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

The properties of the microtubule network are regulated at various levels i ncluding tissue-dependent isotype switching, post-translational modificatio n of alpha- and beta-tubulin, and by a variety of microtubule associated mo lecules (for reviews, see [1-3]). Microtubule nucleation is attributed to g amma-tubulin, which is present in protein complexes at the centrosome and I n the cytoplasm [4,5]. A screen for flagellar mutants in the green alga Chl amydomonas reinhardtii has led to the identification of a fourth member of the tubulin gene superfamily, delta-tubulin. In this unicellular organism, the lack of a functional delta-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 m ouse delta-tubulin homologue and show that the gene is highly expressed in testis. In the elongating spermatid, delta-tubulin associated with the manc hette, a specialised microtubule system present during reshaping of the spe rm head. The protein specifically localised at the perinuclear ring of the manchette, at the centriolar vaults and along the principal piece of the sp erm flagellum. In somatic cell lines, unlike most other tubulins, mammalian delta-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 gamma-tubulin coimmunoprecipitated with delta-tubulin. T ogether, the data indicate a specialised role for mammalian delta-tubulin t hat is distinct from other known tubulins. (C) 2000 Elsevier Science Ltd. A ll rights reserved.