Tissue-specific expression and subcellular localisation of mammalian δ-tubulin

The properties of the microtubule network are regulated at various levels including tissue-dependent isotype switching, post-translational modification of αand β-tubulin, and by a variety of microtubuleassociated molecules (for reviews, see [1–3]). Microtubule nucleation is attributed to γ-tubulin, which is present in protein complexes at the centrosome and in the cytoplasm [4,5]. A screen for flagellar mutants in the green alga Chlamydomonas reinhardtii has led to the identification of a fourth member of the tubulin gene superfamily, δ-tubulin. In this unicellular organism, the lack of a functional δ-tubulin gene copy causes aberrant numbers of flagella, depending on the age of the corresponding basal bodies; mutants also show abnormal ultrastructure of the basal bodies and a misplacement of the cleavage furrow at mitosis [6]. Here, we report the isolation of the mouse δ-tubulin homologue and show that the gene is highly expressed in testis. In the elongating spermatid, δ-tubulin associated with the manchette, a specialised microtubule system present during reshaping of the sperm head. The protein specifically localised at the perinuclear ring of the manchette, at the centriolar vaults and along the principal piece of the sperm flagellum. In somatic cell lines, unlike most other tubulins, mammalian δ-tubulin was both cytoplasmic and nuclear and did not colocalise with microtubules. The protein was enriched at the spindle poles during mitosis and we found that γ-tubulin coimmunoprecipitated with δ-tubulin. Together, the data indicate a specialised role for mammalian δ-tubulin that is distinct from other known tubulins.