Expression and protein localisation of IGF2 in the marsupial placenta.
BACKGROUND
In eutherian mammals, genomic imprinting is critical for normal placentation and embryo survival. Insulin-like growth factor 2 (IGF2) is imprinted in the placenta of both eutherians and marsupials, but its function, or that of any imprinted gene, has not been investigated in any marsupial. This study examines the role of IGF2 in the yolk sac placenta of the tammar wallaby, Macropus eugenii.


RESULTS
IGF2 mRNA and protein were produced in the marsupial placenta. Both IGF2 receptors were present in the placenta, and presumably mediate IGF2 mitogenic actions. IGF2 mRNA levels were highest in the vascular region of the yolk sac placenta. IGF2 increased vascular endothelial growth factor expression in placental explant cultures, suggesting that IGF2 promotes vascularisation of the yolk sac.


CONCLUSIONS
This is the first demonstration of a physiological role for any imprinted gene in marsupial placentation. The conserved imprinting of IGF2 in this marsupial and in all eutherian species so far investigated, but not in monotremes, suggests that imprinting of this gene may have originated in the placenta of the therian ancestor.
Ager
Eleanor I
EI
Department of Zoology, The University of Melbourne, Melbourne, Victoria, 3010, Australia. eager@unimelb.edu.au
Pask
Andrew J
AJ
Shaw
Geoff
G
Renfree
Marilyn B
MB
D000199:Actins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D004622:Embryo, Mammalian / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018392:Genomic Imprinting; D007150:Immunohistochemistry; D007335:Insulin-Like Growth Factor II / Q000235:genetics* / Q000378:metabolism; D008394:Marsupialia / Q000235:genetics* / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D015017:Yolk Sac / Q000378:metabolism
D000199:Actins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D007335:Insulin-Like Growth Factor II