Human Reproduction, Vol 13, 703-708, Copyright © 1998 by Oxford University Press
S Lopes, A Jurisicova and RF Casper
The objective of the present study was to assess the integrity of maternal
and/or paternal chromatin in injected oocytes that remained unfertilized
after intracytoplasmic sperm injection (ICSI). The study was performed on
102 oocytes that failed to show pronuclear formation 18-20 h after ICSI. We
used chromatin labelling with 4,6-diamidino-2- phenylindole (DAPI) to
identify maternal and paternal chromatin, coupled with biotin-mediated
end-labelling to assess DNA fragmentation in each gamete. It was shown that
50% of oocytes without pronuclear formation following ICSI contained
chromatin with damaged DNA, and that the source of the DNA fragmentation
was equally divided between the spermatozoon (25.8%) and the oocyte
(24.4%). A significantly greater proportion of condensed spermatozoa in
human oocytes had damaged DNA, compared to decondensed spermatozoa (24.7
compared to 5.9%, P=0.002). There was a significant increase in the
incidence of DNA fragmentation in oocytes from patients older than 35 years
(65+/-1.2%) compared to those from younger patients (36+/-1.0%) (P <
0.05). Further, 17% of unfertilized oocytes contained no paternal
chromatin. Thus, DNA fragmentation in both spermatozoa and oocytes is
associated with failure of fertilization in ICSI. In some cases of severe
male factor infertility, a significant proportion of spermatozoa injected
into oocytes may contain fragmented DNA. Injection of oocytes with
spermatozoa containing abnormal chromatin will probably result in failure
of sperm decondensation and fertilization. In older women, a significant
proportion of oocytes injected may contain fragmented DNA. These
observations may explain the consistent inability of most clinics to
achieve fertilization rates higher than 65% with ICSI.
ARTICLES
Gamete-specific DNA fragmentation in unfertilized human oocytes after intracytoplasmic sperm injection
Department of Obstetrics and Gynecology, University of Toronto and the Toronto Center for Advanced Reproductive Technology, Ontario, Canada.
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