U73122 causes cleavage furrow regression in crane-fly and Drosophila spermatocytes. (A, B) Phase-contrast images showing time-course of cytokinesis in untreated (A) crane-fly and (B) Drosophila spermatocytes [see Additional files 1, 2]. Times are in min:sec. Bars, 10 μm. (C, D) Phase-contrast time-course of a (C) crane-fly and (D) Drosophila spermatocyte treated with U73122 during cytokinesis [see Additional files 3, 4]. U73122 was added immediately after the time-point depicted in the second panel. Crane-fly and Drosophila spermatocytes were treated with 4.3 μM and 10 μM U73122 respectively. Note that the crane-fly spermatocyte was followed for only a short time after treatment (for a longer time-course, see ). Bars, 10 μm. (E) Plot of the change in cell diameter (ordinate) over time (abscissa) for the treated crane-fly (+) and Drosophila (o) spermatocytes shown in A, B. (F) Plot of the change in cell diameter (ordinate) over time (abscissa) for the crane-fly (+) and Drosophila (o) spermatocytes shown in C, D. Arrows indicate time of drug treatment.