A chemotactic model for the advance and retreat of the primitive streak inavian development

The formation of the primitive streak in early avian development marks the onset of gastrulation, during which large scale cell movement leads to a tr ilaminar blastoderm comprising prospective endodermal, mesodermal and ectod ermal tissue. During streak formation a specialized group of cells first mo ves anteriorly as a coherent column, beginning from the posterior end of th e prospective anterior-posterior axis (a process called progression), and t hen reverses course and returns to the most posterior point on the axis (a process called regression). To date little is known concerning the mechanis ms controlling either progression or regression. Here we develop a model in which chemotaxis directs the cell movement and which is capable of reprodu cing the principal features connected with progression and regression of th e primitive streak. We show that this model exhibits a number of experiment ally-observed features of normal and abnormal streak development, and we pr opose a number of experimental tests which may serve to illuminate the mech anisms. This paper represents the first attempt to model the global feature s of primitive streak formation, and provides an initial stage in the devel opment of a more biologically-realistic discrete cell model that will allow for variation of properties between cells and control over movement of ind ividual cells. (C) 2000 Society for Mathematical Biology.