Fatty acid composition of lipids in immature cattle, pig and sheep oocytes with intact zona pellucida

Abstract

Cattle, pig and sheep oocytes isolated from healthy cumulus-oocyte complexes were pooled, within species, to provide samples of immature denuded oocytes with intact zona pellucida (n = 1000 per sample) for determination of fatty acid mass and composition in total lipid, constituent phospholipid and triglyceride. Acyl-containing lipid extracts, transmethylated in the presence of a reference penta-decaenoic acid (15:0), yielded fatty acid methyl esters which were analysed by gas chromatograph. Mean (+/- SEM) fatty acid content in samples of pig oocytes (161 +/- 18 micrograms per 1000 oocytes) was greater than that in cattle (63 +/- 6 micrograms; P < 0.01) and sheep oocytes (89 +/- 7 micrograms; P < 0.05). Of 24 fatty acids detected, palmitic (16:0; 25-35%, w/w), stearic (18:0; 14-16%) and oleic (18:1n-9; 22-26%) acids were most prominent in all three species. Saturated fatty acids (mean = 45-55%, w/w) were more abundant than mono- (27-34%) or polyunsaturates (11-21%). Fatty acids of the n-6 series, notably linoleic (18:2n-6; 5-8%, w/w) and arachidonic acid (20:4n-6; 1-3%), were the most abundant polyunsaturates. Phospholipid consistently accounted for a quarter of all fatty acids in the three species, but ruminant oocytes had a lower complement of polyunsaturates (14-19%, w/w) in this fraction than pig oocytes (34%, w/w) which, for example, had a three- to fourfold greater linoleic acid content. An estimated 74 ng of fatty acid was sequestered in the triglyceride fraction of individual pig oocytes compared with 23-25 ng in ruminant oocytes (P < 0.01). It is concluded that the greater fatty acid content of pig oocytes is primarily due to more abundant triglyceride reserves. Furthermore, this species-specific difference, and that in respect of polyunsaturated fatty acid reserves, may underlie the contrasting chilling, culture and cryopreservation sensitivities of embryos derived from pig and ruminant (cattle, sheep) oocytes.

In vitro maturation of porcine oocytes with retinoids improves embryonic development

“…However, this beneficial effect was not reflected in embryo cleavage or embryo quality in the present study, in contrast with bovine embryos, where increased cell numbers and proportions of cells allocated to the inner cell mass have been reported (Duque et al 2002). These differences may be dependent on the amount of triglyceride stored in the pig oocyte, higher than that in bovine (McEvoy et al 2000;Genicot et al 2005). Sterification to fatty acids, particularly palmitate, is the preferential form for retinol storage in cells and palmitate is the most abundant fatty acid in oocytes of domestic species, including the pig (McEvoy et al 2000;Kim et al 2001).…”

“…These differences may be dependent on the amount of triglyceride stored in the pig oocyte, higher than that in bovine (McEvoy et al 2000;Genicot et al 2005). Sterification to fatty acids, particularly palmitate, is the preferential form for retinol storage in cells and palmitate is the most abundant fatty acid in oocytes of domestic species, including the pig (McEvoy et al 2000;Kim et al 2001). Therefore, it is feasible that the pig oocyte contains larger amounts of retinol than the bovine oocyte.…”

Specific gene-regulation networks during the pre-implantation development of the pig embryo as revealed by deep sequencing

“…Endogenous lipids are more abundant in pig oocytes and pre-implantation embryos than in mouse, cattle and sheep. This can cause significant damage during cryopreservation [40]. Lipids have important functions in membrane receptor biology, signal transduction, and growth regulation [41–46].…”

Differential genome-wide gene expression profiling of bovine largest and second-largest follicles: identification of genes associated with growth of dominant follicles

“…Expression of SCD2 is hormonally regulated during follicular development because both SCD2 mRNA and protein expression in rat large follicles were stimulated by gonadotropin and IGF-I treatment [42]. Increase of monounsaturated acids synthesize by SCD2 activation during DF growth may be required to maintain membrane fluidity [43] and a major lipid reserve of oocytes [44]. …”