Nucleocytoplasmic interactions during the differentiation of oral structures in Stentor coeruleus

Abstract

Differentiation of the oral apparatus in the heterotrich ciliate Stentor coeruleus is accompanied by striking changes in macronuclear morphology. The macronucleus normally exists as a chain of nodes, but during oral differentiation it coalesces into a rounded, irregular mass in the center of the cell, then elongates into a long rod, and finally renodulates. The technique of nuclear transplantation has been used to analyze each one of these macronuclear changes in terms of nucleocytoplasmic interactions. Macronuclei in various morphological states were transferred into atypical cytoplasmic environments. The experimental results lead to the conclusion that the three changes in macronuclear morphology which accompany oral differentiation are regulated by a corresponding sequence of cytoplasmic states, all of which are experimentally distinguishable from conditions prevailing in the cytoplasm of the non-differentiating cell. Various properties of these nucleocytoplasmic interactions have also been analyzed by nuclear transplantation. Among the findings are evidence that the nucleus cannot respond immediately to the cytoplasmic change initiating its coalescence and that it cannot complete coalescence or elongation in the absence of the cytoplasmic conditions which initiate these processes. The results are discussed with regard to their implication for the control of nuclear morphology and function in ciliates and metazoan cells.