Promoter-Specific Expression and Imprint Status of Marsupial <em>IGF2</em>

<div><p>In mice and humans, <em>IGF2</em> has multiple promoters to maintain its complex tissue- and developmental stage-specific imprinting and expression. <em>IGF2</em> is also imprinted in marsupials, but little is known about its promoter region. In this study, three <em>IGF2</em> transcripts were isolated from placental and liver samples of the tammar wallaby, <em>Macropus eugenii</em>. Each transcript contained a unique 5' untranslated region, orthologous to the non-coding exons derived from promoters P1–P3 in the human and mouse <em>IGF2</em> locus. The expression of tammar <em>IGF2</em> was predominantly from the P2 promoter, similar to humans. Expression of <em>IGF2</em> was higher in pouch young than in the adult and imprinting was highly tissue and developmental-stage specific. Interestingly, while <em>IGF2</em> was expressed throughout the placenta, imprinting seemed to be restricted to the vascular, trilaminar region. In addition, <em>IGF2</em> was monoallelically expressed in the adult mammary gland while in the liver it switched from monoalleleic expression in the pouch young to biallelic in the adult. These data suggest a complex mode of <em>IGF2</em> regulation in marsupials as seen in eutherian mammals. The conservation of the <em>IGF2</em> promoters suggests they originated before the divergence of marsupials and eutherians, and have been selectively maintained for at least 160 million years.</p> </div>