Epipodite and fat cells as sites of hemoglobin synthesis in the branchiopod crustacean Daphnia magna

In contrast to the malacostracan crustaceans that use hemocyanin as the oxy gen carrier, a number of branchiopod crustaceans, such as the water flea Da phnia magna, utilize hemoglobin (Hb) as the respiratory protein. By means o f in situ hybridization (ISH) techniques with subsequent signal amplificati on using catalyzed reporter deposition, sites of Hb synthesis were localize d in Daphnia magna. Based on a previously reported Hb-cDNA sequence, a spec ific ISH probe was designed and hybridized with the Hb-mRNA in histological sections of adult D. magna. The detection of Hb-mRNA was tissue specific a nd revealed that Hb is synthesized in fat cells, which play a role in fat a nd glycogen metabolism, and in epithelial cells of the epipodites, which ar e involved in osmoregulation. Sites of Hb synthesis have been identified in several invertebrate phyla, including Annelida and Nematoda. However, this is the first example in the class Crustacea, and only the second in the ph ylum Arthropoda.