Molecular characterization of a novel type II keratin gene (sseKer3) in the Senegalese sole (Solea senegalensis): Differential expression of keratin genes by salinity

Abstract

Keratins make up the largest subgroup of intermediate filaments and, in chordates, represent the most abundant proteins in epithelial cells. Senegalese sole (Solea senegalensis) is a commercially important flatfish in which only two type I keratin genes, sseKer1 and sseKer2, have been described. We obtained the entire cDNAs encoding for a novel type II keratin, referred to as sseKer3. Main features and sequence identities with other fish and mammalian type II keratins are described. Expression profiles during larval development and in juvenile tissues were analyzed using a real-time PCR approach. In juvenile fish, sseKer3 was strongly expressed in gills, intestine, skin and stomach. During metamorphosis climax a drop in sseKer3 expression was observed. Transcriptional regulation of sseKer3 by thyroid hormones (THs) was also evaluated. Larvae exposed to the goitrogen thiourea (TU) exhibited higher mRNA levels than untreated control. Moreover, adding exogenous T4 hormone to TU-treated larvae restored or even reduced the sseKer3 transcript levels with respect to the untreated control. The possible role of keratins in osmotic stress response was evaluated in juvenile gills exposed to three different water salinities (15, 37 and 60psu). Whereas no significant changes in sseKer2 expression were detected; sseKer1 was early (12h) up-regulated at hypo-osmotic conditions and sseKer3 was down-regulated both at low and high salinity after 24h and 48h. Their possible role is discussed.