Changes in the Activity of the Maturation-Promoting Factor Are Correlated with Those of a Major Cyclic AMP and Calcium-Independent Protein Kinase During the First Mitotic Cell Cycles in the Early Starfish Embryo

Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca²⁺. Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle.     

中国平脉树螽属五新种记述：直翅目：螽斯科：树螽亚科

本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。     

Modulation of the urokinase receptor in human colon cell lines by N,N-dimethylformamide

The present study documents the effect of the planar, polar differentiation promoter N,N-dimethylformamide (DMF) on urokinase binding to colon carcinoma cells. Exposure of the colon carcinoma cell lines to the agent resulted in enhanced specific binding of radioactive urokinase to all cells tested. Insulin binding to the cells was, however, unaffected by DMF. A DMF exposure period of 45 h was required to observe maximum urokinase binding to two representative cell lines FET and RKO. Optimal stimulation of both cell lines occurred with 0.8% DMF. Scatchard analysis revealed the dissociation constants to be unchanged by the agent with the increased binding of radioactive plasminogen activator reflecting an up-regulation of binding sites. In this regard, the cell line RKO upon exposure to DMF, displayed approx. 700,000 receptors/cell, the highest value published, to date, for any cell line.     

Changes in Abscisic Acid Content in Axis and Cotyledons of Developing Phaseolus vulgaris Embryos and their Physiological Consequences

Prevost, I. and Le Page–Degivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.—J.exp. Bot. 36: 1900–1905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radio–immunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability     

Identification of a tumor inhibitory factor in rat ascites fluid

A polypeptide which inhibits the growth of human carcinoma cells has been characterized from Novikoff rat ascites fluid. This tumor inhibitory factor co-purified with transforming growth factor activity through acid/ethanol extraction and Bio-Gel chromatography. The two activities were completely separated by reverse phase HPLC. The tumor inhibitory factor is heat stable and requires disulfide bonds for bioactivity. This factor inhibited the anchorage independent growth of the more differentiated human colon carcinoma cell lines but did not affect the less differentiated carcinoma cells. The presence of stimulatory and inhibitory activities in the same extracts suggests that the relative concentrations of these factors may be important in the control of cell growth.     

Effects of growth stimulatory factors on mitogenicity and c-myc expression in poorly differentiated and well differentiated human colon carcinoma cells

We demonstrate the differential sensitivity of poorly differentiated and well differentiated human colon carcinoma cells to nutrients alone or to nutrients and polypeptide growth factors under completely serum-free conditions. 3H-Thymidine incorporation into trichloroacetic acid precipitable material and autoradiographic analysis indicated that nutrient replenishment alone was sufficient to initiate DNA synthesis in quiescent poorly differentiated cells, whereas defined polypeptide growth factors produced no additional effect. In contrast, well differentiated cells were mitogenically stimulated to a much greater extent by growth factors (epidermal growth factor + insulin + transferrin), than by nutrient replenishment alone. Expression of the c-myc protooncogene was increased approximately 5-fold after growth factor addition to the well differentiated cells. Maximal expression of c-myc occurred at 4 h post stimulation. In contrast, nutrients resulted in only a slight up-regulation of c-myc (1.8-fold) at approximately 90 min after addition. Addition of nutrients and/or growth factors to the poorly differentiated colon carcinoma cells resulted in an initial decline in c-myc expression (90 min), presumably due to removal of endogenous growth stimulators. Expression of c-myc returned to baseline levels by 24 h after additions. The results indicate that differential sensitivity to polypeptide growth factors is related to differentiation status in this model system and suggest that the insensitivity of poorly differentiated cells to exogenous growth factors may be due to a greater production of autocrine growth stimulators.