Cell Substratum Adhesion during Early Development of Dictyostelium discoideum

Abstract

Vegetative and developed amoebae of Dictyostelium discoideum gain traction and move rapidly on a wide range of substrata without forming focal adhesions. We used two independent assays to quantify cell-substrate adhesion in mutants and in wild-type cells as a function of development. Using a microfluidic device that generates a range of hydrodynamic shear stress, we found that substratum adhesion decreases at least 10 fold during the first 6 hr of development of wild type cells. This result was confirmed using a single-cell assay in which cells were attached to the cantilever of an atomic force probe and allowed to adhere to untreated glass surfaces before being retracted. Both of these assays showed that the decrease in substratum adhesion was dependent on the cAMP receptor CAR1 which triggers development. Vegetative cells missing talin as the result of a mutation in talA exhibited slightly reduced adhesive properties compared to vegetative wild-type cells. In sharp contrast to wild-type cells, however, these talA mutant cells did not show further reduction of adhesion during development such that after 5 hr of development they were significantly more adhesive than developed wild type cells. In addition, both assays showed that substrate adhesion was reduced in 0 hr cells when the actin cytoskeleton was disrupted by latrunculin. Consistent with previous observations, substrate adhesion was also reduced in 0 hr cells lacking the membrane proteins SadA or SibA as the result of mutations in sadA or sibA. However, there was no difference in the adhesion properties between wild type AX3 cells and these mutant cells after 6 hr of development, suggesting that neither SibA nor SadA play an essential role in substratum adhesion during aggregation. Our results provide a quantitative framework for further studies of cell substratum adhesion in Dictyostelium.

Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity

“…Dictyostelium cells are not known to form stable focal adhesions although they express homologs of talin, vinculin, and paxillin which localize to the basal surface in puncta with F-actin (1,(50)(51)(52). Because Dictyostelium cells need to migrate over a variety of surfaces in their natural environments, their substrate adhesion is thought to be largely nonspecific (53)(54)(55). For the seven validated mutants reported there was a strong correlation between flatness and adhesion.…”

Genetic control of morphogenesis in Dictyostelium

“…These highly conserved proteins act as heterodimers which have different affinities to matrix proteins such as fibronectin, laminin, collagen, or vitronectin. Dictyostelium does not have the genes for these matrix proteins or for integrins and relies mostly on van der Waals forces to gain traction on its surroundings (Loomis et al, 2012; Tarantola et al, 2014). These innate non-specific interactions may be sufficient for movement of the cells within the sheath.…”

Progress and perspectives in signal transduction, actin dynamics, and movement at the cell and tissue level: lessons fromDictyostelium

“…Dd cells move relatively rapidly, and contact between the cell and a substrate is via 'close contacts', regions where cell surface glycoproteins bind in a non-specific manner through van der Waals forces [10]. Membrane receptors (Phg1,SadA,SibA) that are involved in substrate adhesion have been identified, but they are much less specific than their mammalian counterparts, which form focal adhesions through specific cell surface receptors called integrins.…”