Dividing cells maintain intact protrusions during division in 3D matrices. (A–C) Time-lapse images of dividing cells cultured on 2D untreated glass (A), cultured on 200 µm thick fibrin gels (B), and fully embedded in 3D fibrin gels (C). Cells dividing on glass treated with fibrinogen were similar in appearance to those in B. Images shown were recorded just before division (t = 0 min), at the end of cell rounding (t = 20 min), during cytokinesis (t = 25 min), and after spreading of the daughter cells (t = 90 min). Bars, 20 µm. (D–F) Quantification of normalized protrusion length (current length/initial length) over the course of cell rounding demonstrates that dividing cells on untreated glass substrates (D, n = 12) completely and rapidly retract their protrusions, whereas dividing cells on top of 2D fibrin gels (E, n = 11) gradually and partially retract their protrusions. In contrast, cells in 3D fibrin gels (F, n = 17) maintain intact protrusions for the entire division cycle. (G) Normalized protrusion length at the end of cell rounding (5 min before cytokinesis) is plotted for cells dividing on 2D glass (n = 12), on 2D glass coated with fibrinogen (n = 18), on 200-µm-thick fibrin gels (n = 11), and in 3D fibrin matrices (n = 17). Normalized protrusion length is greater for cells in 3D matrices than on any of the 2D substrates (***, significant difference between 3D and 2D data, ANOVA, P < 10−6). (H) The angle θ between the division and protrusion axes is random (K-S test, P > 0.19) for cells on 2D substrates, but correlated in 3D fibrin matrices (K-S test, P < 0.001).
