biostudies-literatureMeng XNational Science Foundation491https://www.ebi.ac.uk/biostudies/studies/S-EPMC9967165biostudies-literatureUnknown11(2)Locus-specific gene amplification and genome-wide endoreplication generate the elevated copy number of ribosomal DNA (rDNA, 9000 C) and non-rDNA (90 C) chromosomes in the developing macronucleus of <i>Tetrahymena thermophila</i>. Subsequently, all macronuclear chromosomes replicate once per cell cycle during vegetative growth. Here, we describe an unanticipated, programmed switch in the regulation of replication initiation in the rDNA minichromosome. Early in development, the 21 kb rDNA minichromosome is preferentially amplified from 2 C to ~800 C from well-defined origins, concurrent with genome-wide endoreplication (2 C to 8-16 C) in starved mating <i>Tetrahymena</i> (endoreplication (ER) Phase 1). Upon refeeding, rDNA and non-rDNA chromosomes achieve their final copy number through resuMicroorganismsDevelopmentally Programmed Switches in DNA Replication: Gene Amplification and Genome-Wide Endoreplication in <i>Tetrahymena</i>.PMC9967165MCB-0132675Kapler GMDang HQMeng XfalseDevelopmentally Programmed Switches in DNA Replication: Gene Amplification and Genome-Wide Endoreplication in <i>Tetrahymena</i>.Locus-specific gene amplification and genome-wide endoreplication generate the elevated copy number of ribosomal DNA (rDNA, 9000 C) and non-rDNA (90 C) chromosomes in the developing macronucleus of <i>Tetrahymena thermophila</i>. Subsequently, all macronuclear chromosomes replicate once per cell cycle during vegetative growth. Here, we describe an unanticipated, programmed switch in the regulation of replication initiation in the rDNA minichromosome. Early in development, the 21 kb rDNA minichromosome is preferentially amplified from 2 C to ~800 C from well-defined origins, concurrent with genome-wide endoreplication (2 C to 8-16 C) in starved mating <i>Tetrahymena</i> (endoreplication (ER) Phase 1). Upon refeeding, rDNA and non-rDNA chromosomes achieve their final copy number through resu2023-01-01T00:00:00Z2023 Feb2025-04-26T10:22:17.061Z2025-02-18T23:57:52.58ZS-EPMC99671653683845610.3390/microorganisms11020491