Research

Signal-mediated differentiation in the ciliate Tetrahymena vorax

Differentiation of cells into specialized types, a process fundamental to the development of complex multicellular organisms, also occurs in certain unicellular protists. The ciliate, Tetrahymena vorax, undergoes a dramatic change in cellular morphology permitting it to ingest different sources of solid food. T. vorax normally exists in the microstomal form which utilizes bacteria and/or suspended particles. This cell type is also present in nutrient culture medium. When protozoa are suspended in distilled water or buffer, they starve with a corresponding decrease in cell size. If, however, they are exposed to a signal secreted by potential prey, the cell transforms into the macrostomal cell type, a carnivore capable of ingesting prey protozoa. Cellular remodeling into the macrostome includes cytoskeletal reorganization and alteration of the food vacuoles. The pathway that leads to this restructuring is initiated at a point in the life cycle from which the cell may either divide or differentiate. In the absence of prey, the macrostomal cell type is not stable, and differentiation is reversed at the next cell division which produces two cells in the microstomal form.

Cell Types of Tetrahymena vorax

Microstomal cell	Starving microstomal cell after seven hours of nutrient deprivation	Macrostomal cell 7 hours after removal from nutrient medium and exposure to stomatin, the signal derived from prey protozoa

Macrostomal Cells Feeding on Prey Protozoa

Macrostomal cell with prey protozoan entering cytopharyngeal pouch, the macrostomal food vacuole. A phagolysosome contains another protozoan (red). Prey protozoa were stained with neutral red.	Macrostomal cell with a recently ingested prey protozoan in a phagosome.	Macrostomal cell with one phagosome and one phagolysosome, each containing an ingested protozoan	A macrostomal cell attempting to ingest another macrostome

Our current research directions include:

Investigation of iron metabolism

The presence and state of iron in the nutrient medium in which the protozoa are grown appears to affect the ability of populations to differentiate

Characterization of genes and gene products that participate in the initial stages of differentiation

We are investigating the effects of the induction of differentiation on gene expression.

Cytoskeletal proteins during differentiation

The remodeling of the microstome into the macrostome involves replacement of the oral apparatus with one that differs in both quantity and organization of cytoskeletal elements. We are investigating the expression of cytoskeletal proteins to determine whether pools present in the microstomal cell are sufficient for oral development during differentiation.

Phytate uptake and metabolism in Tetrahymena

Updated December 10, 2009