Figure 1. Hyperactivation of myosin contractility by depletion of myosin phosphatase doubles the velocity of polar body ring ingression down the length of the spindle.

(A) Images of GFP:histone and GFP:NMY-2 fluorescence and DIC within a meiotic embryo are shown from a representative time-lapse sequence of chromosome separation and contractile ring movement during polar body formation in meiosis I (t_o = completion of spindle rotation). For the merge column, GFP:histone pixels above an arbitrary threshold were converted to white, then merged with the DIC image to show chromosome placement. White arrows in column one highlight the contractile ring labeled with GFP:NMY-2. Black arrowheads in column two highlight the membrane ingression away from the eggshell. Scale bar, 5 μm. (B) Chromosome and contractile ring movements during polar body formation, measured as distance from the eggshell. Proximal chromosomes are the chromosomes closest to the cortex, which are extruded into the polar body (t_o = completion of spindle rotation). Apparent delayed ingression in mel-11(RNAi) in this example was not reproducible (see Table 1). (C) Spindle length at completion of anaphase and length of the spindle within the polar body at scission. (D) Rate of movement of chromosomes away from each other during anaphase and rate of movement of the GFP:NMY-2-labeled contractile ring away from the eggshell and proximal chromosomes in control, mel-11(RNAi) and mei-1(ct103) embryos (*p < 0.01; **p < 0.005; all others p > 0.05 ).