Contact-mediated cell-assisted cell proliferation in a model eukaryotic single-cell organism: An explanation for the lag phase in shaken cell culture

Abstract

In cell culture, when cells are inoculated into fresh media, there can be a period of slow (or lag phase) growth followed by a transition to exponential growth. This period of slow growth is usually attributed to the cells' adaptation to a new environment. However, we argue that, based on observations of shaken suspension culture of Dictyostelium discoideum, a model single-cell eukaryote, this transition is due to a density effect. Attempts to demonstrate the existence of implicit cell signaling via long-range diffusible messengers (i.e., soluble growth factors) through cell-medium separation and microfluidic flow perturbation experiments produced negative results. This, in turn, led to the development of a signaling model based on direct cell-to-cell contacts. Employing a scaling argument for the collision rate due to fluid shear, we reasonably estimate the crossover density for the transition into the exponential phase and fit the observed growth kinetics.

Spontaneous emergence of large-scale cell cycle synchronization in amoeba colonies

“…The cells grown in suspensions have a broader size distribution ( Fig. 2a) than those on substrates, consistent with previous observations of cell clusters [18] and multinuclear cells [17], since the lack of solid substrate probably impedes cytokinesis. These are all counted as a single particle by automated counting (Fig.…”

“…Next, we investigate the possibility that cells secrete a growth factor or a mitogen that serves as a synchronization signal. We analyzed the microfluidic experiments we performed previously [18] with cells grown on a substrate in a PDMS microfluidic device (Fig. 2c).…”

“…In these experiments the cells naturally adhered to the glass while fresh growth medium flowed above them with 0.6, 1.7 and 17 µm/s flow speeds. If the synchronization signal is a small signaling molecule with diffusion coefficient about 300 µm 2 /s, then these flow speeds correspond to Peclet numbers (see SI), quantifying the ratio of advective to diffusive transport, on the order of 0.4 (diffusion dominated), 1 and 10 (advection dominated), respectively [18].…”

“…There is evidence for quorum sensing factors [18], [25], growth factors and factors repressing cell proliferation in D. discoideum [26], [27], [28] and their potential role in synchronization remains to be determined. But, in fact, in our monoclonal experiments ( Fig.…”

A Retinoblastoma Orthologue Is Required for the Sensing of a Chalone in Dictyostelium discoideum

“…‫ء‬ indicates a P value of Ͻ0.05, ‫ءء‬ indicates a P value of Ͻ0.01, and ‫ءءء‬ indicates a P value of Ͻ0.001 (t test). (34), and at higher densities, high levels of accumulated endogenous AprA and CfaD can interfere with the assay. We measured the effect of rAprA and rCfaD at 18 h, as we have observed that culturing of cells with exogenous recombinant proteins past 24 h leads to degradation and/or ingestion of the recombinant proteins (our unpublished data).…”