Endogenous folates and single-carbon metabolism in the ovarian follicle, oocyte and pre-implantation embryo

Abstract

Maternal B-vitamin status at conception can affect fertility and the health of offspring. This study details transcript expression for genes encoding key enzymes in the linked methionine/folate cycles in the bovine oocyte, somatic cells of the ovarian follicle and pre-implantation embryo. Transcripts for all 12 enzymes that were studied and for the two folate receptors (FOLR1 and FOLR2) and reduced folate carrier (SLC19A1) were expressed in liver cells, but transcripts for betaine-homocysteine methyltransferase and methionine adenosyl transferase 1A were absent in all ovarian cells, and transcripts for FOLR2 were absent in embryonic cells. Transcripts for glycine methyltransferase were also absent/weak in cumulus and granulosa cells. The absence of these enzymes could have a profound effect on single-carbon metabolism within the ovary and pre-implantation embryo. Immunocytochemical analysis revealed SLC19A1 protein expression on the plasma and basal-lateral membranes of the pre-implantation embryo. The folate antagonist methotrexate (MTX) enters the cell via SLC19A1, and in the current study, MTX inclusion in bovine/ovine culture media at either 1 or 10 mM from the 1-cell stage inhibited embryo development beyond the 8-cell stage. Hypoxanthine and thymidine (100 mM) increased the proportion of embryos that developed to blastocysts, but the cell number was reduced by 20%. The reduced uptake of [ 35 S] methionine into intra-cellular S-adenosylmethionine and S-adenosylhomocysteine pools, together with reduced uptake of glutamate and tryptophan, was consistent with depleted intra-cellular pools of reduced folates. These data provide an insight into the importance of maternal dietary folate/B-vitamin status during the peri-conceptional period.Reproduction (2010) 139 705-715

Betaine Homocysteine Methyltransferase Is Active in the Mouse Blastocyst and Promotes Inner Cell Mass Development

“…Kwong et al (36) have done similar but more extensive studies in cow and sheep, and they found that methotrexate reduces blastocyst cell number even when exogenous purines and pyrimidines were provided, implying that methyl pool generation may also be affected. Furthermore, mRNA for the enzymes needed for folate-dependent AdoMet generation were shown to be present in bovine embryos (36,37), as well as in human embryonic stem cells that are analogous to ICM cells (38), also supporting the idea that the folate-dependent pathway is functioning in preimplantation embryos. The relative importance of the folate-and betaine-dependent pathways for AdoMet generation in mouse blastocysts is not known and remains to be investigated.…”

Effects of metformin on fertilisation of bovine oocytes and early embryo development: possible involvement of AMPK3-mediated TSC2 activation

“…Oocyte and embryo culturing were carried out according to previously published protocols (Adamiak et al, 2006;Kwong et al, 2010).…”

Cumulus cell gene expression following the LH surge in bovine preovulatory follicles: potential early markers of oocyte competence

“…glycolysis, steroidogenesis, and carbon metabolism (Krisher & Bavister 1999, Lucidi et al 2003, Kwong et al 2010, Sutton-McDowall et al 2010.…”