Coordinate and selective beta-tubulin gene expression associated with cilium formation in sea urchin embryos.

Abstract

beta-Tubulin mRNAs associated with cilium formation in Strongylocentrotus purpurpatus sea urchin embryos are expressed selectively from a multiple gene family. The accumulations of three beta-tubulin mRNAs (beta 1, beta 2, and beta 3) are temporally coordinated with ciliogenesis during blastula development and with the regeneration of cilia after their amputation. In contrast, another beta-tubulin mRNA, beta 4, is not induced in either case. The zinc-animalized embryo with its exaggerated blastula phenotype forms longer cilia through a protracted period of ciliogenesis, in which the beta-tubulin mRNAs, principally beta 1, accumulate to higher than normal levels. The rate of beta-tubulin transcription per nucleus in the animalized embryo is greater than that of the normal embryo and is not changed through deciliation, although the tubulin mRNAs accumulate to higher levels. However, deciliation raises the beta-tubulin transcription rate in the normal embryo to that in the animalized embryo. Thus, the induction of beta-tubulin mRNA by cilium amputation is regulated transcriptionally in the normal embryo, but post-transcriptionally in the zinc-animalized embryos. Moreover, the beta-tubulin genes that are expressed in association with cilium formation appear to be induced selectively within the framework of ectodermal cell-type specificity.