School of BioSciences - Research Publications

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Type: Journal Article × Start date: 2012 × End date: 2012 × Author: Renfree, Marilyn × Author: Shaw, Geoffrey × Author: STRINGER, JESSICA ×

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    Promoter-Specific Expression and Imprint Status of Marsupial IGF2
    Stringer, JM ; Suzuki, S ; Pask, AJ ; Shaw, G ; Renfree, MB ; Thomas, T (PUBLIC LIBRARY SCIENCE, 2012-07-25)
    In mice and humans, IGF2 has multiple promoters to maintain its complex tissue- and developmental stage-specific imprinting and expression. IGF2 is also imprinted in marsupials, but little is known about its promoter region. In this study, three IGF2 transcripts were isolated from placental and liver samples of the tammar wallaby, Macropus eugenii. Each transcript contained a unique 5' untranslated region, orthologous to the non-coding exons derived from promoters P1-P3 in the human and mouse IGF2 locus. The expression of tammar IGF2 was predominantly from the P2 promoter, similar to humans. Expression of IGF2 was higher in pouch young than in the adult and imprinting was highly tissue and developmental-stage specific. Interestingly, while IGF2 was expressed throughout the placenta, imprinting seemed to be restricted to the vascular, trilaminar region. In addition, IGF2 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 IGF2 regulation in marsupials as seen in eutherian mammals. The conservation of the IGF2 promoters suggests they originated before the divergence of marsupials and eutherians, and have been selectively maintained for at least 160 million years.
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    Selected imprinting of INS in the marsupial
    Stringer, JM ; Suzuki, S ; Pask, AJ ; Shaw, G ; Renfree, MB (BMC, 2012-08-28)
    BACKGROUND: In marsupials, growth and development of the young occur postnatally, regulated by milk that changes in composition throughout the long lactation. To initiate lactation in mammals, there is an absolute requirement for insulin (INS), a gene known to be imprinted in the placenta. We therefore examined whether INS is imprinted in the mammary gland of the marsupial tammar wallaby (Macropus eugenii) and compared its expression with that of insulin-like growth factor 2 (IGF2). RESULTS: INS was expressed in the mammary gland and significantly increased, while IGF2 decreased, during established milk production. Insulin and IGF2 were both detected in the mammary gland macrophage cells during early lactation and in the alveolar cells later in lactation. Surprisingly, INS, which was thought only to be imprinted in the therian yolk sac, was imprinted and paternally expressed in the liver of the developing young, monoallelically expressed in the tammar mammary gland and biallelic in the stomach and intestine. The INS transcription start site used in the liver and mammary gland was differentially methylated. CONCLUSIONS: This is the first study to identify tissue-specific INS imprinting outside the yolk sac. These data suggest that there may be an advantage of selective monoallelic expression in the mammary gland and that this may influence the growth of the postnatal young. These results are not consistent with the parental conflict hypothesis, but instead provide support for the maternal-infant co-adaptation hypothesis. Thus, imprinting in the mammary gland maybe as critical for postnatal growth and development in mammals as genomic imprinting in the placenta is prenatally.