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Biomedical subjects

R A Wallace

Publications and source records attributed to R A Wallace.

At least 91 records · Page 5Linked to original sources
PubMed1978

Long-term growth and differentiation of Xenopus oocytes in a defined medium.

Xenpus laevis oocytes over a size range of 0.15--0.78 mm3 were dissected from their follicles and cultured in a defined medium for up to 28 days. Oocytes grew at average rates of 0.021 mm3.day-1 in the absence of insulin and 0.030 mm3.day-1 in the presence of insulin. The latter average growth rate corresponds to the fastest growth rate reported to date for oocytes in vivo. Oocytes grown in vitro can reach a size of at least 1.43 mm3, which is larger than the maximum size generally found in vivo. During growth in vitro; oocytes also acquire both a normal pigment pattern and, once they reach about 0.7 mm3, the ability to undergo complete maturation as a response to externally applied progesterone. These results show that Xenopus oocytes freed of their follicular investments are able to grow and differentiate in vitro.

Animals↗
PubMed1976

Protein incorporation by isolated amphibian oocytes. V. Specificity for vitellogenin incorporation.

Macromolecules of vitellogenin were sequestered by Xenopus laevis oocytes 20-50 times (on a molar basis) more rapidly than other proteins tested. Selectivity for vitellogenin did not appear to involve molecular size or charge. The Km for vitellogenin incorporation was at least several orders of magnitude less than that for bovine serum albumin (BSA). At concentrations less than 10 mg-ml-1, BSA did not measurably compete with vitellogenin; a slight, apparent competition observed above a BSA concentration of 10 mg-ml-1 was probably spurious. Above a concentration of 2 mg-ml-1, vitellogenin promoted BSA incorporation by about 40%. These results are consistent with the notion that vitellogenin binds to specific receptor sites on the oocyte membrane and is subsequently internalized by micropinocytosis. Other proteins, such as BSA, which do not compete with vitellogenin are most likely to be incorporated by adventitious engulfment during micropinocytosis.

Animals↗
PubMed1974

Steroid inhibition of protein incorporation by isolated amphibian oocytes.

The relationship between blood protein (vitellogenin) incorporation and nuclear maturation was studied in individual amphibian oocytes after in vitro exposure to desoxycorticosterone acetate (DOCA). Isolated Rana pipiens oocytes were incubated in vitro with radioactively labeled oocyte yolk precursor ([(3)H]vitellogenin) obtained from estrogenized Xenopus laevis. Incorporation of labeled vitellogenin into the oocytes continued over a 24-h period. Oocytes simultaneously exposed to DOCA and to labeled vitellogenin exhibited both inhibition of vitellogenin incorporation and stimulation of nuclear maturation and cortical changes. Inhibition of vitellogenin incorporation was observed after approximately 9 h of incubation and was correlated with the time of nuclear breakdown. Preincubation of oocytes in steroid for 9 h essentially terminated vitellogenin incorporation. Incorporation of vitellogenin occurred after removal of follicle cells from the oocyte by a short treatment with EDTA. These results demonstrate the macromolecular vitellogenin transport system remains operative in oocytes which can undergo nuclear maturation and that the steroid DOCA can affect its function. Evidence suggests that the mechanism of steroid inhibition is in part the result of inhibition of the micropinocytotic process in the oocyte cortex.

Animals↗