Interdependence of Cell Cycle Events in Tetrahymena thermophila: Formation of Contractile Vacuole Pore and Fission Gap in Ciliary Meridians*

Abstract

SYNOPSIS The formation of the contractile vacuole pore (CVP) in Tetrahymena thermophila. genotype molb/molb is temporally and spatially associated with the formation of the fission gap in the CVP meridian. New CVPs arise when fission gaps appear in CVP meridians, the new pores being found anterior to the gaps. When, however, CVP meridians are rotated 180°, the fission gaps develop late. In more than 1/3 of the 180°‐rotated CVP meridians, the new CVPs are formed before the appearance of the fission gap. Evidently, the appearance of the gap is not a prerequisite for CVP formation. Nevertheless, mutants exist in which the absence of fission gap and CVP are correlated in some cases and in which the presence of supernumerary fission gap and CVP are correlated in other instances. It is suggested that the 2 developmental events, although not causally related to each other, may be controlled by a common morpho‐genetic signal. This commits a certain site (mid‐body) along a ciliary meridian to develop the fission gap as well as the CVP; however, after this step of commitment, the appearance of the fission gap is delayed in 180°‐rotated CVP meridians.