SPATIAL EXPRESSION OF ALPHA-TUBULIN 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 trans cripts in particular of the Pl beta 1, Pl beta 2 and Pl alpha 2 forms. In order to assign specific functions to the various embryonic tubuli n genes, we have used wholemount in situ hybridization to determine sp atial patterns of expression of five different alpha and beta tubulin embryonic genes. The Pl beta 3 transcripts, as previously shown for Pl alpha 2, start to localize in a few founder cells from which the neur ogenic territory differentiates. The other four embryonic tubulin mRNA s (Pl beta 1/2 and Pl alpha 1/10), are localized in the ciliated band- and gut-territory. These territories originate by morphogenetic proce sses, which occur in late embryogenesis in the sea urchin and depend o n cellular interactions. In particular, the interactions between the o ral and aboral ectoderm specify the position of the ciliated band, whe reas 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 result s show in fact that specific tubulin isotypes, or a mix of them, are e xpressed 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 pe rformed on embryos treated with agents able to induce deciliation or e xogastrulation. Furthermore a putative correlation of Pl beta 2 with c ilium formation has been shown by the results obtained on deciliated e mbryos.