Cells, Specialisation and Development Flashcards
(190 cards)
1
Q
What are the features of cell equilibirum?
A
Proliferation - differentiation - death
2
Q
What do degenerative diseases mean?
A
Cellular equilibrium doesn’t work as well when you get older
3
Q
What is cell cycling?
A
- New cells through cell division
- Replaced lost or damaged tissue
- Allows growth and repair
4
Q
How is cancer related to cellular equilirbrium?
A
- Disruption/imbalance
- Deregualted cell cycle
- Too many cells that arent functional or dont die
5
Q
What is a melanoma?
A
- Cancer that develops on the surface of the skin
- Cell cycle control - no longer regulated
6
Q
What are the different stages of the cell cycle?
A
- G1 - Gap 1 (11hrs)
- G0 (Rest - don’t divide)
- S - DNA synthesis (8hrs)
- G2 - gap 2 (4hrs)
- M - mitosis (1hr)
7
Q
What is meant by Synescent?
A
Can no longer divide - come to the end of their dividng ability
8
Q
Are cells still happening whilst cell division is occurring?
A
Yes
9
Q
Where are the checkpoints during the cell cycle?
A
- G1 - check for damaged DNA
- G2 - unreplicated or damaged DNA
- M - chromosome misalignment
10
Q
Describe Gap Phase 1 (G1)
A
- 2n DNA
- Can be very long or short
- Cell growth
- Synthesis of macromolecules
- Detection of DNA damage and repair
11
Q
Describe the G1 Checkpoint
A
- DNA damage
- Suitable environemntal conditions
- If checkpoint is passed cell become committed to DNA synthesis
12
Q
Describe Gap Phase 0 (G0)
A
- 2n DNA
- Cells leave the cell cycle
- In a quiescent state
- Still living and functional
- Can last for years
- Can re-enter cell cycle
- Stop dividing through contact inhibition (fill up space)
13
Q
Describe Synthesis Phase (S)
A
- Replication = 4n
- Start of S phase each chromosome = one coiled DNA double helix (chromatid)
- End of S phase each chromosome = two identical coiled DNA double helices (sister chromatids)
14
Q
Describe Gap Phase 2 (G2)
A
- 4n complement of DNA
- Preparation for mitosis
15
Q
Describe the G2 Checkpoint
A
- Unreplicated and damaged DNA
- Prevent cell entering mitosis with faulty DNA
- Helps maintain genomic stability
16
Q
What are the stages of Mitosis?
A
Prophase Metaphase Anaphase Telophase Cytokinesis
17
Q
Describe the Mitosis Checkpoint
A
Spindle assembly checkpoint for misaligned chromosomes
18
Q
Describe prophase
A
chromosomes condense (36mins)
19
Q
Describe metaphase
A
chromosomes attach to spindle fibres and align on the equator (3mins)
20
Q
Describe Anaphase
A
sister chromatids pulled to opposite poles by spindle fibres (3 mins)
21
Q
Describe Telophase
A
nuclear membrane reforms and subsequently a cell plate is laid down between daughter cells (cytokinesis) (10 mins)
22
Q
What is meant by cell signalling molecules have mitogenic properties?
A
- Induc cell proliferation by promoting entry into the cell cycle
23
Q
How does PDGF have mitogenic properties?
A
- Platelet-derived Growth Factor
- Widespread effects
- eg during wound healing
24
Q
How does FGF have mitogenic properties?
A
pleiotropic (many different types of effects) effects, fibroblast growth factor
25
How does TGF beta have mitogenic properties?
members can stimulate cell proliferation or inhibit proliferation depending on cell type or concentration
26
How does erythropoietin have mitogenic properties?
more selective, induces proliferation of BFU-E and CFU-E during erythropoiesis
27
How were sea urchins used in a cell cycle control experiment?
- Clear start to the cell cycle
- Fertilised
- Took samples every 10 mins after fertilisation
- Run samples through SDS polioacrolimite gel and analysed them
- One protein got stronger and stronger then faded away
- Protein was coming and going in a distinct cycle
- Called the protein cyclin
28
What is the cell cycle regulated by?
cyclins and cyclin dependent kinases (Cdks)
29
Describe RB dephosphorylated (active)?
