PARENT SESSION

(M379) DEVELOPMENTAL CHANGES IN THE MECHANISM REGULATING INTRACELLULAR pH DURING GROWTH OF THE MOUSE OOCYTE PRIOR TO OVULATION.

Erdogan, Seref¹, Tartia, Alina², Baltz, Jay², ¹ Cukurova University Faculty of Medicine, Adana, Turkey² Ottawa University Ottawa Health Research Institute, Ottawa, ON, Canada

ABSTRACT- HCO3^-/Cl^- exchangers (AE family anion exchangers) regulate intracellular pH (pHi) in almost all mammalian cells, providing the means to correct against pHi increases and maintain optimal pHi. Regulation of pHi by AE has been demonstrated at all preimplantation mouse embryo stages and in the fully–grown, germinal vesicle (GV) stage oocyte. Although highly active in GV oocytes, it is then transiently inactivated during meiosis, only reappearing in eggs after fertilization. However nothing is known about AE activity in growing oocytes before the GV stage. We have now examined AE activity in growing mouse oocytes from ∼ 20–80 m diameter retrieved from 5–21-day-old CF1 mice. pHi was recorded in each oocyte using quantitative fluorescence imaging microscopy with the pH-sensitive fluorophore, SNARF1. AE activity was measured by external Cl^- removal to reveal AE activity as a marked cytoplasmic alkalinization, and also by measuring recovery from imposed alkalosis. We found that AE activity was very low in small growing oocytes, but increased markedly over the course of growth, with the most rapid increase in activity occurring as oocytes grew from ∼ 60–70 m. Resting pHi of oocytes simultaneously increased by ∼ 0.25 pH units. In separate experiments, identically-obtained CF1 mouse oocytes were found to first acquire meiotic competence (ability to progress into meiotic metaphase) as they grew over this same range. Thus, mouse oocytes develop AE–mediated pHi regulation, increase their resting pHi levels, and become meiotically competent at the same stage of growth. The ability to independently control pHi may therefore be a form of competence gained by oocytes as they near ovulation, and may be related to the acquisition of meiotic competence. Supported by Canadian Institutes of Health Research MOP12040, CIHR IHDCYH Program on Oocyte Health (HGG62293) and NATO B–2 fellowship (to SE), Scientific and Technical Research Council, Turkey (TUBITAK).

KEY WORDS: mouse, growing oocyte, anion exchanger, meiotic competence