Neurofilament and tubulin expression recapitulates the developmental program during axonal regeneration: induction of a specific beta-tubulin isotype.

We examined the differential expression of genes encoding three beta-tubulin isotypes (classes I, II, and IV) and the 68-kDa neurofilament protein (NF68) in rat sensory neurons during development, maturation, and axonal regeneration. Expression of the specific beta-tubulin gene encoding the class II isotype was induced to high levels during development and axonal regeneration, whereas the expression of genes encoding the two other isotypes (classes I and IV) remained comparable to mature levels. Conversely, expression of the NF68 gene was relatively low during development and regeneration. Thus, the developmental program for cytoskeletal gene expression is recapitulated during axonal regeneration. The high level of class II beta-tubulin expression found in developing and regenerating neurons occurs during the longitudinal growth of axons. In contrast, induction of NF68 gene expression is associated with the radial growth of axons in maturing neurons.