Preferential Occupancy of R2 Retroelements on the B Chromosomes of the Grasshopper Eyprepocnemis plorans
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AuthorMontiel, Eugenia E.; Cabrero, Josefa; Ruiz-Estévez, Mercedes; Burke, William D.; Eickbush, Thomas H.; Martínez Camacho, Juan Pedro; López-León, María Dolores
Public Library of Science (PLOS)
ChromosomesDNA sequencesDrosophilaEmbryosInvertebrate genomicsPolymerase chain reactionPolymerase chain reaction amplificationRobosomal RNA
Montiel, E.E.; et al. Preferential Occupancy of R2 Retroelements on the B Chromosomes of the Grasshopper Eyprepocnemis plorans. Plos One, 9(3): e91820 (2014). [http://hdl.handle.net/10481/31088]
SponsorshipThis study was supported by grants from the Spanish Ministerio de Ciencia y Tecnología (CGL2009-11917) and Plan Andaluz de Investigacion (CVI-6649), and was partially performed by FEDER funds and a grant from the National Institutes of Health (GM42790).
R2 non-LTR retrotransposons exclusively insert into the 28S rRNA genes of their host, and are expressed by co-transcription with the rDNA unit. The grasshopper Eyprepocnemis plorans contains transcribed rDNA clusters on most of its A chromosomes, as well as non-transcribed rDNA clusters on the parasitic B chromosomes found in many populations. Here the structure of the E. plorans R2 element, its abundance relative to the number of rDNA units and its retrotransposition activity were determined. Animals screened from five populations contained on average over 12,000 rDNA units on their A chromosomes, but surprisingly only about 100 R2 elements. Monitoring the patterns of R2 insertions in individuals from these populations revealed only low levels of retrotransposition. The low rates of R2 insertion observed in E. plorans differ from the high levels of R2 insertion previously observed in insect species that have many fewer rDNA units. It is proposed that high levels of R2 are strongly selected against in E. plorans, because the rDNA transcription machinery in this species is unable to differentiate between R2-inserted and uninserted units. The B chromosomes of E. plorans contain an additional 7,000 to 15,000 rDNA units, but in contrast to the A chromosomes, from 150 to over 1,500 R2 elements. The higher concentration of R2 in the inactive B chromosomes rDNA clusters suggests these chromosomes can act as a sink for R2 insertions thus further reducing the level of insertions on the A chromosomes. These studies suggest an interesting evolutionary relationship between the parasitic B chromosomes and R2 elements.