Impact of genome variation on bovine embryo development

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In spite of the widespread use of advanced reproductive biotechnologies, the overall fertility of cattle is declining at a rate of about 1.5% per decade leading to economic shortfall due to loss in production. In dairy cattle, fertility defined as pregnancy rate per single insemination, may be as low as 35%, with the majority of failed pregnancies resulting from embryo loss within the first 2 to 3 weeks after fertilization. It is therefore imperative that a new and better understanding of bovine embryo development and developmental failure be obtained to devise new strategies to combat this source of economic loss. To further explore bovine embryo development we propose to take advantage of recent discoveries concerning genomic variation, which suggest that over 4% of the bovine genome is composed of DNA sequence of over 1000kilo bases, that are repeated a varying number of times. This variation is known as copy number variation or CNV. These CNV regions include functional genes, which in humans have been shown to be associated with a wide variety of complex diseases, such as Parkinson’s and cancer. The Y-chromosome is particularly rich in multi-copied genes, several of which display CNVs. We have previously shown a CNV effect on bull fertility for a gene, the Testis specific Protein Y-encoded (TSPY), with preliminary data suggests that it could also affect embryo development. Therefore, we are now proposing to examine in details the as yet unexplored effect of CNVs on embryo development. We hypothesize that the number of copies and the expression levels of multi-copied genes influence embryo development. Our specific objectives include: 1) Determine the extent of CNV for Y chromosome-linked multi-copied genes in sibling embryos in vitro produced and derived from single ejaculates of different bulls. 2) Determine mRNA expression levels and correlation to copy number of Y-chromosome linked genes at the blastocyst stage. 3) Determine the effect of down-regulating multi-copied Y-chromosome linked transcripts on early embryonic development. 4) Determine the effect of copy number reduction of multi-copied Y chromosome –linked genes on the embryo developmental outcome. We will employ state of the art tools to determine the number of copies of specific genes and their RNA and protein levels in relation to DNA copies and rate of development in bovine embryos. Subsequently we will alter the number of copies of Y chromosome linked genes and/or the corresponding mRNA transcripts to pin-point the mode of action that affect embryonic development. The results of this novel study will provide key information on the mechanisms of embryo development and assist in the development of strategies for improving reproductive technologies. This is particularly relevant for the 10 billion dollar Canadian cattle industry, which relies on reproductive biotechnologies for genetic advancement and production efficiency