Whorl Formation in Polysphondylium violaceum : Relevance to Organization by Cyclic AMP

Abstract

Whorl formation in Polysphondylium is a simple and good system for the study of pattern formation. The first step of whorl formation is characterized by separation of the rear cell mass from an advancing primary mass during culmination. Using the iontophoresis method, it has been shown that after the establishment of multicellular organization cells respond chemotactically to 3′,5′ ‐cyclic adenosine monophosphate (cAMP), but not to glorin, the chemoattaractant at the aggregating stage. P. violaceum cell masses were also found to secrete actively cAMP. Therefore, morphogenetic movement of P. violaceum cells after aggregation could be controlled mainly by the cAMP signalling system. Vital staining of cells with neutral red (NR) revealed that there are anterior‐like cells stained well with NR in the posterior region of a migrating P. violaceum slug, and that the staining pattern changes markedly during whorl formation. Just before separation of the whorl mass, the anterior‐like cells altered their distribution, and eventually were arranged as an equatorial band on the surface of the presumptive whorl mass, which probably would turn to organizing tip cells of the secondary masses left on the primary stalk. Thus whorl formation may be caused by separation of the strongest cAMP‐source into two regions; the primary (anterior) and secondary (posterior) tips.