Promoter-Specific Expression and Imprint Status of Marsupial IGF2

Jessica M Stringer,Andrew J Pask,Shunsuke Suzuki,Geoff Shaw,Marilyn B Renfree,Tim Thomas

doi:10.1371/journal.pone.0041690

Jessica M Stringer, Andrew J Pask + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0041690

Copy DOI

Abstract

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.

Highlights

Insulin-like growth factor 2 (IGF2) is an important regulator of growth, metabolism and differentiation and was the first imprinted gene identified in eutherians and in marsupials [1,2]
This study investigates the evolution of the IGF2 regulatory regions in a marsupial, the tammar wallaby Macropus eugenii, and identified 3 promoters in the tammar IGF2 region
This study confirmed that marsupials have complex regulation of IGF2, and identified three evolutionarily conserved promoters, each with three distinct non-coding exons that showed tissue specific imprinting and expression in the tammar wallaby

Summary

Introduction

Insulin-like growth factor 2 (IGF2) is an important regulator of growth, metabolism and differentiation and was the first imprinted gene identified in eutherians and in marsupials [1,2]. Human IGF2 has five promoters (huP1 and P0–P3) and transcription start sites (TSS) each adjoining distinct 59 non-coding exons, while rodent IGF2 has only 4 (P0–P3) [3,4,5,6,7,8,9,10,11,12]. Preliminary investigations in the South American marsupial, Monodelphis domestica, detected a single product from total neonatal RNA using 59 RACE and identified only one 59 non-coding exon [13]. Human IGF2 is imprinted in the fetal liver and is paternally expressed from P1, P2 and P3 (orthologous to mouse P1–P3 respectively) with dominant expression from the P2 promoter in the majority of tissues tested [14]. Reciprocal activation patterns of P2 and huP1 before and after birth respectively have been correlated to developmental-specific methylation at the two promoters [16]

Methods

Results

Conclusion