Abstract
The availability of the first marsupial genome sequence has allowed
us to characterize the immunome of the gray short-tailed opossum
(Monodelphis domestica). Here we report the identification of
key immune genes, including the highly divergent chemokines,
defensins, cathelicidins, and Natural Killer cell receptors. It
appears that the increase in complexity of the mammalian immune
system occurred prior to the divergence of the marsupial and
eutherian lineages ~180 million years ago. Genomes of ancestral
mammals most likely contained all of the key mammalian immune gene
families, with evolution on different continents, in the presence
of different pathogens leading to lineage specific expansions and
contractions, resulting in some minor differences in gene number
and composition between different mammalian lineages. Gene
expansion and extensive heterogeneity in opossum antimicrobial
peptide genes may have evolved as a consequence of the newborn
young needing to survive without an adaptive immune system in a
pathogen laden environment. Given the similarities in the genomic
architecture of the marsupial and eutherian immune systems, we
propose that marsupials are ideal model organisms for the study of
developmental immunology.
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