Cell proliferation in the neural tube: An electron microscopic and Golgi analysis in the mouse cerebral vesicle

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Summary

The shape and fine structure of ventricular (primitive ependymal) cells during their generation cycle was studied. Interphase cells are radially oriented bipolar elements with processes spanning the thickness of the brain wall. Zonular junctional complexes joining internal processes at the ventricle consist of gap junctions and wider intermediate junctions. The external limiting layer consists of expanded end-feet in simple apposition; they resemble axonal growth cones and contain a feltwork of 60 Å microfilaments, elements of smooth endoplasmic reticulum but no microtubules. During prophase, nuclei of ventricular cells move to a juxtaventricular position, while their external processes remain fully extended. The internal processes of such cells contain numerous longitudinally arranged microtubules and microfilaments. Subsequent to nuclear migration, in prometaphase or metaphase, the cell withdraws or pinches off its external process and becomes nearly spherical. During telophase an asymmetrical furrow formation results in a thin connector (midbody) between daughter cells which is adjacent to the ventricle and attached there by the junctional complex. Either before or after complete separation, an external process starts regrowing towards the external limiting layer, eventually resulting in a bipolar interphase cell again. Microfilaments are present in telophase cells before outgrowth of external processes and in growing tips of external processes.

This work was supported by United States Public Health Service Research Grant No. NS-08655 from the National Institutes of Neurological Diseases and Stroke. The authors wish to express their sincere thanks to Drs. Peters, Morest, and Grasso for their critical reading of the manuscript and to Patricia Lowary Hinds for the drawing in this paper.