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Comment |
Mouse Oocytes Regulate Metabolic Cooperativity Between Granulosa Cells and Oocytes: Amino Acid Transport Eppig JJ, et al 2005 .
A search for genes expressed more highly in mouse cumulus cells than mural granulosa cells by subtraction hybridization yielded Slc38a3. SLC38A3 is a sodium-coupled neutral amino acid transporter having substrate preference for L-glutamate, L-histidine, and L-alanine. Detectable levels of Slc38a3 mRNA were found by in-situ hybridization in granulosa cells of large preantral follicles, but levels were higher in all granulosa cells of small antral follicles; expression became limited to cumulus cells of large antral follicles. Expression of Slc38a3 mRNA in granulosa cells was promoted by fully-grown oocytes from antral follicles, but not by growing oocytes from preantral follicles. Fully-grown oocytes were dependent upon cumulus cells for uptake of L-alanine and L-histidine, but not L-leucine. Fully-grown, but not growing, oocytes secreted one or more paracrine factors that promoted cumulus cell uptake of all three amino acids, but of L-alanine and L-histidine to a much greater extent than L-leucine. Uptake of L-leucine appeared dependent primarily upon contact-mediated signals from fully-grown oocytes. Fully-grown oocytes also promoted elevated levels of Slc38a3 mRNA and L-alanine transport by preantral granulosa cells, but growing oocytes did not. Therefore fully-grown oocytes secrete one or more paracrine factors that promote cumulus cell uptake of amino acids that oocytes themselves transport poorly. These amino acids are likely transferred to oocytes via gap junctions. Thus, oocytes utilize paracrine signals to promote their own development via metabolic cooperativity with cumulus cells. The ability of oocytes to mediate this cooperativity is developmentally regulated and acquired only in later stages of oocyte development.
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