Fig. S1

Increased microsatellite instability reporter activation in mismatch repair deficient embryos. Images of embryos (2dpf) stained for LacZ expression. One-cell stage embryos were made transgenic via Tol2-transposase mediated transgenesis with the indicated microsatellite instability construct that reports LacZ expression when the LacZ-coding sequence becomes in-frame after a frameshift. Strong LacZ-staining (examples shown in bottom panels) was seen in 20 out of 22 injected viable embryos that were obtained from a cross between an MLH1-/- mother and an MLH1-/+ father. Genotyping of animals showed that also heterozygous embryos from this cross had strong LacZ-staining, suggesting that the compromised mismatch repair pathway (due to MLH1-deficiency in the yolk) is not rescued by the paternal MLH1 wildtype allele during early development. Injected embryos obtained from MLH1-/+ parents, showed LacZ-staining similar to wild type levels (top panels and Fig. 1).