Exploring Sperm Competency

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Research Problem There are gaps in our understanding of male reproduction and assessing sperm function. The male's contribution to reproduction does not end at fertilization of the oocyte. The sperm delivers the paternal genome, which is required for subsequent normal embryo development and the growth of healthy and productive offspring. Sperm, however, are vulnerable to environmental stressors. Unlike the oocyte and most somatic cells, sperm do not possess the cellular machinery to correct damage. Therefore, environmental insults can reduce the ability of the sperm to create a healthy embryo that will develop into normal offspring. My research will address the susceptibility of the sperm epigenome to the environment. The epigenome defines which genes of the genome are expressed in cells. Regulation of gene expression without altering genome sequence is possible by epigenetic modifications, including DNA methylation, chromatin packaging mediated by post-translational histone modifications and non-coding RNAs. Epigenetic patterns are generated during early development and are crucial for differentiation. Unlike the genome, the epigenome responds to environmental signals, providing a connection between the environment, altered gene expression and phenotype. The most current literature suggests that the sperm epigenome may play a role in embryo development and, presumably, offspring health. General Hypothesis Environmental stressors induce epimutations in the sperm chromatin, thereby impeding the production of normal embryos and offspring. Approach We will use cryopreservation as a model of environmental stress that can affect sperm using the bovine and porcine systems as models of agriculturally-significant species, as well as the lab mouse, to test this hypothesis. Epigenome analyses will be carried out on fresh and cryopreserved sperm: the methyome will be assessed using Reduced Representation Bisulfite Sequencing (RRBS), specific posttranslational histone modifications will be monitored using chromatin immunoprecipitation coupled with next-generation sequencing, and the sperm transcriptome will be assessed by next generation RNA sequencing. In vitro fertilization will be carried out with fresh and cryopreserved sperm, and the developmental competence of the embryos will be monitored. We will compare the transcriptomes of embryos produced using fresh and frozen-thawed sperm. Impact This research will demonstrate the importance of the sperm epigenome during embryo development that can impact offspring productivity and health. Such knowledge is of interest to animal production and for conservation of endangered species. It will provide basic knowledge about the impact of cryopreservation on the epigenome, which can be transferred to cell types other than sperm. This program will support 2 PhD students and introduce as many as 5 undergraduates to research.