Lecture 10 Flashcards Preview

BMS237 - Advanced Developmental Biology > Lecture 10 > Flashcards

Flashcards in Lecture 10 Deck (32)
Loading flashcards...
1
Q

Notch signalling is used when a cell has to make a linear fate decision, T or F

A

F – notch signalling is used when a cell needs to make a binary fate decision

2
Q

Due to their specificity, a single ubiquitin ligase acts in the notch pathway, T or F

A

F – multiple ubiquitin ligase act upon the notch pathway

3
Q

Explain the significance of the notch signalling pathway in leukaemia

A

Human notch was first cloned from patients with T-cell acute lymphoblastic leukaemia. These patients has a truncation mutation in notch as a result of a chromosome translocation which lead to the fusion of the TCR-? gene and the intracellular domain of notch. TCR-? is constitutively expressed in immature T-cells resulting in the constituent activity of notch by maintaining T-cells in a stem cell state. This proliferation contributes to tumour formation.

4
Q

Whose is credited with discovering the notch gene by their forward genetic screens in Drosophila

A

Thomas Hunt-Morgan

5
Q

Before its insertion into the membrane, the notch receptor is already partially cleaved, describe how this occurs

A

Furin, a serine protease cleaves the notch receptor in the golgi. This results in a weakening of the connection between intracellular and transmembrane/extracellular domains

6
Q

What enzymes regulates the pairing of cysteine residues in the endoplasmic reticulum

A

Disulphide isomerase

7
Q

The Notch receptor also has internal repeats contained in the intracellular domain, what are these referred to as

A

Ankryin repeats

8
Q

What is the role of the segmentation clock in patterning the mesoderm

A

The segmentation clock determines when and where somites bud off from the axial mesoderm

9
Q

What are the vertebrate homologues of delta/serrate

A

Vertebrates have at least 9 different homologues that all belong to the delta or jagged family – they are collective members of the delta-serrate ligand (DSL) family

10
Q

Explain the roles of Su(deltex) and Sel-10 in the degradation of notch

A

The WW domain of Su(deltex) binds to the notch receptor via its C2 domain which localises it to the membrane by binding to phospholipids. The HECT domain then mediates ubiquitination of the notch receptor. Sel-10 recognises phosphorylated notchintra in the nucleus but doesn’t contain a ubiquitin ligase domain. Instead, Sel-10 recruits a ubiquitin ligase via its F-box domain to unbiquitinate notchintra.

11
Q

What can be said about the degradation of notch and how is this significant in its signalling pathway

A

Notch is rapidly degraded by proteasomes which acts as a regulation mechanism for its activity

12
Q

Which 76 amino acid peptide is added to proteins in order to mark them for degradation

A

Ubiquitin

13
Q

What type of signalling is used by notch-delta

A

Juxtacrine

14
Q

Why is it that despite being a relatively simple organism Drosophila still have two different genes the code of notch ligands

A

As Drosophila has evolved this gene for a notch ligand has been duplicated due to its importance in early patterning

15
Q

What is the significance of the notch signalling pathway in Alzheimer’s disease

A

Amyloid precursor protein (APP) looks very similar in structure to the notch receptor. APP is also cleaved by presenilin after cleavage by an ? or ? secretase in a similar way to how furin and TACE cleave notch. The ?-secretase products are cut by presenilin in one of two positions in its transmembrane domain which results in the production of an extracellular peptide of either 40 or 42 amino acids in length.