- Prevents G1-S transition
| - Breaks the cell cycle when dephosphorylated
30
What is RB?
Retinoblastoma protein
31
What does RB do?
Brakes on the cell cycle - called a tumour supressor protein.
- Controls by slowing it down
32
What controls RB phosphorylation/dephosphorylation?
Cdks
33
Describe what happens when RB is phosphorylated
mitotic stimulus received by the cell and this stimulates the synthesis of Cdk
In this case it's cdk4 → activate → phosphorylase
Pass a restriction point that enables cell to transit through to S phase
34
Which cyclins/Cdks are used at which point in the cell cycle?
```
G1 = cyclin D Cdk4 Cyclin E Cdk2
S = Cyclin A Cdk 2
M = CYclin B Cdk1
```
35
Why do cells die?
- Don't want too many cells
| - Most adult cells have a finite lifespan
36
How do cells die?
Apoptosis or necrosis
37
What is the process of apoptosis?
- Cellular condensation → everything compacts
- Nuclear fragmentation → form apoptotic bodies which can be consumed by surrounding cells → blebbing on the cell surface
- Rapid phagocytosis
38
What is the process of necrosis?
- Organelles swell
- Membranes rupture
- Leakage of cell contents
39
What are the properties of apoptosis?
- Physioloigcal
| - No inflammation
40
What are the properties of necrosis?
- Pathological
| - Marked by inflammation → immune system trying to fight against this necrotic event
41
What are the morpholigical features of necrosis?
- Pathologically induced occurs in response to tissue damage
- Often involves groups of cell that swell and burst, releasing their intracellular contents and frequently induces
- Lack of oxygen is one of the primary reasons
- Eg during a stroke
42
What are the roles of apoptosis?
- Development → eg born with webbed fingers so we have to remove the cells between the fingers
- Tissue homeostasis → eg older cells removed every 4 weeks, lining of gut or liver, cells are removed and regenerate fresh cells
- Removal of damaged cells → if cells do not pass checkpoints in the cell cycle so not passing on damaged DNA, maintained stability
- Elimination of premalignant cells → we carry mutations which if brought forward could cause cancer
43
Why does apoptosis use enzymes?
- To break down internal structures
- Cell collapses and fragments
- Neighbouring cells can take in their contents
44
What is self-renewal?
Gives rise to one stem cell and one daughter cell destined for differeintiaiton
- Production of the stem cell is slef-renewal
45
What do stem cells need to differentiate?
Through a progenitor cell - intermediate stage
46
Describe the satges of embyrogenesis.
```
Day 0 = fertilisation → forms a zygote
Day 2 = 2 cell stage
Day 3-4 = 4 cell stage
Day 4 = 8 cell division
Day 5 = forms a blastocyst
Day 8-9 = implantation of the blastocyst
```
47
Describe the blastocyst
- Formation of a primitive structure
- Sphere structure
- Fluid filled
- Inner cell mass
- Have a trophectoderm
48
What is the inner cell mass?
Aggregation of cell which will form the embryo
49
What is the trophoctoderm?
On the outside. Forms extra embryonic tissues such as the placenta and umbilical cord. Allows embryo to survive
50
What is potency?
Differential potential (range of cells a stem cell can differentiate into)
51
When do you have totipotent stem cells?
Day 3-4 - early stages, fertilised egg and daughter cells
52
Describe totipotent stem cells
- Have the ability to develop into an entire organism
- If implanted into the uterus they can generate an organisms
- They can produce the embryonic tissues
53
When do you have pluripotent cells?
Days 5-8, when you have the formation of the blastocyst and the inner cell mass
54
Describe pluripotent cells
- Have the ability to make every cell in our bodies
- Do not have the capacity to form the placenta and supporting tissues needed for foetal development → this means that they would be unable to generate a new organism on their own
55
Why do we need to grow embryonic stem cells in vitro?
Important for therapies
56
How are embryonic stem cells grown in vitro?
luripotent cells from the ICM of blastocyst separated from the surround trophectoderm
Inner cell masses plated into culture dishes and grown in nutrient medium supplemented with serum, supported by irradiated fibroblast feeder layers
Generate a blastocyst in a lab
Can derive the inner cell masses and expand them by growing them in culture
Feeder layer → supportive cells → sit on the base and secrete nutrients and growth factors to help the stem cells to survive
They can grown in numbers and go through the cell cycle
57
What is a feeder layer?
