Fig. 1. Methylated lysine 9 on histone H3. (A-L) Light and fluorescent micrographs of mouse immature oocytes, fertilized eggs and early embryonic stages stained for the Me(Lys9)H3 modification (E-H, red) and DNA (I-L, green). Chromatin staining for this modification is present with little apparent change in fluorescence intensity at all stages of pre-implantation development tested (E-H). (A,E,I) In immature germinal vesicle (GV) stage oocytes, the Me(Lys9)H3 modification co-localizes with DNA staining that surrounds the nucleolus (GV Stage SN). (B,F,J) In fertilized eggs, the maternal metaphase II plate (MII plate, asterisk) stains strongly for this modification whereas the decondensing sperm nucleus (SpN) does not stain. (C,G,K) At the pronuclear stage, the male pronucleus (MPN) also does not stain for Me(Lys9)H3, whereas the female pronucleus (FPN) stains strongly. The polar body can be seen at this pronuclear stage (PB). (D,H,L) At the blastocyst stage of development, note that chromatin from both metaphase (Met) and interphase (Int) blastomeres stain strongly for the Me(Lys9)H3 mark.