The effects of mercaptoethanol on cellular development in Tetrahymena pyriformis

The effects of β‐mercaptoethanol on cell division, nuclear division, and oral morphogenesis were investigated in two strains of Tetrahymena pyriformis, WH‐6 (micronucleate) and GL (amicronucleate). Mercaptoethanol inhibited division in both strains. In exponentially growing cell cultures, cell multiplication stopped after a 30 minute lag (strain WH‐6); in synchronized cultures, division was prevented or very greatly delayed if the agent was added during the first 60% of the interval between the end of the last synchronizing shock and the synchronous division. In both strains, mercaptoethanol brought about an arrest of oral primordium development in cells which had not yet begun to form visible membranelles at the time of addition of the drug. In cells arrested just prior to the onset of membranelle development the oral primordia became disorganized and in many cases were gradually resorbed. In these cells micronuclear division was generally arrested (strain WH‐6) and macronuclear and cell division did not occur at all (strain WH‐6), or were resumed after a long delay (strain GL). Cells which were in stages of visible membranelle development at the time of addition of mercaptoethanol continued to develop. In strain WH‐6, all of these cells completed oral development and divided, while in strain GL about 40% of these cells were arrested in the course of membranelle development. In these arrested cells, the oral primordia were resorbed, and division did not take place. In the situations in which oral morphogenesis was completed and cell division took place in mercaptoethanol, micronuclear division (in strain WH‐6) was in all cases normally completed. Macronuclear division in strain WH‐6 was also normal at the minimum concentration (4 × 10−2M) which affected morphogenesis when added at earlier stages. However, at a somewhat higher concentration (5 × 10−2M) in strain WH‐6, and at the lowest concentration employed (1.5 × 10−2M) for strain GL, macronuclear division was either prevented (in both strains) or else rendered highly abnormal (in strain GL). These data suggest that mercaptoethanol blocks some process required for the initial organization of oral structures and for the division of the macronucleus. The nature of this process is discussed.