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BIOL2056 > Cell adhesion and communication > Flashcards

Cell adhesion and communication Flashcards

1
Q

Tell me the common features of junction complexes

A

Common features of junction complexes

  • Transmembrane adhesion proteins
  • Intracellular link to cytoskeleton
  • Extracellular link to outside structures
  • Cadherin and Integrin superfamilies
  • Cadherins mediate cell-cell attachments
  • Integrins mediate cell-matrix attachments
  • Some cadherins link to actin forming adherens junctions
  • other cadherins link to intermediate filaments to form desmosome junctions
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2
Q

Name 4 things that help make a tight junction

A

Claudin

Junctional adhesion molecule (JAMs)

Occludin

ZO

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3
Q

What is a claudin?

A

A four-pass transmembrane protein (goes through the membrane 4 times) that constitutes TJ strands

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4
Q

Whats a junctional adhesion molecule (JAMs)?

A

A class of cell-cell adhesion molecules with two Ig repeats that localise to TJs

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5
Q

Whats an occludin?

A

A four pass transmembrane proteins localised at TJs

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6
Q

Whats a ZO?

A

A ZO is a Zonula-occluding family proteins: TJ- undercoating scaffolding proteins

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7
Q

What type of binding is present in tight junctions?

A

Homophilic binding is present in tight junctions

e.g. occludins to occludins e.g.

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8
Q

What are cadherins and where are they found?

What are they important for?

How can they exist?

A

Cadherins (cell-cell attachment)

  • Proteins
  • Found in all multicellular animals and Choanoflagellates
  • Not present in plants, fungi, bacteria or archaea
  • Important component of being an animal
  • Can exist as free-living individual organisms or as a colony
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9
Q

Label the structure of a Choanoflagellates

A
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10
Q

What are cadherins thought to be part of?

What may the presence of them be important for?

A

They are thought to be part of the group of protists from which animals evolved

Presence of cadherin may have been important in this evolutionary process allowing multicellularity

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11
Q

What is the name of cadherins derived from?

A

Name derived from the face that they require Ca2+ to mediate cell-cell adhesion

This can be demonstrated in the image…

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12
Q

Tell me about the role of Ca2+ with cadherins

A
  • Important during embryogenesis to stick cells together
  • Loosely held together until the 8-cell stage – then compaction occurs, and cells become tightly adhered
  • with cell junctions forming
  • Add a chelating agent (EDTA) to remove Ca++ and cells can separate
  • Reassembly when Ca++ is added back
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13
Q

What were the first cadherins identified and how were they named?

A

First cadherins identified were named based on the cell type they were discovered in

  • N-cadherin – nerve cells
  • E-cadherin – epithelia cells
  • P-cadherin – placental cells

However not restricted to single types of cell e.g. N-cadherin also found in fibroblasts

Within a particular tissue there is diversity in the different cadherins present

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14
Q

Tell me the non-classical types of cadherins…

A
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15
Q

Phenotypes of cadherin defects

A
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16
Q

Tell be about binding between cadherins?

A
  • Binding between individual cadherins is relatively weak and the bonds are parallel
  • Strength comes from many such links close together (think of Velcro)
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17
Q

Why is Ca2+ important for cadherin function?

A
  • Flexible hinge regions between the cadherin repeats
  • Ca2+ binding to the hinge prevents it flexing
  • Removal of Ca2+ also reduces binding affinity at N-terminus
  • Destabilisation leads to proteolytic degradation
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18
Q

Tell me about the role that cadherins play in tissue organisation?

A
  • Classic experiment from the 1950’s (Townes & Holtfreter J. Exp. Zool. 128: 53-120)
  • Early amphibian embryo – mesoderm, neural plate and epidermal cells have been disaggregated and mixed
  • The cells are able to arrange themselves according to cell type and assemble into structure
  • Homophilic attachments between cadherins likely to be key in this reassembly
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19
Q

What do changes in cadherin expression help to regulate?

A

Neural tube development

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20
Q

What do catenins form a link between?

A

form a link between the intracellular cadherin domain and actin filament

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21
Q

What do catenins play a key role in?

A

Key role played by β catenin and/or γ catenin (plakoglobin)

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22
Q

What additional things to adheren junctions have?

