Ribonucleoside metabolism by mouse oocytes: metabolic cooperativity between the fully grown oocyte and cumulus cells

Ribonucleoside uptake and metabolism were studied in mouse oocytes arrested at dictyate and metaphase II, with or without attached cumulus cells. Uptake of uridine and guanosine decreased after meiotic maturation, whereas that of adenosine and cytidine remained unaltered. Dictyate oocytes free of cumulus cells (denuded) phosphorylated all of the radiolabeled ribonucleosides. Little radiolabeled ribonucleoside-5'-triphosphate was found. This is in contrast to the early mouse embryo, which rapidly converts ribonucleosides to the 5'-triphosphate (Daentl and Epstein, "71; Clegg and Piko, "77). Following meiotic maturation, the major metabolite present when metaphase II oocytes were cultured with cytidine or uridine was the ribonucleoside, whereas the 5'-monophosphate was still the major species for oocyte cultured with guanosine or adenosine. Ribonucleoside uptake was increased and the distribution of phosphorylated metabolites was different for cumulus-enclosed dictyate oocytes compared to their denuded counterparts. This increase in uptake and alteration in metabolite distribution was not observed for cumulus-enclosed metaphase II oocytes. These results are discussed in terms of gap junction-mediated metabolic cooperatively between the cumulus cells and the fully grown oocyte and the possible role this type of cell-to-cell interaction may serve during oocyte growth.