peer reviewedGlucose metabolism of the bovine embryo is low during the first cleavages and increases sharply after the major resumption of the genome (8-16 cells). The mRNA level for genes involved in glucose metabolism was tested by RT-PCR on individual oocytes and embryos at different stages of development. These genes were: glucose transport GLUT-1, hexokinase (HK), glucose-6-phosphatase-dehydrogenase (G6PDH), and glucose-phosphate-isomerase (GPI); actin was used as a reference transcript. RT-PCR results revealed three types of oocytes or embryos: positive with a PCR signal for each transcript considered, nul with no signal for any transcript, and heterogeneous with a PCR signal for some transcripts and none for others. The number of nul and heterogeneous samples was higher for slow than for fast-cleaving embryos (81% vs. 36%), and the proportion of positive embryos increased significantly at the 16-cell and morula stages (P < 0.002), suggesting a correlation between mRNA content and developmental capacity. In positive embryos, GLUT-1 level was reduced by half during maturation and fertilization. Actin and hexokinase mRNA levels decreased during the first cleavages, but significantly increased at the 16-cell and morula stages, respectively. GPI transcript remained stable throughout development, whereas there was a significant rise for G6PDH at the 4-cell stage, perhaps due to a polyadenylation process. Finally, the absence or decrease in intensity of several transcripts at the blastocyst stage suggests suboptimal culture conditions
