Abstract
BackgroundCellular functions can be regulated by cell-cell interactions that are influenced by extra-cellular, density-dependent signaling factors. Dictyostelium grow as individual cells in nutrient-rich sources, but, as nutrients become depleted, they initiate a multi-cell developmental program that is dependent upon a cell-density threshold. We hypothesized that novel secreted proteins may serve as density-sensing factors to promote multi-cell developmental fate decisions at a specific cell-density threshold, and use Dictyostelium in the identification of such a factor.ResultsWe show that multi-cell developmental aggregation in Dictyostelium is lost upon minimal (2-fold) reduction in local cell density. Remarkably, developmental aggregation response at non-permissive cell densities is rescued by addition of conditioned media from high-density, developmentally competent cells. Using rescued aggregation of low-density cells as an assay, we purified a single, 150-kDa extra-cellular protein with density aggregation activity. MS/MS peptide sequence analysis identified the gene sequence, and cells that overexpress the full-length protein accumulate higher levels of a development promoting factor (DPF) activity than parental cells, allowing cells to aggregate at lower cell densities; cells deficient for this DPF gene lack density-dependent developmental aggregation activity and require higher cell density for cell aggregation compared to WT. Density aggregation activity co-purifies with tagged versions of DPF and tag-affinity-purified DPF possesses density aggregation activity. In mixed development with WT, cells that overexpress DPF preferentially localize at centers for multi-cell aggregation and define cell-fate choice during cytodifferentiation. Finally, we show that DPF is synthesized as a larger precursor, single-pass transmembrane protein, with the p150 fragment released by proteolytic cleavage and ectodomain shedding. The TM/cytoplasmic domain of DPF possesses cell-autonomous activity for cell-substratum adhesion and for cellular growth.ConclusionsWe have purified a novel secreted protein, DPF, that acts as a density-sensing factor for development and functions to define local collective thresholds for Dictyostelium development and to facilitate cell-cell communication and multi-cell formation. Regions of high DPF expression are enriched at centers for cell-cell signal-response, multi-cell formation, and cell-fate determination. Additionally, DPF has separate cell-autonomous functions for regulation of cellular adhesion and growth.
Highlights
Cellular functions can be regulated by cell-cell interactions that are influenced by extra-cellular, density-dependent signaling factors
Dictyostelium secrete a factor that modulates cell-densitydependent, developmental aggregation When deprived of nutrients, Dictyostelium initiate a developmental program leading to multi-cell aggregation
Dictyostelium grow in the wild as individual cells, but when they become starved for nutrients they are poised to enter a multi-cell developmental program
Summary
Cellular functions can be regulated by cell-cell interactions that are influenced by extra-cellular, density-dependent signaling factors. We hypothesized that novel secreted proteins may serve as density-sensing factors to promote multi-cell developmental fate decisions at a specific cell-density threshold, and use Dictyostelium in the identification of such a factor. Cell-density sensing is broadly associated with response to signaling molecules that accumulate in the extracellular milieu in proportion to cellular mass. While perhaps often described as quorum sensing in the context of bacterial sociality and virulence [1], it is recognized that secreted factors in both prokaryotes and eukaryotes are sensed and function most effectively at threshold concentrations that directly reflect local cell density [2]. Thereby, the secretion and accumulation of dependent concentrations of specific molecules can be a read-out for effective cell density. Changing concentrations relative to distance thereby provide an effective parallel for monitoring the local collective cellular environmental
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
