Part 4 Flashcards
Diseases and conditions where stem cell treatment is promising?
- Diabetes
- Crohns disease
- Spinal cord injury
- Deafness, blindness, baldness
- Brain= alzheimers, parkinsons, learning, traumatic brain/stoke
- Bone marrow transplantation
- Mi or Muscular dystrophy
What is multiple sclerosis?
Disorder of imune system- treatment essentially rebuilds a patients immune system using stem cells harvested from their own blood and bone marrow to reset it to a point before it caused ms
Safe efficient, stem cell therapy- a promise in many tissues
In haemetopooitic field, stem cell therapies have been conducted successfully for many years (bone marrow transplants)- used in ms
some tissues- careful trials are holding promise (eyes)
Many tissues less amendable
Stem cell tourism
Patients travel to other countries with few restrictions on stem cell therapies
- dangerous
- many gone through national regulatory process
SC study 2008
Site claimed to treat a range of diseases
Played up benefits and down risks
Each treatment cost $21,500
Haematopoetic system
Relatively early to isolate sc from bone marrow
In other tissues epithelia harder
Gut showing best practise
What is the gut cyrpt?
At the base of the villi
Tube of cells with stem cell like cells in a nice at the distal end and differentiating cells at proximal end
factors identified that regulate proliferation and differentiation
CBC cells identified throuhg expression of wnt target genes
Wnt/notch found to expressed at high levels ventrally
cells identified that respond to wnt signals and express wnt target genes- CBC cells - end up stem cell like
Spatial gradients of Wnt, BMP and ECF signals are found along the cyrpt
How does BMP affect stem cells?
Bmp negatively regulates stemness
Making mini-guts from stem cells gut
Cyrpt- single cells-FACs (fluorescent activating cell)- culture median
How does a single stem cell form a symmetric cyst structure?
Lgr5 CBC cells genetically labelled by EGFP are sorted and embedded in matrigel
The culture medium consists of ECF, noggin and R-spondin
The symmetry is broken by bud formation
The budding formation resembles cyrpt
How would you about making a epithelial mini-gut?
Colonoscopy- Biopsy sample- cyrpts- Epithelial mini-gut
Experimental tool
- Research for- Intestinal sc, intestinal differentiation and epithelial function
Diagnostic tool
- Cystic fibrosis
- Mutational analysis in CRC
- Drug absorption
Therapeutic tool
- Potential regeneration- microvilli disease, Ulcerative colitis
EDTA releases around 3000 crypts from a biopsy
How does growth affect final shape?
Cell proliferation- most cases- cyclin+ cdk drive cycle
Cell enlargement- Cardiac hypertrophy, skeletal muscle
Accretion- Bone
Cylcin and Cdk in the cell cycle
G1 phase- Cdk 4/6, cyclin D
S phase- Cdk 2, Cyclin E
G2 phase- Cdk2, Cyclin A
M phase- Cdk1, Cyclin A/B
Drosophila at initial stage of cell cycle
- Start as syncytium (single cell with multiple nuclei)
- Nuclei go through very rapid synchronous cell cycles consisting of S +M phases (14th cycle= 1000s of nuclei), cycle slows and G2 is introduced
- Nuclei migrate to periphery and become surrounded by involuting cell membrane
- Depends on A/P and D/V coordinates, each acquire own cell division rate/fates- fomr mitotic divisions( controlled by protein string cdk)
- 1-13th division= string uniformly distributed
- 14th onwards produced on patterning genes (slowing)
Exception to the uniform patterning rule
Mesoderm express string in 10th domain of division so cell do not divide
Tribble protein inhibits string
Promotes invagination
Why are tissues continuely replaced and active commonly connected to cancer?
- Already proliferating
2. Mistakes could occur
Teratoma cancer cells
Give rise to all 3 germ layers, can participate normally in formation of animal (mice) so not permanently transformed
Protoncogenes
Loss of growth control due to activating mutations in certain genes
Activated form= Oncogene
Tumour suppressor genes
P53 gene
Cancer can result in loss of genes that suppress tumours
Pathways involved in sc renewal, missregulation of proliferation and differentiation
Ptc regulates Hh
Apc regulates Wnt
Control of organ size
Intrinsic/ extrinsic Thymus- intrinsic, spleen systemic Growth programmes are flexible (liver) Animals- absolute dimensions, not cell number is important- ploidy affects cell size but not overall size of animal Morphogens NOT growth factors
Growth control pathways
TOR- cell size
Hippo- limit organ size
-When it is inactive the TF Yki/Yap/Tap is in the nucleus stimulating growth and survival of cells
-when activated Yki/yap/taz excluded from nucleus
- Hippo/mst1 and 2 integrate various signals to create a “stop growing” signal
Mammals and drosophila stop-growth signal pathway
Mech, stress other signalling pathways- inactivate Yki/yap/Taz nuclear promoting growth
Cell-cell contact, polarisation- active Yki/yap.taz out of nucleus
Hippo mutant, lost growth restriction= Yki in nucleus
Overall size
Growth rate of different parts is not uniform
Size is controlled by rate of growth but also by duration
Edcyson induces metamorphosis
IGF and GH pathway
Somatostain and GHRH both activate and inhibit GH in the hypothalmus
Liver produces IGF-1 which synthesises circulating IGF2 which goes to bone and inhibits GH
Local IGF-1 synthesised from GH to bone
In the Pituitary
How does the maternal environment influence growth?
