Molecular indicators of hypoxia in the blue crab Callinectes sapidus

Abstract

Occurrence of hypoxia in estuarine waters is increasing, and recovery of impacted estu- aries is slow. Detection of early effects of hypoxia is needed for timely remedial action to be taken. Here we examine the use of hypoxia-responsive gene and protein expression profiles in the blue crab Callinectes sapidus as early indicators of impacts of hypoxia. We cloned 23 potential hypoxia- responsive genes, which were used to construct gene macroarrays. Crabs exposed to chronic hypoxia (2.5 ppm dissolved oxygen (DO)) for 15 d showed significant (p < 0.05) changes in gene expression of heat shock protein 70 (Hsp70), copper metallothionein (CuMt3), cytosolic MnSOD (cyt-MnSOD) and ribosomal proteins S15 and L23. In all cases except for CuMt3, gene expression decreased after 5 d exposure to hypoxia. Expression of Hsp70, CuMt3 and cyt-MnSOD also increased (p < 0.05) in nor- moxic crabs held for 15 d, suggesting confounding effects from confinement stress. Hemocyanin pro- tein concentrations changed significantly (p = 0.005) across the 15 d chronic hypoxia exposure. Hemocyanin in crabs exposed to 10 d intermittent hypoxia (2.5 to 8 ppm DO over a 24 h cycle) did not change, but cyt-MnSOD gene expression increased significantly (p = 0.037), whereas cytochrome c oxidase subunit 1 (ccox1) showed a 2.2-fold downregulation. Blue crabs collected from Pensacola Bay, Florida, showed significant (p < 0.006) downregulation of ccox1 and cyt-MnSOD gene ex- pression as well as hemocyanin protein levels at a diurnally hypoxic marsh site. Several hypoxia- responsive genes (elongation factor 2, cryptocyanin, hemocyanin) were also significantly elevated (p < 0.006) in intermolt versus premolt normoxic crabs. The identification of hypoxia-responsive genes and proteins in the blue crab is a promising first step towards the development of sensitive molecular tools for the detection of sublethal effects of hypoxia in estuarine-resident species.