Regulation Mechanism of Imprinted Genes: Pegs and Megs

Fumitoshi Ishino
Gene Research Center; Tokyo Institute of Technology

Coordinated expression of two kinds of imprinted genes, paternally expressed genes (Pegs) and maternally expressed genes (Megs) is essential for normal mammalian development, growth and behavior. In parthenogenetic embryos that have two maternal genomes, Peg genes are not expressed. On the other hand, there are no expression of Meg genes in androgenetic embryos that have two paternal genomes. Using these embryos, we have screened Pegs and Megs systematically by a subtraction hybridization method and isolated 13 imprinted genes on eight different imprinted regions. These Pegs and Megs are very useful tools for expression analyses of imprinted genes in several reconstituted embryos or cell lines at special stages to elucidate mechanisms of genomic imprinting. We have previously reported analysis of ng/fg oocytes that have one nucleus from a non-growing oocyte (ng) and the other from a fully grown oocyte (fg). In the ng/fg embryos, almost all Peg genes were shown to be expressed and Meg genes were not from ng genome except some genes in Igf2/H19 region on distal chromosome 7. These results indicated that maternal imprint that occurred during maturation process of oocyte regulated both Pegs and Megs; Pegs to be repressed and Megs to be induced. We will discuss about regulation mechanism of imprinted genes from analysis of several new reconstituted embryos.