A
  • Adherens junctions have an additional related protein p120-catenin
  • If the intracellular domain of cadherin is absent then cell adhesion is weakened
  • The link to actin is important
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23
Q

Label this adherens junctions

A
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24
Q

What does Beta- catenin have an important role in ?

A

wingless/Wnt signalling

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25
Q

Tell me the dual role of beta- catenin

A

1) Intracellular anchor protein at adherens junctions
2) Transcriptional regulator in Wnt signalling

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26
Q

What does the breakdown of the adherens junction release?

A

Breakdown of adherens junction releases β-catenin to move from cytoplasm into the nucleus - there it can affect transcription

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27
Q

What does Wnt signalling regulate?

A

Wnt signalling regulates phosphorylation and degradation of β-catenin controlling its availability to form adherens junctions

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28
Q

Wnt signalling and cell adhesion is linked…

What happens in the absence of Wnt signalling?

What happens in the presence of Wnt?

A
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29
Q

What is vascular endothelial cadherin (VE Cadherin) required for?

A
  • Vascular endothelial cadherin (VE Cadherin) is required for endothelial cell survival
  • Required for the response to Vascular Endothelial Growth Factor (VEGF)
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30
Q

When VEGF binds to a receptor tyrosine kinase, what does it require?

A

VE cadherin as a cofactor

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31
Q

What do integrins function as and where are they embedded?

A

They function as a dimeric unit and are embedded in the plasma membrane

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32
Q

What domains do integrins have?

A

Intra and extracellular domain

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33
Q

What are integrains comprised of?

A

2 non-covalently associated glycoprotein subunits

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34
Q

Tell me the transmembrane proteins of the integrin?

A
  • short intracellular C-terminal
  • large extracellular N-terminal domain
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35
Q

What do the extracellular domain of the integrin bind?

A

Extracellular matrix proteins or cell surface ligands of other cells

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36
Q

Label this integrin…

A
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37
Q

What does the intracellular domain of the integrin link?

A

(usually via Talin) to the actin cytoskeleton

38
Q

The role of integrins in Hemidesmosomes

A
39
Q

Cell adhesions via integrins needs to be what?

A

dynamic

40
Q

Tell me about cell adhesions via integrains in animals…

A
  • Cells in animals can migrate and so cell adhesions need to be broken and reformed
  • Allosteric regulation allows switching between active and inactive states
  • As an integrin binds or detaches from a ligand, it affects conformation of both intra- and extracellular domains
41
Q

Tell me about outside-in activation of integrins…

A
  • Binding of an extracellular ligand to an integrin results in binding to the cytoskeleton
  • Transmission of a force via the cytoskeleton
42
Q

Tell me about inside-out activation of integrins

A
  • Intracellular regulatory molecules such as phosphoinositide (PIP2) activate Talin
  • Causes strong binding of Talin to β integrin chain
  • In turn this activates the extracellular domain of integrin to bind extracellular ligands
  • PIP2 can be produced in response to extracellular signals.
  • Complex crosstalk between different signalling processes
43
Q

Tell me the consequences of defects in integrins

A
  • Humans have 24 different Integrins – combinations of 8 different β chain and 18 different α chain genes
  • Various combinations eg α5β1 is a fibronectin receptor, α6β1 is a laminin receptor
  • Defects in either the α or β subunits can lead to genetic disorders
44
Q

What are selectins?

A

Subgroup of lectin proteins

45
Q

What type of binding do selectins have?

A
  • Heterophilic binding- bind to molecules of a different type
  • Cell surface carbohydrate binding proteins – lectins
46
Q

What do selectins mediate?

A

Mediate transient cell-cell adhesion in the bloodstream

47
Q

Provide and explain an example of how selectins mediate transient cell-cell adhesion in the bloodstream

A
  • Control binding of white blood cells to the endothelial cells lining the blood vessels
  • White blood cells move between the bloodstream and tissues – requires changes in cell adhesion
  • Controlling where and when selectins and integrins are expressed regulates movement of white blood cells
48
Q

Label this P-selectin…

A
49
Q

Name at least 3 types of selectins and where they are

A

L-selectin on white blood cells

P-selectin on platelets and endothelial cells activated by an inflammatory response

E-selectin on activated endothelial cells

50
Q

In lymph organs, what do endothelial cells express and what are these recognised by?

