The State of the Chromosomes in the Interphase Nucleus

Abstract

In the living interphase nucleus no chromosomal structures are visible. Yet in the injured cell and after treatment with most histological fixatives chromatin structures become apparent. Under certain conditions this appearance of structure in the living interphase nucleus is reversible. We have found that this change in the interphase nucleus is the result of a change in the state of the chromosomes. In the living nucleus the chromosomes are in a greatly extended state, filling the entire nucleus. Upon injury the chromosomes condense and therefore become visible. At the same time the nuclear volume decreases. This behavior of the chromosomes is connected with their content of desoxyribonucleic acid (DNA). This view is based on the following observations: (a) Distribution of DNA in the Nucleus.—(1) The living interphase nucleus of uninjured cells absorbs diffusely at 2537 Å. No chromosomal structures are visible in ultraviolet photographs unless they are also distinct in ordinary light. If the chromosomes are made to condense they become visible and the absorption at 2537 Å is now localized in these structures. (2) After fixation with formalin and osmic acid interphase nuclei stain diffusely with Feulgen. These fixatives preserve the extended state of the chromosomes. (3) If nuclei are teased out in non-electrolytes (sucrose, glycerin) the chromosomes are extended. Such nuclei stain homogeneously with methyl green. On adding salts the chromosomes condense and the methyl green is now restricted to the visible structures. (b) Extension and Condensation of Isolated Chromosomes.—When chromosomes isolated from interphase nuclei of calf thymus are suspended in sucrose, their volume is four to five times larger than in saline, but they retain their characteristic shapes. Chromosomes from which DNA and histone have been removed do not show this reversible extension and condensation, neither do lampbrush chromosomes of frog oocytes which contain very little DNA. During mitosis a partial condensation of the DNA occurs in prophase, so that the mitotic chromosomes now occupy a much smaller volume of the nucleus. At telophase the chromosomes swell again to fill the entire nucleus.

Effect of high temperature on meiosis in Lolium: Nucleolar inactivation

“…The swollen DNA histone component of the chromosomes is then described as existing in an extended state (Ris and Mirsky, 1949 condensation may be interpreted as indicating that the capacities for nucleolar and DNA synthesis are correlated. The reduced synthetic activity of the chromosomes may help to explain their failure of condensation.…”

A Proposed Role for Mucopolysaccharides in the Initiation and Control of Cell Division*,†

“…Measurements of cortical viscosity (Wilson, 1951;Heilbrunn & Wilson, 1952) and cytoplasmic viscosity Heilbrunn & Wilson, 1948) also reflect the calcium influx. Mazia (1954), Ris and Mirsky (1948), Kaufmann and MacDonald (1956), and others have established the fact that chromosomal condensation and structural organization take place in the presence of increased calcium. Finally, it is suggested that the path for the calcium influx might be via the endoplasmic reticulum to the nucleus, a s electron photomicrography reveals that such a path is possible (Porter, 1961), and studies on muscle indicate that such a route is likely.…”

Multifunctionality of the linker histones: an emerging role for protein-protein interactions

“…This structural transition was observed in the earliest studies of chromatin, as dating back over 50 years ago it was reported that isolated rat and chicken nuclei underwent a reversible and cooperative transition from a homogenous to granular state when the buffer included 5 mM MgCl 2 [34-37]. Nucleosomal array model systems and homogenous, recombinant core histone octamers have been used to extensively characterize the self-association transition [20, 38, 39].…”