Programmed expression of beta-tubulin genes during development and differentiation of the chicken.

We have previously demonstrated that the chicken genome contains at least four different, functional beta-tubulin genes. By using gene specific probes we have now analyzed the relative levels of expression of the four encoded messenger RNA (mRNA) transcripts as a function of chicken development and differentiation. We have found that the RNA transcript from the beta 2 gene is present in large amounts in embryonic chick brain and is also preferentially expressed in spinal cord neurons, indicating that this transcript encodes the dominant neuronal beta-tubulin polypeptide. The beta 3 mRNA is present in overwhelming amounts in RNA from chicken testis suggesting that this gene encodes a flagellar or meiotic spindle tubulin. However, both of these genes are transcribed to varying, but lesser, degrees in a number of additional cell and tissue types indicating that they are not neuronal or testis specific, respectively. Beta 4' transcripts are present at moderate levels in all cell and tissue types examined, suggesting that this mRNA encodes a constitutive beta-tubulin polypeptide that is involved in an essential or housekeeping microtubule function. Transcripts from the beta 1 gene are a minor component of the beta-tubulin mRNA populations in all cells and tissues tested. Overall, we conclude that specific beta-tubulin mRNA species are expressed in markedly different ratios in different tissues in the chicken. Such developmental regulation may reflect the function(s) of the individual beta-tubulin polypeptides or, alternatively, may be required for precise control of tubulin gene expression in cells that utilize microtubules for divergent purposes.