Table 3.

Summary of expression, replication timing, and nuclear localization status of the Igf2-H19 locus in different cell types

The expression status is indicated with a male or female symbol if the gene is expressed; symbols between brackets indicate the potential of these genes to be expressed in differentiated ES cells. The localization of the paternal Igf2-H19 loci are shown as horizontal box plots with the scale bar representing the distance in micrometers to the nuclear membrane. The localization of the paternal allele is colored in black, and the localization of the maternal allele is in white. The localization of alleles for which no distinction could be made is colored in gray. Wild-type fetal liver cells express H19 from the maternal allele and Igf2 from the paternal allele. The locus is replicated asynchronously in these cells and RNA FISH analysis shows that the two parental loci are located in distinct places in the nucleus. In mutant ΔH19/+ fetal liver cells the Igf2-H19 locus is replicated synchronously and Igf2 is expressed from both parental alleles. RNA and DNA FISH analysis comparing wild-type and mutant fetal liver cells shows that the mutated locus is shifted toward the periphery of the nucleus, indicating that the paternal allele is located more in the periphery of the nucleus when compared to the maternal allele. Wild-type and parthenogenetic ES cells do not express H19 and Igf2. In wild-type ES cells the maternal allele replicates first in S phase and DNA FISH analysis shows that the parental loci are located in a relatively broad area of the nucleus. However, in parthenogenetic ES cells in which the locus is replicated synchronously localization of the two maternally derived loci is more confined and shifted toward the periphery, indicating that the maternal locus is located more in the periphery compared to the paternal locus.