Lecture 10

Question 1

What are the common features of signalling?

Answer 1

1) Reception= ligand binds to receptor to transduce a signal
2) transduction= the use of secondary messengers from membrane to nucleus
3) Response= the activation of TFs that modulate gene expression

Question 2

What are the 3 main families of TGFB?

Answer 2

1) GDNF
2) BMP like= discovered in bone formation but is required for multiple types of patterning
3) TGFB like family= important in cancer e.g. nodal and activin

Question 3

Describe the TGFB signal transduction

Answer 3

1) Ligand binds to type 2 receptor which binds to type 1 R
2) they cross phosphorylate each other and recruit smad2 and 3 (1 and 5 if ligand is BMP)
3) They are further activated by smad4 and form an active smad complex which acts as a TF that modulates transcription

Question 4

How and why is BMP signalling controlled?

Answer 4

Is controlled EC by antagonists= chordin, noggin, follistatin, gremlin1, DAN. Cells will assume a fate depending on how much BMP signalling they receive. Needs to be controlled as cells are needed to respond at a particular time and place

Question 5

What are the features of RTKs?

Answer 5

20 families with individual ligands and receptors. One receptor can bind one ligand and vice versa or can bind to more than one and vice versa. Are all monomers except for insulin. Have varied EC domains due to ligand binding but have similar features e.g. immunoglobulin domain. Have kinase enzyme activity in IC domain

Question 6

Describe canonical RTK signalling

Answer 6

1) binding of ligand causes receptor dimerization
2) autocatalytic activation of the receptors occurs- they cross phosphorylate
3) this enhances kinase activity and stabilises the receptor, creating docking sites

Question 7

How can RTK activity be analysed?

Answer 7

Use genetic engineering to mutate the sites that need to be phosphorylated- ligand can bind but won’t phos= dominant negative. Can also do gain of function

Question 8

What recognises the docking sites on RTKs?

Answer 8

Proteins that have SH2 domains (recognises phosphotyrosine)- recognise PT- glutamic acid x2- isoleucine. e.g. PLC- gamma, PI3, GTPase

Question 9

What are the properties of Ras and what 2 proteins are involved in its activity?

Answer 9

Is in 2 forms- active and inactive due to being GTP/GDP bound. GEF removes GDP to allow GTP to bind. GAP removes Pi from GTP bound to Ras

Question 10

Describe the Ras pathway

Answer 10

Grb2 and sos are both GEFs and both have SH2 domains. Grb2 binds to a docking site and recruits SOS which binds to Ras and activates it (triggers GDP to GTP exchange)

Question 11

What occurs downstream of Ras?

Answer 11

Ref phosphorylates Mek which phosphorylates Mapk at serine and threonine. Makes the signal more stable.

Question 12

How many members are there in the FGF family?

Answer 12

22

Question 13

Where is FGF8 expressed?

Answer 13

Discrete boundary of expression using ISH in mid/hindbrain. Has distinct segmentation pattern in developing somites

Question 14

What are the features of FGF receptors?

Answer 14

They have ig domains EC and D2 and D3 domains that bind to one of the 22 ligands. There are 4 Rs that trigger activity meaning more than one ligand can bind to the same receptor type

Question 15

What determines FGF specificity?

Answer 15

They require binding to HSPGs (syndecan, perlecan and glypican). Have sugar chains that be modified by sulfation

Question 16

describe FGF signalling and its requirements

Answer 16

Ligand binds and SOS and Grb2 are recruited and activate Ras signalling which induces cell function e.g. mitosis depending on the ligand type. Require secondary messengers- ligand and R binding aren’t sufficient

Question 17

What happens when there are mutations in FGFR?

Answer 17

Causes human disease e.g. mutation in ECR3= congenital bone defects