International Mammalian Genome Society

17th International Mouse Genome Conference

9-12 November 2003, Braunschweig, Germany


POSTER 72 - STRUCTURAL AND FUNCTIONAL COMPARISONS BETWEEN THE IMPRINTED MASH2-IGF2-H19 REGION ON MOUSE CHROMOSOME 7 AND THE ORTHOLOGOUS REGION ON CHICKEN CHROMOSOME 5

Yokomine T
1) National Institute of Genetics, 2) Graduated University for Advanced Studies

Co-Authors: 1) Sirohzu H, 1,4) Purbowasito W, 3) Toyoda A, 3,4) Kato R, 1) Suda C, 5) Hori T, 6) Tsudzuki M, 7) Matsuda Y, 8) Mizuno S, 3) Hattori M, 9) Mukai T, 3,10) Sakaki Y, 1,2) Sasaki H
Institutions: 1) National Institute of Genetics, 2) Graduated University for Advanced Studies, 3) RIKEN, 4) Kyushu University, 5) Kinki University, 6) Hiroshima University, 7) Hokkaido University, 8) Nihon University, 9) Saga Medical School, 10) The University of Tokyo

Previous studies revealed that IGF2 and MPR/IGF2R are imprinted in eutherian mammals but not in birds. IGF2 lies in a large imprinted cluster in mice and humans, and its imprinting is regulated by long-range mechanisms. As a step to understand how the imprinted cluster evolved and how it is regulated, we determined and compared a 582-kb mouse sequence containing Mash2, Igf2 and H19 and a 490-kb chicken sequence of the orthologouse region. We found that most of the genes were conserved between the two species, maintaining the same transcriptional polarities and exon-intron structures. However, H19, an imprinted gene adjacent to Igf2, was missing in chicken. Chicken CASH4 and INS, the orthologuse of imprinted mouse genes Mash2 and Ins2, showed biallelic expression, further supporting the notion that imprinting evolved after the divergence of mammals and birds. Furthermore, mice, but not chickens, contained a unique 210-kb region that consisted exclusively of tandem repeats and retroelements. This region, located between Th and Ins2, may assume a heterochromatin-like structure and could play a role in imprinting. Most, if not all, of the elements involved in imprinting did not exist in chicken. Our findings show that the imprinted genes were clustered before the emergence of imprinting and that many imprinting elements appeared after the divergence of mammals and birds.


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