DNA Damage in Bovine Sperm Does Not Block Fertilization and Early Embryonic Development But Induces Apoptosis After the First Cleavages
Top Cited Papers
- 4 March 2006
- journal article
- Published by Wiley in Journal of Andrology
- Vol. 27 (2), 176-188
- https://doi.org/10.2164/jandrol.04152
Abstract
The main goal of this study was to investigate whether and at what level damage of paternal DNA influences fertilization of oocytes and early embryonic development. We hypothesized that posttesticular sperm DNA damage will only marginally affect sperm physiology due to the lack of gene expression, but that it will affect embryo development at the stage that embryo genome (including the paternal damaged DNA) expression is initiated. To test this, we artificially induced sperm DNA damage by irradiation with x- or gam- ma rays (doses of 0-300 Gy). Remarkably, sperm cells survived the irradiation quite well and, when compared with nonirradiated cells, sperm motility and integrity of plasma membrane, acrosome, and mitochondria were not altered by this irradiation treatment. In con- trast, a highly significant logarithmic relation between irradiation dose and induced DNA damage to sperm cells was found by both terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) and the acridin orange assay. Despite the DNA damage, irradiated sperm cells did not show any sign of apo- ptosis (nuclear fragmentation, depolarization of inner mitochondrial membranes, or phospholipid scrambling) and were normally capable of fertilizing oocytes, as there was no reduction in cleavage rates when compared with nonirradiated sperm samples up to irradiation doses of less than 10 Gy. Further embryonic development was com- pletely blocked as the blastocyst rates at days 7 and 9 dropped from 28% (nonirradiated sperm) to less than 3% by greater than 2.5-Gy- irradiated sperm. This block in embryonic development was accom- panied with the initiation of apoptosis after the second or third cleav- age. Specific signs of apoptosis, such as nuclear fragmentation and aberrations in spindle formation, were observed in all embryos re- sulting from in vitro fertilization with irradiated sperm (irradiation dos- es .1.25 Gy). The results show that sperm DNA damage does not impair fertilization of the oocyte or completion of the first 2-3 cleav- ages, but blocks blastocyst formation by inducing apoptosis. Embry- os produced by assisted reproductive techniques (ART) could have incorporated aberrant paternal DNA (frequently detected in sperm of sub/infertile males). Analogously, in the present work, we discuss the possibility of following embryo development of oocytes fertilized by ART through the blastocyst stage before embryo transfer into theKeywords
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