Lecture 5

Question 1

What are stem cell niches?

Answer 1

Provide support cells that secrete factors that keep stem cells in a plastic state and enable them to respond to signals that are needed by the body e.g. tissue homeostasis

Question 2

Where and how were stem cells first understood?

Answer 2

gonadal niche in C. elegans- use ISH or immunohistochemistry to view. e.g. gut stem cells have a marker

Question 3

What pathways were found to be important for stem cell fate maintenance?

Answer 3

Used drosophila as they are simple organisms= block Wnt, notch, JAK/STAT and BMP (armadillo is an important signalling molecule in Wnt- they are vital for regulating niches. Also if enough Wnt signalling in mice= enough to make cells stem cells

Question 4

How are gut stem cells used?

Answer 4

They are cut and can be cultured in a dish with the signals of the microenvironment- can be grown to make many stem cells that can be used to study aging and drug screens

Question 5

what are the properties of the mammalian gut crypt?

Answer 5

Have villi to increase SA. The stem cells responding to the 4 signals sit in the collar of the crypt (distal end) and are surrounded by Paneth (support) cells. The differentiated cells are at the proximal end

Question 6

Briefly describe how the mammalian gut maintains homeostasis

Answer 6

As gut cells are constantly dying they need to be constantly replaced- the stem cells asymmetrically divide. The first progenitors are amplifying cells- as the cells move away from the crypt they differentiate

Question 7

What signals are seen at high levels at the bottom of the crypt?

Answer 7

Wnt, notch, noggin and gremlin

Question 8

How is lineage tracing carried out in mice CBC cells?

Answer 8

LGR5 is a target of wnt target genes- Wnt is secreted by Paneth cells and the responding CBC cells produce LGR5- make a transgene using restriction enzymes so that the promotors and enhancers of LGR5 are controlling GFP expression. Inject into mouse at one cell stage= can trace green cells live. Called EGFP

Question 9

How are gut organoids grown?

Answer 9

Take the E-GFP gut cells and dissociate into separate cells. Place in machine which carries out fluorescent activating sorting. Grow cells in medium with noggin, Egf and R-spoddin= forms organoid that has buds (crpts)

Question 10

What are the uses of organoids?

Answer 10

1) can test viruses and medical products
2) used for stem cell therapy e.g. if colon cancer- cut out the tumour and seal wound with organoids
3) Axin 2 LacZ= recapitulates Wnt signalling
4) can be used to better understand signals e.g. Wnt induces proliferation and Eph8 induces expansion for bud formation (ephrins are repulsive forces)