Inositol transport in mouse oocytes and preimplantation embryos: effects of mouse strain, embryo stage, sodium and the hexose transport inhibitor, phloridzin.
The uptake of myo-inositol by mouse oocytes and preimplantation embryos of a crossbred (DBA x C57BL/6) and a purebred outbred strain (MF1) was measured using [2-(3)H]myo-inositol. Uptake in crossbred embryos increased about 15-fold between the one- and two-cell stages and increased again by about sixfold at the blastocyst stage compared with the morula stage. Uptake in purebred embryos increased about 42-fold between the one- and two-cell stages and increased more than threefold at the blastocyst stage compared with the morula stage. In all stages examined, except two-cell crossbred embryos, inositol uptake was, depending on the stage, either largely or partly sodium dependent and could be inhibited by the sodium-dependent hexose transport inhibitor, phloridzin. This is consistent with the hypothesis that transport occurs via a sodium myo-inositol transporter (SMIT) protein. In addition, there was strong evidence that a sodium-independent mechanism of uptake, possibly a channel, was switched on at the two-cell stage coincident with zygotic gene activation which resulted in 141-fold and 71-fold increases in sodium-independent uptake from the one-cell to two-cell stages in crossbred and purebred embryos, respectively. This mechanism was either abolished or drastically downregulated at the blastocyst stage, whereas sodium-dependent uptake was markedly upregulated. In two-cell crossbred embryos, there was a complete abolition of sodium-dependent uptake, again possibly regulated by zygotic gene activation. The hypothesis that the changes in mechanism of inositol uptake at about the two-cell stage are due to zygotic gene activation was supported by the finding that these changes did not occur in parthenogenetic two-cell embryos.
Higgins
B D
BD
Department of Physiology, National University of Ireland, Galway, University Road, Galway, Ireland.
Kane
M T
MT
D000818:Animals; D001692:Biological Transport; D001755:Blastocyst / Q000378:metabolism*; D005260:Female; D005865:Gestational Age; D006601:Hexoses / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D009865:Oocytes / Q000378:metabolism*; D010312:Parthenogenesis; D010695:Phlorhizin / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013045:Species Specificity
D006601:Hexoses; D007004:Hypoglycemic Agents; D007294:Inositol; D012964:Sodium; D010695:Phlorhizin