Duplication of calsequestrin genes in teleosts: Molecular characterization in the Senegalese sole (Solea senegalensis)

Calsequestrin is a moderate-affinity, high-capacity Ca2+ binding protein in the sarcoplasmic reticulum of skeletal and cardiac muscle that seems to act as an intralumenal Ca2+ buffer. Two different isoforms have been described in mammals, the skeletal and cardiac isoforms, encoded by CASQ1 and CASQ2 genes, respectively. In this study, we present molecular phylogenetic evidence of a gene duplication event of both calsequestrin genes in teleosts, referred to as casq1a/casq1b and casq2a/casq2b. We obtained the entire cDNAs encoding the four genes in the Senegalese sole (Solea senegalensis Kaup). Main features and sequence identities with other fish and mammalian calsequestrins are described. Expression profiles during larval development and in juvenile tissues were analyzed using a real-time PCR approach. In juvenile fish, casq1a and casq1b were highly expressed in skeletal muscle, whereas the highest casq2a and casq2b transcript levels were detected in heart and brain, respectively. During metamorphosis, casq2a and casq1b expression remained unchanged. In contrast, casq1a and casq2b mRNAs exhibited a continuous increase from the beginning of metamorphosis until post-metamorphosis. Transcriptional regulation of casq1 and casq2 genes by thyroid hormones (THs) was also evaluated. Larvae exposed to the goitrogen thiourea (TU) exhibited higher casq1a mRNA levels than untreated control, whereas expression of the remaining genes did not vary significantly. Moreover, addition of exogenous T4 hormone to TU-treated larvae increased the casq1a steady-state levels with respect to the untreated control at metamorphosis climax. Comprehensively, these results demonstrate the existence of four calsequestrin genes in teleosts differentially regulated by THs.