Terwilliger, N.B.; Ryan, M.: Ontogeny of crustacean respiratory proteins

The respiratory proteins hemocyanin (Hc) and hemoglobin (Hb) share the function of oxygen transport, but the proteins, their active sites and the metal ions that bind the oxygen are totally different. Either Hc or Hb, but not both, is expressed in the hemolymph of many arthropod crustaceans. Hb is present in Branchiopoda, Ostracoda, Copepoda, rhizocephalan Cirripedia and one suborder of amphipodan Malacostraca while Hc has been described in Malacostraca. Recent work by several laboratories have provided new information on the gene structure, site of synthesis and expression of branchiopod Hbs and suggests they are excellent model organisms for studies of hypoxia sensors and oxygen response elements during development and adult stages. Studies on Hc ontogeny have shown functional changes in Nephrops and Homarus Hcs. The focus in our laboratory on the ontogeny of Hc in the Dungeness crab has demonstrated that both structure and function of Hc change from megalopa to adult crab. The Hc of an oceanic megalopa contains 4 subunits. A 5th subunit appears about the time of metamorphosis to 1st juvenile instar, and expression of a 6th subunit begins four or five molts later. The timing of onset of adult Hc can be altered by food availability and/or temperature. Experiments testing the potential role of magnesium concentration on regulation of Hc ontogeny point to non-specific stress as an additional factor in the timing of the development shift from juvenile to adult Hc. We have identified a Hc-like protein in nauplii and juvenile Artemia using mono- and polyclonal antibodies. This may indicate simultaneous expression of both Hb and Hc gene families in the same organism.