Novel endostyle-specific genes in the ascidian Ciona intestinalis

The endostyle is a pharyngeal organ of Urochordata, Cephalochordata and larval Cyclostomata. This organ secretes mucus-proteins for internal filter feeding, a feeding system that must have developed in the common ancestor of these subphyla. Therefore, the endostyle is a key structure to understanding the origin and evolution of chordates. A previous study of the overall gene expression in Ciona intestinalis young adults yielded several candidates for ascidian endostyle-specific genes. In the present study, we determined in detail the expression profiles of six novel endostyle-specific genes. Ci-VWFL1 and Ci-VWFL2 encode related proteins similar to vertebrate von Willebrand factor, and were continuously expressed in zones 4 and 2 of the developing endostyle, respectively. The expression of Ci-Ends8 was observed in the entire region of zone 6 in young adults; however, the expression of this gene was restricted to the dorsal- and ventral-regions of zone 6 in the adult endostyle. The expression of Ci-Ends9 and Ci-Ends10 was observed in zones 6 and 4 in young adults, respectively, and was downregulated in the adult endostyle. Ci-Ends 11 showed an expression pattern similar to that of Ciona TTF-1, which encodes a thyroid-related transcription factor. The predicted amino acid sequence of Ci-Ends10 showed similarity to Trip230, and that of Ci-Ends11 resembled Ptp4E. These molecules might be useful for further analysis of the development, function and evolution of the endostyle.