H3K36 methylation dynamics during embryogenesis. (A) MES-4 is required for the maintenance of H3K36me3 during early embryonic cell divisions. H3K36me3 (left) and DAPI staining (right) in mes-4 (bn85) M-Z- (top panels) and wild type (bottom panels) are shown in grayscale. Note that in mes-4 embryos, H3K36me3 that is prominently observed in dividing 1-cell stage embryo (embryo a), becomes barely detectable by the 2 to 4 cell stage (embryo b) and almost undetectable at the 6 to 8 cell stage (embryo c). Arrows indicate polar bodies. (B) H3K36me3 staining in wild type (top row), met-1(n4337) (middle row) and mes-4(bn85) (bottom row) at different embryonic stages (~50, ~100 and ~550 cells, as indicated on the top). DAPI, red; H5, green; PGL-1, blue in merged images. (C) H3K36me3 staining is not detectable in mes-4(bn73); met-1(n3347) double mutant, Arrows indicate primordial germ cells (PGCs.