Figure 1

Nicotinamide treatment causes arrest in meiotic prophase and prevents macronuclear degradation. a Schematic of nuclear events in conjugation. Macronuclei are represented as large spheres, micronuclei as small spheres. Two mating types (white and shaded) were mixed to initiate conjugation. Asterisks represent the stages of arrest observed after nicotinamide treatment (coinciding with images in parts c and d). Hours represent times at which untreated conjugating cells (0 mM NAM) reach the given stage. Labels below the brackets indicate stages assessed in part b that correspond to different shades in the bar graph. "pOM+OM" are post-meiotic stages that still have a parental macronucleus (old macronucleus; OM); "-OM" is any stage after loss of the old macronucleus. An, anlagen (new macronuclei). b The average percentage of conjugating pairs at each of the three stages illustrated in part a by brackets: "PrM", cells in pre-meiosis (black); "pOM+OM", cells that contain an old macronucleus (dark gray); "-OM", cells that have lost the old macronucleus (light gray). Nicotinamide was added just after mixing (time zero of conjugation) and analyzed at 5, 11, and 24 hrs postmixing. At least 200 cells over two separate trials were counted for each time point and NAM concentration (each bar). ** P < 0.01 in a t-test when compared to 0 mM NAM at the same time point and stage of meiosis; *P < 0.05. c Representative images of DAPI-stained wild-type (0 mM NAM) and 50 mM NAM treated cells analyzed at 24-hrs into conjugation. M, macronucleus; An, anlagen; m, micronucleus. d DAPI images of 25 mM NAM-treated cells analyzed 24 hrs into conjugation. "OM", old (parental) macronucleus.