Macronuclear differentiation in the stichotrichous ciliate Stylonychia lemnae . (A) Schematic diagram of macronuclear differentiation. Time points at which DNA or RNA was isolated are indicated by an arrow. (B-F) Nuclear events during macronuclear differentiation and behavior of the developmentally expressed Mdp1 (Piwi) protein. (B) In the two conjugating cells, Piwi accumulates in the parental macronucleus (p). (C-D) During formation of polytene chromosomes, Piwi relocalizes from the parental macronucleus (p) to the developing macronucleus (a1-3). (E, F) During chromatin elimination in the anlage (e) and subsequent formation of the vegetative macronucleus (m), Piwi is no longer present. (G) Expression of the genes mdp1 and mdp2 during vegetative growth and at the onset of macronuclear differentiation. While no expression of these genes takes place during vegetative growth, they become transcribed approximately 30 hours after the onset of sexual reproduction. IES: sequences interrupting macronuclear-destined sequences in the micronuclear genome. MDS: macronuclear-destined sequences in the macronuclear genome.