TY - JOUR
T1 - Sex-induced silencing defends the genome of Cryptococcus neoformans via RNAi
AU - Wang, Xuying
AU - Hsueh, Yen Ping
AU - Li, Wenjun
AU - Floyd, Anna
AU - Skalsky, Rebecca
AU - Heitman, Joseph
PY - 2010/11/15
Y1 - 2010/11/15
N2 - Cosuppression is a silencing phenomenon triggered by the introduction of homologous DNA sequences into the genomes of organisms as diverse as plants, fungi, flies, and nematodes. Here we report sex-induced silencing (SIS), which is triggered by tandem integration of a transgene array in the human fungal pathogen Cryptococcus neoformans. A SXI2a-URA5 transgene array was found to be post-transcriptionally silenced during sexual reproduction. More than half of the progeny that inherited the SXI2a-URA5 transgene became uracil-auxotrophic due to silencing of the URA5 gene. In vegetative mitotic growth, silencing of this transgene array occurred at an -250-fold lower frequency, indicating that silencing is induced during the sexual cycle. Central components of the RNAi pathway - including genes encoding Argonaute, Dicer, and an RNA-dependent RNA polymerase - are all required for both meiotic and mitotic transgene silencing. URA5-derived -22-nucleotide (nt) small RNAs accumulated in the silenced isolates, suggesting that SIS is mediated by RNAi via sequence-specific small RNAs. Through deep sequencing of the small RNA population in C. neoformans, we also identified abundant small RNAs mapping to repetitive transposable elements, and these small RNAs were absent in rdp1 mutant strains. Furthermore, a group of retrotransposons was highly expressed during mating of rdp1 mutant strains, and an increased transposition/mutation rate was detected in their progeny, indicating that the RNAi pathway squelches transposon activity during the sexual cycle. Interestingly, Ago1, Dcr1, Dcr2, and Rdp1 are translationally induced in mating cells, and Ago1, Dcr1, and Dcr2 localize to processing bodies (P bodies), whereas Rdp1 appears to be nuclear, providing mechanistic insights into the elevated silencing efficiency during sexual reproduction. We hypothesize that the SIS RNAi pathway operates to defend the genome during sexual development.
AB - Cosuppression is a silencing phenomenon triggered by the introduction of homologous DNA sequences into the genomes of organisms as diverse as plants, fungi, flies, and nematodes. Here we report sex-induced silencing (SIS), which is triggered by tandem integration of a transgene array in the human fungal pathogen Cryptococcus neoformans. A SXI2a-URA5 transgene array was found to be post-transcriptionally silenced during sexual reproduction. More than half of the progeny that inherited the SXI2a-URA5 transgene became uracil-auxotrophic due to silencing of the URA5 gene. In vegetative mitotic growth, silencing of this transgene array occurred at an -250-fold lower frequency, indicating that silencing is induced during the sexual cycle. Central components of the RNAi pathway - including genes encoding Argonaute, Dicer, and an RNA-dependent RNA polymerase - are all required for both meiotic and mitotic transgene silencing. URA5-derived -22-nucleotide (nt) small RNAs accumulated in the silenced isolates, suggesting that SIS is mediated by RNAi via sequence-specific small RNAs. Through deep sequencing of the small RNA population in C. neoformans, we also identified abundant small RNAs mapping to repetitive transposable elements, and these small RNAs were absent in rdp1 mutant strains. Furthermore, a group of retrotransposons was highly expressed during mating of rdp1 mutant strains, and an increased transposition/mutation rate was detected in their progeny, indicating that the RNAi pathway squelches transposon activity during the sexual cycle. Interestingly, Ago1, Dcr1, Dcr2, and Rdp1 are translationally induced in mating cells, and Ago1, Dcr1, and Dcr2 localize to processing bodies (P bodies), whereas Rdp1 appears to be nuclear, providing mechanistic insights into the elevated silencing efficiency during sexual reproduction. We hypothesize that the SIS RNAi pathway operates to defend the genome during sexual development.
KW - Meiosis
KW - RNAi
KW - Transposon
KW - siRNA
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U2 - 10.1101/gad.1970910
DO - 10.1101/gad.1970910
M3 - Article
C2 - 21078820
AN - SCOPUS:78349241121
VL - 24
SP - 2566
EP - 2582
JO - Genes and Development
JF - Genes and Development
SN - 0890-9369
IS - 22
ER -