A

In lymph organs endothelial cells express oligosaccharides recognised by L-selectin on lymphocytes causes lymphocytes to bind and become trapped

51
Q

At inflammation sites whats expressed and what recognises these?

A

At inflammation sites endothelial cells express selectins that recognise oligosaccharides on white blood cells and platelets

52
Q

Tell me about ICAMs, VCAMs and NCAMs. What do the names stand for and what type of binding do they do?

A
  • ICAMs – Intercellular Cell Adhesion Molecules
  • VCAMS – Vascular Cell Adhesion Molecules
  • NCAMs – Neural Cell Adhesion Molecules
  • Members of the immunoglobulin (Ig) superfamily
  • ICAMs have an extracellular domain characteristic of antibodies
  • ICAMs and VCAMs – heterophilic binding to integrins
  • NCAMs – homophilic binding
53
Q

Label these structures of the NCAM and ICAM…

A
54
Q

How can multiple forms of NCAM be generated?

A

By alternative splicing

55
Q

What can NCAMs have a high level of?

How does this effect the charge of the molecule?

A

Sialic acid chains making them negatively charged

56
Q

If the NCAM has a negative charge, what does this mean?

A

The negative charge can inhibit cell adhesion

57
Q

Tell me about Cadherins and the Ig superfamily

A
  • Cadherins and Ig superfamily proteins present in the same cell types
  • Cadherins have stronger adhesion properties – important for tissue integrity
  • NCAM likely to function in fine tuning of structures
  • Cadherin mutations usually lethal but NCAM mutations have more subtle effects
58
Q

What does Axon outgrowth rely on?

A

Axon outgrowth relies on regulation of adhesion, chemotaxis and signal factors

59
Q

Do the Ig superfamily have a role in the creation of a synapse?

A

yes

60
Q

Tell me about mutations in Drosophila Fascicilin 2 ?

A
  • Mutations in Drosophila Fascicilin2 (related to NCAM) have abnormal direction of axon growth
  • Fascicilin3 functions in recognition of the target tissue by neuronal growth cones
  • Fascicilin3 forms homophilic adhesions.
  • Transient expression of Fascicilin3 in motor neurones allows synapse formation with muscle expressing Fascicilin3
  • Abnormal synapses can be made by ectopic Fascicilin3 expression
61
Q

Synapse formation is complex with many components

A

Cadherins, Ig superfamily members, neuroligins and neurexins hold the pre- and postsynaptic membranes together

62
Q

Junctions

A
63
Q

How do plant cells attach and detach?

A
64
Q

What do plant cells walls provide ?

A
  • Structural and mechanical support.
  • Maintain and determine cell shape.
  • Resist internal turgor pressure of cell.
  • Control rate and direction of growth.
  • Regulate diffusion through the apoplast.
  • Carbohydrate storage.
  • Defence.
  • Source of signalling molecules.
  • Cell-cell interactions.
65
Q

What are the components of the plant cell wall?

A
66
Q

Tell me about cell adhesion at the middle lamella- Pectin rich domain in the plant cell wall

A
  • Role in cell adhesion
  • Form a hydrated gel in the cell wall
  • Breakdown products, oligogalacturonides (OGAs) function as signalling molecules.
67
Q

What are the different domains of pectin?

  • Homogalacturonan (HGA)
  • Rhamnogalacturonan II (RGII)
  • Rhamnogalacturonan I (RGI)
  • Xylogalacturonan (XGA)

Not much known about the enzymes needed for pectin synthesis

A
68
Q

Cell adhesion via cell wall components?

