The role of the nuclear protein matrix during development of rabbit gr anulocytes

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.

The role of the nuclear protein matrix during development of rabbit gr anulocytes

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.

hnRNA and its attachment to a nuclear protein matrix.

In this study, DNA-depleted nuclear protein matrices are isolated from HeLa S3 cells. These nuclear matrices consist of peripheral laminae, residual nucleoli, and internal fibrillar structures. High molecular weight, heterogeneous nuclear RNA (hnRNA) is quantitatively associated with these structures and can be released intact only by affecting the integrity of the matrices. It is, therefore, concluded that hnRNA is part of a highly organized nuclear structure. By irradiation of intact cells or isolated nuclear matrices with ultraviolet light, proteins tightly associated with hnRNA can be induced to cross-link with the RNA. Performing the cross-linking in vivo is an extra guarantee that only hnRNA-protein (hnRNP) complexes existing in the intact cell are covalently linked. Such hnRNP complexes were isolated and purified under conditions that completely dissociate nonspecific RNA-protein complexes. By comparison of the hnRNP found in nuclear matrices and the published data on the composition of hnRNP particles, it was found that the so-called hnRNP "packaging" proteins (32,000-38,000 mol wt) were not efficiently cross-linked to hnRNA by UV irradiation. They were, however, present in the matrix preparations, bound to hnRNA, because they were released from nuclear matrices after ribonuclease treatment of these structures. On the other hand, two major hnRNPs (41,500 and 43,000 mol wt) were efficiently cross-linked to hnRNA. These proteins were not released by ribonuclease treatment, which suggests that they are involved in the binding of hnRNA to the nuclear matrix.