miRNAs and Developmental Canalisation

Question 1

Canalisation

Answer 1

“Robustness”

Question 2

How many genes are in the human genome?

Answer 2

• urban myth = 100,000 (actually c40,000)
• 21,306

Question 3

Why approximate?

Answer 3

Counting conundra
- pseudogenes
- small ORFs

Question 4

Genes produce functional

Answer 4

ncRNA (>20,000)

Question 5

HOTAIR

Answer 5

• long ncRNA
• several one
• recruits H3K27me3 on Hox

Question 6

HOTTIP

Answer 6

• long ncRNA
• several kb
• recruits H3K4me3 on Hox

Question 7

miRNAs

Answer 7

• c22nt
• 100s/1000s / species
• vibe mRNA

Question 8

miRNA cleavage

Answer 8

• in plants and animals
• perfect match

Question 9

MiRNA blockage

Answer 9

• animals
• approximate match

Question 10

miRNA summary

Answer 10

1) miRNA transcription
2) folds into c70nt pri-miRNA hairpin
3) Drosher and Pasha: pre-miRNA
4) nuclear export
5) DICER
6) RISC complex takes up strand

Question 11

Why use miRNAs for I regulate gene activity during development?

Answer 11

• faster than transcriptional control
• RNA half-life; temporary, highly localised control

Question 12

Paradoxical miRNA findings

Answer 12

• some are highly conserved
• v. few are lethal mutants

Question 13

Finding the targets:

Answer 13

1. Sequence matches (3’UTR) ; false hits
2. Introduction (look for <RNA) ; indirect effects

Question 14

Human miRNA introduction in HeLa cancer cells

Answer 14

• muscle expressed miRNA1 suppresses no muscle genes
• brain expressed miRNA124 suppresses non-brain genes
• microarray; c100 genes go down for each miRNA

Question 15

miRNA non cell-autonomous behaviour

Answer 15

Weed out stochastic / polymerase / chromatin errors

Question 16

miRNA-9A

Answer 16

• non-lethal mutant; changes no of sensory bristles in larva, adults
• subtle differences, controlling precision
• expressed in Drosophila SOPs
• Senseless also expressed here; layers of regulation

Question 17

SOPs

Answer 17

Sensory organ precursors

Question 18

Senseless

Answer 18

TF

Question 19

Mode 1

Answer 19

• express in different cell to targets
• keeps leaky transcription down

Question 20

Mode 2

Answer 20

• express in same cells as targets
• precision

Question 21

Development

Answer 21

• probabilistic
• stochastic variation
• liable to biochemical error
• underpinned by Brownian motion

Question 22

Does canalisation allow the evolution of complexity in Animalia?

Answer 22

• miRNA increases the correlation between genotype and phenotype
• cuts out evolutionary “noise”
• increases trait heritability
• speeds up evolution
• selection works on phenotypes, but genotypes are inherited

Question 23

Does miRNA no correlate with complexity?

Answer 23

• hard to test: incomplete dataset
• increased early in evolution
• lots @ bilaterian base: Cambrian explosion
• hints!