Fig. 4

Topological chromatin density mapping of differentiating myelopoietic cell nuclei. a Upper panel: DAPI stained mid-sections of representative nuclei acquired by 3D-SIM. Mid panel same sections after chromatin density classification, based on seven DAPI intensity classes, are displayed in false colors, ranging from class 1 (blue) representing pixels close to background intensity, largely reflecting the interchromatin compartment (IC), up to class 7 (white) representing pixels with highest density. Bottom panel inset magnifications in progenitors, monoblasts and myeloblasts (precursors) reveal a loosely arranged network of small chromatin domain clusters (CDCs) comprising a compacted core part (classes 5–6/7) and a surrounding low-density layer (class 2–4), the perichromatin region. Largely DNA-free class 1 regions meander between CDCs as part of the IC system. Monocytes are characterized by closed up CDCs forming larger islets, surrounded by a decondensed perichromatin layer (classes 2–3). In the lobed granulocyte nucleus, an extended class 1 region, representing the large IC lacuna in the interior of each lobe is lined by a small rim of decondensed chromatin (classes 2–4) at the interface with the highly compacted peripheral chromatin layer (classes 5–7). b classification scheme. c relative 3D signal distributions of the DAPI intensity classes for each cell type. Note the shift toward higher intensity classes with progressing differentiation but similar values for class 1 despite profoundly different nuclear landscapes. n Number of analyzed nuclei; error bars standard deviation