Ciliary band gene expression patterns in the embryo and trochophore larva of an indirectly developing polychaete

The trochophore larvae of indirectly developing spiralians have ciliary bands with motor and feeding functions. The preoral prototroch ciliary band is the first differentiating organ in annelid and mollusk embryos. Here we report the expression of several ciliary band markers during embryogenesis and early larval stages of the indirectly developing polychaete Hydroides elegans. Genes with similarity to caveolin, β-tubulin, α-tubulin, and tektin are expressed in the eight primary prototroch precursors, 1q221 and 1q212. Blastomeres 1q221 and 1q212 locate at the same equatorial latitude after the complementary asymmetric division of their 1q22 and 1q21 precursors. In addition, caveolin and α-tubulin are expressed in the metatroch and adoral ciliary zone. Caveolin is expressed in foregut ciliated cells, and α-tubulin is expressed in apical tuft ciliated cells. The expression of a β-thymosin homolog is restricted to 1q122 and 1q121 blastomeres, which locate just above and in close association with the eight primary prototroch cells 1q221 and 1q212. In addition, the β-thymosin homolog has a transient expression in the hindgut and apical zone. The expression of all these genes provides a landmark for the early specification of ciliary bands and other ciliated organs.