Synthesis of tubulin during early postgastrula development of Artemia: isotubulin generation and translational regulation.

Isotubulin diversity and the synthesis of tubulin were examined during development of the brine shrimp, Artemia. It was found, by Northern and dot-blot analyses, that Artemia possess constant amounts of one size class of mRNA each for alpha- and beta-tubulin during the first 24 hr of postgastrula development. Two-dimensional gel electrophoresis and fluorography, following the in vitro translation of developmentally staged poly(A)+ mRNA, yielded one alpha- and one beta-tubulin. Clearly, the isotubulin diversity seen on Coomassie blue-stained two-dimensional gels of Artemia tubulin is not generated by differential gene transcription during postgastrula growth, nor is development accompanied by synthesis of novel isotubulins resolvable by the methods employed. Characterization of polysomal poly(A)+ mRNA, and of proteins synthesized in vivo, indicated very little tubulin was synthesized in Artemia as they developed from gastrula to first instar larvae. The results suggest control of tubulin synthesis in Artemia by a mechanism that restricts binding of the message to ribosomes. Of general significance, it appears that a complex metazoan animal is able to undergo extensive growth with limited tubulin synthesis and in the absence of differential expression of tubulin genes. Moreover, the capacity of microtubules to assume changing and/or increased functions associated with cellular development is seemingly not dependent on the synthesis of new tubulin isoforms.