title: A Novel Terminal-Repeat Retrotransposon in Miniature (TRIM) Is Massively Expressed in Echinococcus multilocularis Stem Cells.
abstract: Taeniid cestodes (including the human parasites Echinococcus spp. and Taenia solium) have very few mobile genetic elements (MGEs) in their genome, despite lacking a canonical PIWI pathway. The MGEs of these parasites are virtually unexplored, and nothing is known about their expression and silencing. In this work, we report the discovery of a novel family of small nonautonomous long terminal repeat retrotransposons (also known as terminal-repeat retrotransposons in miniature, TRIMs) which we have named ta-TRIM (taeniid TRIM). ta-TRIMs are only the second family of TRIM elements discovered in animals, and are likely the result of convergent reductive evolution in different taxonomic groups. These elements originated at the base of the taeniid tree and have expanded during taeniid diversification, including after the divergence of closely related species such as Echinococcus multilocularis and Echinococcus granulosus. They are massively expressed in larval stages, from a small proportion of full-length copies and from isolated terminal repeats that show transcriptional read-through into downstream regions, generating novel noncoding RNAs and transcriptional fusions to coding genes. In E. multilocularis, ta-TRIMs are specifically expressed in the germinative cells (the somatic stem cells) during asexual reproduction of metacestode larvae. This would provide a developmental mechanism for insertion of ta-TRIMs into cells that will eventually generate the adult germ line. Future studies of active and inactive ta-TRIM elements could give the first clues on MGE silencing mechanisms in cestodes.
authors.affiliation: Institute of Hygiene and Microbiology, University of Würzburg, Germany Sección Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay ukoziol@gmail.com.
authors.forename: Uriel
authors.initials: U
authors.lastname: Koziol
authors.affiliation: Laboratorio de Interacciones Moleculares, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay Departamento de Genética, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
authors.forename: Santiago
authors.initials: S
authors.lastname: Radio
authors.affiliation: Laboratorio de Interacciones Moleculares, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay Departamento de Genética, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
authors.forename: Pablo
authors.initials: P
authors.lastname: Smircich
authors.affiliation: Parasite Genomics, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zarowiecki
authors.affiliation: Cátedra de Inmunología, Facultad de Química, Universidad de la República, Montevideo, Uruguay.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Fernández
authors.affiliation: Institute of Hygiene and Microbiology, University of Würzburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Brehm
mesh_terms: D000818:Animals; D002589:Cestoda / Q000235:genetics; D048210:Echinococcus multilocularis / Q000235:genetics* / Q000254:growth & development; D019143:Evolution, Molecular; D015870:Gene Expression; D007814:Larva / Q000378:metabolism; D018626:Retroelements; D013234:Stem Cells / Q000378:metabolism*; D020079:Terminal Repeat Sequences
chemical_list: D018626:Retroelements
keywords: long noncoding RNA; neoblast; nonautonomous; pluripotency; retrotransposition