Phd Student University College Dublin Eniskillen, Northern Ireland, United Kingdom
Abstract Authors: L. Thompson1; A.D. Crowe1,2; M.B. Rabaglino3; S.T. Butler2; P. Lonergan1
1. School of Agriculture and Food Science, University College Dublin, Dublin, Ireland.
2. Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.
3. Farm Animal Health, Department of Population Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
Abstract Text: According to data collected by the International Embryo Technology Society, the number of in vitro produced (IVP) bovine embryos transferred annually exceeds 1.5 million, far surpassing the number derived from traditional superovulation techniques. Most studies using IVP embryos report pregnancies/embryo transfer but few follow up on the birth and postnatal development of IVP calves. Culture of the embryo in an suboptimal in vitro environment until transfer potentially results in epigenomic modifications of the embryo genome, including the transcriptome, leading to postnatal alterations in organ function. Recent studies have reported that dairy cows conceived by IVF have a higher incidence of ovarian cysts, which could be associated with de-regulation of energy metabolism ((Lafontaine et al., 2023). Furthermore, 3-month-old male dairy calves derived from an IVP or in-vivo embryo exhibited divergence in hepatic and muscular energy regulation (Rabaglino et al., 2021); however, the molecular changes in these organs in females are unknown. Taking advantage of a large-scale field study examining the feasibility of using IVP embryos in a seasonal pasture-based system of production, the objectives of this study were to identify differences in the liver transcriptome between male and female dairy calves conceived by IVF or AI. Biopsy tissue samples were collected using a percutaneous punch technique from the livers of 4-month-old male and female Holstein-Friesian calves derived from AI or IVP (n = 4 per sex per group) and were processed for RNA sequencing. Raw RNAseq data was aligned to the ARS-UCD1.3 genome, and the processed data were analyzed with the R software. Principal component analysis revealed a distinct separation between the liver transcriptomes of AI and IVP calves, irrespective of sex; however, the distinction was much more pronounced for females than for males. Consistent with that observation, differential expression analysis revealed 7377 differentially expressed genes (DEG) in IVP vs AI female calves compared to just 273 in their male counterparts (false discovery rate (FDR) < 0.05). Of these, 178 genes were commonly differentially expressed between AI and IVP calves, irrespective of sex. Of the total number of DEG between the livers of female calves derived from IVP vs AI, downregulated DEG (n=3566) enriched pathways involving RNA processing, ATP binding, metabolism of RNA, and catalytic activity as well as processes associated with cell cycle and DNA repair. Upregulated DEG (n=3811) strongly enriched pathways involved in the immune system including the innate immune system, protein localization and catabolic processes. There were considerably fewer DEG in the liver of male calves derived from IVP vs AI (121 downregulated and 152 upregulated). While the 121 downregulated genes did not enrich any pathways, the 152 genes upregulated enriched pathways such as metabolism, the endoplasmic reticulum, and cellular response to organic substance. Of the 178 common DEG between IVP vs AI calves irrespective of sex, 103 were upregulated and 62 were downregulated. Only the commonly upregulated genes enriched gene pathways, and these were particularly associated with angiogenesis. In conclusion, these results provide evidence that the IVP process preferentially alters the liver transcriptome in the female postnatal calf. The consequences for the lifetime production characteristics remain to be elucidated.
