The focus of my research has centered on our understanding of morphogenetic events, their influence by cell cycle regulation and environmental switches. At present, students in my laboratory are examining the influence of chemotactic factors both on the behavior and the development of ciliated protozoa. Some years ago, it was necessary for me to drop a pet project for which I know have time, and interested students. It is this project that I would like to briefly describe here.

Since the early nineteenth century, it has been recognized that the stem cells of normal eukaryotic, adult mammalian tissues (with the exception of neural and skeletal and cardiac muscle) undergo cyclic events associated with mitosis; each tissue and cell type has a characteristic, steady-state generation (turnover) time stabilized by stasis and apoptosis. Abnormal cells are, in many cases, known to have their own distinctive, yet aberrant generation time. These are best known in cases of transformed cancer cells and other diseased states such as psoriasis.

In experiments carried out twenty years ago, I began an approach which I believe shows promise to further our understanding of events associated with the cell cycle chronology and its control. These experiments made use of a steady-state continuous culture technique (the chemostat) which allows for the exogenous control of cell growth rate by controlled manipulation of the limiting nutrient to cellular growth. In the initial study (Antipa, 1980), events of cell surface morphogenesis were investigated over an eight-fold range of cell division times and under stringent limitation of growth by either carbon source, nitrogen source, or availability of oxygen. The results by this method show cell surface morphogenesis to be a time-dependent, deterministic sequence of events. In the case of carbon limitation, there were a series of observations that suggested the interval was not strictly deterministic as would have been expected, but rather may be a proportion of the total cell division time. At the time this observations was unique for eukaryotic cells. Subsequently, others have observed a slowing down of the cell division cycle in concert with what is believed to be a slowing down in the rate of DNA synthesis. Although these observations are consistent with one another, in the intervening years, there has been no follow-up or explanation of these results which are inconsistent with present dogma.

We have the system, tools, and opportunity to pursue these observations to the next level of understanding. 1) We will establish the effect of different cell generation times on the interval of S by standard flow cytometric methods and by autoradiography as well as by the innovative one used in our 1980 observations in order to document our suspicions. As earlier, we will accomplish this with Tetrahymena thermophila in chemostat culture. 2) Chemostat analysis will be carried out under three different conditions of nutrient limitation such that the influence of limiters to growth and the interval S can be observed. 3) If these unusual results are verified, we will extend our observatons to other cell types (preferably mammalian) which lend themself to our chemostat methodology. Inasmuch as Tetrahymena must be handled with kid gloves, we have no reason to expect any problems with modification of our culture apparatus to suspension culture of mammalian cells.

In addition, my laboratory concentrates on other basic problems which can be best approached with the use of protozoa as either model systems or pragmatic solutions to fundamental problems in biology. They center around: 1) issues of general ecology, 2) cellular development, and 3) structure/function relationships. With respect to the latter, inasmuch as the protozoa are both cells and organisms, the emphasis has been on just what cellular adaptations have been made to accomplish life as a unicellular eukaryote. In the case of development, my laboratory has paid special attention to the role of basal bodies and centrioles in their regulation & semiautonomy during growth and cellular division. Insofar as ecology is concerned, the cell's program of division can be determined and use to estimate the growth of the organisms. Other student projects include investigation of the behavior of ciliated protozoa as they respond to chemical environmental cues and the evaluation of the role protozoa play in the decomposition of organic wastes, particularly during the activated sludge process.