Molecular characterization of TgHBox4, a Drosophila Abd-B homolog found inthe sea urchin Tripneustes gratilla

We have isolated and sequenced a cDNA clone that, as judged by the sequence of the homeobox region, encodes a sea urchin homolog of the homeobox conta ining the gene Abdominal-B of Drosophila. The total length of the cDNA is 3 634 nucleotides and includes an open reading frame, which encodes a protein that is 32,321 Da. The N-terminal region of the homeodomain includes conse nsus sequences found in some of TgHBox4's Abominal-B relatives. A genomic c lone representing the 5' part of the message was also isolated. This clone and a previously isolated clone were found to represent the full-length cDN A sequence. We have also raised antibodies against a bacterially expressed portion of the TgHBox4 protein and used them to determine the location of T gHBox3 proteins during development. The protein displays ubiquitous express ion early in development but becomes more restricted, to posterior regions, late in embryogenesis. Thus, in contrast to its Abd-B homologs in bilatera l metazoans, TgHBox4 is probably not involved in pattern formation but may have a posterior-defining role late in embryogenesis.