Interspecific micronuclear transplantation in Paramecium: nucleogenesis and stomatogenesis in asexual and sexual reproduction

The micronucleus of Paramecium plays an essential role in the development of the oral apparatus in both asexual and sexual cycles. The present study analyses this somatic function of the micronucleus by interspecific transplantation of the micronucleus between two species, P. jenningsi and P. tetraurelia. The two species are similar in nucleogenesis in the sexual cycle, in the dependence of stomatogenesis on the micronucleus and in the pattern of the oral ciliature. P. jenningsi, however, has a longer oral apparatus. Renucleated cell lines were derived from heterospecific transplantation (P. jenningsi amicronuclcates implanted with micronuclei of P. tetraurelia), and also from homospecific transplantation (P. jenningsi). Both homoand heterospecific transplants exhibited abnormal micronuclear propagation during cell division. In the sexual cycle, the heterospecific transplants exhibited more severe micronuclear anomalies, suggesting interspecific incompatibility. On the other hand, the stomatogenic consequences of the two types of transplants in the asexual and sexual cycles were similar. It is concluded that micronuclear functions, in the assembly and normal patterning of the oral ciliature in the sexual cycle, are not species-specific. However, the oral apparatuses developed by the homoand heterospecific transplants were similar in length, and approaching that of normal P. jenningsi. Hence, even though the micronucleus is necessary for developing normal oral length, the oral length characteristic of a species is determined by species-specific nonmicronuclear factors. The present findings resemble heterospecific dermal-epidermal inductive interactions in multicellular development, with the micronucleus exerting a nonspecies-specific 'intracellular inductive stimulus' on the oral anarchic field to promote oral development.