Fig. 2: S. arctica undergoes closed mitosis.
From: Life-cycle-coupled evolution of mitosis in close relatives of animals
a, Representative maximum intensity projections of synchronized S. arctica interphase (top) and mitotic (bottom) coenocytes labelled for tubulin (red) and DNA (grey). b, Dot plot showing MTOC–MTOC distances for interphase (I), metaphase (M), anaphase (A) and telophase (T) (nI = 29, nM = 75, nA = 49, nT = 19) nuclei. Three biological replicates. In telophase, distance was measured from the MTOC to the end of spindle microtubules (MTs). Statistical analysis using a Kruskal–Wallis test; P < 0.0001 with Dunn’s test for several comparisons. Adjusted P values, I versus M; P < 0.0001, M versus A; P < 0.0001, I versus T; P = 0.1909. Data are mean ± s.d. c, Mitotic microtubule (red), DNA (grey) and NPC (blue) configurations. Representative maximum intensity projections from three biological replicates. d, S. arctica carries out closed mitosis forming a dumbbell-shaped nucleus in anaphase. Representative maximum intensity projections of nuclei with pan labelling (NHS-ester, grey) and tubulin labelling (red) from three biological replicates. e, NE is maintained during S. arctica mitosis. Representative maximum intensity projections of central slices of nuclei with membrane (BODIPY, grey) and tubulin labelling (red). f, NPC density is maintained throughout the life cycle. Dot plot showing NPC density in interphase and mitosis, either proximal to the MTOC or per nucleus (ninterphase = 21, nmitosis = 29 nuclei) (****P < 0.0001; NS, not significant). Statistical analysis using a two-tailed Mann–Whitney U-test; I-NE versus M-NE P = 0.5266; I-SPB versus M-SPB P = 0.3403; I-NE versus I-SPB and M-NE versus M-SPB P < 0.0001. From three biological replicates. Data are mean ± s.d. g, Single slice from a representative electron tomogram volume of early (top) and late dumbbell-shaped (bottom) S. arctica mitotic nuclei overlaid with a 3D model showing the intranuclear spindle (red), MTOC (yellow) and NE (blue) and NPCs (light blue). Scale bars, 5 μm (a,c,d,e), 500 nm (g).
