A Sizer model for cell differentiation in
            <i>Arabidopsis thaliana</i>
            root growth

Pavelescu, Irina; Vilarrasa-Blasi, Josep; Planas-Riverola, Ainoa; González-García, Mary-Paz; Caño‐Delgado, Ana I.; Ibañes, Marta

doi:10.15252/msb.20177687

Cited by 49 publications

(47 citation statements)

References 58 publications

(118 reference statements)

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“…To correlate the CMT activity with distinct phases of cell growth, we defined root zones based on criteria described in previous reports (Verbelen et al, 2006;Ivanov & Dubrovsky, 2013;Slovak et al, 2016;Pavelescu et al, 2018). In the transition zone (TZ), cells start to elongate until they reach a length of~45 lm; the elongation zone (EZ) includes cells longer than 45 lm until they enter the differentiation zone (DZ) characterized by initiation of root hairs ( Fig 1A).…”

Section: Resultsmentioning

confidence: 99%

Phytohormone cytokinin guides microtubule dynamics during cell progression from proliferative to differentiated stage

et al. 2020

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Cell production and differentiation for the acquisition of specific functions are key features of living systems. The dynamic network of cellular microtubules provides the necessary platform to accommodate processes associated with the transition of cells through the individual phases of cytogenesis. Here, we show that the plant hormone cytokinin fine‐tunes the activity of the microtubular cytoskeleton during cell differentiation and counteracts microtubular rearrangements driven by the hormone auxin. The endogenous upward gradient of cytokinin activity along the longitudinal growth axis in Arabidopsis thaliana roots correlates with robust rearrangements of the microtubule cytoskeleton in epidermal cells progressing from the proliferative to the differentiation stage. Controlled increases in cytokinin activity result in premature re‐organization of the microtubule network from transversal to an oblique disposition in cells prior to their differentiation, whereas attenuated hormone perception delays cytoskeleton conversion into a configuration typical for differentiated cells. Intriguingly, cytokinin can interfere with microtubules also in animal cells, such as leukocytes, suggesting that a cytokinin‐sensitive control pathway for the microtubular cytoskeleton may be at least partially conserved between plant and animal cells.

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Section: Resultsmentioning

confidence: 99%

Phytohormone cytokinin guides microtubule dynamics during cell progression from proliferative to differentiated stage

et al. 2020

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“…where mitosis is triggered upon reaching a prescribed size threshold 2V , is perhaps the simplest (and the oldest proposed) mechanism for size homeostasis [40][41][42] . In this case, the duration of the first cell cycle decreases with increasing initial size V 0 .…”

Section: Sizer-based Cell Division Is Incompatible With a Non-monotonmentioning

confidence: 99%

Modeling homeostasis mechanisms that set the target cell size

Vargas-García

Björklund

Singh

2020

Sci Rep

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How organisms maintain cell size homeostasis is a long-standing problem that remains unresolved, especially in multicellular organisms. Recent experiments in diverse animal cell types demonstrate that within a cell population, cellular proliferation is low for small and large cells, but high at intermediate sizes. Here we use mathematical models to explore size-control strategies that drive such a non-monotonic profile resulting in the proliferation capacity being maximized at a target cell size. Our analysis reveals that most models of size control yield proliferation capacities that vary monotonically with cell size, and non-monotonicity requires two key mechanisms: (1) the growth rate decreases with increasing size for excessively large cells; and (2) cell division occurs as per the Adder model (division is triggered upon adding a fixed size from birth), or a Sizer-Adder combination. Consistent with theory, Jurkat T cell growth rates increase with size for small cells, but decrease with size for large cells. In summary, our models show that regulation of both growth and cell-division timing is necessary for size control in animal cells, and this joint mechanism leads to a target cell size where cellular proliferation capacity is maximized. Cell size control is a fundamental aspect of biology observed at different domains of life, but in most cases remains poorly understood 3-9. Two popular models for cell size control have been extensively studied and debated 10. In the "sizer" or the size-checkpoint model, cell-cycle transitions occur after attainment of a minimum cell mass or size, whereas in the "adder" model cells add a fixed amount of size in each division cycle independent of the daughter size. Strong evidence for adder has been reported in a diverse set of prokaryotes 11-21 and budding yeast 22. In cultured mammalian cell lines both adder, sizer and intermediate models can be observed 23,24 , while in the mouse epidermis in vivo, a sizer behavior is apparent 25. Recent experiments in animal cells revealed an intriguing observation about cellular proliferation that ties deeply into size control, suggesting an evolutionary reason why cells aim to maintain a certain size. In these experiments 1 , cells within a population were first sorted into several subpopulations based on cell size, and then the net proliferation (relative fold-change in cell count) was quantified for each cultured subpopulation after 72 h. Throughout the paper we refer to this relative increase in cell counts as the proliferation capacity. Interestingly, data across several cell types shows a non-monotonic bell-shaped profile, where the proliferation capacity is maximized at a target cell size (Fig. 1). Importantly, apoptosis rates were similar for large and average-sized cells, and hence the decrease in proliferation at higher sizes is not simply due to elevated cell death 1,26-30. Cellular proliferation measured via dye-dilution experiments showed identical trends for varying cells sizes (see supplementary figure S4 in 1), providing...

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“…The second is non-cell-autonomous, where extrinsic signals impinge on cells at the boundary and modify behavior. In distinguishing these views, we note that cell autonomy has been considered to underlie certain root growth behaviors ( Band et al., 2012 ; Cole et al., 2014 ; Pavelescu et al., 2018 ) but in contrast to generate discontinuous growth patterns that are contrary to observations of root anatomy ( De Vos et al., 2014 ). These mechanisms are not exclusive, and indeed both probably are operating to delimit boundaries effectively.…”

Section: Introductionmentioning

confidence: 89%

Positioning the Root Elongation Zone Is Saltatory and Receives Input from the Shoot

et al. 2020

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Summary In the root, meristem and elongation zone lengths remain stable, despite growth and division of cells. To gain insight into zone stability, we imaged individual Arabidopsis thaliana roots through a horizontal microscope and used image analysis to obtain velocity profiles. For a root, velocity profiles obtained every 5 min over 3 h coincided closely, implying that zonation is regulated tightly. However, the position of the elongation zone saltated, by on average 17 μm every 5 min. Saltation was apparently driven by material elements growing faster and then slower, while moving through the growth zone. When the shoot was excised, after about 90 min, growth zone dynamics resembled those of intact roots, except that the position of the elongation zone moved, on average, rootward, by several hundred microns in 24 h. We hypothesize that mechanisms determining elongation zone position receive input from the shoot.

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A Sizer model for cell differentiation in Arabidopsis thaliana root growth

Cited by 49 publications

References 58 publications

Phytohormone cytokinin guides microtubule dynamics during cell progression from proliferative to differentiated stage

Phytohormone cytokinin guides microtubule dynamics during cell progression from proliferative to differentiated stage

Modeling homeostasis mechanisms that set the target cell size

Positioning the Root Elongation Zone Is Saltatory and Receives Input from the Shoot

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