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Live imaging-based model selection reveals periodic regulation of the stochastic G1/S phase transition in vertebrate axial development.

Sugiyama M, Saitou T, Kurokawa H, Sakaue-Sawano A, Imamura T, Miyawaki A, Iimura T - PLoS Comput. Biol. (2014)

Bottom Line: This G1/S transition did not occur in a synchronous manner, but rather exhibited a stochastic process, since a mixed population of red and green cells was always inserted between newly formed red (G1) notochordal cells and vacuolating green cells.To obtain a better understanding of this regulatory mode, we constructed a mathematical model and performed a model selection by comparing the results obtained from the models with those from the experimental data.This approach may have implications for the characterization of the pathophysiological tissue growth mode.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, Wako-city, Saitama, Japan.

ABSTRACT
In multicellular organism development, a stochastic cellular response is observed, even when a population of cells is exposed to the same environmental conditions. Retrieving the spatiotemporal regulatory mode hidden in the heterogeneous cellular behavior is a challenging task. The G1/S transition observed in cell cycle progression is a highly stochastic process. By taking advantage of a fluorescence cell cycle indicator, Fucci technology, we aimed to unveil a hidden regulatory mode of cell cycle progression in developing zebrafish. Fluorescence live imaging of Cecyil, a zebrafish line genetically expressing Fucci, demonstrated that newly formed notochordal cells from the posterior tip of the embryonic mesoderm exhibited the red (G1) fluorescence signal in the developing notochord. Prior to their initial vacuolation, these cells showed a fluorescence color switch from red to green, indicating G1/S transitions. This G1/S transition did not occur in a synchronous manner, but rather exhibited a stochastic process, since a mixed population of red and green cells was always inserted between newly formed red (G1) notochordal cells and vacuolating green cells. We termed this mixed population of notochordal cells, the G1/S transition window. We first performed quantitative analyses of live imaging data and a numerical estimation of the probability of the G1/S transition, which demonstrated the existence of a posteriorly traveling regulatory wave of the G1/S transition window. To obtain a better understanding of this regulatory mode, we constructed a mathematical model and performed a model selection by comparing the results obtained from the models with those from the experimental data. Our analyses demonstrated that the stochastic G1/S transition window in the notochord travels posteriorly in a periodic fashion, with doubled the periodicity of the neighboring paraxial mesoderm segmentation. This approach may have implications for the characterization of the pathophysiological tissue growth mode.

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Summary of methodology and findings.(A) Schematic summary of our methodology. Our methodological approach consisted of three successive processes: 1) live imaging and image processing, 2) model establishment and 3) model selection. Each process was further divided into sub-processes, as noted in each box. (B) Schematic illustration of the regulatory mode of the G1/S transition in the developing notochord. (B-i, B-ii) Once the G1/S transition window was established between populations of anterior green (S) and posterior (G1) red cells, the G1 cells in the window stochastically transitioned into the S phase (B-i), after which the window was finally filled with green (S) cells (B-ii). (B-iii, B-iv) The next transition window was established posteriorly adjacent to the previous window. As observed in the previous cycle, an increasing number of green (S) cells filled the window as time progressed (B-iii), until the window was finally filled with green cells (B-iv).
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pcbi-1003957-g008: Summary of methodology and findings.(A) Schematic summary of our methodology. Our methodological approach consisted of three successive processes: 1) live imaging and image processing, 2) model establishment and 3) model selection. Each process was further divided into sub-processes, as noted in each box. (B) Schematic illustration of the regulatory mode of the G1/S transition in the developing notochord. (B-i, B-ii) Once the G1/S transition window was established between populations of anterior green (S) and posterior (G1) red cells, the G1 cells in the window stochastically transitioned into the S phase (B-i), after which the window was finally filled with green (S) cells (B-ii). (B-iii, B-iv) The next transition window was established posteriorly adjacent to the previous window. As observed in the previous cycle, an increasing number of green (S) cells filled the window as time progressed (B-iii), until the window was finally filled with green cells (B-iv).

Mentions: As an inventive application of Fucci technology [48]–[50], the integrative approach we applied in this study was comprised of three parts, including quantitative data acquisition from live imaging, model establishment and model selection (Figure 8A), and revealed that the progressive mode of the G1/S transition window travels in a periodic fashion in newly formed notochordal cells during embryonic axis elongation, as schematically demonstrated in Figure 8b. Once notochordal cells are formed from their precursor pool located at the tip of an embryo, the cells in the G1 phase shown in red are arranged in a line. In the next step, a group of G1 cells enters the S phase. This G1/S transition is temporally stochastic; therefore, a mixed population of green and red cells is established between a group of posterior red cells and a group of anterior green cells, which we described as the G1/S transition window (Figure 8B i). In this window, an increasing number of G1 cells enters the S phase shown in green; therefore, this region is eventually filled with green cells (Figure 8B ii). In the subsequent cycle, the next G1/S transition window shifts a width of 16 cells (two somite widths) posteriorly, thus establishing a new window (Figure 8B iii). The G1 cells in this window enter the S phase in a stochastic manner, finally filling the window (Figure 8B iv).


