatozoa had a significantly lower frequency of aneuploidy than the swim-up motile fraction or the pellet fraction (P < 0.0001). The incidence of chromosome 18 aneuploidy, including both chromosome 18 disomy and nullisomy, in the swim-up motile fractions was significantly increased in patients with an abnormal or borderline hemizona index compared with those with a normal hemizona index (P < 0.05). We also found that a high incidence of sperm aneuploidy was associated to a certain extent with low fertilization rate, and with failure to achieve pregnancy through ICSI. This study suggests that the human zona pellucida has the capacity to select against aneuploid spermatozoa by an as yet undetermined mechanism.