Temperature-sensitive mutations affecting cortical morphogenesis and cell division in Paramecium tetraurelia

Abstract

Nine temperature-sensitive gene mutations affecting cellular morphogenesis were analysed and shown to be single recessive genes. Their phenotypes fall into three classes: small mutants (sm) which interfere with cell surface and basal body proliferation to produce short cells; defective fission zone mutants (dfz) which do not form a complete fission zone during cell division; and defective constriction mutants (dc) which form a normal fission zone, but do not constrict properly. In sm2 cells there is a reduction in the number of basal bodies and in the amount of cell surface produced preceding fission. This results in the production of truncated daughter cells in which most of the normal structures of either the anterior or posterior part of the cell are highly reduced or missing. Production of basal bodies in gullet primordia is also abnormal. The dfz mutants act early in the fission process to block the formation of the fission zone which precedes the formation of the fission furrow. The dc mutations act later in the fission process and lead to failure of daughter cell separation. One mutant, dc3, also shows slightly reduced proliferation of cell surface. This defect occurs prior to fission.