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Y2 Mol Bio > Cell polarity > Flashcards

Cell polarity Flashcards

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1
Q

Why is cell polarity necessary?

A

For cells to generate forms with a diverse array of functions
Create distinct protein compositions. giving different cell capabilities and functions

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2
Q

What are cell surface landmarks important for?

A

Adapting common pathways for cytoskeleton assembly, protein transport and membrane trafficking.
This creates cell polarity

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3
Q

Outline a general pathway to form a polarity axis

A
  1. Marking the site (usually binding to something)
  2. Decoding the site (signalling)
  3. Establishing the site (recruiting machinery)
  4. Maintaining the site (Keeping machinery in place)
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4
Q

What creates a polarity axis?

A

Changes in cytoskeleton and vesicle formation

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5
Q

What yeast is used to study polarity and why?

A

Saccharomyces cerevisiae
Entire genome sequence is annotated so can be used to track genes
Has been used to understand cell cycle, secretion and polarity

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6
Q

Give an internal signal for polarity

A

Growth and division signals

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7
Q

Give an external signal for polarity

A

Pheromones for mating and nutritional signals

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8
Q

What structures form when yeast cells bud and divide?

A

Spatial patterns- axial, bipolar

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9
Q

How are yeast budding events tracked?

A

Calcofluor which binds to chitin
These show birth scars where sites of previous cell divisions are marked as bright rings on the cell wall

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10
Q

How are yeast budding events tracked?

A

Calcofluor which binds to chitin
These show birth scars where sites of previous cell divisions are marked as bright rings on the cell wall

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11
Q

What does the position of a new bud on yeast depend on?

A

Cell type (haploid/diploid)

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12
Q

What sort of yeast cells bud in an axial pattern? (mother and daughter cells form buds adjacent to the previous site of cell separation)

A

Haploid a and α cells

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13
Q

What sort of yeast cells bud in a bipolar manner? (mother and daughter cells bud at the poles of their ellipsoidal cells

A

Diploid cells. This contains the pattern to adapt more advantageously

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14
Q

What genes are involved in marking a mother yeast bud neck during a cycle for budding in the next cycle?

A

BUD3
BUD4
BUD10
septins

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15
Q

What do mutations in BUD3, BUD4 and BUD10 in haploid yeast cells cause?

A

Change budding to a bipolar pattern

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16
Q

What do mutations in BUD8, BUD9 and RAX2 in yeast cause?

A

Disrupt the bipolar budding pattern

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17
Q

What genes encode the ends of diploid yeast cells?

A

BUD8
BUD9
RAX2

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18
Q

What genes encode proteins that decode axial and bipolar marks in yeast?

A

BUD1
BUD2
BUD5

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19
Q

What do mutations in BUD1, 2 and 5 cause in yeast?

A

Random budding pattern of haploid and diploid cells

20
Q

What Rho-GTPase families are important in establishing a yeast polarity site?

A

Cdc42
Cdc43
Cdc24

21
Q

Explain what Cdc42 is

A

small rho GTPase
Activated by Cdc24 binding to the marked budding site and activating Bud1.
Cdc42 then establishes the polarity site

22
Q

How do haploid yeast allow mating?

A

They polarise and redirect growth to allow them to mate with a partner.

23
Q

Give a mechanism of how Cdc42 is activated

A
  1. Bud1 has GTP added by Bud5 (its GEF)
  2. Bem1 generates new actin filaments to drug Cdc24 to inactive Cdc42
  3. Cdc24 acts as a GEF and acitvates Cdc42
24
Q

What proteins are required for asymmetric inheritance of certain factors in yeast?

A

Myo2
Myo4

25
Q

What is cell polarity critical for?

A

Asymmetric cell division
Epithelial cells (barrier)
Cell migration

26
Q

What was Whitman’s 1878 hypothesis of yeast cells generating daughter cells?

A

Distinct cytoplasmic domains are differentially partitioned, differences reflected in different cell lineages

27
Q

What was Conklin’s 1905 hypothesis of yeast cells generating daughter cells?

A

5 cytoplasmic types of ascidna oocyte that are differentially inherited to determine tissue types

28
Q

What are Candidasis and Candidaemia?

