Freezing and anoxia stresses induce expression of metallothionein in the foot muscle and hepatopancreas of the marine gastropod Littorina littorea.

Differential screening of cDNA libraries constructed from the foot muscle of marine snails Littorina littorea revealed several cDNAs that are upregulated during anoxia or freezing exposures, environmental stresses that are naturally endured by this species. One full-length clone of 1196 nucleotides (GenBank accession number AY034179) hybridized with a 1200-nucleotide band on northern blots and encoded a 100-amino-acid protein that was identified as belonging to the metallothionein (MT) family. L. littorea MT shared 45% and 56% identity with the copper- and cadmium-binding MT isoforms, respectively, from another gastropod, Helix pomatia and 43-47% identity with marine bivalve MTs. The L. littorea sequence included the mollusc-specific C-terminal motif Cys-X-Cys-X(3)-Cys-Thr-Gly-X(3)-Cys-X-Cys-X(3)-Cys-X-Cys-Lys that identifies it as a family 2 (mollusc) MT. Northern blot analysis showed that L. littorea MT was upregulated in both foot muscle and hepatopancreas in response to both freezing and anoxia stresses; within 1 h of the beginning of the stress transcript levels rose 2.5- to sixfold of control levels, reaching maximal levels at 12 or 24 h. After 24 h recovery from either stress, transcript levels were reduced again in three cases but remained elevated in hepatopancreas from anoxia-treated snails. Upregulation of MT during environmental stress could serve one or more possible roles, including a function in antioxidant defense.