| dc.description | Development in most organisms is accompanied by changes in their tubulin composition, commonly due to differential gene expression and/or post-translational modifications. The brine shrimp, Artemia, undergoes a period of post-gastrular morphogenesis in the absence of mitosis, resulting in the formation of a free-swimming nauplius. Two-dimensional gel electrophoresis revealed that the isotubulin family, composed of three $\alpha$- and two $\beta$-tubulins, does not change during development of Artemia franciscana. The generation of isotubulin diversity in this unusual organism was investigated. One size class each of $\alpha$- and $\beta$-tubulin mRNA, 1.9 kB in length, was detected on Northern blots using cloned Drosophila tubulin gene probes. Only a small amount of the tubulin mRNA was present on polysomes. The amount of tubulin mRNA on polysomes or in the cytoplasm did not change over development. In vitro translation of Artemia poly(A)$\sp{+}$ RNA yielded one $\alpha$- and a maximum of two $\beta$-tubulins on two-dimensional gels; total cytoplasmic RNA gave a larger amount of tubulin synthesized in vitro than did polysomal RNA. In vivo labelling of Artemia proteins showed a low level of tubulin synthesis. It appears that there is translational regulation of Artemia tubulin synthesis during early post-gastrular development. Analysis of post-translational modifications to Artemia tubulin revealed the presence of acetylated and tyrosinated $\alpha$-tubulin; acetylated $\alpha$-tubulin localized to only one of the $\alpha$-isotubulin spots on two-dimensional gels. Isotubulin diversity in Artemia is provided at least in part by post-translational modifications. Detyrosinated $\alpha$-tubulin was absent until 20 h of development had passed, which demonstrates that this tubulin is not required for early development in a complex, metazoan animal. Evidently a small number of tubulins can carry out the numerous microtubule activities in a multicellular organism, supporting the theory that tubulins are multifunctional. | en_US |
