Modification of the tropomyosin isoform composition of actin filaments in the brain by deletion of an alternatively spliced exon.

Tropomyosin (Tm) in non-muscle cells is involved in stabilisation of the actin cytoskeleton. Some of the 40 isoforms described are found in the brain and exhibit spatial and developmental regulation. Non-muscle isoforms from the gamma Tm gene can be subdivided into three subsets of isoforms differing at the C-terminus, all of which are found throughout the brain and some of which are implicated in different aspects of neuronal function. We have approached the role of different gamma isoforms in neuronal function by knocking out a subset of isoforms. We show here that we can successfully knock out all isoforms containing the brain-specific 9c C-terminus. Brains from these mice did not show any gross abnormalities. Western analysis of adult brains showed that 9c isoforms are reduced in +/- and absent in -/- mice but that a compensation by 9a-containing isoforms resulted in total levels of gamma products remaining the same. No other Tm isoforms were altered. We have therefore specifically altered the Tm composition in these neurons which allows us to study the effects of these changes on the cytoskeleton of neurons during growth, differentiation and maturation and give us insights into the normal roles of these isoforms.