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. 2007 Sep 6:7:157.
doi: 10.1186/1471-2148-7-157.

The evolution of imprinting: chromosomal mapping of orthologues of mammalian imprinted domains in monotreme and marsupial mammals

Carol A Edwards  1 , Willem Rens, Oliver Clarke, Andrew J Mungall, Timothy Hore, Jennifer A Marshall Graves, Ian Dunham, Anne C Ferguson-Smith, Malcolm A Ferguson-Smith
Affiliations

The evolution of imprinting: chromosomal mapping of orthologues of mammalian imprinted domains in monotreme and marsupial mammals

Carol A Edwards et al. BMC Evol Biol. .

Abstract

Background: The evolution of genomic imprinting, the parental-origin specific expression of genes, is the subject of much debate. There are several theories to account for how the mechanism evolved including the hypothesis that it was driven by the evolution of X-inactivation, or that it arose from an ancestrally imprinted chromosome.

Results: Here we demonstrate that mammalian orthologues of imprinted genes are dispersed amongst autosomes in both monotreme and marsupial karyotypes.

Conclusion: These data, along with the similar distribution seen in birds, suggest that imprinted genes were not located on an ancestrally imprinted chromosome or associated with a sex chromosome. Our results suggest imprinting evolution was a stepwise, adaptive process, with each gene/cluster independently becoming imprinted as the need arose.

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Figures

Figure 1
Figure 1
FISH mapping on platypus metaphase chromosomes of BACs containing orthologues of imprinted genes. (A) DIO3, (B) DLK1, (C) IGF2R, (D) SLC38A4, (E) IGF2, (F) GRB10, (G) GNAS (and platypus 8 paint in green) and (H) UBE3A. Scale bar is 10 μm.
Figure 2
Figure 2
FISH mapping on tammar metaphase chromosomes of BACs containing orthologues of imprinted genes. (A) DIO3 (green) and DLK1 (red), (B) GNAS, (C) IGF2, (D) CD81, (E) IGF2R, (F) GRB10, (G) MRPL23, and (H) SLC38A4 (red) with chromosome 3 in green. Scale bar is 10 μm.
Figure 3
Figure 3
Location of orthologues of mammalian imprinted genes on the karyotypes of platypus (A) and tammar wallaby (B) in red. Gene names in black are those previously mapped genes from other studies, (reviewed in [25, 44]). The position of the orthologous genes in human are shown on the left.
See this image and copyright information in PMC

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