Regeneration of amicronucleate fragments in the hypotrichous ciliate Pseudourostyla levis

This work aims to elucidate the micronuclear functions in regeneration of the hypotrichous ciliate Pseudourostyla levis. A micronucleate stock DH-1 and an amicronucleate cell line DH-1a-6 obtained from a cell of the same stock by microsurgical enucleation were used in this work. In the operation, cells at the early stationary phase were transected at their equatorial zone by a fine glass needle. These fragments (promers and opimers) were impregnated by the protargol technique. Developmental processes of the adorai zone of membranelies (AZM), frontal-ventral-transverse (FVT) cirri, marginal cirri (MC) and dorsal kineties were very similar between micro- and amicronucleate fragments. Splitting of old membranelles in the lapel part (LP-membranelles) of the AZM, however, always occurred at stage 5 in micronucleate promers, whereas the same developmental event was observed during stages 2-3 in amicronucleate promers. These observations indicate that the absence of micronuclei does not affect cortical development and cortical organelle assembly during regeneration. At stage 9 a bare area without membranelles in the lapel part of the AZM appeared only in amicronucleate regenerants after the formation of the new AZM. After the appearance of the bare area (stage 9), the mean number of LP-membranelles (22.7 ± 3.8) of regenerants was significantly smaller than that of regenerants (42.0 ± 4.7) at stage 8 (p ≤ 0.01). These findings indicate that a considerable number of LP-membranelles were lost. Therefore, the micronuclei might play some important role in fixing LP-membranelles firmly in the cell cortex.