Isolation of SFRS3 gene and its differential expression during metamorphosis involving eye migration of Japanese flounder Paralichthys olivaceus

Both eyes of flatfishes are located on one side of the body due to asymmetrical eye migration. The molecular mechanisms underlying such asymmetry is poorly understood. As an initial step, we have adopted suppression subtractive hybridization for the identification of upregulated genes during metamorphosis involving eye migration in Japanese flounder, Paralichthys olicaceus. One of the upregulated genes was identified as the splicing factor arginine/serine rich-3 (SFRS3). Sequence analysis of SFRS3 revealed that it encodes a protein of 168 amino acids containing the typical eukaryotic RNA recognition motif (RRM) and an arginine/serine-rich region. The overall amino acid sequences of the Japanese flounder SFRS3 was highly conserved with that of other organisms. The expression of flounder SFRS3 gene increased sharply from the beginning of metamorphosis and reached a high level of expression at stage H of metamorphosis 43 days after hatching. The SFRS3 gene upregulation was mainly limited to the head region, particularly in the rapidly proliferative tissues, the lateral ethmoid and "skin thickness" on blind side, which are thought as two proliferative tissues to push the eye movement. In spite of the upregulated expression of SFRS3 during metamorphosis, its role in metamorphosis involving eye migration requires further studies.