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Supplementary information
Acini were cultured in collagen IV-coated chamber flasks. Five hours after medium
change from CME to WHME on day 5, the flasks were mounted onto a motorised
stage for time-lapse videomicroscopy. Images were obtained either at 6-minute
intervals using a 10x objective and a 0.63x condenser (videos 2, 3, 5, 6) or at 15minute intervals using a 20x objective and a 0.63x condenser (videos 1, 4).
Video 1
Cultured acinar-like cells undergo profound morphological changes representing
acinar-ductal transdifferentiation.
Video 2
Abortive cytokinesis of mononuclear progenitor generates binuclear daughter cell.
The initial stages of mitosis are completed successfully and the membrane, around the
middle of the progenitor cell, invaginates to form a cleavage furrow reducing the
cytoplasm to a thin intercellular bridge. Subsequently, cytokinesis is abruptly aborted
generating a binuclear cell.
Video 3
Binuclear cell nuclei form a single metaphase plate. The two nuclear genomes appear
to be assembled into a V-shaped prometaphase formation before the two sets of
chromosomes converge at a single metaphase equator. Presumably this mechanism
can apply only to binuclear cells with 2 interphase centrosomes. Abortive cytokinesis
preserves nuclearity but increases nuclear ploidy.
Video 4
Cytokinesis may be circumvented altogether. Restricted poleward movement of sister
chromatids at anaphase leads to an inadequate distance between decondensing
chromosome bundles at telophase. Enclosure of the entire formation within a single
reforming nuclear envelope culminates in a mononuclear polyploid cell.
Video 5
Binuclear progenitor generates binuclear daughter cell with increased ploidy. The
daughter nuclei progress into the next mitosis, combining their chromosomes on a
multifaceted metaphase plate.
Video 6
Consecutive mitoses of multinuclear cell with formation of aberrant spindles. Two
nuclei enter mitosis yielding three daughter nuclei with three-way chromosome
allocation. These then enter a further round of mitosis involving a fourth nucleus.