H4K20me1 becomes concentrated on the X chromosome after the DCC.

<p>Wild-type embryos at (A) 20-cell, (B) 40-cell, (C) bean, (D) comma, and (E) three-fold stages stained for DNA (DAPI, blue, left column), DPY-27 (red, second column), and H4K20me1 (green, third column). Boxed regions in B and E are enlarged in F and G, respectively. In very early embryos (A) DPY-27 exhibits weak and diffuse nuclear staining while H4K20me1 is diffuse in interphase nuclei and associated with condensed chromatin during mitosis. By the ∼40-cell stage (B, F) DPY-27 is enriched on the X chromosome, while H4K20me1 continues to show a uniform nuclear distribution. Comma-stage embryos (D) contain some nuclei with H4K20me1 enrichment on the X. This enrichment becomes more apparent as embryogenesis progresses, and by the 3-fold stage (E, G) H4K20me1 is concentrated in bright foci that co-localize with DPY-27 on the X. Scale bars represent 10 um (A–E) and 2 um (F, G). Monoclonal antibody15F11 was used to detect H4K20me1.