Cooperativity Between The Beta-Tubulin Carboxy Tail And The Body Of The Molecule Is Required For Microtubule Function

Using Drosophila spermatogenesis as a model, we show that function of the beta-tubulin C-terminal tail (CTT) is not independent of the body of the molecule. For optimal microtubule function, the beta-tubulin CTT and body must match. beta 2 is the only beta-tubulin used in meiosis and spermatid differentiation. beta 1-tubulin is used in basal bodies, but beta 1 cannot replace beta 2. However, when beta 1 is co-expressed with beta 2, both beta-tubulins are equally incorporated into all microtubules, and males exhibit near wild type fertility. In contrast, co-expression of beta 2 beta 1C and beta 1 beta 2C, two reciprocal chimeric molecules with bodies and tails swapped, results in defects in meiosis, cytoskeletal microtubules, and axonemes; mates produce few functional sperm and few or no progeny. In these experiments, all the same beta-tubulin parts are present, but unlike the co-assembled native beta-tubulins, the "trans" configuration of the co-assembled chimeras is poorly functional. Our data thus reveal essential intra-molecular interactions between the CTT and other parts of the beta-tubulin Molecule, even though the CTT is a flexible surface feature of tubulin heterodimers and microtubules. In addition, we show that Drosophila sperm tail length depends on the total tubulin pool available for axoneme assembly and spermatid elongation. D. melanogaster and other Drosophila species have extraordinarily long sperm tails, the length of which is remarkably constant in wild type flies. We show that in males of experimental genotypes that express wild type tubulins but have half the amount of the normal tubulin Pool size, sperm tails are substantially shorter than wild type. Cell Motil. Cytoskeleton 65: 955-963, 2008. (C) 2008 Wiley-Liss, Inc.