Hiromu Sugino

Production of activin-binding protein by rat granulosa cells in vitro.

We have developed an assay method for activin-binding protein, which exploits its high affinity for sulfated polysaccharides. We used this method to investigate the production of activin-binding protein by rat ovarian granulosa cells, in vitro. The production of activin-binding protein by granulosa cells was dependent on the cell density; the maximum was observed at 6 x 10(5) cells/ml. Follicle-stimulating hormone (FSH), but not luteinizing hormone (LH), enhanced production significantly. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and ligand blotting analyses of the activin-binding protein secreted by rat granulosa cells demonstrated it was the same protein molecule as that purified from rat ovaries. It is inferred from these results that the granulosa cell is a source of ovarian activin-binding protein and that its secretion is regulated by FSH.

Follistatin inhibits the mesoderm-inducing activity of activin A and the vegetalizing factor from chicken embryo

SummaryThe induction of mesoderm is an important process in early amphibian development. In recent studies, activin has become an effective candidate for a natural mesoderm-inducing factor. In the present study, we show that follistatin, an activin-binding protein purified from porcine ovary, inhibits the mesoderm-inducing activity of recombinant human activin A (rh activin A), which is identical to the erythroid differentiation factor (EDF). The quantity of follistatin required for effective suppression of activin was more than three-fold that of activin (w:w). Follistatin also inhibited the mesoderm-inducing activity of the vegetalizing factor purified from chick embryos, suggesting that the vegetalizing factor is closely related to activin.

Follistatin inhibits activin-induced differentiation of rat follicular granulosa cells in vitro

The effect of follistatin on activin-induced granulosa cell differentiation was investigated in freshly harvested granulosa cells from diethylstilbestrol (DES)-treated rats. Activin induced a remarkable change in granulosa cellular morphology from elongated fibroblast-like to round cells, which follistatin prevented. Follistatin itself had no influence on the cellular morphology. We studied the action of follistatin on activin-induced differentiation of granulosa cells cultured in a chemically defined medium. Addition of activin (30 ng/ml) to the culture increased the FSH binding site approximately 2-fold compared with the control (spontaneous expression) level, whereas follistatin reduced the activin-induced expression level to the control level in a concentration-dependent manner. Activin (30 ng/ml) markedly augmented FSH-induced hCG binding and progesterone production by approximately 20-fold, and these effects were suppressed by follistatin in a concentration-dependent manner. Similarly, addition of follistatin to the culture induced a concentration-dependent decrease of activin-enhanced inhibin-producing activity, but had no effect on FSH-induced inhibin production. These results suggest that follistatin/activin-binding protein binds to activin stoichiometrically to suppress the activin-induced differentiation of rat granulosa cell in vitro, but follistatin itself has no direct effect on activin-independent reactions.

The vegetalizing factor from chicken embryos: its EDF (activin A)-like activity.

The erythroid differentiation capacity of the HPLC-purified mesoderm- and endoderm-inducing vegetalizing factor from chicken embryos and of recombinant erythroid differentiation factor (EDF = activin A), an evolutionary highly conserved member of the TGF-beta protein superfamily have been compared. Both factors stimulate the synthesis of hemoglobin in erythroleukemia cells in the same concentration range. The EDF-activity of the mesoderm-inducing HPLC-fractions is inhibited by follistatin, an EDF-binding protein. The factor induces in ectoderm of Triturus taeniatus all kinds of mesodermal organs. The wide spectrum of organs is very likely to be induced by secondary interactions. At higher concentration (15 ng/ml), notochord- and endoderm-like tissues are induced in a high percentage.

The Activin A‐Dependent Proliferation of PCC3/A/1 Embryonal Carcinoma Cells in Serum‐Free Medium

Examination of the growth requirements of murine embryonal carcinoma cells (EC cells) or embryonic stem cells (ES cells) in serum‐free medium revealed that PCC3 EC cells required activin A to grow and/or survive in such medium. In the absence of activin A, PCC3 cells began to disintegrate within 3 days under any serum‐free conditions examined. P19 and AT805 EC cells grew even in serum‐free medium without activin A but their growth rates were slightly facilitated by its addition. F9 EC cells also grew in the medium without activin A and its addition somewhat inhibited their growth rate. Three independently isolated ES cell lines and feeder‐dependent PSA‐1 EC cells also grew in serum‐free medium without activin A if leukemia inhibitory factor (LIF) was supplemented. The addition of activin A had little effect on their growth rates. These findings suggest that PCC3 EC cells are a sort of nutritional mutant requiring activin A, thus making them useful in stidies on the growth regulatory mechanisms of EC/ES cells and/or the action of activin on EC/ES cells.