Involvement of MEK-mitogen-activated protein kinase pathway in follicle-stimulating hormone-induced but not spontaneous meiotic resumption of mouse oocytes.

Mitogen-activated protein (MAP) kinase has been reported to be activated during oocyte meiotic maturation in a variety of mammalian species. However, the mechanism(s) responsible for MAP kinase activation and the consequence of its premature activation during gonadotropin-induced oocyte meiotic resumption have not been examined. The present experiments were conducted to investigate the possible role of MAP kinase in FSH-induced and spontaneous oocyte meiotic resumption in the mouse. MAP kinase kinase (MAPKK, MEK) inhibitor, PD98059 or U0126, produced a dose-dependent inhibitory effect on both FSH-induced oocyte meiotic resumption and MAP kinase activation in the oocytes. However, the same inhibitor did not block spontaneous meiotic resumption of either denuded or cumulus cell-enclosed mouse oocytes, despite the activity of MAP kinase being totally inhibited. Immunoblotting the oocytes and the cumulus cells with the anti-active MAP kinase antibody showed that MAP kinase activity in the oocytes was detected at 8 h of FSH treatment, prior to germinal vesicle breakdown and increased as maturation progressed in the following culture period. In the cumulus cells, MAP kinase was activated even faster, its activity was detected at 1 h of FSH stimulation and increased gradually until 8 h of FSH treatment, then decreased and diminished after 12 h of FSH action. These data demonstrated that the MEK-MAP kinase pathway is implicated in FSH-induced but not spontaneous oocyte meiotic resumption.

Differential localization of conventional protein kinase C isoforms during mouse oocyte development.

Protein kinase C (PKC), the major cell target for tumor-promoting phorbol esters, plays a central role in signal transduction pathways. In many biological systems where Ca(2+) serves as a second messenger, regulatory control is mediated by PKC. The activation of PKC depends on its binding to RACK1 receptor, which is an intracellular protein anchor for activated PKC. We demonstrate that the conventional PKC (cPKC) isoforms, PKC-alpha, PKC-betaI, and PKC-betaII, as well as RACK1, are expressed in mouse oocytes (germinal vesicle [GV]) and mature eggs (metaphase II [MII]). In GV oocytes, PKC-alpha, PKC-betaII, and RACK1 were uniformly distributed in the cytoplasm, while PKC-betaI was localized in the cytoplasm and in the plasma membrane as well. Treatment of GV oocytes with the biologically active phorbol ester, 12-o-tetradecanoyl phorbol-13-acetate (TPA), resulted in a rapid translocation of the cytosolic PKC-alpha, but not PKC-betaI, PKC-betaII, or RACK1, to the plasma membrane. This was associated with inhibition of GV breakdown. In MII eggs (17 h post-hCG), PKC-alpha was uniformly distributed in the cytoplasm while PKC-betaI and -betaII were distributed in the cytoplasm and in the plasma membrane as well. Treatment with TPA resulted in a rapid translocation of PKC-alpha from the cytoplasm to the plasma membrane and a significant decrease of PKC-betaI throughout the cytoplasm, while it also remained in the cell periphery. No change in the distribution of PKC-betaII or RACK1 was observed. TPA also induced pronucleus formation. Physiological activation of MII eggs by sperm induced cortical granule exocytosis associated with significant translocation of PKC-alpha and -betaI, but not -betaII, to the plasma membrane. Overall, these results suggest a possible involvement of cPKC isoforms in the mechanism of mouse oocyte maturation and egg activation.

Protein kinase inhibitors induce the interphase transition by inactivating mitogen-activated protein kinase in mouse eggs.

The role of mitogen-activated protein (MAP) kinase in mouse egg activation induced by protein kinase inhibitors and a protein tyrosine kinase (PTK) inhibitor was investigated. Separated egg proteins were first probed with anti-Active MAP kinase antibody and then re-probed with anti-ERK2 antibody. Staurosporine and Ro-31-8220, at concentrations that normally inhibit protein kinase C, did not affect egg activation or MAP kinase activity, while higher dosages caused egg activation. Staurosporine at 2 microM induced the metaphase-interphase transition without emission of the second polar body (PB2), while Ro-31-8220 at 40 microM induced PB2 emission, first cleavage, and then the transition to interphase. Half the eggs were also activated by the PTK inhibitor genistein. In each treatment, the proportion of eggs that entered interphase was well correlated with the degree of MAP kinase inactivation. Artificial activation of this kinase by okadaic acid overcame the interphase transition. These data suggest that protein kinase inhibitors and a protein tyrosine kinase inhibitor induce the interphase transition by inactivating MAP kinase in mouse eggs.

Sunlight and other risk factors for cataracts: an epidemiologic study.

A case control study was conducted in North Carolina to explore the relation between individual exposure to sunlight and the risk of cataracts. One hundred thirteen cases and 161 controls aged 40-69 at diagnosis were studied. Sunlight exposure was inferred from interview data on residency and time spent in the sun, combined with solar radiation data from the National Climatic Data Center. Sunlight exposure was very slightly related to all types of opacities combined. Although the numbers of cases with each type of opacity was small, the risk of cataracts was slightly increased in medium and high exposure categories for persons having cortical or posterior subcapsular opacities only, but not nuclear sclerotic changes. Persons with dark brown or hazel eyes are at increased risk. An unexpected finding was that persons who reported using tranquilizers for six months were at increased risk.

On the problems of speech compensation and fluctuating intellectual performance.

Some of the factors involved in compensation of speech deficits following local brain lesions are enumerated. An illustrative case is presented of a right-handed patient who failed to become aphasic despite massive resections for glioma from the left hemisphere. The surprising degree of speech intactness is discussed according to theories of interhemispheric transfer of speech function and the possibility that the right hemisphere had originally been the dominant hemisphere for speech, a so-called "ectopic speech center." It has been known for many years that an aphasic patient with a left hemisphere lesion has a better prognosis if a family history of left handedness is present. A sister of the patient reported here, although right-handed, is shown by dichotic listening studies to be right hemisphere dominant for speech. Thus, it is suggested that this finding on dichotic listening tests in a close relative may prove to be a favorable prognostic sign for compensation of the speech function. The patient also showed fluctuating intellectual performance and a curious "warming up" phase for the individual neuropsychological tasks. Data is presented from simultaneous neuropsychological testing and an integrated EEG frequency analysis which demonstrates an electrophysiological and behavioral correlation. The question arises as to whether the fluctuations frequently seen in brain-damaged patients might have a similar electrophysiological association.