In silico identification of opossum cytokine genes suggests the complexity of the marsupial immune system rivals that of eutherian mammals.
BACKGROUND
Cytokines are small proteins that regulate immunity in vertebrate species. Marsupial and eutherian mammals last shared a common ancestor more than 180 million years ago, so it is not surprising that attempts to isolate many key marsupial cytokines using traditional laboratory techniques have been unsuccessful. This paucity of molecular data has led some authors to suggest that the marsupial immune system is 'primitive' and not on par with the sophisticated immune system of eutherian (placental) mammals.


RESULTS
The sequencing of the first marsupial genome has allowed us to identify highly divergent immune genes. We used gene prediction methods that incorporate the identification of gene location using BLAST, SYNTENY + BLAST and HMMER to identify 23 key marsupial immune genes, including IFN-gamma, IL-2, IL-4, IL-6, IL-12 and IL-13, in the genome of the grey short-tailed opossum (Monodelphis domestica). Many of these genes were not predicted in the publicly available automated annotations.


CONCLUSIONS
The power of this approach was demonstrated by the identification of orthologous cytokines between marsupials and eutherians that share only 30% identity at the amino acid level. Furthermore, the presence of key immunological genes suggests that marsupials do indeed possess a sophisticated immune system, whose function may parallel that of eutherian mammals.
Wong
Emily Sw
ES
Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.
Young
Lauren J
LJ
School of Chemical and Biomedical Sciences, Central Queensland University, Rockhampton, Queensland, Australia.
Papenfuss
Anthony T
AT
Division of Bioinformatics, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia.
Belov
Katherine
K
Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.