GLUCOSE-METABOLISM DURING BOVINE PREIMPLANTATION DEVELOPMENT - ANALYSIS OF GENE-EXPRESSION IN SINGLE OOCYTES AND EMBRYOS

Glucose metabolism of the bovine embryo is low during the first cleava ges 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 stage s of development. These genes were: glucose transport GLUT-1, hexokina se (HK), glucose-6-phosphate-dehydrogenase [G6PDH), and glucose-phosph ate-isomerase (GPI]; actin was used as a reference transcript. RT-PCR results revealed three types of oocytes or embryos: positive with a PC R signal for each transcript considered, nul with no signal for any tr anscript, and heterogeneous with a PCR signal for some transcripts and none for others. The number of nul and heterogeneous samples was high er for slow than for fast-cleaving embryos (81% vs. 36%), and the prop ortion of positive embryos increased significantly at the 16-cell and morula stages (P < 0.002), suggesting a correlation between mRNA conte nt and developmental capacity. In positive embryos, GLUT-1 mRNA level was reduced by half during maturation and fertilization. Actin and hex okinase mRNA levels decreased during the first cleavages, but signific antly increased at the 16-cell and morula stages, respectively. GPI tr anscript remained stable throughout development, whereas there was a s ignificant rise for G6PDH at the 4-cell stage, perhaps due to a polyad enylation process. Finally, the absence or decrease in intensity of se veral transcripts at the blastocyst stage suggests suboptimal culture conditions. (C) 1997 Wiley-Liss, Inc.