PMC

(A–B) Distribution of the differences in elongation rate (A) and birth length (B) between sister cells inheriting the old pole and the new pole. The distributions are skewed (p<0.05; red lines denote zero), indicating that the sister inheriting the older pole elongates faster (in 71% of the 161 sister pairs) and is larger at division (in 74% of the 161 sister pairs). In 7.5% of the 161 sister pairs, the sister that inherited the new pole elongated faster and was longer at birth than its sister. (C) Schematic model for mycobacterial growth. A labeled cell (green) is shown to elongate from one pole (red arrow). Two sister cells are created at division: an accelerator (Acc) cell inheriting the old (growing) pole and an alternator (Alt) cell inheriting the new pole. Growth pole age (in generations) is labeled in purple. (D–E) Elongation rate (D) and birth lengths (E) are plotted for ten microcolonies, with cell subpopulations grouped by growth pole age. Growth pole age was scored by mapping the pedigrees of unlabeled cells through several generations via live cell imaging. Subpopulation means (large ovals) are plotted along with data from individual cells (small circles). Elongation rate and birth length increase within a colony as the growth poles age (p<0.05 for alternator vs. accelerator elongation rates; and p<0.05 for alternator vs. accelerator and age two vs. age three birth lengths).

Cell chirality in snails and C. elegans. (a) Upper: in Lymnaea, the blastomere spindles slant clockwise as viewed from the animal pole at the four-cell stage, and blastomeres are rearranged clockwise at the eight-cell stage. Bottom: Pulmonata is a snail species with counter clockwise-coiling shells and internal organs that mirror those of Lymnaea. In Pulmonata, blastomere spindles slant anticlockwise as viewed from the animal pole, resulting in a counter clockwise blastomere rearrangement at the eight-cell stage. In both cases, blastomere chirality determines the shell coiling direction and LR asymmetry of the body. Schema is adopted from Shibazaki et al. []. (b) Top: in C. elegans, mitotic spindles are skewed during the transition from four cells to six cells. Bottom: at the six-cell stage, changing the LR-asymmetric arrangement of blastomeres to their mirror-image positions results in situs inversus. Thus, in both snails and C. elegans, blastomere chirality is completely responsible for the subsequent LR-asymmetric development. Schema is adopted from Wood & Kershaw [].

Comparison between theoretical predictions and experimental data for three multi-flagellated species of bacteria: Escherichia coli, Salmonella typhimurium and Bacillus subtilis. Our predicted critical number of normal flagella (circles) and semicoiled flagella (triangles) is compared against the real number of flagella counted in experiments (diamonds). For the filled circles and triangles we have assumed that flagella are uniformly distributed over the cell body, while for the empty symbols we have used a non-uniform distribution that is skewed towards one pole of the cell (for Escherichia coli and Bacillus subtilis, this data was available in the literature^,; no equivalent data was available for Salmonella typhimurium). The error bars represent one standard deviation.

Eyespot position varies over a wider, longer range in the pey1 and cmu1 mutants compared to wild-type, and eyespot position correlates with the length of the D4 rootlet. A: Diagram of a C. reinhardtii cell showing basis for positioning measurements. Eyespot angle (Θ_eye) along the anterior-posterior axis was defined from the center of the cell. For wild-type cells, the distribution of Θ_eye centers on the cell equator. B: Histogram showing the distribution of Θ_eye in populations of wild-type, pey1, and cmu1 cells. The distribution of eyespot angles in the pey1 mutant is skewed toward the posterior of the cell, and eyespots in cmu1 cells are always observed in the posterior range. C: Diagram showing basis for distance measurements. Distances from the anterior pole to the distal ends of the eyespot (E1) and D4 rootlet (R1) were measured as straight lines. Distance between end of eyespot staining and rootlet staining was calculated from E1/R1. D: Graph plotting the mean E1/R1 ratio (± S.D.) between the eyespot and end of the D4 rootlet in populations of wild-type, pey1, and cmu1 cells scored by indirect immunofluorescence staining of ChR1 photoreceptor and acetylated tubulin.