Involvement of Nucleic Acids and Microtubules in Ciliogenesis: Implications for Cytoplasmic Inheritance
The ciliated protozoan, Stentor coeruleus, undergoes a process of oral development which occurs when cells prepare to divide or when the oral area is artificially removed. This process involves the production of thousands of new cilia and basal bodies in an eight hour period. A location on the cell cortex, the stripe contrast zone, defines the site of ciliogenesis. The data indicate that DNA synthesis is not required. RNA and protein synthesis are required during early stages of regeneration. At late stages a limiting factor is assembly of microtubule protein as demonstrated by sensitivity to the drugs colchicine and podophyllotoxin. A regulatory model based on the polymerization-depolymerization equilibrium of microtubule protein is offered which explains both these results and classic experiments involving grafts between two cells at different stages of regeneration. Such grafts regenerate synchronously (the older cell is retarded and the younger accelerated until they reach the same stage). This result may be expected if cells at different stages have unequal pools of cilia percursors and if these pools mix when cells are grafted together. The polarity of proteins in the cell cortex is thought to determine cortical patterns and basal body location. Assembly of proteins on these basal bodies would be determined by the cilia precursor protein pool. This model does not require involvement of the cell cortex, nuclear-cytoplasmic ratio, or specific cortical nucleic acids in the regulation of morphogenesis. (Supported by USPHS Grant CA5060 from NCl).