Differentiation

Question 1

Definition of differentiation

Answer 1

unspecialized cells becoming specific during embryo development AND tissue homeostasis

tissue homeostasis = throughout life

Question 2

Housekeeping proteins vs specialised proteins

Answer 2

housekeeping= non-cell-type specific (ie actin)
Specialised = cell-type specific (ie antibody chain, only in immune cells)

Question 3

Cell fate determination

Answer 3

cells fate becoming progressively defined

driven by interplay between cell lineage and cell environment

Question 4

Cell lineages

Answer 4

being able to trace a cell back where it came from

Question 5

Lineage restriction

Answer 5

ability to differentiate

eg blastocysts to blood cells

Question 6

Developmental potency

Answer 6

at different stages, cells have different potential to give rise to different cell types

Question 7

What do blastocysts differentiate into?

Answer 7

1. Ectoderm
2. Mesoderm
3. Endoderm
   as well as germ cells and trophectoderm->placenta

Question 8

What does the ectoderm differentiate into?

Answer 8

1. Skin -> hair, sweat glands
2. CNS -> neurons, glila, retina (photoreceptors and pigment cells)

Question 9

What does mesoderm differentiate into?

Answer 9

1. Bone
2. Muscle-> smooth, cardiac, skeletal
3. Kidney
4. connective tissue
5. adipose tissue
6. Vessels
7. Blood stem cells-> Erythrocytes, Macrophages, lymphocytes

Question 10

What does the endoderm differentiate into?

Answer 10

1. Liver
2. Gut
3. Lungs
4. Pancreas-> exocrine and endocrine

Question 11

What does the endoderm differentiate into?

Answer 11

1. Liver
2. Gut
3. Lungs
4. Pancreas-> exocrine and endocrine

Question 12

Haematopoeisis

Answer 12

All germ cells shared one common ancestor, example of cell fate determination (ie CLP to NK cells)

Question 13

What experiements support gene constancy?

Answer 13

1. Frog embryo nucleus implanted into adult skin cell results in cloned tadpole
2. If apply myosin TF in a red blood cell it starts forming muscle fibres

Question 14

Where and when is transcription regulated?

Answer 14

Where: at a start site (ie TATA, RNA polymerase is guided to start site by helper proteins)
When: whenever a TF binds to the enchancer region

TF is found in the nucelus and sometimes in the cytoplasm

Question 15

What does control gene expression do?

Answer 15

Determines differentiation which determines protein content which determines morphology and function which determines behavior during development

Question 16

How does an activator TF regulate transcription?

Answer 16

Binds to enhancer domain and turns gene expression on

Question 17

How does a repressor TF regulate transcription?

Answer 17

Binds to enhancer domain and turns gene expression off

Question 18

How do TF recruit RNA polymerase?

Answer 18

1. Histone aceytl transferase (loosens the histones to make genes more accessible)
2. Chromatin remodelling complex (promote RNA polymerase binding by straightening out section of chromosome to make DNA more accessible)

Question 19

Do TF regulate multiple target genes?

Answer 19

They can. For example: E-Box is found in myosin II, troponin, tropomysoin, creatine phosphate kinase, so they are all target genes bc all have E-box which is turned on by MyoD

Question 20

What steps are in muscle cell differentiation?

Answer 20

1. Proliferation (dividing myoblasts)
2. Cell cycle exit (cells align)
3. Terminal differentiation (specific proteins arise resulting in working muscle fibre

Question 21

What does MyoD do? What experiments proved this?

Answer 21

Binds to E-box promoter region on genes needed for muscle cell differentiation
Loss-of- function experiement: Knockout MyoD then myoblasts never differentiate, stalled after cell cycle exit.
Gain of function experiement: transfect a plasmid with expressed MyoD and they turn into muscles

Question 22

What does Glabra1 do?

Answer 22

TF for plant leaf trichomes. No Glabra1=no trichomes

Question 23

What does GATA1 do?

Answer 23

TF for erythrocytes. No GATA1= no RBC, differentiation at proerythroblast.

RBC= red blood cells

Question 24

What is a homeodomain?

Answer 24

example of a DNA binding domain. 5’-ATTA-3’. TF is pushed into the major groove of DNA by two other helices so residues from the TF interact with base pairs. Pattern of H-bonding dictates whether TF activates anything?

Question 25

What are some transcription factor families?

Answer 25

bHLH, Homeodomain, Myb, Zinc-finger, MADS box ## Footnote bHLH and homeodomain and zinc finger is present in all organisms, Myb only in arabodopsis, MADS box only in arabodopsis and humans

Question 26

What affect does phosphorylation have on TF?

Answer 26

Phosphorylation is a commong post translational modification. It may activate or inhibit the TF. Eg GF actiavte MAP kinase that phosphorylates TF and activates gene expression Eg2. EGF binds its receptors and MYC phosphorylated and becomes stable and activates transcription of cyclins

Question 27

What are the three bHLH TF involved in guard cell differentiation?

Answer 27

SPCH-> Mute-> FAMA No SPCH= no cell fate determination after progenitor No Mute= no cell fate determination after meristemoid No FAMA= no cell differenentiation into guard cells

Question 28

What bHLH TF are involved in muscle cell differentiation? Any other signals involved?

Answer 28

bHLH: MyoD, Myf5, Mrf4, Myogenin Homeodomain: Pax3 Regulatory signals= GF, WNT, SHH, BMP

Question 29

What is the muscle gene regulatory network? (GRN)

Answer 29

SHH activates Myf4 which activates Myf5 (determination) and MyoD. Pax3 activates MyoD and Myf5 as well, MyoD and Myf5 both activate themselves. Both activate myogenin, GF inhibits this. Myogenin leads to muscle specific proteins production ## Footnote Myf5 present means the signal is received, and Pax3 means its correct lineage. Both these need too be present to turn MyoD on.

Question 30

What targets MyoD for degradation?

Answer 30

CDK phosphorylate MyoD and Myf5 which target it for proteolytic degradation

Question 31

What is the effect of master regulator PAX6 mutation?

Answer 31

The whole eye is gone in drosphilia, this is bc PAX6 encodes a paired box and homeodomain TF. PAX6 needed for multiple different cell types. Expressing PAX6 in the leg or wing results in eyes forming there. PAX6 is highly conserved (as master regulators usually are) and specifies eye promordium in jellyfish and worms too

Question 32

What is Waddingtons landscape?

Answer 32

Ball rolling down the hill with vallies and such, represents binary cell fate choices a cell makes Eg Pu.1 and GATA1 compete for different pathways. Pu.1 antagonizes GATA1 and binds to it after GATA1 binds DNA and knocks off the coactivator protein and induces methylation

Question 33

Why is Waddingtons theory not the best? What two factors determine cell fate decisions?

Answer 33

Cell fate descions are determined by cell lineage (what choices is available) and environment (what choice is appropriate) Cdx2 expression gives gut cells competence (cell lineage) and if FGF2 received then Cdx2 activates Pdx1 (environment)