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General Comment |
Williams CJ, et al reported G protein gene expression during mouse oocyte growth and maturation, and preimplantation embryo development.
Using a reverse transcription-polymerase chain reaction (RT-PCR) assay, the relative levels of mRNAs encoding specific G protein alpha, beta, and gamma subunits were determined in meiotically incompetent oocytes, fully-grown competent oocytes, metaphase II-arrested eggs, one-, two-, and eight-cell embryos, and blastocysts. mRNA transcripts representing all of the heterotrimeric G protein families were present at all of the stages examined, and all underwent significant changes in their patterns of expression. The following heterotrimeric G protein mRNA transcripts were present in oocytes, eggs, or preimplantation embryos: G alpha q family (q, 11, and 14), G alpha 12 family (12 and 13), G alpha i family (i1, i2, i3, t2, z, and s), beta subunits 1, 2, 4, and 5, and gamma subunits 2, 3, 5, and 7. A recently described large molecular weight G protein, G alpha h (Nakaoka et al., 1994: Science 264:1593-1596), was also present, G alpha 15, G alpha t1, G alpha olf, G alpha oA, G beta 3, G gamma 1, and G gamma 8 mRNA transcripts were not detected using this method. The most common pattern of expression observed was a maturation-associated decrease followed by an increase after the two-cell stage. Some transcripts, however, were expressed at low levels until the eight-cell to blastocyst stages, whereas others were expressed at high levels in the oocyte but following maturation declined and remained at a low level throughout preimplantation development.
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Comment |
Collado B, et al 2004 reported that Luteinizing hormone-releasing hormone antagonist Cetrorelix regulates the expression of Galphas and Galphai protein subunits and adenylate cyclase activity in rat ovary, breast and pituitary.
Thirty days after a single i.m. injection of 3 mg Cetrorelix pamoate depot to female rats, normal or ovariectomized, we evaluated the effects of this chronic treatment on the expression of alphas and alphai G-protein subunits in the ovary, breast and pituitary, as well as the adenylate cyclase response in vitro to LH-RH, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP). Varied patterns of response to Cetrorelix, depending on the gland and estrogenic status were observed. Western blot analysis showed a modest decrease of alphas and a modest increase of alphai G-protein subunit levels in ovary, a marked increase of alphas and alphai levels in breast, and a lack of effect on alphas/alphai levels in pituitary. In the ovary, adenylate cyclase activity was not changed by in vitro addition of LH-RH, but the responses to VIP and PACAP increased after Cetrorelix treatment. In the breast, chronic administration of the LH-RH antagonist decreased the adenylate cyclase response to PACAP, which returned to normal after ovariectomy. In the pituitary, Cetrorelix abolished the stimulatory effect of VIP upon adenylate cyclase activity. Thus, the LH-RH antagonist Cetrorelix exerted selective modifications at different steps of the G-protein coupled receptors/adenylate cyclase system of signal transduction in the rat ovary, breast and pituitary.
Meiotic resumption in response to luteinizing hormone is independent of a G(i) family G protein or calcium in the mouse oocyte. Mehlmann LM et al. The signaling pathway by which luteinizing hormone (LH) acts on the somatic cells of vertebrate ovarian follicles to stimulate meiotic resumption in the oocyte requires a decrease in cAMP in the oocyte, but how cAMP is decreased is unknown. Activation of G(i) family G proteins can lower cAMP by inhibiting adenylate cyclase or stimulating a cyclic nucleotide phosphodiesterase, but we show here that inhibition of this class of G proteins by injection of pertussis toxin into follicle-enclosed mouse oocytes does not prevent meiotic resumption in response to LH. Likewise, elevation of Ca(2+) can lower cAMP through its action on Ca(2+)-sensitive adenylate cyclases or phosphodiesterases, but inhibition of a Ca(2+) rise by injection of EGTA into follicle-enclosed mouse oocytes does not inhibit the LH response. Thus, neither of these well-known mechanisms of cAMP regulation can account for LH signaling to the oocyte in the mouse ovary.
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