Expression and activity of hexokinase in the early mouse embryo.
The maximal activity and Michaelis constant, KM, of hexokinase have been measured in the peri-implantation mouse embryo using an ultramicrofluorescence technique. In addition, transcript detection of the predominant isoenzyme hexokinase I has been determined in single preimplantation mouse embryos at successive stages of development using reverse transcriptase-mediated cDNA amplification. Maximal hexokinase activity decreased dramatically peri-implantation, from 0.97 +/- 0.19 nmol/microgram protein/h at the blastocyst stage to 0.31 +/- 0.05 nmol/microgram protein/h on day 6.5. The KM remained relatively low and constant over this period (0.23-0.39 mM), indicating the absence of the hexokinase type IV isoenzyme. The pattern of hexokinase activity resembled that of glucose consumption suggesting a possible regulatory role for the enzyme during this period of development. Hexokinase I mRNA was detected in the oocyte and all preimplantation stages of development. The blastocyst polymerase chain reaction (PCR) product, when cloned and sequenced was found to be 98% homologous with mouse tumour hexokinase I. Taken together, these data suggest that the hexokinase gene is not under transcriptional control during early mouse embryo development but plays a significant role in the regulation of glucose consumption. A role for hexokinase in the phosphate-induced inhibition of early embryo development is also proposed.
Houghton
F D
FD
Department of Biology, University of York, UK.
Sheth
B
B
Moran
B
B
Leese
H J
HJ
Fleming
T P
TP
D000818:Animals; D001755:Blastocyst / Q000201:enzymology*; D018076:DNA, Complementary / Q000235:genetics; D010064:Embryo Implantation; D004790:Enzyme Induction; D005260:Female; D005326:Fetal Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006593:Hexokinase / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008808:Mice, Inbred CBA; D009363:Neoplasm Proteins / Q000737:chemistry; D009865:Oocytes / Q000201:enzymology; D009928:Organ Specificity; D010710:Phosphates / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D005326:Fetal Proteins; D007527:Isoenzymes; D009363:Neoplasm Proteins; D010710:Phosphates; D006593:Hexokinase