RR14

Question 1

How can we introduce dsRNA to impact a gene?

Examples of flies, plants and mice

Answer 1

• dsRNA allows introduction of specific transgenes to make loop (folds back on itself) that correspond to specific targets
• flies: have red eyes due to a white gene, if we eliminate by introducing snap back, gives white eyes
• plants: introduction of transgene gives mRNA that causes multiple stem cells
• mice: introduction of siRNAs allows us to make a phenocopy of Tay-Sachs. disease eliminates siRNA early - do the same things

This process is essentially the introduction of dsRNA or siRNA to recap the phenotype of certain diseases

Question 2

Explain the DICER-RISC system

Answer 2

• DICER chops up dsmicroRNAs into small fragments
• RISC (RNA inducing silencing complex) has a protein calles Argonaute which binds to these fragments
• Helicase unwinds the fragments with ATP hydrolysis, creating ssRNA
• ssRNA targets an mRNA to be degraded, binds to it
• this new complex is now cleaved and degraded

Question 3

What is RNAi vs microRNA

Answer 3

• microRNA will be destabilized for inhibition of translation, interacts with RISC and is no 100% complementary
• siRNA/RNAi is 100% complementary, and will be degraded - it is sequence specific suppression

Question 4

How is chromatin involved in cell division?

Answer 4

Chromatin MUST be silenced within the centromere for accurate cell division to take place

Question 5

What does H3K9me3 do?

Answer 5

It is a repressor of lineage innapropriate genes
Make by dsRNA nucleate complex

Question 6

Describe piRNA and PIWI

Answer 6

piRNA is transcribed from a DNA cluster made up of integrated disabled transposable elements
- We use argonaute PIWI to cleave their RNA

They regulate mRNA stability and enhance protein synthesis

Question 7

What is the role of ncRNA?

Answer 7

Fine tunes physiological processes as organisms develop

novel cellular RNA

Question 8

What are two strategies used by viruses on RNA during RISC process?

Answer 8

• Make long RNA with repeating units, binding up all micromRNA
• Make circular RNA that soak up the micromRNA important for defense

Question 9

What is a Barr body?

Answer 9

Females have barr bodies - inactivated X chromosome
Can see it in calico cats- different coat colour shows deactivation of X chromosome

Question 10

Explain the XIST gene

Answer 10

XIST locus encodes lncRNA (long non-coding RNA)
- it binds to X chromosome region and extinguishes its gene expression
- inactive X chromosome is due to XIST expression or not
- it recruits complexes that modify chromatin, condensing chromosome, making it inaccessible to transcription factors

Question 11

Explain XIST vs TSIX

Answer 11

• XIST silences X chromosome
• TSIX antagonizes XIST expression