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Hello, my name is Long-Cheng Li.
I'm a professor at the Peking
Union Medical College Hospital,
of the Chinese Academy of Medical Sciences.
The title of my talk today
is "Activation of Gene Expression
by Double-Stranded RNAs".
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So my topic on small-RNAs or sRNAs,
such as siRNAs and the microRNAs
are known to trigger an evolutionary conservative phenomenon, known as RNAi.
In RNAi,
siRNA is either exogenously introduced
or produced within the cells are loaded
by a protein called Argonaute
or Ago in short.
The Ago protein would even discard
one of the RNA strand in the RNA duplex.
And it uses the remaining RNA strand
as the guide to form an active complex
called RNA-induced
silencing complex or RISC.
The complex then bonds to complementary
mRNA sequences leading to mRNA degradation.
If the guide RNA is a microRNA,
they often bind to the 3’UTR region
of mRNA, resulting in mRNA degradation
and/or suppression of the translation.
RNAi is mainly a set proximate event.
The nuclear function of small RNAs
and the protein partners Argonautes
is naturally alone,
except in plants and in some lower eukaryotes,
such as fission yeast and Drosophila.
In plants, the small RNA-Ago pathway
can initiate lower DNA methylation,
a phenomenon known
as RNA-directed DNA methylation or RdDM,
leading to transcriptional gene silencing.
In fission yeast and in Drosophila, RNA pathway
can mediate the assembly and maintenance
of heterochromatin
at the centromere regions,
which is required
to silence repetitive sequences.
However, the nuclear function
of this small RNA-Ago pathways
in mammalian cells remains a mystery,
which will be the topic
of my presentation today.
