left/right assymetry

Question 1

give some examples of organs that display left/right asymmetry

Answer 1

heart, spleen, liver, gut, lung lobes, brain

Question 2

when left/right asymmetry is correct what is this called

Answer 2

situs solitus

Question 3

what is the inverse of situs solitus and how many people are affected?

Answer 3

situs invertus

1/10,000

Question 4

which organ develops in the midline and then moves to the left side and loops to the right?

Answer 4

the heart

Question 5

what does tbx5 mutation cause?

Answer 5

stronger limb malformation on the left hand side

Question 6

name a ventricle signal in the developing embryo

Answer 6

Shh

Question 7

name three genes that are expressed only in L or R side of embryo?

Answer 7

Shh
FGF
nodal

Question 8

how is L/R asymmetry made in organogenesis?

Answer 8

• directional looping
• increased proliferation
• regulated branching
• cell death

Question 9

describe two past theories of what causes L/R assymetry

Answer 9

• electric/magnetic fields

- chiral molecules

Question 10

what causes Kartagener syndrome?

Answer 10

immotile cilia

Question 11

name 3 symptoms of Kartagener syndrome

Answer 11

• chronic respiratory infection
• male infertility
• situs invertus in 50% of cases

Question 12

what was suggested about L/R asymmetry from the finding of Kartagener syndrome

Answer 12

that cilia are involved in the development of L/R asymmetry

Question 13

what was observed in some situs invertus mice?

Answer 13

dynein motor protein defects (involved in cilia movement)

Question 14

why does a combination of situs solitus and situs invertus lead to problem?

Answer 14

organs do not fit together well and can crush each other

Question 15

what is the node called in chicks (where it was discovered)

Answer 15

Hensen’s node

Question 16

what is the node

Answer 16

a major conserved signalling centre essential for gastrulation

Question 17

what does each cell of the node have?

Answer 17

a single cilia of the 9+0 class

Question 18

what is the 9+0 class cilia made up of?

Answer 18

dynein arms on 9 microtubule doublets

Question 19

are cilia chiral?

Answer 19

yes

Question 20

what does KIF stand for?

Answer 20

kinesin like protein

Question 21

what was observed in KIF3-A and KIF3-B knock out mice? and what was different about their nodes?

Answer 21

randomised organ L/R asymmetry

nodes displayed no cilia

Question 22

are nodal cilia motile?

Answer 22

yes, they create a nodal flow towards the left

Question 23

where are the cilia located and what signalling causes this?

Answer 23

cilia are on the posterior end of the node cell

Wnt planar cell polarity signalling causes this

Question 24

what is special about the cilia positioning?

Answer 24

they don’t interfere with each other or produce turbulence

Question 25

what was observed when cilia removed from nodes and artificial rightward flow induced?

Answer 25

situs invertus

Question 26

what causes polycystic kidney disease?

Answer 26

mutation in Pkd2 (polycystin 2), a calcium channel associated with mechanosensing cilia

Question 27

what is are the symptoms of polycystic kidney disease?

Answer 27

enlarged kidneys full of cysts

Question 28

does the node also have mechanosensing cilia?

Answer 28

yes, located on specific regions of node

Question 29

what are mechanosensing cilia?

Answer 29

cilia that respond to bending with a calcium influx through Pkd2

Question 30

what do Pkd2 mutants show?

Answer 30

L/R asymmetry defects

Question 31

how does nodal flow affect L/R asymmetry?

Answer 31

bending of mechanosensing cilia leads to influx in calcium on the left hand side
this leads to activation of left handed genes

Question 32

name three left bias genes in the nodal area? what happens to these if mutated in mice?

Answer 32

Nodal, lefty and PitX

mid-gestational death

Question 33

how many people are left handed?

Answer 33

1/9

Question 34

what occurs in Kartagener syndrome and what does it suggest?

Answer 34

situs invertus in all organs than the brain

suggests an independent mechanism for brain asymmetry

Question 35

how is L/R asymmetry achieved in chicks? and what happens if this is disrupted?

Answer 35

only R eye see light

if chicks develop in dark then there is no asymmetry

Question 36

why is the brain asymmetrical?

Answer 36

to allow us to parallel process/multi-task