Cititf1 and endoderm differentiation in Ciona intestinalis

Studies on the initial formation of the endoderm have lead to the identification, mostly in Xenopus, of numerous genes relevant for the formation of this tissue during early embryogenesis (reviewed by Date, Curr. Biol. 9 (1999) R812-R815 and by Yasuo and Lemaire, Curr. Biol. 9 (1999) 869-879). In ascidians, the most primitive chordates, endoderm differentiation is an autonomous process which is almost complete at 64 cells stage. Cititf1, a gene homologous to mammalian Titf1, is the first specific endodermal marker isolated from the ascidian Ciona intestinalis (Ristatore et al., Development 126 (1999) 5149-5159). Here we study the in vivo role of Cititf1 by using two different approaches: interference and ectopic expression. The results presented here show that interference with Cititf1 function seems to affect gastrulation movements, while ectopic expression of Cititf1 mRNA into the notochord alters differentiation of this tissue probably by recruiting notochord blastomeres to an endodermal fate. These data together with studies, still in progress in our laboratory, on the transcriptional regulation of Cititf1, strongly indicate that Cititf1 plays an important role in the process of endoderm formation in Ciona embryogenesis.