PARENTAL IMPRINTING OF RAT INSULIN-LIKE GROWTH-FACTOR-II GENE PROMOTERS IS COORDINATELY REGULATED

The insulin-like growth factor II (IGF-II) gene is parentally imprinte d in the mouse and human species. By following the inheritance of natu ral polymorphisms of IGF-II mRNA, we demonstrated that the tissue-spec ific parental imprinting of the IGF-II gene is conserved in the rat. T he expression of the paternal IGF-II allele exceeded by more than 3 or ders of magnitude that of the maternal allele in livers of 3-day-old W istar x Fisher interstrain rat crosses. In contrast, the two alleles w ere both expressed in the rat central nervous system, which is also th e only district of the organism where this gene is active in adult rod ents. We also analyzed the allelic usage of the three IGF-II promoters , which generate alternatively spliced transcripts, and showed that pa rental imprinting of all transcription starts sites is coordinately re gulated since P1, P2, and P3 are all repressed on the maternal allele in neonatal rat liver, and all of them are activated on both alleles i n the choroid plexus of the central nervous system. RNase protection a ssays demonstrated that the activity ratio of the three IGF-II promote rs can be different in tissues that show the same imprinting mode.