Live imaging-based model selection reveals periodic regulation of the stochastic G1/S phase transition in vertebrate axial development.

Sugiyama M, Saitou T, Kurokawa H, Sakaue-Sawano A, Imamura T, Miyawaki A, Iimura T - PLoS Comput. Biol. (2014)

Summary of methodology and findings.(A) Schematic summary of our methodology. Our methodological approach consisted of three successive processes: 1) live imaging and image processing, 2) model establishment and 3) model selection. Each process was further divided into sub-processes, as noted in each box. (B) Schematic illustration of the regulatory mode of the G1/S transition in the developing notochord. (B-i, B-ii) Once the G1/S transition window was established between populations of anterior green (S) and posterior (G1) red cells, the G1 cells in the window stochastically transitioned into the S phase (B-i), after which the window was finally filled with green (S) cells (B-ii). (B-iii, B-iv) The next transition window was established posteriorly adjacent to the previous window. As observed in the previous cycle, an increasing number of green (S) cells filled the window as time progressed (B-iii), until the window was finally filled with green cells (B-iv).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256085&req=5

pcbi-1003957-g008: Summary of methodology and findings.(A) Schematic summary of our methodology. Our methodological approach consisted of three successive processes: 1) live imaging and image processing, 2) model establishment and 3) model selection. Each process was further divided into sub-processes, as noted in each box. (B) Schematic illustration of the regulatory mode of the G1/S transition in the developing notochord. (B-i, B-ii) Once the G1/S transition window was established between populations of anterior green (S) and posterior (G1) red cells, the G1 cells in the window stochastically transitioned into the S phase (B-i), after which the window was finally filled with green (S) cells (B-ii). (B-iii, B-iv) The next transition window was established posteriorly adjacent to the previous window. As observed in the previous cycle, an increasing number of green (S) cells filled the window as time progressed (B-iii), until the window was finally filled with green cells (B-iv).
Mentions: As an inventive application of Fucci technology [48]–[50], the integrative approach we applied in this study was comprised of three parts, including quantitative data acquisition from live imaging, model establishment and model selection (Figure 8A), and revealed that the progressive mode of the G1/S transition window travels in a periodic fashion in newly formed notochordal cells during embryonic axis elongation, as schematically demonstrated in Figure 8b. Once notochordal cells are formed from their precursor pool located at the tip of an embryo, the cells in the G1 phase shown in red are arranged in a line. In the next step, a group of G1 cells enters the S phase. This G1/S transition is temporally stochastic; therefore, a mixed population of green and red cells is established between a group of posterior red cells and a group of anterior green cells, which we described as the G1/S transition window (Figure 8B i). In this window, an increasing number of G1 cells enters the S phase shown in green; therefore, this region is eventually filled with green cells (Figure 8B ii). In the subsequent cycle, the next G1/S transition window shifts a width of 16 cells (two somite widths) posteriorly, thus establishing a new window (Figure 8B iii). The G1 cells in this window enter the S phase in a stochastic manner, finally filling the window (Figure 8B iv).

Bottom Line: This G1/S transition did not occur in a synchronous manner, but rather exhibited a stochastic process, since a mixed population of red and green cells was always inserted between newly formed red (G1) notochordal cells and vacuolating green cells.To obtain a better understanding of this regulatory mode, we constructed a mathematical model and performed a model selection by comparing the results obtained from the models with those from the experimental data.This approach may have implications for the characterization of the pathophysiological tissue growth mode.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, Wako-city, Saitama, Japan.

ABSTRACT
In multicellular organism development, a stochastic cellular response is observed, even when a population of cells is exposed to the same environmental conditions. Retrieving the spatiotemporal regulatory mode hidden in the heterogeneous cellular behavior is a challenging task. The G1/S transition observed in cell cycle progression is a highly stochastic process. By taking advantage of a fluorescence cell cycle indicator, Fucci technology, we aimed to unveil a hidden regulatory mode of cell cycle progression in developing zebrafish. Fluorescence live imaging of Cecyil, a zebrafish line genetically expressing Fucci, demonstrated that newly formed notochordal cells from the posterior tip of the embryonic mesoderm exhibited the red (G1) fluorescence signal in the developing notochord. Prior to their initial vacuolation, these cells showed a fluorescence color switch from red to green, indicating G1/S transitions. This G1/S transition did not occur in a synchronous manner, but rather exhibited a stochastic process, since a mixed population of red and green cells was always inserted between newly formed red (G1) notochordal cells and vacuolating green cells. We termed this mixed population of notochordal cells, the G1/S transition window. We first performed quantitative analyses of live imaging data and a numerical estimation of the probability of the G1/S transition, which demonstrated the existence of a posteriorly traveling regulatory wave of the G1/S transition window. To obtain a better understanding of this regulatory mode, we constructed a mathematical model and performed a model selection by comparing the results obtained from the models with those from the experimental data. Our analyses demonstrated that the stochastic G1/S transition window in the notochord travels posteriorly in a periodic fashion, with doubled the periodicity of the neighboring paraxial mesoderm segmentation. This approach may have implications for the characterization of the pathophysiological tissue growth mode.

Show MeSH
Related in: MedlinePlus