Wallaby serum amyloid A protein: cDNA cloning, sequence and evolutionary analysis

Area of Science:

• Mammalian genetics
• Evolutionary biology
• Comparative genomics

Background:

• Serum amyloid A (SAA) proteins are key acute phase reactants involved in inflammation.
• Understanding SAA evolution across diverse mammalian groups can illuminate gene duplication events and functional divergence.
• Marsupials, like the Tammar wallaby, represent a distinct evolutionary lineage crucial for comparative studies.

Purpose of the Study:

• To isolate and characterize a serum amyloid A (SAA) gene from the Tammar wallaby.
• To investigate the evolutionary placement of the wallaby SAA within the broader mammalian SAA superfamily.
• To infer the timing of gene duplication events in the evolution of acute phase SAA genes.

Main Methods:

• Construction and screening of a Tammar wallaby cDNA library.
• Bioinformatic analysis of the isolated SAA clone, including prediction of amino acid sequence and homology assessment.
• Phylogenetic analysis using both protein and nucleotide sequences to determine evolutionary relationships.

Main Results:

• Isolation of a Tammar wallaby SAA cDNA clone encoding a pre-protein of 127 amino acids (18 residue leader, 109 mature protein).
• The wallaby SAA sequence exhibits significant homology to other mammalian SAAs.
• Evolutionary analysis places the wallaby SAA within the cluster of acute phase SAAs, indicating ancient origins.

Conclusions:

• The presence of an acute phase SAA in the Tammar wallaby demonstrates that key duplications within the SAA gene family predated the divergence of marsupial and placental mammals.
• This finding supports the concept of concerted evolution within the SAA superfamily.
• The study provides a crucial data point for understanding the early evolution of mammalian immune response genes.