Thermosensitivity of pattern formation in a ciliate Chilodonella cucullulus

Abstract

AbstractDuring divisional morphogenesis of the ciliate protozoan Chilodonella cucullulus different thermosensitivity is observed at early and advanced stages of development.Thermic shocks (of 31 or 32°C) applied to cells early in division bring about resorption of new developing cortical organelles, while the same shocks do not prevent further development and cell division if applied to advanced dividers. Thus as in many other cells a transition point in thermosensitivity occurs during the cell cycle.The period before the transition point corresponds to primary pattern formation of primordia of new cortical organelles, the post transitional period corresponds to final pattern formation of sets of organelles for offspring. In control (unheated) cells some simultaneous processes of differentiation and dedifferentiation are observed both in the pre‐transitional and post‐transitional periods. Therefore the stability of development at high temperature which is attained in the post‐transitional period concerns specific selection of organelles for further development rather than over‐all stability of formed structures.The effect of preincubation at low temperature and at mild temperature on thermosensitivity at 31°C is compared. Cells preincubated at low temperature can go through one round of divisional morphogenesis, while those preincubated at mild temperature are not able to do this; instead they regress into a resorption stage. Cells preincubated at low temperature and shifted to high temperature also sometimes manifest abnormalities in the number and disposition of contractile vacuole pores (CVPs). Hence in these cells thermosensitivity of pattern formation is demonstrated.