Fig. 6. Interior central spindles can initiate cleavage furrows in primary spermatocytes. Time-lapse sequence of a klp67A mutant during cytokinesis. 0 minutes: Image of the cell at anaphase onset. Note the characteristic rings of astral microtubules encircling the dense spindle. After dyad disjunction the interior central spindle (9 minutes; white arrowhead) undergoes anaphase B elongation causing it to buckle outwards. During this time the peripheral astral microtubules concentrate and contact the cell boundary at the equator where they initiate a primary furrow (arrows). The interior central spindle further protrudes and approaches the cell cortex in a region of diminished peripheral microtubule density (9-16 minutes; white arrowheads). As the primary furrow continues to advance (16-23 minutes; arrows), an ectopic furrow (19 minutes; black arrowhead) initiates where the interior central spindle apposes the cell membrane (white arrowhead). This ectopic furrow then ingresses towards the cell centre (21-23 minutes; black arrowheads). Time is in minutes relative to anaphase onset. Bar, 10 µm.