An Arabidopsis VPS45p homolog implicated in protein transport to the vacuole : Bassham DC, Raikel NV: Plant Physiol 1998, 117:407–415

Abstract

We investigated mitosis in amoebae of Acytostelium leptosomum, grown in liquid culture, by video microscopy of live cells, by indirect immunofluorescence with antibodies against tubulins, and by transmission electron microscopy of ultrathin sections. Amoebae in interphase contain a single microtubule-organizing center (MTOC, [30]) at each nucleus, from which microtubules (MTs) radiate into the cytoplasm. These disappear as the intranuclear spindle forms. Concomitantly, the nucleolus disperses, and the chromosomes that are visible in phase contrast congress to the spindle equator. The spindle is closed except for polar fenestrae occupied by broad, amorphous spindle pole bodies (SPBs). The chromosomes at metaphase are joined to form several blocks, each attached to several kinetochore MTs. Anaphase was accomplished within 2.2 min (s.d. = 0.5 min, n = 11). Anaphase A was virtually absent, but anaphase B contributed substantially to chromosome segregation. The mean velocity of pole separation was 3.2 μm/min (s.d. = 0.8 μm/min) and the mean elongation factor was 2.8 (range 1.9 to 3.4). The telophase spindle was a shaft consisting of a few MTs traversing each incipient daughter nucleus and joining in the interzone. The amorphous SPBs were reconverted to compact interphase MTOCs as the chromosomes decondensed and the nucleolus re-formed during cytokinesis. Duration of mitosis and velocities of its movements are within values typical for lower eucaryotes. In most aspects of mitosis A. leptosomum is very similar to two other dictyostelid cellular slime molds, Dictyostelium discoideum and Polysphondylium violaceum, and the three lower eucaryotes are clearly distinct from other mycetozoans.