Lecture 11; Organogenesis 3 Flashcards
What two major cell types are found in the pancreas?
Exocrine; Acinar cells
Endocrine; Islets of langerhan (a,b,d,f cells) (b insulin) (a glucagon)
What is the function of acinar cells?
• Acinar cells secrete pancreatic juice (enzymes that degrade proteins, carbohydrates & lipids). Transported to small intestine via pancreatic ducts.
Write some notes on the exocrine function;
Contain zymogen granules
acinar and duct cells
95% of pancreatic mass
What is the first step in pancreas forming following the formation of the endoderm tube?
Gut derived derivatives (eg pancreas, liver) form as buds from endoderm
(dorsal and ventral buds the pancreas forms from)
Give an overview of what happens in pancreating budding;
- Endoderm budding
- Outgrowth and lumen formation (cells are multipotent and it will be determined if they form tip or trunk cells)
Trunk cells go on to form primitive ductal system and tip cells form primitive acinar cells (ends of ducts)(i.e the ducted pancreatic system)
What can also happen to the trunk cells?
They can delaminate and migrate out into the space in between the ducts, giving rise to the endocrine progenitor and thus the five cell types in the islet
Thus forming islets clusters and blood vessels grow to these
Duct cells are bipotential progenitors
Describe how the two pancreatic buds fuse;
As the gut tube develops in rotates and the ventral bud fuses with the dorsal pancreatic bud
Gut rotation
(morphogenesis)
Describe the role of tissue cross talk in the formation of the pancreas;
Signals from the mesoderm (cardiac and notochord) induce dorsal and ventral pancreas from endoderm
i.e primitive heart that is near ventral pancreas inhibits its formation in different endodermal parts, but stimulates it at a specific location
What signals are key for pancreatic formation;
Shh inhibits pdx1 and pfta1 (genes that are mastor regulators of pancreatic precursor formation)
The primitive heart + notochord inhibits Shh
RA promotes the master regulator genes
Key singals in pancreas formation
Describe the signalling pathway that results in pancreatic formation;p
Cross talk signals inhibit Shh
pdx1 and pfta1 upregulation (multipotential endoderm bud forms)
Notch signalling (1)
Tip cells (PFTa1)
Trunk cells(nkx6.1)
- Notch signal (2)
= Duct cells
- Endocrine progenitor (ngn3)
What does notch signalling one promote?
Notch signalling one switches from a tip fate to a trunk fate
How can tip and trunk cell tracription factors interact?
There is mutual inhibiton of PFTa1 and NKX6.1
i.e cant be both on at the same time thus stablising the fate
What does notch 2 do?
Notch signal 2 will promote duct cell formation over endocrine progenitor
(master regulator for these endocrine precursors)
How is pfta1 consistant?
It is present right down the acinar lineage
It also promotes upregulation of nra52 in a positive feedback loop to promote itself
Positive feed back loop with Ptfla maintains acinar fate
What else occurs in the singalling pathway?
The recycling of factors
Where do embryonic stem cells come from?
They are derived from the ICM
What did researches find when the cultivated ICM?
They formed outgrowths
Providing they receive the right factors they can grow indefinitely and remain pluripotent
What is a test that can be done to test pluripotency?
Inject ES from black mouse into blastcyst of brown mouse and place in surrogate
Chimera is born with all three germ layers recieving contribution from black mouse ES
What is another test for pluripotency?
Teratoma test
What is the teratoma test?
- Inject ES under kindey capsule in mouse (if they are truly pluripotent they will spontaneously differentiate forming all three germ layers and what is called a teratoma tumor)
Disorganised mass containing tissues from all 3 germ layer
What is the application of truly pluripotent tissue?
Could form any tissue!!!
but ethical issues
What was the solution of ES ethical tissues?
Took mature cells and used transcription factors to reverse them into induced pluripotent stem cells( iPS)
What master regulators were used in iPS?
transcription factors: Oct4, Sox2, cMyc, Klf4
forced pools of expression of these regulators in mouse fibroblasts and found he had created iPS
What is the promise of iPS?
If signals / regulators are known then any tissue can be created;
- Tissue engineering
- Cell based therapies
- Disease in a dish
Whats an example of using brain organoids? (organoids is the bio engineered attempt at organ, not there yet)?
ZIK virus
- placed in organoid to show reduced brain growth
- morphogenic changes to neurosphere
- cell death
showed side effects of developing fetus and zika
What is the melton protocol?
The creation of beta cells from iPS (protocol)
- Blocked Shh
- RA stimulation of TFs
Notch signalling
i.e basically copied embryonic knowledge to create beta cell organoids
Developmental biology of the pancreas informs the ‘directed differentiation’ of iPS cells
What is melton doing now?
Future clinical trials: Encapsulated iPS cell-derived beta cells
- semipermable barriers
- nutrients in and hormones out
