An electron microscope study of intranuclear canaliculi in Novikoff hepatoma cells.

SUMMARY An intranuclear canalicular system connecting the nuclear envelope to the nucleolus has been found in interphase cells of the Novikoff hepatoma in both the ascitic and the solid forms. Throughout the nucleoplasm, flattened canaliculi are seen in sections as parallel membranes covered by thin layers of chromatin material. Membrane-bounded tubules exist in direct contact with the nucleolus, where they are often stacked in parallel array and embedded in an amor phous matrix substance. Those intranuclear membranes dis appear at metaphase and reappear at telophase. It seems likely that the canaliculi are formed by deep invagination of only the inner layer of the nuclear envelope and reach into the nucleolus. The interspace of intranuclear canaliculi is continuous with the perinuclear cisterna of the nuclear envelope, which, in turn, is confluent with the cisternae of the rough endoplasmic reticulum.