Intracellular ATP levels influence cell fates in Dictyostelium discoideum differentiation

Cell-cell heterogeneity in phosphoenolpyruvate carboxylase biases early cell fate priming in Dictyostelium discoideum

Glucose metabolism is a key factor characterizing the cellular state during multicellular development. In metazoans, the metabolic state of undifferentiated cells correlates with growth/differentiation transition and cell fate determination. Notably, the cell fate of the Amoebozoa species Dictyostelium discoideum is biased by the presence of glucose and is also correlated with early differences in intracellular ATP. However, the relationship between early cell-cell heterogeneity, cell differentiation, and the metabolic state is unclear. To address the link between glucose metabolism and cell differentiation in D. discoideum, we studied the role of phosphoenolpyruvate carboxylase (PEPC), a key enzyme in the PEP-oxaloacetate-pyruvate node, a core junction that dictates the metabolic flux of glycolysis, the TCA cycle, and gluconeogenesis. We demonstrate that there is cell-cell heterogeneity in PEPC promoter activity in vegetative cells, which depends on nutrient conditions, and that cells with high PEPC promoter activity differentiate into spores. The PEPC null mutant exhibited an aberrantly high prestalk/prespore ratio, and the spore mass of the fruiting body was glassy and consisted of immature spores. Furthermore, the PEPC null mutant had high ATP levels and low mitochondrial membrane potential. Our results suggest the importance of cell-cell heterogeneity in the levels of metabolic enzymes during early cell fate priming.

mTORC1 pathway activity biases cell fate choice

Pluripotent stem cells can differentiate into distinct cell types but the intracellular pathways controlling cell fate choice are not well understood. The social amoeba Dictyostelium discoideum is a simplified system to study choice preference as proliferating amoebae enter a developmental cycle upon starvation and differentiate into two major cell types, stalk and spores, organised in a multicellular fruiting body. Factors such as acidic vesicle pH predispose amoebae to one fate. Here we show that the mechanistic target of rapamycin complex 1 (mTORC1) pathway has a role in cell fate bias in Dictyostelium. Inhibiting the mTORC1 pathway activity by disruption of Rheb (activator Ras homolog enriched in brain), or treatment with the mTORC1 inhibitor rapamycin prior to development, biases cells to a spore cell fate. Conversely activation of the pathway favours stalk cell differentiation. The Set1 histone methyltransferase, responsible for histone H3 lysine4 methylation, in Dictyostelium cells regulates transcription at the onset of development. Disruption of Set1 leads to high mTORC1 pathway activity and stalk cell predisposition. The ability of the mTORC1 pathway to regulate cell fate bias of cells undergoing differentiation offers a potential target to increase the efficiency of stem cell differentiation into a particular cell type.

Single-cell phenotypic plasticity modulates social behavior in Dictyostelium discoideum

In Dictyostelium chimeras, "cheaters" are strains that positively bias their contribution to the pool of spores, i.e., the reproductive cells resulting from development. On evolutionary time scales, the selective advantage; thus, gained by cheaters is predicted to undermine collective functions whenever social behaviors are genetically determined. Genotypes; however, are not the sole determinant of spore bias, but the relative role of genetic and plastic differences in evolutionary success is unclear. Here, we study chimeras composed of cells harvested in different phases of population growth. We show that such heterogeneity induces frequency-dependent, plastic variation in spore bias. In genetic chimeras, the magnitude of such variation is not negligible and can even reverse the classification of a strain's social behavior. Our results suggest that differential cell mechanical properties can underpin, through biases emerging during aggregation, a "lottery" in strains' reproductive success that may counter the evolution of cheating.

Microbial models of development: Inspiration for engineering self-assembled synthetic multicellularity

While the field of synthetic developmental biology has traditionally focused on the study of the rich developmental processes seen in metazoan systems, an attractive alternate source of inspiration comes from microbial developmental models. Microbes face unique lifestyle challenges when forming emergent multicellular collectives. As a result, the solutions they employ can inspire the design of novel multicellular systems. In this review, we dissect the strategies employed in multicellular development by two model microbial systems: the cellular slime mold Dictyostelium discoideum and the biofilm-forming bacterium Bacillus subtilis. Both microbes face similar challenges but often have different solutions, both from metazoan systems and from each other, to create emergent multicellularity. These challenges include assembling and sustaining a critical mass of participating individuals to support development, regulating entry into development, and assigning cell fates. The mechanisms these microbial systems exploit to robustly coordinate development under a wide range of conditions offer inspiration for a new toolbox of solutions to the synthetic development community. Additionally, recreating these phenomena synthetically offers a pathway to understanding the key principles underlying how these behaviors are coordinated naturally.

ATP levels influence cell movement during the mound phase in Dictyostelium discoideum as revealed by ATP visualization and simulation

Cell migration plays an important role in multicellular organism development. The cellular slime mold Dictyostelium discoideum is a useful model organism for the study of cell migration during development. Although cellular ATP levels are known to determine cell fate during development, the underlying mechanism remains unclear. Here, we report that ATP-rich cells efficiently move to the central tip region of the mound against rotational movement during the mound phase. A simulation analysis based on an agent-based model reproduces the movement of ATP-rich cells observed in the experiments. These findings indicate that ATP-rich cells have the ability to move against the bulk flow of cells, suggesting a mechanism by which high ATP levels determine the cell fate of differentiation.

Intracellular ATP levels influence cell fates in Dictyostelium discoideum differentiation

Multicellular organisms contain various differentiated cells. Fate determination of these cells remains a fundamental issue. The cellular slime mold Dictyostelium discoideum is a useful model organism for studying differentiation; it proliferates as single cells in nutrient-rich conditions, which aggregate into a multicellular body upon starvation, subsequently differentiating into stalk cells or spores. The fates of these cells can be predicted in the vegetative phase: Cells expressing higher and lower levels of omt12 differentiate into stalk cells and spores, respectively. However, omt12 is merely a marker gene and changes in its expression do not influence the cell fate, and determinant factors remain unknown. In this study, we analyzed cell fate determinants in the stalk-destined and spore-destined cells that were sorted based on omt12 expression. Luciferase assay demonstrated higher levels of intracellular ATP in the stalk-destined cells than in the spore-destined cells. Live-cell observation during development using ATP sensor probes revealed that cells with higher ATP levels differentiated into stalk cells. Furthermore, reducing the ATP level by treating with an inhibitor of ATP production changed the differentiation fates of the stalk-destined cells to spores. These results suggest that intracellular ATP levels influence cell fates in D. discoideum differentiation.