H19 IS IMPRINTED IN THE CHOROID-PLEXUS AND LEPTOMENINGES OF THE MOUSEFETUS

It has been proposed that either the Igf-2 gene or the H19 gene - but not both - can be expressed from a given chromosome. Igf-2 is known to be biallelically expressed in the choroid plexus and leptomeninges, h owever, raising the question of whether H19 is down-regulated or absen t there. We found by in situ hybridization that H19 is indeed expresse d in the choroid plexus and leptomeninges of the developing mouse foet us. Comparison with the expression pattern of Igf-2 showed that the ge nes are coexpressed in all areas, with the exception of the choroid pl exus epithelium. To evaluate whether H19 is also biallelically express ed in these tissues, we microdissected embryos from interspecific cros ses and performed RNAse protection analysis on the isolated RNA. This revealed that H19 maintains its imprint in the choroid plexus/leptomen inges, being transcribed from the maternal allele at a level comparabl e to that in normal liver. We discuss the significance of these result s for current models of Igf-2 and H19 imprinting.