The distribution of β-tubulin isotypes in cultured neurons from embryonic, newborn, and adult mouse brains

Tubulin, the subunit protein of microtubules, is an alpha/beta heterodimer. Both alpha- and beta-tubulin exist as numerous isotypes, differing in their amino acid sequences and encoded by different genes. The differences are highly conserved in evolution, suggesting that they are functionally significant. Neurons are a potentially very useful system for elucidating this significance, because they are highly differentiated cells and rich in tubulin isotypes. We have examined the distribution of beta-tubulin isotypes in mouse primary cultured cortical neurons from embryonic fetus, newborn pups and adults. Neurons from both embryonic and adult mouse brains express the beta I, beta II, and beta III isotypes, but apparently not beta IV or beta V. beta I, beta II, and beta III are found in both cell bodies and neurites. However, the situation is different in newborn mice. Although beta I and beta III are present in these neurons in both cell bodies and neurites and beta IV is absent, just like in embryonic and adult mice, two striking differences were noted in the neurons from newborn mice. First, beta V is apparently present evanescently in the neurons in both cell bodies and neurites. Interestingly, the beta V was expressed strongly in newborn neurons after one day of culture; expression became much weaker after 3 days, and almost disappeared after 5 days. Second, the distribution of beta II is different from other isotypes. After newborn mouse neurons were cultured for 3 days, beta II started to disappear partly from the cell bodies; this was much more pronounced after five days in culture. Our findings suggest that beta II's major function may involve the neurites and not the cell body. They also raise the possibility that beta V has a unique role in the neurons of newborn mice. (C) 2011 Elsevier B.V. All rights reserved.