How does Dicty find its way?

As a cell chemotaxes, moves towards a chemical signal,~it transduces external chemical signals into mechanical motion.~~ Efficient chemotaxis is crucial for many biological processes~from wound healing to the spread of cancer.~~ We present our experimental investigations on \textit{Dictyostelium discodeum} a model organism for chemotaxis.~ We expose cells to three types of external signals: a shallow background gradient of the signaling molecule cyclic-AMP~a localized signal composed of cyclic-AMP attached to beads~and a mechanical stimulus caused by pushing beads against the exterior of the cell.~ For each stimulus we ask: what is the stability of the gradient sensing pathway and how does it influence the mechanical response. We find that the cell speed increases with increasing concentration of cyclic-AMP. In addition, Dictyostelium cells relay the signal by releasing internally manufactured cyclic-AMP out of the back of the cell. A collection of cells moves in streams, where cells follow closely behind one another. We find that the cells moving in a stream move slower towards a source of attractant than cells that are chemically treated such that they do not stream.