Cell Differentiation, Stem Cells, and Reprogramming- Lectures 58 and 59

Question 1

What is a differentiated cell?

Answer 1

cells the have a specific set of genes expressed that are unique to the kind of cell it is

Question 2

What are the steps on the way to a fully differentiated cell?

Answer 2

uncommitted precursor cell
determination (cell becomes committed to a single lineage and acquires the competence to undergo terminal differentiation)
differentiation

Question 3

Outline the events associated with myoblast differentiation.

Answer 3

exit from cell cycle
expression of muscle-specific genes
fusion to form multinucleated myotubes
expression of ACh receptors and other proteins of the neuromuscular junction

Question 4

Describe the roles in sequence of the MyoD family of muscle regulatory factors.

Answer 4

Myf5 and MyoD are used for determination (somitic cell to myoblast)
MyoD myogenin and MRF4 are used for differentiation (myoblast to terminally differentiated myofiber)

Question 5

Desribe the pathway of positive feedback in transcriptional regulation of myoblast differentiation.

Answer 5

Myogenic inducers (eg. Wnt, Shh) added –>
transcription activation of Myf5 and MyoD whose proteins activate Myogenin transcription, the product of which activates Mef2 whose product activates itself and myogenin
MyoD, Myog, and Mef2 all activate muscle-specific terminal differentiation genes (eg. Mck)

Question 6

Describe what happens when cultured myoblasts are switched to a depleted growth factor environment.

Answer 6

1. decrease in cyclin D1/Cdk4 activity –> decrease in phospho-pRb –> cell cycle exit
2. increase in MyoD transcriptional activity –> increase in p21 expression –> decrease in cyclin E/Cdk2 activity –> decrease in phospho-pRb –> cell cycle exit

Question 7

What are stem cells?

Answer 7

cells that can self-renew and generate differentiated cell types

Question 8

What are adult stem cells?

Answer 8

responsible for homeostatic maintenance and repair to injury (eg. hematopoietic stem cells; skeletal muscle satellite cells)

Question 9

What are embryonic stem cells (ES)?

Answer 9

cells derived from the inner cell mass of the blastocyst that have been placed into culture and can divide indefinitely and differentiate into all lineages of the three germ layers in vitro and in vivo

Question 10

What is unipotency?

Answer 10

the ability to form a single cell type or lineage (eg. testes stem cells)

Question 11

What is multipotency?

Answer 11

the ability to give rise to multiple cell types (eg. hematopoetic stem cells)

Question 12

What is pluripotency?

Answer 12

the ability to give rise to all the cells of an organism, EXCLUDING extraembryonic tissues (eg. ES cells)

Question 13

What is somatic cell nuclear transfer (SCNT)?

Answer 13

transfer of a somatic nucleus into an enucleated oocyte

Question 14

What is reproductive cloning?

Answer 14

generation of a new organism following SCNT or other means

Question 15

What is therapeutic cloning?

Answer 15

generation of a blastocyst following SCNT from which ES cells are isolated and used as a source of differentiated cells for therapy

Question 16

What are induces pluripotent (iPS) cells?

Answer 16

reprogramming of somatic cells into an ES cell-like phenotype by expression of pluripotency genes (Oct4, Sox2, Nanog, c-myc)

Question 17

What are some challenges of application of pluripotency reprogramming as a therapeutic tool?

Answer 17

1. potential oncogenicity of required factors
2. vectors (viruses can cause insertional mutations)- though this can be overcome by transient expression of Yamanaka factors via several different mechanisms
3. low efficiency
4. potential acquisition of genetic changes during the generation of iPS cells (not the largest problem)

Question 18

Describe one application of these new technologies in pluripotency reprogramming as a therapeutic tool.

Answer 18

epidermolysis bullosa (junctional, simplex, or dystrophic blistering disease of the skin)
successful transplant of viral laminin (mixture of cell and gene therapy) that improved disease after application of lab grown skin to patient's affected areas

Question 19

What is todipotency?

Answer 19

property of zygotes where they can form all cells of the body as well as extraembryonic structures such as the placenta