Fuller M T, Caulton J H, Hutchens J A, Kaufman T C, Raff E C
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347.
J Cell Biol. 1988 Jul;107(1):141-52. doi: 10.1083/jcb.107.1.141.
The testis-specific beta 2 tubulin of Drosophila is required for assembly and function of at least three architecturally different microtubule arrays (Kemphues et al., 1982). Two recessive male-sterile mutations in the B2t locus that encode partially functional, stable, variant forms of beta 2 tubulin cause defects in only certain microtubule-based processes during spermatogenesis. These mutations could thus identify aspects of beta tubulin primary structure critical for function only in specific microtubule arrays. In males carrying the B2t6 mutation, meiotic chromosome segregation and nuclear shaping are normal and flagellar axonemes are formed, but there is a subtle defect in axoneme structure; the outer doublet microtubules fill in with a central core normally seen only in the central pair and accessory microtubules. In homozygous B2t7 males, chromosome movement is usually normal during meiosis but cytokinesis often fails, cytoplasmic microtubules are assembled and nuclear shaping appears to be normal, but the flagellar axoneme lacks structural integrity. In contrast, the B2t8 allele affects a general property of tubulin, the ability to form normal side-to-side association of protofilaments (Fuller et al., 1987), and causes defects in meiosis, axoneme assembly and nuclear shaping. Certain combinations of these beta 2 tubulin mutations show interallelic complementation; in B2t6/B2t8 males functional sperm are produced and both variant subunits are incorporated into mature sperm, in the absence of wild-type beta 2 tubulin. Comparison of the phenotypes of the three partially functional beta 2 tubulin alleles reveals some aspects of tubulin primary structure more important for function in specific subsets of microtubule arrays, and other aspects required for the construction of microtubules in general.
果蝇睾丸特异性β2微管蛋白是至少三种结构不同的微管阵列组装和功能所必需的（肯普休斯等人，1982年）。B2t基因座中的两个隐性雄性不育突变编码β2微管蛋白的部分功能性、稳定的变体形式，仅在精子发生过程中某些基于微管的过程中导致缺陷。因此，这些突变可以确定仅在特定微管阵列中对功能至关重要的β微管蛋白一级结构的各个方面。在携带B2t6突变的雄性中，减数分裂染色体分离和核形态正常，鞭毛轴丝形成，但轴丝结构存在细微缺陷；外部双联体微管填充有通常仅在中央对和辅助微管中可见的中央核心。在纯合B2t7雄性中，减数分裂期间染色体运动通常正常，但胞质分裂经常失败，细胞质微管组装且核形态似乎正常，但鞭毛轴丝缺乏结构完整性。相比之下，B2t8等位基因影响微管蛋白的一般特性，即原纤维形成正常侧向关联的能力（富勒等人，1987年），并导致减数分裂、轴丝组装和核形态缺陷。这些β2微管蛋白突变的某些组合表现出等位基因间互补；在B2t6/B2t8雄性中，在没有野生型β2微管蛋白的情况下产生了功能性精子，并且两种变体亚基都被整合到成熟精子中。对三种部分功能性β2微管蛋白等位基因的表型比较揭示了微管蛋白一级结构的某些方面在特定微管阵列子集中对功能更重要，以及在一般微管构建中所需的其他方面。
