Gene expression in sows with high and low ovulation rate, high and low birth weight litter and the effect of sow catabolic status on embryonic gene expression

Abstract

In pig production, both litter size and embryonic viability are important economic traits. Nutritional pressures on the lactating sow have impaired the quality of the subsequent litters. This study was divided in three experiments that aimed to: 1) investigate the follicular dynamics and gene expression pattern in corpus luteum (CL), granulosa cells (GC) and denuded oocytes during the estrous cycle in pig breeds with high (commercial-line: n=24) and low (local Brazilian Piau: n=21) ovulation rates and prolificacy; 2) investigate the expression of genes involved in angiogenesis, apoptosis and encoding intrafollicular growth factors in CL, GC and denuded oocytes recovered from commercial sows characterized as high (n=5) and low (n=5) birth weight litter phenotype at Day 5 of gestation; 3) use a refined feed restriction model to investigate global changes in expression in Day 9.5 embryos recovered from commercial sows breed at the first heat (FH, n=3) or at second post-weaning estrus (skip). Skip sows were further divided in subgroups according their previous catabolic state in lactation: highly (CH, n=4), moderately (CL, n=4) and non-catabolic (NC, n=4). In the first experiment, the low ovulating Piau gilts were associated with a different pattern of follicle development, with lower numbers of small follicles at day 18, fewer large follicles at days 0 and 18 (P≤0.05) and a higher proportion of atretic follicles at days 0 and 18 (P≤0.05). Compared to commercial-line gilts, less prolific Piau gilts showed higher expression of apoptotic genes during luteolysis (CASP3 and FASL, P≤0.05), decreased expression of TGFBR2 and BAX mRNA in CL (P≤0.05), higher expression of apoptotic genes (FAS, BCL2 and CASP8, P≤0.05) in GC, and a greater abundance (P≤0.05) of genes controlling oocyte secreted factors (GDF9, BMP15 and BMP6), suggesting underlying mechanisms controlling differences in follicular development, ovulation rate and inherent prolificacy in this pig breed. In the second experiment, quantitative real time PCR (QPCR) analysis revealed that apoptotic genes were differentially expressed between commercial high and low groups in CL and GC. Most of the viiangiogenesis-related genes investigated were higher expressed in CL tissue in the low group. Among intrafollicular growth factors, only IGFR1 and BMPR2 were differently expressed in GC and denuded oocytes, respectively. Findings from the present study suggest that differences in CL vascularity and function, as well as in follicle development, may be in part, driving differences between-litter variation in birth weight in contemporary sows. Finally, microarray data from the third experiment revealed different pattern of distribution of biological functions across treatments for the commercial sows. Validation by QPCR showed a differential expression for CYR61 and MYOF, specifically for the female sex, in the pair-wise contrast FHvsNC and CLvsNC, respectively (P≤0.05). Additional contrasts in female sex were marginally significant (P≤0.10) for MYOF, BCSL1, CYR61, RAD21 and SOD1, but no difference was found for ETFA, ACDSB, TFPI2 and TNFRSF21. Furthermore, skip sows showed higher total corpus luteum weight, total corpus luteum average and litter growth average compared to first heat sows. These results suggest that the differential expression observed in female embryos may be an adaptive response to the intrauterine conditions, which may mediate epigenetic programming in the offspring. This study reinforces and provides additional insights into the role of nutrition and maternal metabolic state in determining the dynamics of early embryonic development and embryo quality in pigs.