Cumulus‐oocyte complexes from sows show differences in lipid metabolism compared to cumulus‐oocyte complexes from prepubertal gilts during in vitro maturation

Abstract

This study aimed to evaluate the effects of donor age on lipid metabolism during in vitro maturation (IVM) of pigs cumulus-oocyte complexes (COCs). We evaluated transcript levels of genes, the percentage of ooplasm occupied by lipid droplets (LD) and evaluated DNA methylation in COCs from sows and prepubertal gilts. Transcript levels of six genes (ACACA, ACSS2, FASN, FABP3, SLC27A4, PLIN2), which were analyzed in cumulus cells (CCs), increased after 44 h of IVM in the sow group. In the gilt group, only FASN expression increased, while NR3C1 expression decreased after IVM. The measurement of LD in oocytes showed an accumulation of lipids in sow oocytes during IVM, while gilt oocytes showed a decrease in LD. FABP3 and NR3C1 methylation patterns exhibited a demethylation pattern in CCs and oocytes from gilts and sows and showed statistical differences between groups. CCs from sows had a better capacity to change transcription levels of the major genes involved in lipid metabolism during IVM than CCs from gilts. This difference may be involved in accumulation of lipids, acquisition of competence, and maturation of enclosed oocytes. Our results contribute to a better understanding of mechanisms involved in lipid metabolism and acquisition of competence in porcine COCs.

Epigenetic-related transcriptional reprogramming elucidated by identification and validation of a novel reference gene combination for RT-qPCR studies in porcine oocytes of contrasting quality

“…Gilt oocytes do not appear to have completed the accumulation of RNA and the associated transcriptional quiescence at the time of aspiration. This implies prepubertal gilt oocytes are less developed at aspiration than sow oocytes, in accordance with similar studies [ 27 , 31 , 32 ]. Altogether, ACTB and PFKP combined appeared to provide the most appropriate normalisation of the oocyte RT-qPCR data, by demonstrating acceptable stability and generating results consistent with expectations from the literature.…”

“…Although the results were for the most part above the significance p-value, this pattern is worth questioning, as it implies sow oocytes were less advanced than prepubertal gilt oocytes at the time of aspiration and transcriptional quiescence occurred at a later stage. This contradicts numerous previous studies of prepubertal vs. adult oocyte donors [ 1 , 8 , 26 , 31 , 32 ] and HPRT1 should be applied with caution as a reference gene in oocyte maturation studies as it might not give results in accordance with similar studies. Interestingly, O’Connor et al [ 7 ] reported a similar (unpublished) observation, where employing only GAPDH or HPRT1 for normalisation of oocyte RT-qPCR data generated completely different expression profiles of the experimental genes.…”

Biochemical profiling of the follicular environment to predict oocyte competence in cattle

“…Another piece of information that may be relevant in studies on oocyte competence and gene expression is the behavior of gene expression during IVM [ 46 , 47 ]. Here, we noted that the transcript levels of most genes changed during IVM for both groups, which was expected considering the events that occurred during this period and the function of the genes evaluated.…”

“…This result may suggest that lower quality COCs do not have enough SERPINE2, VCAN, EGFR and GHR increase the number of transcripts to support IVM processes. Two studies involving evaluation of gene expression in CC during IVM of pigs COCs, observed that there was difference in expression between CC of prepubertal animals (less oocyte competence) and cycling females (greater oocyte competence), where CC of sows had better rates of transcription changes during IVM compared to prepubertal gilts [ 46 , 47 ]. Results that are in line with the present study, where CC originating from COC that did not give rise to embryos, did not show a significant increase in the number of transcripts of the genes SERPINE2, VCAN, EGFR and GHR during IVM.…”

Cumulus Cell and Oocyte Gene Expression in Prepubertal Gilts and Sows Identifies Cumulus Cells as a Prime Informative Parameter of Oocyte Quality

“…Besides genetic factors, the intrinsic developmental potential of oocytes is primarily determined by the follicle environment [4,14,35], and oocytes collected from prepubertal animals have demonstrated reduced developmental capacity compared to those from adult animals [5,[36][37][38][39][40]. Based on this, the model of prepubertal and adult oocyte donors has previously been employed to study oocytes of low versus high developmental competence in, e.g., cows [41], sheep [35,42] and pigs [27,43].…”