Figure 1.
Figure 1. Septation comprises an evolving septum structure consisting of two consecutive phases with different ingression rates and levels of calcofluor staining. (A) Model of the septum synthesis and formation of a cleavage furrow. Septation and CR constriction start in early–mid anaphase B with the activation of PS synthesis by the action of Bgs1 glucan synthase. Septum ingression is slow during anaphase B and increases during telophase (adapted from Cortés et al., 2018). (B) Scheme of the timing of the stable localization of different proteins as a ring at the cell middle with respect to the onset of septation and CR constriction (T = 0), first PS detection by CW staining (T = +0.5 min), and the mitotic phases (adapted from Cortés et al., 2018). (C) Model of septation (adapted from Muñoz et al., 2013). A PS incipient rudiment formed by the sole action of Bgs1 becomes a fast-ingressing septum during telophase, which is a three-layered structure formed by the simultaneous synthesis of PS and SS by the action of Bgs1, Bgs4, and Ags1. The septum increases in thickness throughout ingression, and the complete septum maturation proceeds by additional SS synthesis. Finally, cell separation proceeds by PS degradation, forming a fission scar. Right: TEM magnifications from rudiments to longer septa increasing in thickness throughout ingression are shown. Large arrow, direction of septum ingression and CR constriction; small arrow, direction of septum thickness increase; line points inside the CR, glucan synthase rings, PS, and SS. Scale bar = 1 μm. (D) WT septation showing two phases with different ingression rates and levels of CW staining. Early log-phase cells grown in YES at 28°C were examined by phase-contrast and CW staining time-lapse video microscopy. Arrows, first CW-stained septum detection; green arrowhead, septum completion (31.3 ± 1.1 min, n = 12 cells). Scale bar = 5 μm. (E) Kymograph of the CW-stained cell depicted in D (dashed rectangle). Arrows, phase 1 septum rudiment exhibiting brighter CW fluorescence; bracket, ensuing phase 2 longer septum with weaker CW fluorescence. A scheme of the septum progression during both ingression phases (phase 1, 4–12 min, and phase 2, 12–32 min) in the kymograph is shown. Scale bar = 2 μm. (F) Distinct progression of the septum length along the two ingression phases. The CW-stained septum length was quantified from time-lapse videos as in D, and the average septum length was calculated (n = 12 cells). (G) The septum ingression rates (nanometer/minute ± SD) were calculated for the indicated time intervals of phase 1 and 2 from time-lapse sequences as in D (n = 12 cells). GS, glucan synthase; SPB, spindle pole body. Error bars show SD.

Septation comprises an evolving septum structure consisting of two consecutive phases with different ingression rates and levels of calcofluor staining. (A) Model of the septum synthesis and formation of a cleavage furrow. Septation and CR constriction start in early–mid anaphase B with the activation of PS synthesis by the action of Bgs1 glucan synthase. Septum ingression is slow during anaphase B and increases during telophase (adapted from Cortés et al., 2018). (B) Scheme of the timing of the stable localization of different proteins as a ring at the cell middle with respect to the onset of septation and CR constriction (T = 0), first PS detection by CW staining (T = +0.5 min), and the mitotic phases (adapted from Cortés et al., 2018). (C) Model of septation (adapted from Muñoz et al., 2013). A PS incipient rudiment formed by the sole action of Bgs1 becomes a fast-ingressing septum during telophase, which is a three-layered structure formed by the simultaneous synthesis of PS and SS by the action of Bgs1, Bgs4, and Ags1. The septum increases in thickness throughout ingression, and the complete septum maturation proceeds by additional SS synthesis. Finally, cell separation proceeds by PS degradation, forming a fission scar. Right: TEM magnifications from rudiments to longer septa increasing in thickness throughout ingression are shown. Large arrow, direction of septum ingression and CR constriction; small arrow, direction of septum thickness increase; line points inside the CR, glucan synthase rings, PS, and SS. Scale bar = 1 μm. (D) WT septation showing two phases with different ingression rates and levels of CW staining. Early log-phase cells grown in YES at 28°C were examined by phase-contrast and CW staining time-lapse video microscopy. Arrows, first CW-stained septum detection; green arrowhead, septum completion (31.3 ± 1.1 min, n = 12 cells). Scale bar = 5 μm. (E) Kymograph of the CW-stained cell depicted in D (dashed rectangle). Arrows, phase 1 septum rudiment exhibiting brighter CW fluorescence; bracket, ensuing phase 2 longer septum with weaker CW fluorescence. A scheme of the septum progression during both ingression phases (phase 1, 4–12 min, and phase 2, 12–32 min) in the kymograph is shown. Scale bar = 2 μm. (F) Distinct progression of the septum length along the two ingression phases. The CW-stained septum length was quantified from time-lapse videos as in D, and the average septum length was calculated (n = 12 cells). (G) The septum ingression rates (nanometer/minute ± SD) were calculated for the indicated time intervals of phase 1 and 2 from time-lapse sequences as in D (n = 12 cells). GS, glucan synthase; SPB, spindle pole body. Error bars show SD.

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