Nutrients
| - Fibroblast - MEF - used as feed layers
58
How can we determine the pluripotency of ES cells?
- Assay to test → teratoma assay
- Teratoma → benign tumour that contain cells from all 3 cell layers
- If a stem cell population is pluripotent it will give rise to a teratoma
- Inject SCID mice to form teratomas
59
Why are SCID mice used?
Severe combined immunodeficiency. Lack T cells and B cells and do not reject foreign tissue
60
What are teratomas?
Contain differentiated cell types derived from all 3 germ layers
61
What are the 3 germ layers?
Ectoderm. Mesoderm. Endoderm.
62
What makes cells pluripotent?
- Transcriptional factors
| - eg Oct-4, Sox2 and Nanog
63
How does Oct-4 work?
transcription factor expressed by embryonic stem cells. At the blastocyst stage, Oct-4 is only expressed by ES cells in the inner cell mass
64
How does Sox2 work?
transcription factors that forms a complex with Pct-4. Expression pattern similar to Oct-4
65
How does Nanog work?
Transcription factors specifically expressed by pluripotent ES cells (in the inner cell mass) slightly later than Oct-4
66
Why can't most cells in the body divide infintely like stem cells?
Due to telomeres
67
What are telomeres?
Repeat sequences. Chopped off each time a cell divides. When telomeres have gone the cell can't divide anymore.
68
What cells express high levels of telomerase?
ES stem cells and cancer cells
69
What is telomerase?
helps maintain the protective function of telomeres at the end of chromosomes → adds back the repeating sequences
70
What is TERC?
Telomerase RNA component
71
What is TERT?
Telomerase reverse transcriptase
72
What do TERC and TERT do?
Act as a template and reverse transcriptase to add back the repeating sequence
73
What are Induced Pluripotent Stem Cells (iPS)?
Take a somatic cell and apply it with transcription factors you can revert it to a pluripotent ES cell
74
What are some potential uses of iPS cells?
- Produce human organs
- Reprogramme them back
- Can form every cell and tissue type in the body
- In theory you can take them back and put them in the donor
- Correct developmental diseases
75
What are the risks of iPS?
- Form teratomas
76
What is meant by multipotent?
- Have a restricted differentiated potential
| - Only make cells/tissues in which they reside
77
What is special about the liver?
Regenerative capacity. Cant take 3/4 away and it will grow back to its original size
78
What are the properties of adult stem cells?
- Multipotent
- Can self reneew
- Reduced telomerase levels
- Differentiate into different cell types with specialised functions
- Primarily function to maintain the steady state activity of a cell and its resident tissue
- May help replace cells that are lost through injury or disease
79
What self preservation mechanisms are there?
- Slowly cycling - often quiescent
- Enhanced DNA repair mecahnisms
- Anti-apoptotic
80
What are the intermediates called?
Precursor or transit amplifying cell
81
Give an example of a multipotent cell becoming specialised.
Multipotent stem cells → multipotent progenitor cells → lineage committed progenitor cells → mature cells
82
What is terminal differentiation?
Eventually drop of through apoptosis
83
What is meant by commitment?
Cells dont go backwards. Won't de-differentiate
84
What are Hematopoietic stem cells?
- Blood: neutrophils, erythrocytes, megakaryocytes
- Can make all the blood cell lineages
- In bone marrow and in the circulation
- Carry oxygen, clot blood etc
85
What are epidermal stem cells?
Skin: keratinocytes, hair, gland cells
86
What are mesenchymal stem cells?
Bone: osteoblasts
Cartilage: chondrocytes
Adipose tissue: adipocytes
87
What are cell surface markers expressed by human hematopoeitic stem cells?
- Identified by proteins they expressed
| - There are positive and negative expression
88
What are some examples of negative cell surface markers?
1. CD38- (should not express this)
| 2. Lin- (lack expression of lin markers)
89
What are some examples of positive cell surface markers?
CD34+, CD133+, Thy1+
90
Where are HSCs located?
