Spatial expression of alpha and beta tubulin genes in the late embryogenesis of the sea urchin Paracentrotus lividus.

In Paracentrotus lividus sea urchin embryos, at blastula stage, there is an abrupt increase in the abundance of alpha and beta tubulin transcripts in particular of the PI beta 1, PI beta 2 and PI alpha 2 forms. In order to assign specific functions to the various embryonic tubulin genes, we have used whole-mount in situ hybridization to determine spatial patterns of expression of five different alpha and beta tubulin embryonic genes. The PI beta 3 transcripts, as previously shown for PI alpha 2, start to localize in a few founder cells from which the neurogenic territory differentiates. The other four embryonic tubulin mRNAs (PI beta 1/2 and PI alpha 1/10), are localized in the ciliated band- and gut-territory. These territories originate by morphogenetic processes, which occur in late embryogenesis in the sea urchin and depend on cellular interactions. In particular, the interactions between the oral and aboral ectoderm specify the position of the ciliated band, whereas the invagination of the vegetal plate forms the gut territory. We suppose that the increase in alpha and beta tubulin transcripts could be functionally related to these two morphogenetic events. Our results show in fact that specific tubulin isotypes, or a mix of them, are expressed in and mark the ciliated band and the neighboring oral/aboral ectoderm cells of the ciliated band, in addition to the cells of the gut territory. The same localization of all these tubulin transcripts has been confirmed by whole-mount in situ hybridization experiments performed on embryos treated with agents able to induce deciliation or exogastrulation. Furthermore a putative correlation of PI beta 2 with cilium formation has been shown by the results obtained on deciliated embryos.