The adventures of Dicty, the Dictyostelium cell

The amoeba Dictyostelium discoideum is a model system for the study of cellular migration, an important physiological process that occurs in embryonic development, wound healing, and cancer metastasis. We studied the motion of D. discoideum on surfaces with various topographies, particularly those that affect the direction of cellular migration. Topographical features, such as ridges (speed bumps) and cliffs, were fabricated using multiphoton absorption polymerization.¹ As the cells encountered these topographical features, we tracked their motion.

When cells undergoing chemotaxis, directed migration in response to a chemical signal, are directed off of a cliff, they do not fall off the cliff. Instead, they search for new attachment points, eventually change direction, and continue moving along the edge of the cliff [Figs. 1(b) and 1(c)]. When a tightrope is suspended between cliffs, some cells find the tightrope and migrate along it, as shown in Fig. 1(d).

To disentangle motion directed by chemical signals from that directed by surface topography, we used mutant aca- D. discoideum that do not emit cyclic adenosine monophosphate and thus do not provide each other with directional chemical signals. Figure 2 shows the tracks of aca- cells undergoing chemokinesis, migration in response to a uniform chemical stimulus, on a flat surface. This image provides a visually striking indication that such cells migrate randomly. When these randomly migrating cells encounter a ridge, they tend to move along that ridge, even if it is not as high as the cell [Fig. 1(a)].