In specialised microenvironments in bone marrow - called the HSCs niche
91
How does the HSC cell maintain itself in a multipotent state?
Stromal cells interact with HSC cells → form cell - cell interacts → physical signaling interactions → eg notch → enable that cell to maintain itself in the multipotent state
92
What triggers differentiation?
Cell signalling
93
What is functional repopulation?
A single HSC can repopulate the entire haematopoietic system following lethal irradiation
94
What is lethal irradtiation?
not longer capable of marrow function → ability to create circulating blood cells is lost
95
Describe functional repopulation experiment.
- Lethal irradiation arrest haematopoiesis
- Inject healthy HSC
- Self-renew and give rise to a daughter cell
- New blood cells
- Mouse will survive
96
What are some potential therapeutic uses of hematopoietic stem cells?
Reconstitution of function after: Leukaemia, lymphoma, immunodeficiency diseases, autoimmune
97
What are epidermal stem cells?
epidermis forms the outermost layer of the skin
98
What makes up most of the cells in the epidermis?
keratinocytes which are organised into several distinct layers
99
How does the epidermis work?
Continuously renewed (normal keratinocyte life span about 28-35 days)
100
How could epidermal stem cells be used in therapies?
Treatments for burns → large amounts of the skin have been lost
101
What are the different stages of the differentation of the epidermis to keratinocytes?
- Basal layer → at the bottom → find the epidermal stem cells
- Spinous layer
- Granular layer → accumulate granulates
- Horny layer → become flattened, lose nuclei
102
What is the proliferative potential of basal layer keratinocytes?
- Subdivided into epidermall stem cells and transit amplifying cells
- Epidermal cells self renew
- Transit amplifying cells are the progeny of stem cell and undergo rounds of divigion before entering the terminal differentiation
103
What is Psoariasis?
Hyperproliferative disorder of the epidermis
Characterised by inflamed plaques raised above the skin surface
Life span of psoriatic keratinocytes approximately 4 days
104
What is lineage?
Direct descent from a praticular ancestor
105
What is haematopoiesis?
the formation of blood or blood cells in the body
106
Describe a blood cells life span.
- Short
| - Need to be renewed and stay in a young state
107
Where do HSCs reside?
Bone marrow (1.1%). Peripheral blood (0.06%)
108
What is the blood composed of?
Plasma and blood cells
| Erythrocytes (transport oxygen and CO2), granulocytes, platelets (blood clotting), lymphocytes
109
What are granulocytes?
Contain secretory granules
110
What is differential gene expression?
Process of development generate different patterns of gene activity - cell lineage restriction is dependent upon thise
111
Describe early haematopoiesis
- Development HSCs are in the embyronic aorta gonad mesonphros (AGM) region
112
What happens to the HSCs when the aorta develops?
- Cells that line the aorta generate hematopoietic cells
- Happens in the wall of the AGM
- From the wall HSCs emerge
- Haematopoiesis then moves to the bone marrow
113
What is the HSC niche?
Stromal cell - closely associated with the hematpoeitic stem cells
114
What happens when the HSCs differentiate?
- Slow specialisation
- Committed to lineages
- Lose their proliferation capacity as they become more differentiated
- Unidirectional
- Decreased capacity for cell division
115
What are the different lineages that a HSC can become committed to?
CLP = Common Lymphoid Progenitor. CMP = Common Myeloid Progenitor
116
What cells are part of the CLP?
T cells. B cells.
117
What cells are part of the CMP?
```
Erythrocytes
Platelets
Neutrophil
Basophil
Eosinophil
```
118
Why is controlling the process of haematopoietic complicated?
Need to recieve signalling inputs to differentiate or stay as stem cells
119
What are HSCs controlled by?
- Signalling factors - cytokines, growth factors and hormones
120
What are HSCs regulated by?
Intercellular signalling using a variety secreted factors that modulate proliferation and differentation pathways
121
What are other factors that control/regulate hematopoiesis?
Stem cell factor. Interleukins. Colony stimulating factors. Erythropoitin. Thrombopoietin
122
What is erythropoiesis?
Formation of blood cells
123
What is erythropoiesis regulated by?
Erythrpoietin (EPO)
124
What does erythropoietin do?
