miRNAs

Question 1

What are microRNAs?

Answer 1

ss RNAs regulating many process by modulating translational efficiency and / or stability of mRNA targets.
Encoded endogenously - human genome encodes over 1000.
Products of DNA transcription but don’t encode proteins.

Question 2

How were multiple miR genes identified?

Answer 2

2001 - 3 independent bioinformatically driven groups identified small ncRNAs in other different organisms and cell systems.

Question 3

Describe how short interfering RNAs are formed.

Answer 3

dsRNA in cell triggers RNAi by attracting dicer
Dicers cleaves dsRNA into siRNA fragments of ~23 nts.
siRNAs bound by RISK and argonaute
passenger strand ejected and ssRNA directs RISC back to complementary RNAs produced by virus or transposable genetic elements.

Question 4

How can incompletely base-paired miRNAs regulate gene expression?

Answer 4

Deadenylation and degradation -

Inhibition of initiation - bind and direct formation of repressive chromatin on attached DNA template.

Question 5

Give two examples of normal functions of miRNAs.

Answer 5

Stem cell maintenance e.g. miR-371, miR-302 in human ES cells inhibit p21 and Lats
Neuron development in nematodes - binary cell fate decision.

Question 6

Give an example of post-transcriptional control of miRNAs in cancer.

Answer 6

p53 can associate with Drosha and promote processing of certain TS-miRNAs in response to DNA damage e.g. miR15-16. Loss of p53 in cancer –> reduced levels.

Question 7

Which argonaute paralogue is involved in RNA interference?

Answer 7

AGO2 - can cleave mRNA removing the mRNA’s polyA tail.