Abstract
The copper-based respiratory protein hemocyanin undergoes a developmental shift in subunit composition and function analogous to that seen in many hemoglobins. We studied hemocyanin gene expression in the Dungeness crab (Cancer magister) by Northern blot analysis. Animals were raised under controlled conditions, and total RNA was isolated from 13 developmental stages as well as from six tissue types in the adult animal. RNA was run on formaldehyde-agarose gels, blotted onto nylon membranes, and probed with 32P-labeled cDNA probes specific for C. magister adult hemocyanin. Results indicate that adult hemocyanin biosynthesis occurs in hepatopancreas tissue only. Analysis of developmental stages shows that expression of adult-type hemocyanin, as indicated by the appearance of hemocyanin subunit 6 mRNA, begins during the sixth juvenile instar.
Highlights
The developmental shift in subunit composition results in a new population of adult Hc molecules that have a higher affinity for oxygen than does juvenile Hc [8, 9]
Because several different tissues have been proposed as possible sites of Hc synthesis in arthropods [13], it could potentially be made in multiple locations within the crab
Because the CuA-binding site in arthropod Hc domain 2 is highly conserved in all crustacean and chelicerate Hc subunits far sequenced [19], we predicted that it would be a conserved feature in all six C. magister Hc subunits as well
Summary
The developmental shift in subunit composition results in a new population of adult Hc molecules that have a higher affinity for oxygen than does juvenile Hc [8, 9]. The Hc of C. magister is interesting because it changes in both subunit composition and function during development of the crab from megalopa and early juvenile instar stages to adult [6]. For the larger developmental stages, sixth instar and older, 100-mg samples of hepatopancreas tissue were dissected and prepared as described above for adult crabs.
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