Abstract
Historically, less attention has been paid to paternal effects on early embryogenesis than maternal effects. However, it is now apparent that certain male factor infertility phenotypes are associated with increased DNA fragmentation and/or chromosome aneuploidies that may compromise early embryonic development. In addition, there is a growing body of evidence that the fertilizing sperm has more function than just carrying an intact, haploid genome. The paternally inherited centrosome is essential for normal fertilization, and the success of higher order chromatin packaging may impact embryogenesis. Epigenetic modifications of sperm chromatin may contribute to the reprogramming of the genome, and sperm delivered mRNA has also been hythesized to be necessary for embryogenesis. There is less information about the epigenetic factors affecting embryogenesis than genetic factors, but the epigenetics of gamete and early embryogenesis is a rapidly advancing field.
Highlights
The contributions of sperm to embryogenesis are more than just providing a haploid genome
Male factor infertility is responsible for approximately 50% of in vitro fertilization (IVF) cases and the vast majority of male factor infertility is classified as idiopathic
The fertilizing spermatozoon is associated with more functions than only providing half of the genetic material to the oocyte
Summary
The contributions of sperm to embryogenesis are more than just providing a haploid genome. An increased sperm aneuploidy rate has been associated with lower implantation and pregnancy rates and a higher incidence of miscarriage in ICSI cycles [36,65,68,69]. Lower rates of recombination between chromosomes are associated with a higher risk of producing disomic sperm [76] These studies suggest that more care has to be taken with those patients who have severe oligoastenoteratozoospermia, non-obstructive azoospermia or unexplained recurrent pregnancy lost. No differences in the global DNA methylation patterns were seen in protamine-deficient sperm samples indicating that this assay might not sensitive enough to detect variation in epigenetic modification [108] More informative techniques such as bisulfite genomic sequencing or CpG island microarrays [99] should be used to analyze methylation patterns of imprinted genes rather than global DNA methylation to identify possible differences in infertile males. The correlation between the sperm mRNA fingerprint and embryogenesis needs further clarification in the future
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