Stem Cells

Question 1

Examples of what ectoderm forms

Answer 1

• Outer surface- skin cells of epidermis
• CNS- neuron of the brain
• Neural crest- melanocytes

Question 2

Examples of what mesoderm forms

Answer 2

• Dorsal notochord
• Paraxial- skeletal muscle cells
• Intermediate- tubule cell of the kidney
• Lateral- RBCs
• Head- facial muscle

Question 3

Examples of what endoderm form

Answer 3

• Digestive tube- pancreatic cell
• Pharynx- thyroid cell
• Respiratory tube- lung cell (alveolar cell)

Question 4

Examples of germ cell development

Answer 4

• Sperm
• Egg

Question 5

Main cellular processes that are key to successful development

Answer 5

1. Cell proliferation- an increase in cell number due to mitosis
2. Differentiation – a gradual process by which specialized cell types develop from a pool of cells
3. Morphological changes and cell migration- changes to structure
4. Apoptosis- programmed cell death, mediated via enzymes including caspases and DNases

Question 6

What are the additional key decisive factors/processes in embryonic development?

Answer 6

1. Cell-to-cell communication
2. Signaling pathways
3. Induction and competence
4. Adhesion and migration
5. Morphogens
6. Genes
7. Transcription factors

Question 7

Cell communication and cell growth and differentiation

Answer 7

• Communication between cells is very important for the growth and differentiation of cells
• Includes paracrine signaling, contact-dependent signalling, autocrine signalling, synaptic signalling, endocrine signalling

Question 8

Signaling Pathways

Answer 8

• 11 main signaling pathways involved in development
• Each signal is transmitted in a linear manner, and act on signal response elements in target genes
• Specific patterns of signalling for a given species
• Changes elicited by these signals during development are irreversible

Question 9

Examples of signalling pathways

Answer 9

Examples: Notch, Wingless (Wnt), Transforming Growth Factor (TGF-Beta), Fibroblast growth factor (Fgf)

Question 10

Induction

Answer 10

Process by which a particular group of cells influences the fate of an adjacent group of cells. This is generally mediated via paracrine or contact-dependent signaling

Question 11

Competence

Answer 11

This refers to the ability of cell to respond to an inductive signal. A competent cell must express the receptors for the inducer(s).

Eg. Response of a group of cells to a transcription factor

Question 12

What mediates Adhesion?

Answer 12

Cell adhesion is mediated by cadherins and integrins

Question 13

How do Cadherins help with adhesion?

Answer 13

Cadherins in one cell interact with cadherins in adjacent cells

Question 14

How do Adherins help with adhesion?

Answer 14

Help with the adhesion of cells to various ligands

Question 15

Heavy cell migration and its determinants

Answer 15

• Cells use different forms of movement for migration, depending on the stage of development. Ex. cytoskeletal movement, etc.

Determinants of migration: molecular composition of extracellular matrix and matrix architecture

Question 16

Morphogens

Answer 16

A substance that can determine the fate of a cell/cell’s differentiation by way of its presence in the cellular microenvironment

• Effects are concentration dependent
• Can have stimulatory or inhibitory effects

Question 17

Chromatin

Answer 17

• Composed of DNA + Protein
• Has a heavy influence on gene expression

Question 17

Sonic hedgehog (Shh) signalling molecule Morphogen example

Answer 17

Important for the formation of the spinal cord.

Effects of Shh are dependent on its concentration, duration of the exposure, and interaction with other target genes and/or signals/pathways

Question 17

Epigenome

Answer 17

• A determinant of how cells remember their identity.
• Composed of processes and signals including DNA methylation, histone modification, and other factors including small RNAs

Question 18

Transcription Factors

Answer 18

• Proteins that can bind to the enhancer or promoter region of the DNA to up-regulate or down-regulate the gene transcription to form mRNAs

Ex. high mobility group (Sox) = sex determination

Ex. T box family (Tbx) = limb development

Question 19

Stem cells

Answer 19

• Specialized cells able to undergo self-renewal and produce daughter cells that possess the same features of the cells from which they are originally derived.
• Play a key role in forming tissues and organs

Question 20

Different classifications of stem cells

Answer 20

1. Totipotent
2. Pluripotent
3. Multipotent
4. Unipotent
5. Progenitor cells

Question 21

Two types of stem cells

Answer 21

1. Embryonic stem cells
2. Adult stem cells

Question 22

Trophoblastic placental cells

Answer 22

• Trophoblasts, cells forming outer layer of blastocyst
• Provide nutrients to embryo and develops into large part of the placenta

Question 23

Why is there variation in stem cell classifications?

Answer 23

Early on they have ability to express many transcription factors, later on they are more specialized and only express certain transcription factors

Question 24

Totipotent

Answer 24

- Most versatile stem cells - Develops from the inner cell mass in the developing embryo, and can develop into any of the cell type in the embryo, including the trophoblastic placental cells

Question 25

Pluripotent

Answer 25

Arise from the embryonic cells and can differentiate into any cell within the embryo, except the trophoblastic placental cells

Question 26

Multipotent

Answer 26

Derived from embryonic cells, but have limited lineage capabilities

Question 27

Unipotent

Answer 27

- Least versatile stem cell - These cells are destined to become specific cell type after a limited number of divisions

Question 28

Progenitor cells

Answer 28

More differentiated than stem cells and have limited self-renewal capability

Question 29

Terminal differentiation

Answer 29

Cells within a specific lineage reaches a mature stage, where further differentiation or division does not occur

Question 30

Embryonic stem cells

Answer 30

- Stem cells in embryo - Originating from the inner cell mass - Those that are from multiple lineages contribute to embryonic development including the formation of primary germ layers

Question 31

Adult stem cells

Answer 31

- Resident stem cells within adult tissues and organs enable tissue self-renewal and repair - Help to maintain tissue integrity and function, especially when adverse events occur (eg. Infection, trauma, degenerative changes) Eg. Bone marrow Eg. Intestinal crypts

Question 32

Intestinal crypts

Answer 32

Resident stem cells at base of crypt give rise to all of the different cell types further up the crypt *Proliferating transit-amplifying cells are in between stage

Question 33

Induced pluripotent stem cells (iPSCs)

Answer 33

- Somatic cells can be reprogrammed to develop cells of a specific lineage by introducing specific transcription factors and providing the supportive milieu for the cells to differentiate and grow - Transcription factors cause nuclear reprogramming - Need specific growth factors eg. TGF-beta in media for determining specific lineage of stem cells - Need the right kind of media to create specific cell

Question 34

Ex. 4 transcription factors- Yamanaka factors

Answer 34

Can induce pluripotency and have a lot of cell differentiation