The mystery of how meiotic arrest is maintained in mouse oocytes is revealed this week in Science by Lisa M. Mehlmann and colleagues at the University of Connecticut Health Center. The team reports that meiotic arrest requires the presence of a G-protein–coupled receptor in the oocyte that elevates cAMP, which has been previously shown to be critical for preventing completion of meiosis.

Meiosis begins when oocytes are still very small cells, but it then arrests for a long period after the oocyte has reached its full size, according to co-author Laurinda A. Jaffe, and depends on signals from the follicle. In a previous study, the team had found that the heterotrimeric G protein, Gs, in the oocyte is required to maintain meiotic arrest; Gs activates adenylyl cyclase to keep cyclic AMP elevated.

Jaffe looked for the means by which Gs is stimulated. "If there's an oocyte adenylyl cyclase that...

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