Tissue Homeostasis

Question 1

What are two uses for stem cells in tissues?

Answer 1

-Renewing a constantly turning over tissue (like blood)
-Renewing a tissue after injury (muscle)

Question 2

What are traits of stem cells?

Answer 2

-Immortal
-Slowly dividing
-Can give rise to fast dividing daughters (transit amplifiers)
May give rise to either a differentiated cell or an undifferentiated copy of itself

Question 3

How can asymmetric divisions be induced?

Answer 3

Either by:
-outer environmental signals (growth factors, surrounding ecm…)
-Internal localised cell components that only end up in one daughter

Question 4

What is a technique which can be used to uniquely label implanted cells.

Answer 4

Lightly irradiating the cells will cause unique DNA damage in each of them.

Question 5

What is a niche?

Answer 5

The environment of a stem cell which provides factors needed for stem cell maintenance. If a daughter cell is no longer in its niche then it will differentiate.

Question 6

What is the niche for Germline stem cells in drosophila?

Answer 6

Cap cells

Question 7

What is the purpose of Bam gene in drosophila Germline stem cell differentiation?

Answer 7

Bam gene is activated in daughter cystoblasts produced by GSCs due to a lack of signalling received from the cap cell niche.

Question 8

What causes oriented division in drosophila Germline stem cells

Answer 8

The spectrosome (a condensed organelle composed of spectrin) is oriented towards the cap cell niche in GSCs and inherited by the GSC daughter. Orients division towards and away from the cap cell.

Question 9

What differentiated cells are present in the gut?

Answer 9

-Enterocyte: nutrient absorption
-Goblet cell: secretes mucus
-Enteroendocrine cell: secretes hormones
-Paneth cell: mediates microbial immunity
-Crypt base columnar (CBC) cells: express LGR5 (are stem cells)

Question 10

What is the niche for Crypt base columnar cells?

Answer 10

Paneth cells

Question 11

Which signals do Paneth cells release to allow CBC cell survival?

Answer 11

Wnt3

Question 12

How do CBC daughters move away from the Paneth cells in order to differentiate?

Answer 12

Paneth cells do not divide and so form a small net in the crypt. CBCs divide symmetrically and compete for space in the crypt. Some of them get pushed away from and lose contact with the Paneth cells and so go on the become transit amplifying region cells.

Question 13

How is the gut regenerated after CBC stem cells are removed?

Answer 13

Transit amplifying cells further toward the villus regenerate the CBC (de-differentiation?)
Organoids can also be implanted to reintroduce CBCs

Question 14

What is the structure of different tissue layers in the skin?

Answer 14

-Undifferentiated basal cells at bottom (stem cells). These give rise to cells which divide for several rounds and then give rise to suprabasal cells.
-suprabasal cells are above, which progress toward outer surface and lay down a protein matrix coated in specialised cell membrane, these cells then enucleate and die to make a barrier
-outer layer (epidermis) is consistently lost

Question 15

Out of the 3 colony types in cultured skin cells, which can sustain long term propagation?

Answer 15

Holoclones

Question 16

What are the stem cells in muscles?

Answer 16

Satellite cells (located between the basement membrane and cell cytoplasm of the multinucleate muscle fibre)

Question 17

What is the mechanism of regeneration in hydra?

Answer 17

-Cells always sensing what structure and location in the body they make up
-organism knows what is missing in injury and can re-specify cells as missing ones
-head and foot end produce dynamic gradient of diffusing molecules that specify head and foot and inhibit the wrong differentiation

Question 18

What is the mechanism of regeneration in Planarians?

Answer 18

-morphogen gradient in the planarians body specify head and tail ends
-regenerate from stem cells
-at the cut sites stem cells forms proliferating region called a blastema which will then grow the new structure.

Question 19

What is the machanism of regeneration in axolotls?

Answer 19

-Blastema forms at injury site
-each differentiated cell type in the blastema de-differentiate, proliferate and then re-differentiate
-not multipotent as they can only redifferentiate into the cell type from which they arose

Question 20

What genes are involved in both limb development and regeneration in axolotls?

Answer 20

Sonic hedgehog and FGFs

Question 21

What is the difference between embryonic gut development and Gut maintenance?

Answer 21

Gut development doesn’t require Paneth cells as they only appear at day 15 after gut has already formed

Paneth cells are also not confined to crypt base 1 day postnatal, difference between embryo and adult guts.

Question 22

What is the difference between stem cells in embryos and foetuses?

Answer 22

Embryonic stem cells are from a not yet implanted embryo and are pluripotent.

A foetus is made of already partly specialised tissue, stem cells are multi or oligopotent

Question 23

Which cells in a compacted embryo will give rise to all embryonic tissues?

Answer 23

Inner cells, forming the inner cell mass (ICM). Pluripotent ES cells

Question 24

What signal maintains ES stem cells as stem cells?

Answer 24

LIF, secretes from outer trophoblast cells

Question 25

What is the in Vivo use for pausing ES cells?

Answer 25

Mice holding fertilised embryos in uterus while the mother weans the previous batch
Known as Diapause

Question 26

What cell types can neural stem cells become?

Answer 26

Neurons and Glial cells

Question 27

What are some medical uses for ES cells?

Answer 27

Resupplying lost cell types in Parkinson’s and Type I diabetes patients