Decreased expression of cell proliferation-related genes in clonally derived skin fibroblasts from children with Silver-Russell syndrome is independent of the degree of 11p15 ICR1 hypomethylation

The in vitro analysis of the hypomethylation of imprinting control region 1 (ICR1) within the IGF2/H19 locus is challenged by the mosaic distribution of the epimutation in tissues from children with Silver-Russell syndrome (SRS). To exclude mosaicism, clonal cultures of skin fibroblasts from four children with SRS and three controls were analyzed. Cell proliferation, IGF-II secretion, and IGF2 and H19 expression were measured, and a microarray expression analysis was performed.

The analysis of severely ICR1 hypomethylated clonal fibroblasts did not reveal functional differences compared to normomethylated clones with respect to IGF2 and H19 expression. A difference compared to the clones from healthy individuals was present in the form of a lower proliferation rate, presumably due to impaired cell cycle progression.

Single-cell expansion established severely ICR1 hypomethylated clones (SRShypo) and normomethylated clones (SRSnormo) from the patients and controls (Cnormo). IGF2 expression was below the detection limit of the quantitative real-time PCR (qRT-PCR) assay, whereas H19 expression was detectable, without differences between fibroblast clones. Cell count-related IGF-II release was comparable in SRShypo and Cnormo supernatants. Cell proliferation was diminished in SRShypo compared to Cnormo (p = 0.035). The microarray analysis revealed gene expression changes in SRS clones, predicting a decrease in cell proliferation and a delay in mitosis. Conclusions: The analysis of severely ICR1 hypomethylated clonal fibroblasts did not reveal functional differences compared to normomethylated clones with respect to IGF2 and H19 expression. A difference compared to the clones from healthy individuals was present in the form of a lower proliferation rate, presumably due to impaired cell cycle progression.