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. 2020 Jan 14;11:277. doi: 10.1038/s41467-019-14068-3

Fig. 5. Asymmetric actin nucleation leads to biased direction of spindle migration.

Fig. 5

a A representative of 15 simulations showing each time that if the initial distribution of actin nucleation is asymmetric between the two spindle halves, the spindle will move to the side opposite to the one with more actin nucleation, as a result of more pushing force at the end with more actin nucleation. (The black arrow shows the pole of spindle that has more actin nucleation). b Top: constructs used for optogenetic activation of additional actin nucleation at one end of the spindle, the C-terminal half of FMN2 was fused to mCherry-mSSPBR73Q domain, Sec61β fused to miLID-EYFP. Bottom: illumination with 488 nm light leads to miLID domain binding with mSSPBR73Q, thus recruiting FMN2-C-mCherry or the control mCherry alone to the ER. c Recruitment of FMN2-C-mCherry-mSSPBR73Q to one spindle pole (green strike) by photoactivation of the miLID-EYFP-Sec61β induced the spindle movement with the opposite pole leading. Red ellipses show the positions of chromosomes. Red lines show the initial positions of chromosomes. n = 21. Scale bar, 20 µm. d Recruitment of the control mCherry-mSSPBR73Q to one spindle pole (green strikes) resulted in roughly equal frequency for each pole to lead the spindle movement. Red ellipses show the positions of chromosomes. Red lines show the initial chromosomes positions. n = 19. Scale bar, 20 µm. e Quantification of spindle migration direction after recruiting mCherry-mSSPBR73Q or FMN2-C-mCherry-mSSPBR73Q to one spindle pole. n = 19 (mCherry-mSSPBR73Q), n = 21 (FMN2-C-mCherry-mSSPBR73Q). f Schematics of the experiment in which FMN2-C-mCherry-mSSPBR73Q was recruited to one of the spindle poles by the first light exposure (green strike at 2 min), and after the spindle initiated apparent movement, a second illumination recruited FMN2-C-mCherry-mSSPBR73Q to the opposite pole (green strike at 86 min). g A representative montage from the experiment described in f, showing the second illumination reversed the direction of spindle migration. Red ellipses show the positions of chromosomes. Red lines show the initial chromosome positions. n = 5. Scale bar, 20 µm. h A plot of the movement of chromosome position in g. Green strike represents the time of two different activations by 488 nm light. Source data are provided as a Source Data file.