Identification of eight homeobox-containing transcripts expressed during larval development and at metamorphosis in the gastropod mollusc Haliotis rufescens.

The red abalone, Haliotis rufescens, is an especially tractable experimental model for studying molecular and cellular changes that occur at metamorphosis, because synchronous settlement and metamorphosis of the planktonic larvae can be induced in the laboratory. Using reverse transcription-polymerase chain reaction with degenerate primers based on the Drosophila Antennapedia-class homeodomain consensus sequence, eight differentially transcribed homeoboxes were identified from Haliotis larvae prior to and during metamorphosis. These are the first homeoboxes isolated from the phylum Molusca. Five of the partial homeobox sequences presented appear to represent Antennapedia-like genes of the putative Haliotis HOM-C/Hox complex; the remainder show similarity to homeoboxes of divergent classes. Analysis of RNA from a range of early developmental, larval, and metamorphic stages revealed that Antennapedia-like homeobox transcripts are present in trochophore and veliger larvae and in settled individuals undergoing metamorphosis, but not in the egg or early embryo.