Gene disruption technology has long been beneficial for the study of male reproductive biology. However, because of the time and cost involved, this technology was not a viable method except in specialist laboratories. The advent of the CRISPR/Cas9 system of gene disruption has ushered in a new era of genetic investigation. Now, it is possible to generate gene-disrupted mouse models in very little time and at very little cost. This Highlight article discusses the application of this technology to study the genetics of male fertility and looks at some of the future uses of this system that could be used to reveal the essential and nonessential genetic components of male reproductive mechanisms.

Mice are one of the most ideal organisms to study mammalian reproduction. This is because of their relatively fast reproductive cycle coupled with their similarity to the human genome. [1] However, reproduction remains one of the most complex yet poorly understood biological processes, despite decades of dedicated research. Numerous genes have been thought to play essential roles in fertilization, because of their localization or specific expression in the male and/or female gonads, yet analysis of their specific roles has been problematic due to the difficulty in maintaining gametes and embryos in vitro. [2]

Thus, gene manipulation experiments in animal models have played an essential role in the investigation of reproductive processes. Reproduction is arguably one of the best-suited biological systems to which gene knockout (KO) can be applied, for several reasons. First, genes essential for fertility are most often highly specific to the gonads, eliminating the need for conditional gene knockout models to be utilized. Often spermatogenic or haploid male germ cell genes are comprised of a single exon, eliminating the issues of alternate splicing. Another benefit of utilizing gene-disrupted mice is the incidental discovery of genes involved in reproduction by groups investigating other body systems. [3],[4] The breeding schemes involved in producing homozygous genetic manipulations for any target gene automatically highlight genes involved in gametogenesis, fertilization and pregnancy. Whatever the reason, there is a higher level of specific homologues in reproductively related genes than in those coding for somatic cell phenotypes, making the use of gene-disruption essential to uncover the truly essential factors of fertility. This review will look at the history of gene manipulation techniques for the study of mammalian reproduction, with a focus on discoveries in the male system and analyze the application of the latest in these technologies, the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR associated (Cas) protein number 9) system.

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