The Structure of the Nucleus Studied by Electron Microscopy in Ultrathin Sections with Special Reference to the Chromonema-An Advocation of “Subchromonema” and “Protochromonema”

Abstract

1. In our previous phase microscope studies, various interkinetic nuclei were described, in which the chromonema structure is either (a) uncoiled completely, or (b) remained in varied degree after mitosis. The cells belonging to the latter group (b) such as lymphocytes, monocytes and plasma cells in mice, referring especially to their chromonema structure as seen in ultrathin section by an electron microscope, are herewith reported.
2. In the interkinetic nucleus of lymphocytes, monocytes and plasma cells, varying spiral structures were recognized corresponding to the configuration of coiled and uncoiled chromonema. Among the spiral fibers the following varieties according to the modes of the arrangement and their diameterical sizes may be distinguished:
Chromosome 500mμ, 440-480mμ
Chromonema 100-120mμ in contraction, 60mμ, 30-35mμ in loosening
Subchromonema 26-30mμ in contraction, 13mμ in loosening
Protochromonema ca. 2-3mμ
The diametrical size of these elements fluctuates according to the intensity of the coiling, namely, it is large in high contraction, while small in loosening.
3. The protochromonemata belong to the morphological limit capable of being observed by an electron microscope in ultrathin sections. The size (in diameter) of this fiber is very similar to the fibers of the extracted nucleoprotein recently reported by Kahler and Lloyd (24Å). The fine filament of protochromonema found in monocytes is wristed even in an extremely unravelled state.
4. This observation was confirmed also with a structure of the more or less loosely coiled chromosomes found in mitotic lymphocytes in prophase.
5. The size and structure of the chromonema and subchromonema in mitotic and interkinetic stages were discussed.