Investigation of Elements Sufficient To Imprint the Mouse Air Promoter

Abstract

Imprinted maternal-allele-specific expression of the mouse insulin-like growth-factor type 2 receptor (Igf2r) gene depends on a 3.7-kb element named region 2, located in the second intron of the gene. Region 2 carries a maternal-allele-specific methylation imprint and contains an imprinted CpG island promoter (Air) that expresses a noncoding antisense RNA from the paternal inherited allele only. Here, we use transgenes to test the minimal requirements for imprinting of Air and to test if the action of region 2 is restricted to Igf2r. Transgenes up to 9 kb with Air as a single promoter are expressed but not imprinted. When coupled to the Igf2rCpG island promoter on a 44-kb transgene, Air was imprinted in one of three lines. However, Air on a 4.6-kb fragment is also imprinted in 2 of 14 lines when inserted in an intron of an adenine phosphoribosyltransferase (Aprt) transgene, and in one line, the imprinted methylation and expression ofAir have been transferred onto the AprtCpG island promoter. These data suggest that a dual CpG island promoter setting may facilitate Air imprinting as a short transgene and also show that Air can transfer imprinting onto other genes. However, for reliable Air imprinting, elements are necessary that are located outside a 44-kb region spanning the Air-Igf2r promoters.

ACKNOWLEDGMENTS

We thank Rene Bobeldijk, Karin van Veen, Karin van het Wout, and Paul Krimpenfort for generating the transgenic mice; Loes Rijswijk, Fina van der Ahé, Tania Maidment, and Nel Bosnie for care of the mice; Harry Vrieling, Leiden University, forAprt-deficient mice and an Aprt genomic clone; Mitchell Turker, University of Oregon, for anAprt genomic clone; Anton Berns and all members of H5 for discussion; and Hein te Riele and Piet Borst for reading the manuscript.

This research was supported by the Dutch Cancer Society (KWF).