Das et al.: Convergent and divergent evolution of genomic imprinting in the marsupial Monodelphis domestica. BMC Genomics 2012 13:394.
Abstract:
Background: Genomic imprinting is an epigenetic phenomenon resulting in parent-of-origin specific monoallelic
gene expression. It is postulated to have evolved in placental mammals to modulate intrauterine resource
allocation to the offspring. In this study, we determined the imprint status of metatherian orthologues of eutherian
imprinted genes.
Results: L3MBTL and HTR2A were shown to be imprinted in Monodelphis domestica (the gray short-tailed opossum).
MEST expressed a monoallelic and a biallelic transcript, as in eutherians. In contrast, IMPACT, COPG2, and PLAGL1
were not imprinted in the opossum. Differentially methylated regions (DMRs) involved in regulating imprinting in
eutherians were not found at any of the new imprinted loci in the opossum. Interestingly, a novel DMR was
identified in intron 11 of the imprinted IGF2R gene, but this was not conserved in eutherians. The promoter regions
of the imprinted genes in the opossum were enriched for the activating histone modification H3 Lysine
4 dimethylation.
Conclusions: The phenomenon of genomic imprinting is conserved in Therians, but the marked difference in the
number and location of imprinted genes and DMRs between metatherians and eutherians indicates that imprinting
is not fully conserved between the two Therian infra-classes. The identification of a novel DMR at a non-conserved
location as well as the first demonstration of histone modifications at imprinted loci in the opossum suggest that
genomic imprinting may have evolved in a common ancestor of these two Therian infra-classes with subsequent
divergence of regulatory mechanisms in the two lineages.
Keywords: Genomic imprinting, Marsupials, Eutherians