Controls differentiation of HSCs into erythrocytes via intermediated stages
125
What is the intermediate stage BFU - E in erythropoiesis?
Burst forming Unit Erythrocyte
126
What is the intermediate stage CFU - E in erythropoiesis?
Colony-forming Unit Erythrocyte
127
Outline the process of erythropoiesis
HSC → CMP → BFU-E → CFU-E → Proerythroblast → erythroblast → reticulocyte → erythrocyte
128
What is a reticulocyte?
loses its nucleus and then forms a function erythrocyte
129
What is multipotent HSC?
Goes through one or two rounds of division to produce BFU-E
130
How does BFU-E become CFU-E?
Goes through more rounds of cell division
131
What would a shortage of erythrocytes do?
Stimulate the kidney to produce EPO
132
Describe the process of EPO production
drop in oxygen → detection of low oxygen at proximal tubule → send a signal to drive EPO production → detected by the early stages of the hematopoietic stimulating HSCs in the bone marrow → increased erythrocyte formation → increased oxygen transport → negative feedback
133
What does a drop in EPO production cause?
Anaemia
134
How does EPO control the process?
increase in concentration in circulate in response to low oxygen levels → demand to increase RBC production to increase oxygen eg if you are wound
135
What is Megakaryocytopoiesis?
formation of platelets (thrombocytes)
136
What are megakaryocytes?
- Rare
- Give rise to platelets
- Large
- Multilobed nucleus
137
What is the major hormone controlling megakryotcyte production?
Thrombopoietin (TPO) - primary regulator
138
Why do megakryocytes have multilobed nucleus?
go through the cell cycle → dont go through cytokinesis → don't divide → endomitosis → just get massive nuclei → make lots of different proteins
139
What is the dilated demarcation membrane system?
Increase surface area, edges will form platelelts through proplatelet formation
140
How are platelets produced?
Stick projections between endothelial cells into the circulation
Proplatelets experience the blood flow and break off
Entire cell fragments → bits of cell which become platelets
141
Describe TPO regulation of megakaryocytopoiesis.
Uses similar biological apparatus as FGF signalling
| TPO initiates Ras-dependent signalling cascade
142
What are needed for megakaryocytopoiesis differentiation?
Transcriptional factors
143
outline megakaryocytopoiesis differentiation.
HSC → megakaryocyte progenitor → mature megakaryocyte → proplatelet megakaryocyte → platelets
144
How is the transcriptional factor FOG 1 involved in megakaryocytopoiesis
required to initiate the initial process driven by TPO to form megakaryocyte progenitor
145
How is the transcriptional factors GATA 1 and FOG 1 involved in megakaryocytopoiesis
needed to produce the mature megakaryocyte
146
How is the transcriptional factor NF-E2 involved in megakaryocytopoiesis
takes the mature megakaryocytes all the way through to the final stage of platelet production
147
What are myeloproliferative disorders the result of?
abnormal proliferation and differentiation of HSCs
148
What is an example of a myeloprofilerative disorder?
Primary thrombocythemia → hypersensitivity to TPO
149
What did the switch from exoskeleton to endoskeleton allow?
- Diversity
- Can grow
- Can live as land vertebrates
150
What is articular cartialige?
Ends of bone. lubricating. shock absorbing.
151
What is the cortical bone?
Hard bone. round the outside of the long bone. thick
152
what is the trabecular bone?
spongy bone. high surface area. indside
153
what is marrow?
where the stem cells divide and give rise to all lineages
154
what is the tendon?
enables you to move
155
what is the perichondirum?
around the cartilage
156
what is periosteum?
round the outside of the bone
157
what the different types of bone cells?
osteoblasts. osteoclasts. osteocytes.
158
what are osteoblasts?
bone forming cells
159
what are osteoclasts?
bone absorbing cells (is multinucleated)
160
what does hematopoietic marrow give rise to?
hematopietic stem cells and mesenchymal stem cells
161
what are homatopoitic stem cells?
give rise osteoclasts
162
what are mesenchymal stem cells?
