A Hox class 3 orthologue from the spider Cupiennius salei is expressed in a Hox-gene-like fashion.
The class 3 Hox gene orthologue in insects, zerknüllt (zen), is not expressed along the anterior-posterior axis, but only in extra-embryonic tissues, suggesting that it has lost its function as a normal Hox gene. To analyse whether this loss of Hox gene function has already occurred in a basal arthropod lineage, we have isolated a Hox3 orthologue from the spider Cupiennius salei. In contrast to the insect zen sequences, which have a highly diverged homeobox, the spider Hox3 gene orthologue, Cs-Hox3, shows a high sequence similarity to the class 3 Hox genes of other phyla, including chordates. In situ hybridization in early embryos shows that it is expressed in a continuous region covering the pedipalp segment and the four leg-bearing segments. This expression pattern suggests a Hox-gene-like function for Cs-Hox3. On the other hand, the expression pattern does not strictly follow the colinearity rule, as it overlaps fully with the expression domain of the class 1 orthologue of the spider, Cs-lab. Still, our data suggest that the ancestor of the arthropods must have had a class 3 Hox gene with a function in anterior-posterior axis specification and that this function has been lost in the lineage leading to the insects.
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Zoologisches Institut der Universität München, Luisenstrasse 14, D-80333 München, Germany.
Tautz
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013112:Spiders / Q000196:embryology* / Q000235:genetics*
D017931:DNA Primers; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D012097:Repressor Proteins; C085607:Zen protein, Drosophila