Figure 4

The histone signature of early developing macronuclear anlagen. Nuclear types occurring during early macronuclear development: New micronuclei (m) are formed at this stage from one daughter nucleus after mitotic division mitotic division of the zygote nucleus. The other daughter nucleus develops into a macronuclear anlage (a₁/a₂), which is characterized by chromatin decompaction, beginning of chromosome polytenization, and an increase in size at this early stage of differentiation. Fragmented parental macronuclei (p) persist at this stage. In situ antibody staining (color code as described in Figure 2): Exclusively H3K9ac (A), H3K14ac (B), and H3S28p (J) are detected in the very early macronuclear anlagen (a₁/early a₂), whereas 'active' chromatin markers H3K4me1 (C) and H3K4me3 (D) are not observed (a vegetative cell with a prominently stained macronucleus (M) is shown additionally in (D) as a positive control). At best, sporadic foci-like signals of H3K36me3 (E), H3K9me3 (G), and H3K27me3 (I) are observed at the earliest at stage a₂. In micronuclei (m) H3K36me3 (E) is observed to accumulate de novo, whereas H3K27me3 (I) persists, and H3S28p (J) is lost at this stage.