76 Effects of serum type in maturation medium on in vitro development of bovine embryos

Abstract

This study investigated the effect of bovine serum albumin (BSA), charcoal:dextran stripped fetal bovine serum (CDS FBS), and heat-inactivated FBS (HI FBS) in maturation medium on their ability to support in vitro oocyte maturation, cumulus cell-oocyte gap junctional communication, and development of bovine embryos. Charcoal:dextran treatment of FBS removes lipophilic chemicals, certain steroid hormones, and certain growth factors; however, HI FBS have a lot-to-lot variation in steroid hormones level that can affect the reproducibility of experimental findings. Oocytes were cultured in TCM-199 supplemented with either 8% (w/v) BSA, 10% (v/v) CDS FBS, or 10% (v/v) HI FBS and 1 µg mL⁻¹ oestradiol-17β, 10 µg mL⁻¹ FSH, 10 ng mL⁻¹ epidermal growth factor, 0.6 mM cysteine, 0.2 mM sodium pyruvate, and followed by IVF, and the zygotes were cultured in SOF-BE1 medium. The developmental ability and quality of bovine embryos were determined by assessing their cell number, lipid content, mitochondrial activity, gene expression, immunocytochemistry, and cryo-tolerance. The differences in embryo development between experimental groups were analysed by 1-way ANOVA. The Duncan’s multiple range tests were used to test the differences between the treatments. The level of statistical significance was set at P < 0.05. We have shown that CDS FBS significantly improved (P < 0.05) the percentage of MII oocytes compared with that in the BSA supplemented group (77.2 ± 1.0% v. 69.3% ± 2.3%, respectively). Moreover, CDS FBS had a higher significant (P < 0.05) effect on the rate of blastocyst formation compared with HI FBS and BSA (45.2 ± 0.7% v. 37.4 ± 1.5% and 31.1 ± 3.9%, respectively; 6 replicates were performed). Culture of oocytes with CDS FBS increased (P < 0.05) the expression of gap junction proteins, CX37 and CX43, at both transcriptional and translation levels as determined by quantitative RT-PCR and immunofluorescence analysis, respectively. We also found that CDS FBS significantly increased total cell number and decreased the apoptotic index in Day-8 blastocysts compared with the BSA group. Furthermore, the beneficial effects of CDS FBS on embryos were associated with significantly reduced intracellular lipid content and increased mitochondrial activity in both oocytes and blastocysts as identified by Nile red and MitoTracker Green staining, respectively. Taken together, these data suggest that supplementation of maturation medium with CDS FBS, as an alternative to HI FBS, affected cumulus cell-oocyte gap junctional communication, and subsequently improved in vitro developmental competence of bovine oocytes and embryos.

Research was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries (IPET) through Agri-Bio industry Technology Development Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (grant numbers: 117029-3 and 315017-5).