We report the complete sequence analysis of the entire complement of eight typical homeobox (Hox) genes (Lab, Pb, Dfd, Scr, Antp, Ubx, Abd-A, and Abd-B) and two other genes (Hox3 and Ftz) in a 324.6-kb region in the water flea Daphnia magna. In the cluster of D. magna Hox genes, we found one long interspersed nuclear element (LINE)/R2-NeSL between Ubx and Abd-A that was not present in Daphnia pulex Hox genes. In basal expression of Hox genes at different developmental stages, biothorax complex genes (Ubx, Abd-A, and Abd-B) and some antennapedia complex genes (Lab, Scr, Antp) were moderately expressed, but the Hox3 gene was barely expressed. Three homeobox genes (Antp, Ubx, Abd-A) were highly expressed at 6-7 days after release from the brood chamber and/or in the adult stage. The structural array and transcribed orientation of Dm-Hox genes were identical to those of the sister species D. pulex (∼340 kb), indicating that the Hox gene structure in daphnids is highly conserved. However, Dm- and Dp-Hox3, -deformed (Dfd), and -fushi tarazu (Ftz) genes varied from orthologous genes in pancrustacean species.
Keywords: Daphnia magna; LINE; single Hox cluster; water flea.
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