Kishi Y, Mahadeo D, Cervi D N, Clements C, Cotter D A, Sameshima M
Department of Physics, Rikkyo (St. Paul's) University, 3-34-1 Nishi-ikebukuro, Toshima-ku, Tokyo, 171-0021, Japan.
Exp Cell Res. 2000 Nov 25;261(1):187-98. doi: 10.1006/excr.2000.5061.
In the presence of germination signals, dormant spores of Dictyostelium discoideum rapidly germinate to start a new life cycle. Previously we have shown that half of the actin molecules in spores are maintained in a tyrosine-phosphorylated state, and a decline of the actin phosphorylation levels is a prerequisite for spore swelling. In this study, we have established d-glucose as a trigger molecule for the actin dephosphorylation. Present in a nutrient germination medium, d-glucose both may act as a trigger molecule and/or may serve as a substrate within a pathway for actin dephosphorylation depending upon spore age. However, the glucose-induced actin dephosphorylation was insufficient for spores to swell. Other factors in the nutrient medium were required for complete germination of young spores aged 1 to 5 days. In contrast, dispersion in nonnutrient buffer was necessary and sufficient for a decline of actin phosphorylation levels and even the emergence of amoebae in older spores (6 days and beyond). Moreover, the dephosphorylation pathway in the older spores was independent of energy production. We propose that the diversification of the actin dephosphorylation pathway may enable spores to increase their probability of germination upon spore aging.
在存在萌发信号的情况下，盘基网柄菌的休眠孢子会迅速萌发，开始新的生命周期。此前我们已经表明，孢子中一半的肌动蛋白分子保持在酪氨酸磷酸化状态，而肌动蛋白磷酸化水平的下降是孢子膨胀的先决条件。在这项研究中，我们确定了d -葡萄糖是肌动蛋白去磷酸化的触发分子。d -葡萄糖存在于营养萌发培养基中，根据孢子的年龄，它既可以作为触发分子，也可以作为肌动蛋白去磷酸化途径中的一种底物。然而，葡萄糖诱导的肌动蛋白去磷酸化不足以使孢子膨胀。对于1至5天龄的年轻孢子，营养培养基中的其他因素是完全萌发所必需的。相比之下，在非营养缓冲液中分散对于肌动蛋白磷酸化水平的下降甚至对于6天及更老的孢子中变形虫的出现是必要且充分的。此外，老孢子中的去磷酸化途径与能量产生无关。我们提出，肌动蛋白去磷酸化途径的多样化可能使孢子在老化时增加其萌发的概率。
