Control of chicken CR1 retrotransposons is independent of Dicer-mediated RNA interference pathway.
BACKGROUND
Dicer is an RNase III-ribonuclease that initiates the formation of small interfering RNAs as a defence against genomic parasites such as retrotransposons. Despite intensive characterization in mammalian species, the biological functions of Dicer in controlling retrotransposable elements of the non-mammalian vertebrate are poorly understood. In this report, we examine the role of chicken Dicer in controlling the activity of chicken CR1 retrotransposable elements in a chicken-human hybrid DT40 cell line employing a conditional loss-of-Dicer function.


RESULTS
Retrotransposition is detrimental to host genome stability and thus eukaryotic cells have developed mechanisms to limit the expansion of retrotransposons by Dicer-mediated RNAi silencing pathways. However, the mechanisms that control the activity and copy numbers of transposable elements in chicken remain unclear. Here, we describe how the loss of Dicer in chicken cells does not reactivate endogenous chicken CR1 retrotransposons with impaired RNAi machinery, suggesting that the control of chicken CR1 is independent of Dicer-induced RNAi silencing. In contrast, upon introduction of a functionally active human L1 retrotransposable element that contains an active 5' UTR promoter, the Dicer-deficient chicken cells show a strong increase in the accumulation of human L1 transcripts and retrotransposition activity, highlighting a major difference between chicken CR1 and other mammalian L1 retrotransposons.


CONCLUSIONS
Our data provide evidence that chicken CR1 retrotransposons, unlike their mammalian L1 counterparts, do not undergo retrotransposition because most CR1 retrotransposons are truncated or mutated at their 5'UTR promoters and thus are not subjected to Dicer-mediated RNAi-silencing control.
Lee
Sung-Hun
SH
The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 2601, Australia. Sunghun.Lee@anu.edu.au
Eldi
Preethi
P
Cho
Soo-Young
SY
Rangasamy
Danny
D
D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens / Q000235:genetics*; D018628:Gene Dosage; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D016678:Genome; D006801:Humans; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000502:physiology*; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering; D018626:Retroelements / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D043244:Ribonuclease III / Q000172:deficiency / Q000378:metabolism*; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D019076:Transgenes
D020121:5' Untranslated Regions; D034741:RNA, Small Interfering; D018626:Retroelements; D043244:Ribonuclease III
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