Heterogeneity of Microtubule‐Associated Proteins and Brain Development

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Abstract
Developmental changes in the composition of brain microtubule-associated proteins have been studied in three species the rat and the mouse, which are characterized by post-natal brain development, and the guinea-pig, whose Drain is mature at birth. 1 At an adult stage, and whatever the species, two major microtubule-associated proteins, which have been referred to MAP2 and τ, have been identified by polyacrylamide gel electrophoresis Rat τ is composed of four closely spaced bands; mouse τ contains only three components with one of them being present in higher proportion than the others; adult guinea-pig τ is essentially present as a single band. 2 Microtubule-associated proteins were also prepared at different stages of brain development. In the three species only two bands were seen in the τ region at immature stages of development (fast τ and slow τ). However adult τ factors progressively replace the young entities. In contrast, only small changes were seen in the proportion of MAP2. 3 Peptide mapping analysis of the purified T entities confirmed that the four adult rat proteins are very similar. In contrast, peptide mapping of the two young rat T proteins were very different from each other and from those of the adult ones. Peptide mappings of young and adult MAP2 were only slightly different. 4 The activities of young T proteins and young MAP2 in promoting pure tubulin assembly were much lower than those of the adult ones. Young fast T and young slow T were purified and both show to be active in promoting pure tubulin polymerization. 5 These data demonstrate the existence of two types of heterogeneity of microtubule-associated proteins: plurality of protein species at every stage of brain development and changes in composition ana activity dependent on development.