Mutations in α-tubulin promote basal body maturation and flagellar assembly in the absence of δ-tubulin

Abstract

We have isolated suppressors of the deletion allele of δ-tubulin, uni3-1, in the biflagellate green alga Chlamydomonas reinhardtii. The deletion of δ-tubulin produces cells that assemble zero, one or two flagella and have basal bodies composed primarily of doublet rather than triplet microtubules. Flagellar number is completely restored in the suppressed strains. Most of the uni3-1 suppressors map to the TUA2 locus, which encodes α2-tubulin. Twelve independent tua2 mutations were sequenced. Amino acids D205 or A208, which are nearly invariant residues in α-tubulin, were altered. The tua2 mutations on their own have a second phenotype - they make the cells colchicine supersensitive. Colchicine supersensitivity itself is not needed for suppression and colchicine cannot phenocopy the suppression. The suppressors partially restore the assembly of triplet microtubules. These results suggest that the δ-tubulin plays two roles: it is needed for extension or stability of the triplet microtubule and also for early maturation of basal bodies. We suggest that the mutant α-tubulin promotes the early maturation of the basal body in the absence of δ-tubulin, perhaps through interactions with other partners, and this allows assembly of the flagella.

Centriole structure

“…Gene silencing of d-tubulin in Paramecium also resulted in loss of the C-tubule without affecting cilia or basal body formation [22]. This requirement for d-tubulin in C-tubule formation and genetic interactions between d-tubulin and a-tubulin [23], lead Li et al [10] to speculate that d-tubulin may be a component of a unique linker they observed between the B-and C-tubules.…”

Building the Centriole

“…In Chlamydomonas and Paramecium cells defective for δ-tubulin, the C-tubule is often missing and most centrioles are composed of doublet microtubules [1,92]. The requirement for δ-tubulin in C-tubule formation can be bypassed by suppressor mutations in α-tubulin, suggesting that δ-tubulin may be required for triplet stabilization rather than for C-tubule assembly [94]. Furthermore, genes encoding ε- and δ-tubulins are absent from the Drosophila genome, despite the fact that centrioles containing triplet microtubules are formed in this species [95].…”

Basal body and flagellum mutants reveal a rotational constraint of the central pair microtubules in the axonemes of trypanosomes

“…The first of these was ␦-tubulin -a protein associated with basal bodies. In Chlamydomonas, disruption of the gene encoding ␦-tubulin results in loss of the C-tubule of the basal body microtubules (Dutcher and Trabuco, 1998;Fromherz et al, 2003). In Paramecium, silencing of the gene encoding ␦-tubulin similarly results in loss of the C-tubule, but additionally loss of B-and even A-tubules was observed (Garreau de Loubresse et al, 2001).…”