16
Q

Describe the pattern of mutations in jagged1 that lead to alagille syndrome

A

Many of these missense and non-sense mutations occurs within the cysteine repeats contained in the EGF repeats of the Jagged1 protein. This causes improper folding of the protein and may influence binding of the jagged1 ligand to the notch receptor

17
Q

What is the role of jagged1 in notch signalling

A

Jagged1 is a delta homologue and a ligand that binds to notch receptors

18
Q

Alagille syndrome is an autosomal dominant mutation associated with mutations in jagged1. What are the symptoms of this condition

A

Chronic liver disease in children but also heart disease, mental retardation and skeletal abnormalities

19
Q

Give an overview of the notch-delta pathway

A

Delta binds to the notch receptor and activates it. When notch is activated the intracellular domain, Notchintra is cleaved off and translocates from the membrane to the nucleus. Here Notchintra interacts with CSL which shifts CSL from being a transcriptional repressor to a transcriptional activator via Co-A. This leads to the upregulation of notch target genes

20
Q

What are the similarities between delta and notch proteins

A

Both are single pass transmembrane proteins with many EGF repeats in the extracellular domain

21
Q

What is significant about the jagged1 being a gene involved in early development

A

Unlike most other developmental genes, jagged1 is haploinsufficient

22
Q

Explain the paradoxical role of ubiquitination and Neur/Mib in activation of the notch pathway

A

Neur/Mib binds to delta and the RING domain acts as a ubiquitin ligase. As well as degradation, ubiquitination can also mediate endocytosis. Once delta has bound to Notch an enzyme cleaves extracellular Notch domain which is still bound to the delta ligand. Ubiquitination of delta causes endocytosis which brings the Delta-Notch complex into the signalling cell. This pulls the extracellular domain of the Notch receptor in as it is endocytosed into the other cell with the delta ligand. This causes the release of Notchintra which can translocate to the nucleus of the target cell where is can act to upregulate target genes

23
Q

Unlike most genes involved in early development, notch is haploinsufficient, T or F

A

T

24
Q

Explain the final step of notch receptor activation

A

In the final stage presenilin, a ?-secretase cuts within the transmembrane domain and releases the intracellular domain of the receptor, notchintra which then translocates to the nucleus where is can interact with CSL to upregulate notch target genes

25
Q

Describe in detail what happens upon ligand binding to the notch receptor

A

Ligand binding to the partially cleaved notch receptor results in the activity of a second protease known as metalloprotease (TACE) cleaving off the extracellular domain, leaving the transmembrane and extracellular domains still inserted into the membrane. This is referred to as the ligand dependant step

26
Q

What is the significance of these extracellular peptides produced by presenilin in Alzheimer’s pathology

A

The 42 amino acid peptide produced by presenilin is a major component of the amyloid plaques found in Alzheimer’s brains. Mutations in human presenilins account for most early onset autosomal-dominant cases of Alzheimer’s as a result of increase 42 amino acid peptide being produced.

27
Q

How often intermediate filaments a new somite formed in chick embryos

A

Every 90mins

28
Q

Explain the cysteine connection in diseases that affect notch signalling

A

The clustered mutations all affect codons for cysteines within the EGF repeats. These would lead to an unpaired cysteine and may alter the overall structure of Notch3

29
Q

What is the significance of the EGF repeats in the extracellular domains of delta and notch

A

This commonality mediates receptor-ligand recognition. Extracellular protein-protein interactions are often mediate by domains that contain a repeated amino acid sequence. These EGF repeats are made up of 30-40 amino acids and contain repeated 6 cysteines in regular intervals which form sulphide bridges with cysteines in the other EGF containing protein.

30
Q

There are three different types of enzymes that are involved in marking a protein for degradation, E1, E2 and E3. Explain the different roles of these enzymes in mediating the degradation of proteins such as notch

A

E1 is known as ubiquitin activating enzyme and along with E2, ubiquitin conjugating enzyme is expressed in all cells. These enzymes are referred to as housekeeping enzymes and are non-specific to the proteins which the mark for degradation. E3, known as ubiquitin ligase enzymes are specific for individual proteins or set of proteins and are responsible for adding the ubiquitin peptide.

31
Q

Recall some of the target genes upregulated by Co-A and CSL

A

Suppressor of Hairless, LAG1 and CBF1

32
Q

What are the two notch receptor ligands found in Drosophila

A

Delta, Serrate