Lecture 11; Organogenesis 3

Question 1

What two major cell types are found in the pancreas?

Answer 1

Exocrine; Acinar cells

Endocrine; Islets of langerhan (a,b,d,f cells) (b insulin) (a glucagon)

Question 2

What is the function of acinar cells?

Answer 2

• Acinar cells secrete pancreatic juice (enzymes that degrade proteins, carbohydrates & lipids). Transported to small intestine via pancreatic ducts.

Question 3

Write some notes on the exocrine function;

Answer 3

Contain zymogen granules

acinar and duct cells

95% of pancreatic mass

Question 4

What is the first step in pancreas forming following the formation of the endoderm tube?

Answer 4

Gut derived derivatives (eg pancreas, liver) form as buds from endoderm

(dorsal and ventral buds the pancreas forms from)

Question 5

Give an overview of what happens in pancreating budding;

Answer 5

• 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)

Question 6

What can also happen to the trunk cells?

Answer 6

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

Question 7

Describe how the two pancreatic buds fuse;

Answer 7

As the gut tube develops in rotates and the ventral bud fuses with the dorsal pancreatic bud

Gut rotation
(morphogenesis)

Question 8

Describe the role of tissue cross talk in the formation of the pancreas;

Answer 8

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

Question 9

What signals are key for pancreatic formation;

Answer 9

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

Question 10

Describe the signalling pathway that results in pancreatic formation;p

Answer 10

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)

Question 11

What does notch signalling one promote?

Answer 11

Notch signalling one switches from a tip fate to a trunk fate

Question 12

How can tip and trunk cell tracription factors interact?

Answer 12

There is mutual inhibiton of PFTa1 and NKX6.1

i.e cant be both on at the same time thus stablising the fate

Question 13

What does notch 2 do?

Answer 13

Notch signal 2 will promote duct cell formation over endocrine progenitor

(master regulator for these endocrine precursors)

Question 14

How is pfta1 consistant?

Answer 14

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

Question 15

What else occurs in the singalling pathway?

Answer 15

The recycling of factors

Question 16

Where do embryonic stem cells come from?

Answer 16

They are derived from the ICM

Question 17

What did researches find when the cultivated ICM?

Answer 17

They formed outgrowths

Providing they receive the right factors they can grow indefinitely and remain pluripotent

Question 18

What is a test that can be done to test pluripotency?

Answer 18

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

Question 19

What is another test for pluripotency?

Answer 19

Teratoma test

Question 20

What is the teratoma test?

Answer 20

• 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

Question 21

What is the application of truly pluripotent tissue?

Answer 21

Could form any tissue!!!

but ethical issues

Question 22

What was the solution of ES ethical tissues?

Answer 22

Took mature cells and used transcription factors to reverse them into induced pluripotent stem cells( iPS)

Question 23

What master regulators were used in iPS?

Answer 23

transcription factors: Oct4, Sox2, cMyc, Klf4

forced pools of expression of these regulators in mouse fibroblasts and found he had created iPS

Question 24

What is the promise of iPS?

Answer 24

If signals / regulators are known then any tissue can be created;

• Tissue engineering
• Cell based therapies
• Disease in a dish

Question 25

Whats an example of using brain organoids? (organoids is the bio engineered attempt at organ, not there yet)?

Answer 25

ZIK virus

• placed in organoid to show reduced brain growth
• morphogenic changes to neurosphere
• cell death

showed side effects of developing fetus and zika

Question 26

What is the melton protocol?

Answer 26

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

Question 27

What is melton doing now?

Answer 27

Future clinical trials: Encapsulated iPS cell-derived beta cells

• semipermable barriers
• nutrients in and hormones out