179 RELATIONSHIP BETWEEN GENE EXPRESSION IN INDIVIDUAL BLASTOMERES OF 2-CELL STAGE BOVINE EMBRYOS AND THE NORMALITY OF FIRST CLEAVAGE

Abstract

Previously early first and second cleavages after IVF associated with even blastomeres without fragments or protrusions were found to be a potent criterion for the selection of embryos with high development competence (Sugimura et al. 2012 PLOS One 7, e36627). The aim of this study was to examine the relationship between an early normal first cleavage pattern and the transcript abundance in each blastomere in 2-cell stage bovine embryos. IVF-derived bovine embryos were cultured individually in microwells culture dish in CR1aa medium supplemented with 5% calf serum and 0.25 mg mL^–1 linoleic acid albumin at 38.5°C in 5% CO₂, 5% O₂, and 90% N₂. First cleavage and cleavage patterns were categorised as being either normal (the first cleavage within 28 h after IVF with 2 even blastomeres without fragment or protrusion) or abnormal (2 uneven blastomeres, with/without fragment/protrusion and/or later than 28 h after IVF at the first cleavage). Next, cleaved embryos were placed in 0.5% actinase-E in Ca- and Mg-free PBS and blastomeres were separated by pipetting. Individual blastomeres (n = 71, 10 replicates) were analysed for gene expression by quantitative RT-PCR. Primers were designed for 19 target genes related to pluripotency, cell cycle, metabolism, pregnancy reorganization, placentation and fetal growth (NANOG, OCT4, PLAC8, ATP1A1, CCNB1801, CDH1, COX1, CTNNB1, G6PDH, Glut8, MNSOD-3end, SOX2, DYNLL1, IGF1R, IGF2, IGF2R, IGFBP2, IGFBP3, and PMSB1) and a reference gene (PPIA). Transcript abundance of target genes in both of individual blastomeres of cleaved embryos was examined in embryos that cleaved early with a normal cleavage pattern and in those that showed abnormal cleavage pattern. Values were normalised to the average values of the reference genes and means were compared by the student t-test. Transcript abundance of OCT4, ATP1A1, CCNB1801, CDH1, COX1, CTNNB1, MNSOD-3end, IGF2R, and IGFBP2 was significantly higher in blastomeres associated with all categorised abnormal blastomeres compared towith an early normal cleavage (P < 0.05). Furthermore, the expression of PLAC8, IGF1R, and PMSB1 in embryos having 2 uneven blastomeres, Glut8 and SOX2 in 2 uneven blastomeres with fragment/protrusion was higher than that in normal cleavage (P < 0.05). However, the level of G6PDH was lower in embryos having 2 uneven blastomeres than that in those showing normal cleavage (P < 0.05). Our results reveal blastomere gene expression in bovine embryos at the first cleavage may correlated with oocyte developmental competence.

This study was supported by JSPS KAKENHI (26450388).