Edward Cox
Princeton University
The cellular slime mold Dictyostelium begins
life as a population of autonomous free living
amoebae. When they exhaust the food supply,
they signal to each other, eventually forming
a community of amoebae that cooperates as
a chemotactic, thermosensitive population
of cells that move together as a primitive
tissue. The chemotactic signal for cooperation
is cyclic AMP. Cells emit and respond to
it, and many thousands of cells on a surface
behave as an excitable system, relaying the
cyclic AMP signal as a complex pattern of
wave forms. These waves interact, and from
these early interactions, spiral waves quickly
evolve. Computational and genetic experiments
suggest that the formation of spiral waves
is under genetic control, and further suggest
that a particular enzyme involved in controlling
threshold sensitivity of the chemotactic
system breaks the circular symmetry of early
waves to form spirals. This expectation has
been confirmed with mutant strains. Since
spiral wave forms are ubiquitous in
nature, I will discuss how these findings
might be related to reentrant waves in heart
muscle, Ca waves in the fertilized egg, and
emerging evidence of excitable 2D dynamics
in populations of animals.