title: The piggyBac transposon-derived genes TPB1 and TPB6 mediate essential transposon-like excision during the developmental rearrangement of key genes in Tetrahymena thermophila.
abstract: Ciliated protozoans perform extreme forms of programmed somatic DNA rearrangement during development. The model ciliate Tetrahymena thermophila removes 34% of its germline micronuclear genome from somatic macronuclei by excising thousands of internal eliminated sequences (IESs), a process that shares features with transposon excision. Indeed, piggyBac transposon-derived genes are necessary for genome-wide IES excision in both Tetrahymena (TPB2 [Tetrahymena piggyBac-like 2] and LIA5) and Paramecium tetraurelia (PiggyMac). T. thermophila has at least three other piggyBac-derived genes: TPB1, TPB6, and TPB7 Here, we show that TPB1 and TPB6 excise a small, distinct set of 12 unusual IESs that disrupt exons. TPB1-deficient cells complete mating, but their progeny exhibit slow growth, giant vacuoles, and osmotic shock sensitivity due to retention of an IES in the vacuolar gene DOP1 (Dopey domain-containing protein). Unlike most IESs, TPB1-dependent IESs have piggyBac-like terminal inverted motifs that are necessary for excision. Transposon-like excision mediated by TPB1 and TPB6 provides direct evidence for a transposon origin of not only IES excision machinery but also IESs themselves. Our study highlights a division of labor among ciliate piggyBac-derived genes, which carry out mutually exclusive categories of excision events mediated by either transposon-like features or RNA-directed heterochromatin.
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Chao-Yin
authors.initials: CY
authors.lastname: Cheng
authors.affiliation: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: Janet M
authors.identifier: 0000-0001-8220-8427
authors.initials: JM
authors.lastname: Young
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.|Genome and Systems Biology Degree Program, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Chih-Yi Gabriela
authors.initials: CG
authors.lastname: Lin
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Ju-Lan
authors.initials: JL
authors.lastname: Chao
authors.affiliation: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.|Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: Harmit S
authors.identifier: 0000-0001-6005-0016
authors.initials: HS
authors.lastname: Malik
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Meng-Chao
authors.initials: MC
authors.lastname: Yao
mesh_terms: D004251:DNA Transposable Elements / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D055786:Gene Knockout Techniques; D015321:Gene Rearrangement / Q000235:genetics*; D017125:Genes, Protozoan / Q000235:genetics*; D018503:Genome, Protozoan / Q000235:genetics*; D008018:Life Cycle Stages; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D016808:Tetrahymena thermophila / Q000235:genetics* / Q000254:growth & development; D014617:Vacuoles / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D015800:Protozoan Proteins
keywords: Tetrahymena; domesticated transposon; piggyBac; programmed genome rearrangement; vacuoles