Figure 1. Heterochromatin clusters internally in the absence of peripheral tethers. (A) Temporal expression of LBR and lamin A/C in mouse retinal tissues. Tissues were stained simultaneously for lamin A/C (LA/C, red), LBR (green) and DNA (white, DAPI staining, where heterochromatin stains brightest). The distribution of one peripheral stain combined with DAPI is shown in each half-panel. Rod and ganglion cells express only LBR at stage P0; in adult tissue, ganglion cells have switched to lamin A/C (middle row) while rod cells uniquely express neither tether protein and exhibit the inverted nuclear architecture (top row). Endothelial cells express LBR and lamin A/C at both stages of development (bottom row). Scale bar = 2 µm. (B) Models for lamin A/C and LBR tethering of peripheral heterochromatin. Chromatin/DNA binding by lamins is indicated by dotted circles to show that lamins are not sufficient for heterochromatin tethering. From Solovei et al.⁴ with permission from Elsevier.