Characterization of a rainbow trout Mx gene

Area of Science:

• Molecular Biology
• Immunology
• Fish Genetics

Background:

• The Mx gene is known to play a role in the innate immune response of vertebrates.
• Previous identification of rainbow trout Mx was based on hybridization, lacking full-length sequence information.
• Understanding fish Mx genes is vital for aquaculture health and disease resistance.

Purpose of the Study:

• To obtain a full-length cDNA clone of the rainbow trout (Oncorhynchus mykiss) Mx gene.
• To characterize the rainbow trout Mx protein and its expression patterns.
• To investigate the presence of homologous Mx genes in other salmonid species.

Main Methods:

• Rapid Amplification of cDNA Ends (RACE) polymerase chain reaction (PCR) was used to amplify the full-length Mx gene from induced rainbow trout gonad cells (RTG-2).
• Sequence analysis was performed to determine the open reading frame, protein size, and identify conserved motifs.
• Southern blot analysis was conducted to detect homologous Mx genes in other fish species.
• Poly (I:C) treatment and Infectious Hematopoietic Necrosis Virus (IHNV) infection were used to study Mx gene expression.

Main Results:

• A 2.5 kb cDNA clone of the rainbow trout Mx gene was successfully obtained, encoding a 621 amino acid protein (70.6 kD) with a characteristic GTP-binding motif.
• Mx homologous genes were detected in chinook salmon, coho salmon, kokanee salmon, and brook trout.
• Poly (I:C) treatment induced two Mx transcripts in both rainbow trout (RTG-2) and chinook salmon (CHSE-214) cells.
• IHNV infection also stimulated Mx mRNA synthesis in rainbow trout.

Conclusions:

• The characterized rainbow trout Mx protein shares high homology with mammalian Mx proteins, suggesting conserved antiviral functions.
• The Mx gene is present in multiple salmonid species, indicating its importance in fish antiviral immunity.
• Mx gene induction by viral mimics and viral infection highlights its role in the innate immune response of rainbow trout.