A

Benign members of mucosal flora
Yeast overgroeth can cause oral/vaginal thrush
Can have 30-50% fatality if it becomes infectious in the bloodstream
Candida switch between yeast and hyphal form (adhere to mammalian cells and penetrate)

29
Q

What are the two ways diversity is established in yeast

A

Intrinsic: polar cells divide to generate daughter cells that have inherited different components
Extrinsic: Daughter cells can be equal at birth but differentiate due to environmental signals

30
Q

What do PAR proteins do?

A

Recognise and localise cell material
Define a cell’s polarity axis via mutual antagonism by opposing and complementary membrane domains

31
Q

How is the anterior-posterior axis established in oocytes?

A

The position of entry of sperm into the oocyte determines the posterior end.
The oocyte splits into a smaller posterior cell P1 and a larger anterior cell AB.

32
Q

What do par genes encode?

A

par1-6 and atypical PKC (aPKC (PKC in C. elegans)).

33
Q

What par protein is conserved in yeast but not other metazoans

A

Par2

34
Q

Outline how par proteins are involved in creating the anterior-posterior axis

A
  1. Symmetry is broken in fertilisation when sperm delivers a mitotubule organising centre (MTOC)
  2. Microtubules recruit Par1 and Par2 to anterior par proteins to the anterior cortical domain
  3. Par3/Par6/aPKC localise to the anterior cortex, Par1 and 2 localise to the posterior cortex
    Par5 maintains the boundary
  4. Microtubules pull on the cortexes, displacing mitotic spindles to the posterior end
  5. Par proteins redistribute, determining cell fate
35
Q

How do CNS progenitor cells (neuroblasts) undergo cell division?

A

Rounds of asymmetric cell division give rise to a small basal daughter cell (ganglionic mother cell) and apical daughter cell
GMCs divide to give a neuron and glia cell.
Apical daughter cells divide asymmetrically to produce another GMC

36
Q

What happens when neuroblast delaminate (split into layers)?

A

Par3, Bazook/Par6 are found in a stalk that extends into the epithelium
Baz/Par6 localises into the apical region
Baz anchors Insc/Pins at the membrane to orient the mitotic spindle
The scribble complex helps spindle alignment

37
Q

Outline the epithelial polarity programme (EPP)

A

Epithelium is the first tissue formed after an egg is fertilised
Epithelial cells have a polarised actin cytoskeleton, allowing the apical surface to constrict, important in gastrulation and tubulation

38
Q

How do epithelial cells generate diversity?

A

They can orient their mitotic spindle to allow division parallel to the epithelial sheet
They can have an epithelial-mesenchymal transition (EMT) to non-epithelial cells
or mesenchymal-epithelial transition (MET) back to epithelial

39
Q

What are two of the main complexes that interact with the Par complex to form polarity in Drosphila?

A

Crumbs/CRB complex
Scribbled/SCRIB complex

40
Q

How can invertebrates maintain apical-basolateral polarity?

A

Tight junctions are formed, maintaining this polarity through homophilic interactions

41
Q

How can invertebrates maintain apical-basolateral polarity?

A

Tight junctions are formed, maintaining this polarity through homophilic interactions

42
Q

What happens in an epithelial-mesenchymal transition?

A

Signals lead to a loss of E-cadherin, leading to EMT
Apical-basal polarity axis is converted to a migration axis which has front-rear polarity

Asymmetric activation of small Rho GTPases (Cdc42 and Rac1 at the front, RhoA at the rear)

43
Q

Outline the steps in cell locomotion

A
  1. Protrusion: the plasma membrane is pushed out in front of the cell
  2. Attachment: actin cytoskeleton is attacked via proteins across the plasma membrane to the substratum
  3. Traction: cell body is drawn forward through contraction
44
Q

What are the main structures in actin

A

RAK activates filopedia (microspikes with a actin bundles) and lamellipodia (short, cross-linked actin)
Stress fibres are activated by small GTPases and involved in contractility

45
Q

What is chemotaxis

A

Movement towards a diffusible chemicale,g movement of neutrophils towards a bacterial infection

Y2 Mol Bio (10 decks)

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