Cell Cycle Regulation of Microtubule Assembly

本研究的目的是确定在发育中的海胆胚胎间期向有丝分裂转变过程中参与微管组装调节的大分子。未受精的海胆卵在第一次有丝分裂周期的G1期就停止了，尽管有大量的微管亚基，但它们几乎没有组装好的微管。受精后，第一次卵裂有丝分裂器的微管同步组装。因此，发育中的海胆胚胎可以作为研究微管组装调控的诱导模型系统。最近发现，间期阻滞卵细胞含有两种新的微管组装抑制剂-负端抑制剂和ph依赖性正端抑制剂。提出的研究目标是在细胞周期中分离和表征这些独特的因素。对海胆卵、蛤卵母细胞、小鼠B16培养黑色素瘤细胞、鱿鱼视叶和哺乳动物脑组织等不同来源的初步实验表明，这些负控制因素可能存在于所有真核细胞中，特别是在细胞周期中细胞质微管以受控方式快速组装和拆卸的地方。细胞周期中有丝分裂和间期微管阵列的相互转化是细胞形态发生的一个基本问题。这一过程不仅对细胞分裂具有重要意义，而且对神经元生长和可塑性等发育过程也具有重要意义。这些研究有望增加我们对微管组装在活细胞中受到调节的基本机制的理解。

The intent of this study is to identify the macromolecules involved in the regulation of microtubule assembly during the interphase-to- mitosis transition in developing sea urchin embryos. Unfertilized sea urchin eggs are arrested at G1 of the first mitotic cycle and have few, if any assembled microtubules despite a large pool of tubulin subunits. Following fertilization microtubules of the first cleavage mitotic apparatus are synchronously assembled. Therefore the developing sea urchin embryo can be viewed as an inducible model system for studying the regulation of microtubule assembly. It has been recently discovered that interphase-arrested egg cells contain two novel inhibitors of microtubule assembly- a minus-end inhibitor and a pH-dependent plus-end inhibitor. The goal of the proposed research is to isolate and characterize these unique factors during the cell cycle. Preliminary experiments with such diverse sources as sea urchin eggs, surf clam oocytes, mouse B16 cultured melanoma cells, squid optic lobe and mammalian brain tissue suggest that these negative control factors may exist in all eukaryotic cells, particularly where cytoplasmic microtubules are rapidly assembled and disassembled in a controlled manner during the cell cycle. The interconversion of mitotic and interphase microtubule arrays during the cell cycle is a fundamental problem of cellular morphogenesis. The process is of obvious importance for cell division but also for developmental processes such as neuronal growth and plasticity. These studies are expected to increase our understanding of fundamental mechanisms whereby microtubule assembly is regulated in the living cell.