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PubMed1985

Immunological identification of the karyophilic, histone-binding proteins N1 and N2 in somatic cells and oocytes of diverse amphibia.

A polypeptide pair designated N1/N2 (Mr 100 000 and 110 000) is an exceptionally acidic and abundant nuclear protein of oocytes of the toad, Xenopus laevis, and is characterized by a pronounced karyophilia. These proteins have been shown to form specific complexes with free, i.e., non-chromatin-bound histones H3 and H4 (Kleinschmidt & Franke, Cell 29 (1982) 799) [3]. In order to study these proteins and their possible counterparts in other species, antibodies were produced in guinea pigs against proteins N1/N2 purified from Xenopus oocyte nuclei. Using gel electrophoresis, peptide map analysis, immunoblotting techniques and immuno fluorescence microscopy the existence of polypeptides identical in Mr value and charge to polypeptide N1 of oocytes was demonstrated in cultured somatic cells of Xenopus laevis, where it was also highly enriched in cell nuclei, although the cellular concentration was much lower than in oocytes. A similar, if not identical protein, was recognized in nuclei of diverse other cell types including hepatocytes, enterocytes, ovarian follicle cells, and Sertoli cells of testis, of Xenopus, Rana temporaria, R. esculenta, Pleurodeles waltlii but not in erythrocytes and later stages of spermiogenesis. When nuclear proteins from oocytes of different amphibian species were examined with these antibodies it was found that the Mr values of N1/N2 proteins were considerably different in different species, ranging from Mr 110 000 to 190 000. Immunoprecipitation and gel electrophoretic analysis under non-denaturing conditions showed that a significant proportion of these proteins was contained in complexes with histones H3 and H4. The results demonstrate that proteins N1/N2 are not special proteins of oocytes of Xenopus laevis but occur in various other cells of diverse amphibian species. The widespread occurrence of these karyophilic proteins indicates that at least one function of these proteins, i.e., selective binding of the arginine-rich histones H3 and H4, is not exclusive to oocytes but may also contribute to the regulation of histone pools and chromatin formation in other cell types.

Amphibians↗
PubMed1986

Plasma T4 and T3 levels in naturally metamorphosing Eurycea bislineata (Amphibia; Plethodontidae).

We measured the circulating T4 and T3 levels in the plethodontid salamander Eurycea bislineata at various stages of metamorphosis using radioimmunoassay (RIA). Seven distinct metamorphic stages were defined based on specific developmental events concerning the remodeling and differentiation of skeletal elements. Special effort was made to study individual variation in the levels of plasma thyroid hormones. For this reason we did not pool serum from several specimens. The RIA was conducted in aliquots of 2 microliters (T4) and 5 microliters (T3), with minimum detectable levels of 100 ng/dl (T4) and 20 ng/dl (T3). In agreement with previous studies on other amphibians, we found metamorphosis in E. bislineata to be accompanied by a sharp increase in the circulating plasma levels of T3 and T4. No hormones were detectable in the larval and adult stages. Our technique allowed for simultaneous measurement of T3 and T4 levels in some individuals. These data indicated that, although both the onset of the production of the two thyroid hormones is simultaneous, T3 remains in the system longer than T4. However, at all metamorphic stages a large proportion of specimens did not exhibit any measurable levels of T3 and/or T4. These results underscore the need to reassess the mode of operation and production of thyroid hormones in amphibian metamorphosis.

Animals↗
PubMed1987

Seasonal plasma and intraovarian sex steroid profiles, and influence of temperature on gonadotropin stimulation of in vitro estradiol-17 beta and progesterone production, in Rana esculenta (Amphibia: Anura).

Seasonal plasma and intraovarian estradiol-17 beta (E) and progesterone (P) fluctuations were studied by specific radioimmunoassay in the frog, Rana esculenta. Moreover, incubations of ovine-luteinizing hormone (oLH)-stimulated ovarian pieces at two different temperatures (15 and 24 degrees) have been carried out in order to evaluate the dependence of E and P output on this exogenous factor. Estradiol showed similar changes in plasma and ovaries, while P profile was better evidenced in the gonads since this hormone fluctuated in plasma, giving pulses of difficult interpretation. A shift from E to P production by the ovary near the ovulatory period (February-March) was noted. In vitro experiments were carried out using approximately equal-sized ovarian fragments containing follicles ranging from 0.7 to 1 mm and classified as early vitellogenic. High temperature induced oLH-stimulated P production within 6 h, while E increased after 24 h concomitantly with a P decline. At 15 degrees the stimulatory effect of oLH was achieved only on E output in the incubation medium after 24 h. In conclusion, our results in the frog, R. esculenta, show that E and P intervene at peak values separately during the annual cycle and that the temperature has an important role in the regulation of the steroid hormone-releasing activity.

Animals↗