- Low birth weight associated with CDH (coronary heart disease)
- Dutch famine (ww2 1944-45) short but severe, calonic restriction- babies exposed to famine early
- Early embryogenesis- weight and size will be compensated but increased risk of obesity, diabetes and probs CHD
What is cancer?
Creation and maintenance of tissues , requires strict control
- imbalance between gain/ loss of cells can over time have large effects
(excess 5% per year- 4 fold increase in 30 years)
Cancer in epithelial/ blood
85% of cancer in epithelial
Often linked to a failure in the normal differentiation process that occuras during the development or maintenance of structures
Usually mutations acquired
Aberrant developmental signals ‘drive’ cancer
- Activated Wnt- Colon, hepatoceullar cancer
- Activated Hh- Basal cell carcinoma, medulloblastoma
- Activated nodal- Melanona
- Activated notch- leukemia
- Activated EGF-lung and breast
Dominantly inherited cancer syndromes
Occasional deletion of 1/2 Rb genes
Herditary retinoblastoma- inherited mutant
-occasional inactivation of other functional Rb copy
-excessive cell proliferation- Rb
Molting and metamorphosis
Many adults do not directly develop into an adult form
Insects develop from larva etc
Signals involved in development- short range, small size
Embryonic devel environment - CNS - hormones
What are arthropods?
Have to molt to grow
Intermolt - apolysis (separation of epidermis from cuticle) - secretion of fluid growth of epidermis - secretion of new cuticle - activation of enzymes of molting fluid - shredding old cuticle
Control of metamorphosis
Influence of environment cues (light, temp etc),
Fly
- Juvenile hormone= prevents metamorphosis
- ecdysome= promotes metamorphosis
Frog
- Prolactin= delays metamorphosis
- T4, T3= Promtoes metamorphosis
- Corticotropin releasing hormone (CRH)> thyroid stimulating hormone (TSH)> thyroxin (T4T3)
Different effects in different tissues-Limb growth, but tail degeneration
What is metamorphosis?
The process of transformation from an immature form to an adult form in two or more distinct stages.
How would the fully developed organism replace appendages and organs?
Growth and re-patterning
NOT linked to complexity of organism
Mophallaxis= Repatterning without growth
Epimorphosis= Growth
Regeneration of hydra
Simple organism- 2 layers (ectoderm and endoderm- no mesoderm)
Mouth region= Hypostome, surrounded by tentacles an en elongated column
Hydra grow continuously therefore cells have to change their positional value, re-patterning also occurs during reproduction
Head regeneration in 2 gradients
- Gradient in positional value (inducing 1-5)- pv determinants= head inducing ability
- Head inhibitor gradient
Experiment to look at regeneration of hydra
A piece of region 1 is translated to an intact hydra
- Region 1 fails to induce secondary axis of intact hydra
- When hosts head is removed graft 1 induces a secondary axis
- Region 1 successfully induces a secondary axis when grafted further from head of an intact host
What does experiement 1 of the hydra show
Effect of positional value/ host head inducing capacity
Experiment 2- looked at after 6 and 30 hours
- Head of hydra removed and after 6 hours region 1 is transplanted into the body column of the host
- Gained stronger head inducing head capacity 2 - piece of region 5 cant do this after 6 hours need to wait 30 before this region had similar inducing power
What determines positional value?
Wnt/ beta catenin signalling may determine top Pv (involved in head formation)
- Gsk3beta inhibition- beta catenin nuclear conc up- So activates wnt
- all regions acquire characteristics of head organiser
- wnt expressed in head and regeneration tip
Regeneration of a flatworm
1/8 of animal can regenerate entire flatworm again
Why can certain organisms regenerate tissues whereas others cant?
Not linked to complexity of organism
Epimorphic- lens from iris
In urodele amphibians (tailed)- regenerate dorsal crest, limbs, jaw and tail
- regeneration occurs at level appropriate to where the cut i made
-after amputation- epidermal cell migration, cell below differentiate= blastoma (dermis and muscle/cartilage)
regeneration/generation must be different- morphogen work over a 10x larger range
What is surprising about this example?
Muscle can participate in regeneration as muscle cels are multinucleate- revert mononuceleate cells in cell culture under the influence of thrombin (expression of Msx and inactivation of Rb genes)
Muscle cells remain muscle and schwan remain schwan- dermis different= produces cartilage
Rules of regeneration
- Limb regeneration is always distal to the wound
- According to positional value at site of cut
- Not just replacing missing parts
Regeneration of amputated hand
Hand amputated
Limb injected into belly then humerus cut
Regeneration starts proximal and distal
Both proximal and distal regeneration distal structures
Wound can sense discontinuity in positional value between distal blastema and cut site
Remaining tissue formed from intercalary growth
How do distal and proximal blastema cells sort (moleculer and cellular basis)
Sort via differential adhesion
Distal and proximal tissues combined- The more cohesive tissue envelops the other
Anti-prod1 antibody added- Tissue remain separate
What is capable of resetting positional values
RA
Effect dependent on dose
increase level= More regeneration
RA may occur via upregulation of meis homobox genes or Prod1
Innervation is required for regeneration
Normal limb- NAG expression in nerve sheet upon cut= regeneration
Dennervated limb-no NAG persisting= No regeneration
NAG expression persists in epidermis= regeneration
What is NAG?
Newt anterior gradient- a protein that can replace the nerve in supporting outgrowth, binds prod1
expressed in response to wound
Innervation leads to downreulation of NAG
Anueurogenic limb= persistant epidermal NAG expression
Insect regeneration- cockroaches
Sensing discontinuous in positional values
Intercalation to regenerate missing one- irrespective of overall structure
