Structural analysis of mutations in the Drosophila beta 2-tubulin isoform reveals regions in the beta-tubulin molecular required for general and for tissue-specific microtubule functions.
Structural analysis of mutations in the Drosophila beta 2-tubulin isoform reveals regions in the beta-tubulin molecular required for general and for tissue-specific microtubule functions.
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果蝇 β2-微管蛋白亚型突变的结构分析揭示了一般和组织特异性微管功能所需的 β-微管蛋白分子区域。
DOI：
10.1093/genetics/139.1.267
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发表时间：
1995
期刊：
影响因子：
3.3
通讯作者：
Raff,EC
中科院分区：
文献类型：
--
作者：
Fackenthal,JD;Hutchens,JA;Turner,FR;Raff,EC
我们已经确定了βTub85D基因的一些突变等位基因的损伤，βTub85D基因编码果蝇睾丸特异的β2-微管蛋白亚型。导致不同功能表型的突变分布在整个β2-微管蛋白分子中。改变的残留物的系统发育保守程度与被病变破坏的不同微管类别的数量之间存在明显的相关性。大多数损伤发生在进化上在所有β-微管蛋白中高度保守的位置；这些损伤破坏了多类微管共同的一般功能。然而，单个等位基因B2t6在可变氨基酸的内部簇中包含氨基酸替换，该可变氨基酸簇已被确定为脊椎动物β-微管蛋白的同型定义域。相应地，B2t6只破坏微管功能的一部分，导致对精子尾轴突双微管形态的错误指定。我们先前已经证明，发育调节的果蝇β-微管蛋白亚型β3与野生型β2-微管蛋白在睾丸中共表达时，以显性方式赋予相同的限制性形态表型。我们在这里通过互补分析表明，Beta3和B2t6产物破坏了微管组装的一个共同方面。因此，我们得出结论，β2-微管蛋白内部可变区的氨基酸序列是产生正确的轴丝形态所必需的，而不是一般微管功能所必需的。正如我们之前报道的，轴丝的超结构组织需要β2-微管蛋白羧基末端同型定义域。我们在这里证明，缺乏羧基末端的β2变体和B2t6变体对于轻度到中度的减数分裂缺陷是互补的，但对于正常的轴丝形态来说并不是互补的。我们的结果与通过比较脊椎动物β-微管蛋白得出的假设是一致的，即在野生型β-微管蛋白中，两个同型定义结构域在三维结构中相互作用。我们认为，果蝇睾丸β2-微管蛋白异构体的这种结构的完整性是正确组装轴丝所必需的，但不一定是一般微管功能所必需的。在我们观察的基础上，我们提出了轴丝微管形态作为微管组装动力学函数的调节模型。
We have determined the lesions in a number of mutant alleles of beta Tub85D, the gene that encodes the testis-specific beta 2-tubulin isoform in Drosophila melanogaster. Mutations responsible for different classes of functional phenotypes are distributed throughout the beta 2-tubulin molecule. There is a telling correlation between the degree of phylogenetic conservation of the altered residues and the number of different microtubule categories disrupted by the lesions. The majority of lesions occur at positions that are evolutionarily highly conserved in all beta-tubulins; these lesions disrupt general functions common to multiple classes of microtubules. However, a single allele B2t6 contains an amino acid substitution within an internal cluster of variable amino acids that has been identified as an isotype-defining domain in vertebrate beta-tubulins. Correspondingly, B2t6 disrupts only a subset of microtubule functions, resulting in misspecification of the morphology of the doublet microtubules of the sperm tail axoneme. We previously demonstrated that beta 3, a developmentally regulated Drosophila beta-tubulin isoform, confers the same restricted morphological phenotype in a dominant way when it is coexpressed in the testis with wild-type beta 2-tubulin. We show here by complementation analysis that beta 3 and the B2t6 product disrupt a common aspect of microtubule assembly. We therefore conclude that the amino acid sequence of the beta 2-tubulin internal variable region is required for generation of correct axoneme morphology but not for general microtubule functions. As we have previously reported, the beta 2-tubulin carboxy terminal isotype-defining domain is required for suprastructural organization of the axoneme. We demonstrate here that the beta 2 variant lacking the carboxy terminus and the B2t6 variant complement each other for mild-to-moderate meiotic defects but do not complement for proper axonemal morphology. Our results are consistent with the hypothesis drawn from comparisons of vertebrate beta-tubulins that the two isotype-defining domains interact in a three-dimensional structure in wild-type beta-tubulins. We propose that the integrity of this structure in the Drosophila testis beta 2-tubulin isoform is required for proper axoneme assembly but not necessarily for general microtubule functions. On the basis of our observations we present a model for regulation of axoneme microtubule morphology as a function of tubulin assembly kinetics.