Micromanipulation in Paramecium: From non-mendelian inheritance to the outlook for versatile micromachines

Abstract

This review addresses nine areas of knowledge revealed by micromanipulations performed with Paramecium. Microinjection has shown that sexual maturation and senescence of Paramecium caudatum is a programmed process conducted by a specific gene and its product protein. In Paramecium tetraurelia, autogamy was revealed to depend on the number of DNA syntheses rather than the number of cell divisions in clonal aging. The cytoplasmic complementarity test established that microinjection of wild-type cytoplasm can correct genetic defects of mutants. The concept of complementarity together with protein chemistry revealed compounds that control membrane excitability. In non-Mendelian inheritance, noncoding small RNAs made from the parental micronucleus regulate the rearrangement of the progeny's macronuclear DNA. The macronucleus has the potential to be used as a factory for genetic engineering. The development and differentiation of progeny's nuclei in mating pairs are controlled by the parental macronucleus. The chemical reaction processes associated with exocytosis have been revealed by microinjection of various enzymes and antibodies. Using the fusion gene of histone H2B and yellow-fluorescence protein, it was revealed that the fusion gene-mRNA is transferred between cells during mating. Experiments with endosymbiotic bacteria and the host shed light on the conditions needed to establish sustainable symbiotic relationships.

Keywords: behavioral mutants; complementarity test; conjugation; endosymbiosis; exocytosis; life history; membrane excitation; nucleus differentiation; scnRNA.

FIGURE 1

Synkaryon formation during conjugation of Paramecium caudatum. The diagram shows the changes in the micronucleus when cells of complementary mating types (O‐type and E‐type) mate. Micronuclei undergo meiosis in both cells, eventually resulting in two haploid (n) nuclei in each cell. One of them is exchanged with the partner cell, and the nuclei fuse to form a diploid (2n) synkaryon. A circle with an X inside indicates a degenerating nucleus

FIGURE 2

Nuclear differentiation and karyonide formation in Paramecium caudatum. Stages 1 to 4: A synkaryon (light green) undergoes three fissions to form eight nuclei. Stage 5: the most anterior nuclei (red) become micronuclei, and the posterior nuclei (light blue) become the macronuclear anlagen which are destined to become macronuclei. Stage 6: Three micronuclei degenerate and disappear, and the remaining one conveys the genome to the next generation. The macronuclear anlagen (blue) initiates DNA synthesis. Stage 7: Cell division occurs, the micronucleus undergoes mitosis and one product passes to each daughter cell. The macronuclear anlagen do not divide, and two pass to daughter cells (Stage 8). Stage 9: The two cells divide to produce cells each with one micronucleus and one macronuclear anlage. The macronuclear anlage continues DNA synthesis, and at stage 10, four karyonides are completed. This process forms eight karyonides from one mating pair. A circle with an X indicates a degenerating nucleus. Double‐headed arrows indicate nuclear replication