Gong Z Y, Brandhorst B P
Biology Department, McGill University, Montreal, Quebec, Canada.
Mol Reprod Dev. 1988;1(1):3-9. doi: 10.1002/mrd.1080010103.
The mass of tubulin protein in developing embryos of the sea urchin Lytechinus pictus was measured using a radiodilution immunoassay based on densitometric analysis of immunoprecipitated tubulins resolved electrophoretically. The tubulins constitute an average of 360 +/- 35 pg per egg, or 0.66% of the total protein, and there is no significant change in their concentration during embryogenesis. The masses of soluble and polymerized tubulin were measured for extracts prepared under conditions that stabilize microtubules. In eggs, a maximum of 14% of the tubulin is insoluble, and this increases throughout embryogenesis to 67% at pluteus stage (72 hr). The concentration of tubulin in eggs is at least 500 micrograms/ml, well above the critical concentration for tubulin assembly in vitro, yet microtubules have not been observed in eggs. The mass of newly synthesized tubulin, estimated from the mass of tubulin mRNA per embryo, accounts for a small fraction of the total tubulin by the end of gastrulation but for over half of the tubulin by the 72-hr pluteus stage. These observations are consistent with a model in which the declining level of unpolymerized tubulin controls the stability of tubulin mRNa, providing an autogenous regulation of the ontogenetic pattern of tubulin synthesis during sea urchin embryogenesis (Gong and Brandhorst, Development 102: 31-43).
利用基于对经电泳分离的免疫沉淀微管蛋白进行光密度分析的放射性稀释免疫测定法，对花斑海胆发育胚胎中的微管蛋白质量进行了测量。微管蛋白在每个卵中的平均含量为360±35皮克，占总蛋白的0.66%，在胚胎发育过程中其浓度没有显著变化。对在稳定微管的条件下制备的提取物，测定了可溶性和聚合态微管蛋白的质量。在卵中，最多14%的微管蛋白是不溶性的，并且在整个胚胎发育过程中这一比例增加，到长腕幼虫期（72小时）时达到67%。卵中微管蛋白的浓度至少为500微克/毫升，远高于体外微管蛋白组装的临界浓度，但在卵中未观察到微管。根据每个胚胎中微管蛋白mRNA的质量估算的新合成微管蛋白的质量，在原肠胚形成末期占总微管蛋白的一小部分，但到72小时长腕幼虫期时占微管蛋白总量的一半以上。这些观察结果与一个模型相符，在该模型中，未聚合微管蛋白水平的下降控制着微管蛋白mRNA的稳定性，从而在海胆胚胎发育过程中对微管蛋白合成的个体发育模式进行自体调节（龚和布兰德霍斯特，《发育》102: 31 - 43）。
