La. Thompson et al., A MORPHOMETRIC COMPARISON OF THE NUCLEAR MORPHOLOGY OF FRESH AND FROZEN-THAWED HUMAN ZONA-BOUND AND UNBOUND SPERM, Journal of andrology, 15(4), 1994, pp. 337-342
The role of sperm nuclear morphology in zona binding and the effect of
cryopreservation on sperm nuclear morphology have been investigated u
sing objective criteria. The nuclear dimensions of fresh and frozen-th
awed sperm heads that had been prepared by the swim-up (SU) technique,
and bound to human oocytes in vitro, were measured using a computer-a
ssisted image analyzer. These were compared with each other and also t
o sperm in the SU samples and those that had not bound to the zona pel
lucida. The unbound (UB) sperm and SU sperm had very similar nuclear m
orphology. In contrast, the nuclear morphology of the zona-bound (ZB)
sperm differed significantly (P < 0.05) from that of the SU and UB spe
rm. These differences were found specifically between area, breadth, a
nd roundness in the SU and ZB sperm preparations, and between area and
roundness in the UB and ZB sperm preparations; the ZB sperm had small
er but rounder nuclei than either the SU or UB sperm. In addition, the
frozen-thawed sperm in the SU and UB groups showed a trend towards sm
aller nuclei than the corresponding fresh groups, whereas the frozen-t
hawed ZB sperm had significantly (P < 0.05) smaller nuclear dimensions
than the fresh ZB sperm. From the present study it appears that the Z
B sperm are a morphologically distinct population, although it is not
yet clear whether these differences reflect functional events that occ
ur in the sperm head during its maturation or changes at the level of
the sperm's DNA after the initial stage of zona binding. In addition,
cryopreservation was found to cause a marked reduction in the head dim
ensions of the ZB sperm. Such a reduction might reflect a compaction o
f the sperm's DNA as a result of the freeze-thawing process.