Begg D A, Rebhun L I, Hyatt H
J Cell Biol. 1982 Apr;93(1):24-32. doi: 10.1083/jcb.93.1.24.
We have investigated the relationship between the formation of actin filament bundles and the elongation of microvilli (MV) after fertilization in sea urchin eggs. In a previous study (1979, J Cell Biol. 83:241-248) we demonstrated that increased pH induced the formation of actin filaments in isolated sea urchin egg cortices with the concomitant elongation of MV. On the basis of these results we suggested that increased cytoplasmic pH after fertilization causes a reorganization of cortical actin, which in turn provides the force for MV elongation. To test this hypothesis, we compared the morphology of microvilli in eggs activated with and without the release of fertilization acid. Activation of eggs in normal sea water with the calcium ionophore A23187 causes the release of fertilization acid and the elongation of MV containing core bundles of actin filaments. Eggs activated with A23187 in NA(+)-free water do not undergo normal fertilization acid release but develop elongated, flaccid MV. These MV contain an irregular network of actin filaments rather than the parallel bundles of filaments found in normal MV. The addition of 40 mM NaCl to these eggs results in the release of H(+) and the concomitant conversion of flaccid MV to erect MV containing typical core bundles of actin filaments. Identical results are obtained when 10 mM NH(4)Cl is substituted for NaCl. The induction of cytoplasmic alkalinization in unactivated eggs with NH(4)Cl does not cause either MV elongation or the formation of actin filament bundles . These results suggest that: (a) the elongation of MV is stimulated by a rise in intracellular free Ca(++) concentration; (b) actin filament bundle formation is triggered by an increase in cytoplasmic pH; and (c) the formation of actin filament bundles is not necessary for MV elongation but is required to provide rigid support for MV.
我们研究了海胆卵受精后肌动蛋白丝束的形成与微绒毛（MV）伸长之间的关系。在之前的一项研究（1979年，《细胞生物学杂志》83:241 - 248）中，我们证明增加pH值可诱导分离的海胆卵皮质中肌动蛋白丝的形成，并伴随MV的伸长。基于这些结果，我们认为受精后细胞质pH值的升高会导致皮质肌动蛋白的重组，进而为MV伸长提供动力。为了验证这一假设，我们比较了在有无受精酸释放情况下激活的卵中微绒毛的形态。用钙离子载体A23187在正常海水中激活卵会导致受精酸的释放以及含有肌动蛋白丝核心束的MV伸长。在无钠（Na⁺）水中用A23187激活的卵不会经历正常的受精酸释放，但会发育出伸长、松弛的MV。这些MV含有不规则的肌动蛋白丝网络，而不是正常MV中发现的平行丝束。向这些卵中添加40 mM氯化钠会导致氢离子（H⁺）的释放，并使松弛的MV随之转变为含有典型肌动蛋白丝核心束的直立MV。用10 mM氯化铵（NH₄Cl）替代氯化钠时可获得相同结果。用NH₄Cl诱导未激活卵中的细胞质碱化既不会导致MV伸长，也不会导致肌动蛋白丝束的形成。这些结果表明：（a）MV的伸长受到细胞内游离钙离子（Ca²⁺）浓度升高的刺激；（b）肌动蛋白丝束的形成由细胞质pH值的升高触发；（c）肌动蛋白丝束的形成对于MV伸长不是必需的，但对于为MV提供刚性支撑是必需的。
