title: Elimination of DNA sequences during macronuclear differentiation in Tetrahymena thermophila, as detected by in situ hybridization.
abstract: Previous studies have indicated that certain sequences in the micronuclear genome are absent from the somatic macronucleus of Tetrahymena (Yao and Gorovsky, 1974; Yao and Gall, 1979; Yao, submitted). The present study used in situ hybridization to follow the elimination process during the formation of the new macronucleus. Micronuclear-specific DNA cloned in recombinant plasmids was labelled with 3H and hybridized to cytological preparations of T. thermophila at various stages of conjugation. Despite a smaller size and lower DNA content, the micronucleus has more hybridization than the mature macronucleus. Hybridization initially increased in the anlage (newly developing macronucleus) to reach a maximal level right after the old macronuclei has disappeared. The hybridization in the anlage than decreased to a significant extent prior to the first cell division. The results suggest that the micronuclear-specific sequence is first replicated a few rounds before it is eliminated from the anlage, and the elimination process occurs without nuclear division.
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000502:physiology; D004247:DNA / Q000235:genetics*; D004262:DNA Restriction Enzymes; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D013768:Tetrahymena / Q000502:physiology*
chemical_list: D004247:DNA; D004262:DNA Restriction Enzymes