Regulation of metallothionein genes in the American oyster (Crassostrea virginica): ontogeny and differential expression in response to different stressors.
Metallothioneins (MTs) are typically low molecular weight (6-7 kDa), metal-binding proteins with characteristic repeating cysteine motifs (Cys-X-Cys or Cys-Xn-Cys) and a prolate ellipsoid shape containing single alpha- and beta-domains. While functionally diverse, they play important roles in metals homeostasis, detoxification and the stress response. The present study, combined with previous observations (e.g., Jenny et al., Eur. J. Biochem. 2005; 271:1702-1712) defines an unprecedented diversity of MT primary structure and domain organization in the American oyster, Crassostrea virginica. Two novel molluscan MT families are described. One of these (CvMT-III) is characterized by the presence of two beta-domains and the absence of alpha-domains. This family exhibits constitutive expression during larval development and is the dominant CvMT isoform expressed in larvae. CvMT-III displays low basal levels of expression in adult tissues and only moderate responsiveness to metal challenges in both larvae and adults. A second novel MT isoform (CvMT-IV) was isolated from hemocytes by subtractive hybridization techniques following a 4-hour immune challenge with heat-killed bacteria (Vibrio, Bacillus, Micrococcus spp. mixture). Based on conservation of the cysteine motifs, this isoform appears to be a sub-family related to the molluscan alphabeta-domain MTs. A series of amino acid substitutions has resulted in four additional cysteines which give rise to a Cys-Cys motif and three Cys-Cys-Cys motifs. Northern blot analyses demonstrate that CvMT-IV is down-regulated upon sterile wounding and immune challenge, displays moderate expression in larvae and adults and differential gene induction in response to metals exposure.
Jenny
Matthew J
MJ
Hollings Marine Laboratory, Charleston, SC, USA. mjenny@whoi.edu
Warr
Gregory W
GW
Ringwood
Amy H
AH
Baltzegar
David A
DA
Chapman
Robert W
RW
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002104:Cadmium / Q000494:pharmacology; D003001:Cloning, Molecular; D049896:Crassostrea / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D007814:Larva / Q000187:drug effects / Q000378:metabolism; D008668:Metallothionein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015533:Transcriptional Activation; D015032:Zinc / Q000494:pharmacology
D020033:Protein Isoforms; D002104:Cadmium; D008668:Metallothionein; D015032:Zinc