The relationship of isolated chromosome fibers to the fibers of the embedded nucleus

Abstract

Nuclei and chromosome fibers isolated from the amphibians Triturus viridescens and Rana pipiens , and the milkweed bug, Oncopeltus fasciatus , by the Langmuir trough—critical point method were investigated in an effort to relate the 250 A fiber of the isolated nucleus to the chromosome fibers in the typical thin-sectioned nucleus, which are significantly smaller in dimensions, 100 A and less. It has been shown that a change in diameter in the chromosome fibers occurs early in the breakdown of cells, whether spread on a water surface or lysed in hypotonic solutions. This change probably occurs at the time of rupture of the cell membranes. Since chromosome fibers isolated from lysed cells prove to have the same diameter and morphology as fibers isolated by the spreading method, the 250 A diameter is not considered to result from the spreading forces of the Langmuir trough. Similarly, no further changes in structure or diameter occurring as a result of the critical point method were detected. The effect of these findings on concepts of chromosome structure based on the Langmuir trough—critical point isolation technique is discussed.