GENOMIC IMPRINTING AND THE DIFFERENTIAL ROLES OF PARENTAL GENOMES IN BRAIN-DEVELOPMENT

Certain genes are expressed either from the maternal or the paternal g enome as a result of genomic imprinting, a process that confers functi onal differences on parental genomes during mammalian development. In this study we focus on the cumulative effects of imprinted genes on br ain development by examining the fate of androgenetic (Ag: duplicated paternal genome) and parthenogenetic/gynogenetic (Pg/Gg: duplicated ma ternal genome) cells in chimeric embryos. Striking cell autonomous dif ferences in the phenotypic properties of the uniparental cells were ob served. Ag cells contributed substantially to the hypothalamic structu res and not the cortex. By contrast, Pg/Gg cells contributed substanti ally to the cortex, striatum and hippocampus but not to the hypothalam ic structures. Furthermore growth of the brain was enhanced by Pg/Gg a nd retarded by Ag cells. We propose that genomic imprinting may be res ponsible for a change in strategy controlling brain development in mam mals. In particular, genomic imprinting may have facilitated a rapid n on-linear expansion of the brain, especially the cortex, during develo pment over evolutionary time.