Specialized formations of the endoplasmic reticulum in cultures of murine neuroblastoma cells

Ultrastructural features of cytodifferentiation in monolayer cultures of mouse neuroblastoma cells (clone neuro-2A) was further characterized by the presence of annulate lamellar arrays with up to 10 lamellae. The lamellae were made up of fused smooth surfaced cisternae forming pores or annuli and were surrounded by a dense filamentous to granular material. Stacks of nonfenestrated, parallel, regularly spaced cisternae, designated as lamellar bodies, also appeared in the cytoplasm in association with the endoplasmic reticulum and the nucleus. Such flattened cisternae were also seen to be formed from transformed endoplasmic reticulum. Furthermore a relatively large number of concentric whorled lamellar bodies were presented as well as dense whorled structures reminiscent of the cytoplasmic laminar bodies. All of these structures are derived from the rough endoplasmic reticulum, the tubules of which are coexistent with those of the latter. In addition there is a topographic relationship of these bodies with mitochondria and with the nucleus. There is a relative persistence of most of these organelles in old or atropic cells which show marked changes including loss of endoplasmic reticulum. The significance of all of these cytoplasmic inclusions is discussed.