Fig. 2. Methylated lysine 4 on histone H3. (A-L) Light and fluorescent micrographs of mouse immature oocytes, fertilized eggs and early embryonic stages stained for the Me(Lys4)H3 modification (E-H, red) and DNA (I-L, green). Chromatin staining is present at all stages of pre-implantation development with little apparent change in fluorescence intensity between the stages tested (E-H). (A,E,I) In immature oocytes, the Me(Lys 4)H3 modification co-localizes with DNA staining surrounding the nucleolus. (B,F,J) In fertilized eggs, the maternal metaphase II plate (F, asterisk) stains strongly for this modification whereas the decondensing sperm nucleus does not stain (F, arrow). (C,G,K) As with the Me(Lys9)H3 mark, there was little to no staining for the Me(Lys4)H3 modification in the male pronucleus.