Human Molecular Genetics Advance Access originally published online on August 14, 2009
Human Molecular Genetics 2009 18(22):4255-4267; doi:10.1093/hmg/ddp379
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The interval between Ins2 and Ascl2 is dispensable for imprinting centre function in the murine Beckwith–Wiedemann region
1 Department of Medical Genetics and Molecular Epigenetics Group, Life Sciences Institute, The University of British Columbia, Vancouver, BC, Canada, V6T 1Z3, 2 Dana-Farber Cancer Institute, Boston, MA 02115, USA, 3 Applied Molecular Oncology, Ontario Cancer Institute, Princess Margaret Hospital, Toronto, ON, Canada, M5G 2M9, 4 Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, M5G 2M9, 5 Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, ON, Canada, M5G 1X5 and 6 Department of Medical Genetics, University of Toronto, Toronto, ON, Canada, M5G 1X5
* To whom correspondence should be addressed. Tel: +1 6048225310; Fax: +1 6048225348; Email: louis.lefebvre{at}ubc.ca
Received June 20, 2009; Revised July 24, 2009; Accepted August 5, 2009
Imprinted genes are commonly clustered in domains across the mammalian genome, suggesting a degree of coregulation via long-range coordination of their monoallelic transcription. The distal end of mouse chromosome 7 (Chr 7) contains two clusters of imprinted genes within a 
1 Mb domain. This region is conserved on human 11p15.5 where it is implicated in the Beckwith–Wiedemann syndrome. In both species, imprinted regulation requires two critical cis-acting imprinting centres, carrying different germline epigenetic marks and mediating imprinted expression in the proximal and distal sub-domains. The clusters are separated by a region containing the gene for tyrosine hydroxylase (Th) as well as a high density of short repeats and retrotransposons in the mouse. We have used the Cre-loxP recombination system in vivo to engineer an interstitial deletion of this 280-kb intervening region previously proposed to participate in the imprinting mechanism or to act as a boundary between the two sub-domains. The deletion allele, Del7AI, is silent with respect to epigenetic marking at the two flanking imprinting centres. Reciprocal inheritance of Del7AI demonstrates that the deleted region, which represents more than a quarter of the previously defined imprinted domain, is associated with intrauterine growth restriction in maternal heterozygotes. In homozygotes, the deficiency behaves as a Th null allele and can be rescued pharmacologically by bypassing the metabolic requirement for TH in utero. Our results show that the deleted interval is not required for normal imprinting on distal Chr 7 and uncover a new imprinted growth phenotype.
Present address: Department of Pathology and Molecular Medicine, Queen's University, Kingston, ON, Canada, K7L 3N6.