A
69
Q

defect in plant cell adhesion

A
70
Q

Why do we use model systems in cell biology

A
  • A simplified/convenient version of a complex entity.
  • The model captures key characteristics of the entity needed to address the task at hand.
  • It is not possible/ethical to study what we want directly (e.g., human disease)
71
Q

Model organisms are non-human species used to help understand biological processes

A
72
Q

Tell me the advantages and disadvantages of single cell organisms- E. Coli (Escherichia Coli)

A

Advantages

  • Fast growth in chemically defined media
  • Relatively cheap culture media
  • Several molecular tools for manipulation
  • Extensive knowledge of its genetics and genomics
  • Extensive knowledge on its transcriptome, proteome, and metabolome
  • Several strains are considered biosafety level 1 (K12)

Disadvantage

  • doesn’t have a nucleus/chromatin, not all protein modification mechanisms e.g. glycosylation
73
Q

What are the two types of single cell organisms of yeast?

A

Simple eukaryotic organism

  • many essential cellular processes are the same in yeast and humans.
  • S. pombe resembles animal cells in terms of (division pattern; centromeres; introns; heterochromatin)
  • S. cerevisiae is more similar to animal cells in terms of (relative lengths of G1 and G2; synaptonemal complexes).
74
Q

Tell me the advantages of yeast?

A
  • Rapid growth (1.5 or 2.5 hours)
  • Non-pathogenic
  • Efficient transformation by exogenous DNA
  • Efficient homologous recombination
  • Simple genetic screens
75
Q

Why are the multinuclear organisms- Nematode worm (Caenorhabditis elegans) Less complex than humans?

A
  • No bones, heart or circulatory system.
  • But does share many genes. and molecular pathways with us.
76
Q

What is each nematode worm made up of and what can this be used to study?

A
  • Each worm is made up of about 1,000 somatic cells, a third of which are nerve cells.
  • Can be used to study reproduction and development.
77
Q

Why is the mouse Mus Musculus) closely related to humans?

A

The mouse is closely related to humans with a striking similarity to us in terms of anatomy, physiology and genetics.

78
Q

Tell me about time taken for a mouse being born and giving birth

A
  • The time between a mouse being born and giving birth (generation time) is short, usually around 10 weeks. This means several generations can be observed at once.
  • Amenable for genetic manipulation
  • Many knock out, knock in and conditional expression lines exist
79
Q

Tell me about mammalian systems cell culture?

A
  • Cells isolated from a system and grown in vitro
  • Cheaper to study cells in culture than a whole organism
  • Can do more perturbation and measurements
  • Most cell lines are transformed
  • loose some properties compared to normal cells in vivo – can lead to artefacts
80
Q

Organoids are a recent advance, Tell me about their growth?

A
  • in vitro 3D cellular cluster (retain more structure and architecture than other in vitro cells)
  • derived from stem cells
  • ESCs, iPSCs or tissue resident stem cells
  • self-renewal
  • self-organization
81
Q

How do you grow and organoid?

A
82
Q

Modulating cell signalling is key…

What is Matrigel comonly used as?

A
83
Q

When and what was the first organoid system to be described?

A

2009- mouse intestinal organoids (first organoid system to be described)
Distinct crypt-like and villus-like domains border a central lumen containing dead cells extruded from the constantly renewing epithelial layer.

84
Q

Organoid development through the years

A
85
Q

What do organoids represent an important bridge between?

Why is this the case?

A

Organoids represent an important bridge between traditional 2D cultures and in vivo models.

  • more physiologically relevant than monolayer culture models.
  • far more amenable to manipulation of niche components, signalling
86
Q

Tell me some advantages of organoids?

A
  • Drug efficacy testing / Drug safety testing
  • Disease modelling
  • Regenerative medicine
  • As model systems for basic research: In particular for human biology
87
Q

A simplified view of cell biology

A
88
Q

At a transcriptional level, how can mRNA be measured?

A
  • in situ hybridisation
  • qPCR
89
Q

At the transcriptional level, how can proteins be detected?

A
  • SDS PAGE + Coomassie (A)/ Western blot B
  • Immunochemistry
  • ELISA
90
Q

Summary of lecture 18 and 19

A
  • Plants and animals stick cells together in different ways
  • Animals – predominantly via protein interactions

Cadherins

Integrins

Selectins

Immunoglobulin superfamily members

  • Plants – predominantly via polysaccharides
  • There are different types of model’s systems each with their specific advantages & limitations
  • Recent advances have generated new types of models to study cell biology

organoids

  • When designing an experiment, it is important to consider what you need to measure and what techniques you may use

BIOL2056 (7 decks)

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