The role of the nuclear protein matrix during development of rabbit granulocytes

A proteinaceous nuclear substructure (nuclear protein matrix or nuclear pore complex-lamina) has been described in a number of cells and may be a universal feature of cell nuclei. We have investigated the nuclear protein matrix (NPM) in the rabbit blood granulocyte and its precursor cells to determine (A) whether the NPM composition is similar to other cells that have been studied and (B) to determine whether the dramatic morphological changes that the granulocyte nucleus undergoes during cell maturation are related to changes in the composition or structure of the NPM. NPM preparations from rabbit granulocytes were similar but not identical to those found in HeLa cells or rat liver nuclei. The NPM structure of more mature cells retained more DNA during the isolation procedures than did immature cell NPMs, and the DNA was less accessible to DNAse in the mature cell nuclei. Scanning and transmission electron microscopy revealed a continuous outer covering of the NPM preparation and a lattice-like internal structure. Recognizable nuclear form persisted although the preparations represented less than 20% of the original nuclear protein. NPM preparations from mature cells were similar in overall dimensions and internal structure to NPM from immature cells, suggesting reexpansion during isolation of a previously compacted NPM structure in segmented neutrophils. NPM proteins are synthesized primarily in early stages of cell development. The NPM appears to play a major, but passive, structural role in the nuclear changes observed during maturation of granulocytes.