Evidence for stretch-regulation of fission in a sea anemone

Abstract

Fission is a natural method of reproduction in some sea anemones. Previous studies implicate various exogenous factors in influencing fission rates in anemone populations, yet little is known of endogenous regulation of fission in anemones. The tensegrity model proposes that mechanical forces drive large-scale processes by acting on the structural scaffolding of tissues to induce and propagate mechanically sensitive responses within cells. In longitudinal fission, stretching of the anemone precedes division. To explore the applicability of the basic premise of the tensegrity model, this study tests whether stretch is a mechanical stimulus involved in regulating longitudinal fission in an anemone. Natural stretching during successful and unsuccessful fission is quantitatively analyzed from time-lapse recordings. Successful fission is characterized by patterned stages of progressive stretch requiring a few hours to complete. In contrast, unsuccessful fission deviates early from this pattern. Treatment with 100 μM gadolinium, a blocker of several types of ion channel including stretch-activated ion channels, inhibits successful fission in anemones in earlier stages of natural stretch but not in later stages. Further, imposing mild artificial stretch onto anemones induces successful fission, whereas imposing more extensive stretch leads to unsuccessful fission. Unsuccessful fission in artificially stretched, or naturally stretched, gadolinium-treated anemones results in an abnormal stretched morphology and scar formation that persist until division, days later. Together, these results support a model in which stretch functions as an early regulatory mechanism in the endogenous control of longitudinal fission in a sea anemone. J. Exp. Zool. 282:344–359, 1998. © 1998 Wiley-Liss, Inc.