Chapter 22: Regeneration

Question 1

What is regeneration

Answer 1

the reactivation of development in post embryonic life to restore missing and damaged tissues.

Question 2

4 main types of regernation

Answer 2

1) stem cell mediated regeneration 2)epimorphorphosis 3) morphallaxis 4) compensatory regeneration

Question 3

what is stem cell mediated regeneration and example

Answer 3

when stem cells are used to regenerate tissues. ex/ hair from hair follicular stem cells

Question 4

what is epimorphosis and example

Answer 4

when an adult stem cell becomes dedifferentiated, forming a blastoma: mass of undifferentiated cells, which then redifferentiate into a new structure ex/ amphibian limb regeneration

Question 5

what is a blastoma

Answer 5

mass of undifferentiated cells, which then rediffereniate into a new structure

Question 6

what is morphallaxis and example

Answer 6

when existing tissues become repatterned that requires cell death and a change of cell type (transdifferentiation) ex/ hydra regeneration results in resizing of entire organism and components

Question 7

what is compensatory regeneration

Answer 7

when differentiated cells divide but do not become undifferentiated or transdifferentiated; they rather produce more cells of itself ex/ human liver regeneration

Question 8

How does regeneration and embryogenesis differ in terms of immune response?

Answer 8

regeneration invovles an immune response, and usually occurs following an injury (apoptotic and nectrotic cells, fluid accumulation etc). The immune response is the initial fixer for an injury. There is no immunte response in a newly forming embryo

Question 9

How does regeneration and embryogenesis differ in terms of induced reprograamin?

Answer 9

during regeneration, cells must become reprogrammed. Cells must become activated so they can revert back to an immature stat before they rebuilt tissus. this does not happen in embryogenesis. this is an example fo epimorphosis

Question 10

How does regeneration and embryogenesis differ in terms of system integration?

Answer 10

as opposed to embryogenesis in which cells are part of the initial tissues that form in a human, new cells in regeneration must become integrated into an already existing tissue.

Question 11

How does regeneration and embryogenesis differ in terms of size recognition:

Answer 11

regernated cells must be able to sense and communicate with cells around them so that thye only grow to the appropriate size.

Question 12

4 ways that regeneration differs from embryogenesis

Answer 12

1.immune response 2.induced reprograamin 3.system integration 4.size recognition

Question 13

three types of whole body regeneration seen in the hydra

Answer 13

1. stem cell mediated regeneration 2. morphallaxis 3.epimorphosis.

Question 14

why are hydra diploblastic

Answer 14

they are considered to be diploblastic because they only have an ectoderm and an endoderm. Generally they reproduce asexually via budding.

Question 15

cells of a hydra body are constantly undergoing mitosis and moving towards either a __ or __, where they become shed.

Answer 15

cells of a hydra body are constantly undergoing mitosis and moving towards either a HEAD or FOOT, where they become shed. each cell must be able to take on multiple functions as it moves along the body column

Question 16

what three stem cells are seen in hydra, which allows them to have stem cell mediated regeneration capabilities?

Answer 16

1. endothelial unipotent progenitor cells (produces lineage-specific epithelia) 2. ectodermal unipotent progenitor cells (produces lineage-specific epithelia) 3. interstitial stem cells (also found within ectoderm layer): generates neurons, secretory cells, nematocytes and hametes.

Question 17

hydra contains three stem cell types which proliferate when they are at the:

Answer 17

center of the body column.

Question 18

why can interstitial stem cells of a hydra proliferate faster than endothelial and ectodermal unipotent progenitor cells?

Answer 18

interstitial stem cells are maintained in G2 stage of replication and replicate faster than ectoderm or endothelial cells.This allows stem cells to response rapidly to the needs of the organism.

Question 19

the animal polarity of a hydra is coordinated by morphogenic gradients that permit the head to form only at one place, and the basal foot/disc to form only at another. How so?

Answer 19

because of the head activator. A head activation factor is concentrated in the hypostome (the head of the hydra) and decreases towars the basal disc.

Question 20

How does the hypostome (head) of the hydra act as an organizer/head activator?

Answer 20

the hypostome produces the head activation signal by secreting Wnt proteins, that act through canonical Betacatenin pathway within the hypostome, producing a head.

-Recall: Gsk3 is a betacatenin (and thus wnt) inhibitor expressed in regions other than the hypostome. If you were to inhibit Gsk3, there will be random head formation throughout the hydra.

Question 21

if a hydra is decapitated, the Wnt pathway becomes activated in an apical portion to form a new head. If a hydra is cut just under the hypostome, ____ is upregulated in ___ cells adjacent to the cut. What kind of regeneration does this induce?

Answer 21

if a hydra is decapitated, the Wnt pathway becomes activated in an apical portion to form a new head. If a hydra is cut just under the hypostome, WNT3 is upregulated in EPITHELIAL cells next to the cut.

• this induces the remodelling of existing cells to form the head without additional proliferation –> morphallactiv regeneration aka transdifferentiation. Because there is no proliferation, the new hydra changes shape.

Question 22

if a hydra is cut at the midsection of the body, what allows it to reform a head?

Answer 22

cells derived from the interstitial stem cells undergo apoptosis just under the incision point, but as they die, the release a burst of Wnt3, which activates the betacatenin in the interstitical cells beneath them, fostering CELL PROLIFERATION AND FORMATION OF THE HYPOSTOME. therefore this is epimorphosis: regeneration by cell DEdifferentiation