Expression of otd orthologs in the amphipod crustacean, Parhyale hawaiensis
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The arthropod head is a complex metameric structure. In insects, orthodenticle (otd) functions as a ‘head gap gene’ and plays a significant role in patterning and development of the anterior head ectoderm, the protocerebrum, and the ventral midline. In this study, we characterize the structure and developmental deployment of two otd paralogs in the amphipod crustacean, Parhyale hawaiensis. Photd1 is initially expressed at gastrulation through germband stages in a bilaterally symmetric, restricted region of the anterior head ectoderm and also in a single column of cells along the ventral midline. Late in embryogenesis, Photd1 is expressed within the developing anterior brain and the expression along the embryonic midline has become restricted to a stereotypic group of segmentally reiterated cells. The second ortholog Photd2, however, has a unique temporal–spatial expression pattern and is not detected until after the head lobes have been organized in the developing ectoderm of the germband during late germband stages. Anteriorly, Photd2 is coincident with the Photd1 head expression domain; however, Photd2 is not detected along the ventral midline during formation of the germband and only appears in the ventral midline late in embryonic development in a restricted group of cells distinct from those expressing Photd1. The early expression of Photd1 in the anterior head ectoderm is consistent with a role as a head gap gene. The more posterior expression of Photd1 is suggestive of a role in patterning the embryonic ventral midline. Photd2 expression appears too late to play a role in early head patterning but may contribute to latter patterning in restricted regions of both the head and the ventral midline. The comparative analysis of otd reveals the divergence of gene expression and gene function associated with duplication of this important developmental gene.
KeywordsCrustacean Amphipod Parhyale Orthodenticle Head development Brain development CNS Midline Neurogenesis
This work has been supported by the NSF (WEB, DBI-0310269), the NIH (WEB, NCRR-P20RR16467), the Boehringer Ingelheim Foundation (EAW), the Deutsche Forschungsgemeinschaft (EAW, DFG Wi 1797/2-2), the European Community’s Marie Curie Research Training Network ZOONET under contract MRTN-CT-2004-005624 (EAW). EAW also acknowledges support from the EMBO Young Investigator Programme. We thank Kevin Pang and Andreas Hejnol for Otx sequences, Frank Poulin and Nipam H. Patel for D. pulex otd information, and Casey Dunn for computation advice. We also thank the following for providing critical comments that have significantly improved this communication: Elaine Seaver, Amy Maxmen, Andreas Hejnol, Casey Dunn, Nipam H. Patel, and two anonymous reviewers.
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