- Less well defined than haemopoietic cells
- Provide structural tissues
- Produce supportive Stroma
- Can make bone tissue, fat tissue → undergo osteogenesis and adipogenesis
- Can produce cartilage → wouldn’t normally make cartilage (during fractures mainly) → chondrogenesis
163
Why does bone need to be light?
so can move around
164
Describe osteoblasts structure
- Mononuclear cells
| - Fat and plump and sit on the surface
165
Describe osteoblasts function
- Produce an unmineralised collagen matrix → called osteoid
- Osteoid becomes mineralised over time
- Osteoblasts deposit packets of mineralized
- Osteoblasts bury themselves alive in the bone matrix → they then exist as osteocytes
- Role in life to make type 1 collagen
166
What do mesenchymal stem cells give rise to?
osteoblasts
167
what is the structure of an osteoclast?
- sits on the bone surface
- large multinucleated cells
- differentaite form monocytes
168
what is the function of an osteoclast?
- Secretes acids and protons and enzymes to enable them to digest the bone matrix
- Form a resorption pit → remove bone
- Differentiate from hematopoietic stem cells
- Form tight seals on bone matrix using alpha-v-beta-3 integrins → cell matrix interactions
- Primary function: secrete H+ and Cl- ions to form acidic environment, cathepsin K and tartrate resistant acid phosphatase to aid bone (TRAP) resorption
169
what are osteocytes?
Differentiated osteoblasts (about 15% become osteocytes) embedded in the bone matrix
170
what is the function of osteocytes?
detect damage and changes to mechanical environment → mechanosensors
Stick out projections → through tunnels in the bone → make contact with other osteocytes and cells on the cell surface
171
What is bone remodelling?
- Highly coordinated turnover of bone tissue
- Bone removed and replaced
- can repair microfractures
- renewal of old bone tissue
- maintains calcium homeostasis
172
What is mechanical loading?
Muscle mass increases when we exercise - bones have to become stronger
173
What happens to your bones when you go into space?
Bone loss. Centrifuge helps to load bone mass
174
Describe age related bone loss.
- Osteoporosis, abnormal bone function
- 1 in 2 women, and 1 in 5 men will have osteoporosis
- Bones become weakened
175
What are the the 2 process as the skeleton develops during embryogenesis?
1. Intramembranous ossification
| 2. Endochondral ossification
176
What bones does intramembranous ossification form?
Flat bones - eg those in the skull
177
What type of process is intramembranous ossification?
Direct process - forms primitive mesenchymal stem cell to an osteoblast to a bone
178
Describe the process of intramembranous ossification
- Mesenchyma stem cells condense together
- Differentiate in osteoblasts
- Osteoblasts bury themselves in the bond becoming osteocytes
- Structure becomes vascualirsed
- Trabecular bone will form
- Later forms a flat layer
179
What type of process is enodochondral ossification?
- Indirect
- Process goes via a cartilage intermediate
- Allows bones to elongate (and us to grow)
180
Describe the process of endochondral ossification
- Primitive mb bud
- Mesenchymal condensation
- Form cartilage and within the cartilage bone is formed
- Cartilage cells later become surrounded by osteoblasts
- Undergo hypertrophy (cells grow large)
- Growth of mb bud
- More blood vessels going in
- Gives rise to the marrow space where heamtopoiesis takes place
- Within the elongated structure is where bone ossification starts to happen
- Grows in length
- Proliferating chondrocytes, grow
- Chondrocytes start differentiating
- Site of hematopoiesis moves
181
What signal is important in bone development?
FGF signalling
182
Describe FGF receptor 3 in bone development.
Expressed mainly around the perichondrial region - outside the cartilage
183
Describe FGF 18 in bone development.
Expressed by perichondirum and targets proliferating chondrocytes - inhibits
184
What does FGF do overall?
Slows down the growth of long bones
185
What can mutations in the FGF3 gene do?
Result in over-active FGFR3 signalling, enhancing the inhibitory effect. Leads to dwarfism
186
Where is the primary ossification centre?
Marrow space where hematopoiesis takes place
187
Where is the secondary ossification centre?
Develops postnatally and lasts through to adolescence
188
What happens when the ends of bones start to mineralise?
Won't grow any more
189
What do both intramembranous and endochodnral ossification have in common?
Mesenchymal condensation
190
What is Renx2?
An osteoblast transcription factor that is essential for normal bone development
