Microtubule arrays in differentiated cells contain elevated levels of a post-translationally modified form of tubulin

Abstract

Tyrosinated (Tyr) and detyrosinated (Glu) alpha-tubulins are post-translationally modified species that differ by a single amino acid at their respective C-termini. We have examined the distribution of these two species by immunofluorescence in proliferating and differentiated cells using antisera specifically reactive with each of the forms. In proliferating PtK1 cells, Tyr tubulin was the predominant form in almost every cytoplasmic microtubule (MT); only a few MTs contained detectable Glu tubulin. In contrast, staining of centrioles and primary cilia of PtK1 cells suggested that Glu tubulin was the predominant form in these stable assemblies of MTs. An examination of the distribution (by immunofluorescence) and relative amount (by immunoblot analysis) of the two forms of tubulin in the stable assemblies of MTs present in cultured neuronal cells (neurites), sperm and tracheal cells (axonemes and basal bodies), and platelets and erythrocytes (marginal bands) revealed that, in general, the MTs in these arrays contained substantially elevated levels of Glu tubulin in comparison with the levels in MTs of cultured cells. The one exception, the marginal band of toad erythrocytes, which contained only Tyr tubulin, demonstrates that an elevated level of Glu tubulin is not an obligate feature of a stable array of MTs. Nonetheless, an elevated level of Glu tubulin may be a useful indicator of stable MTs in differentiated cells. It is important to note that commonly used sources of tubulin (e.g., brain or flagella) necessarily yield tubulin that differs strikingly from tubulin of proliferating cells in its content of Glu tubulin.(ABSTRACT TRUNCATED AT 250 WORDS)