Embryonic stem cells

Question 1

What are the two aspects of development and what is the difference between the two?

Answer 1

• growth (increase in number of cells)
• differentiation (specialization of cells)

Question 2

What is the zygote?

Answer 2

the fertilised egg

Question 3

what does the inner cell mass form in the blastocyst?

Answer 3

two kinds of cells
- epiblast - becomes the cells in the organism
- other cells develop into the placenta and amniotic membranes

Question 4

What are the three germ layers and what do they form?

Answer 4

• ectoderm makes the nervous system and skin
• mesoderm forms the blood, heart, muscle, connective tissue
• endoderm forms the pancreas, liver gut lungs

Question 5

Describe the three step process involved in differentiation of cells

Answer 5

• specification: fate is not yet absolute and cell identity is subject to change
• determination: fate is fixed and will not change in response to environment
• differentiation: changes in cell structure and function - cell is committed

Question 6

How does cell plasticity change throughout development?

Answer 6

at the start, cells are very plastic and can change but as we age our cells become less plastic and more differentiated and unable to change form and function

Question 7

At which point do cells turn from totipotent to pluripotent in development?

Answer 7

blastocyst formation

Question 8

Which stage in development do embryonic stem cell lines come from?

Answer 8

inner cell mass in the blastocyst

Question 9

define potency

Answer 9

the sum of developmental options accessible to cell

Question 10

define totipotent

Answer 10

can form all cell lineages of an organism. in mammals, only the zygote and first cleavege blastomeres are totipotent

Question 11

define multipotent

Answer 11

the ability of an adult stem cell to form multiple cell types of one lineage for example haematopoetic stem cells

Question 12

define unipotent

Answer 12

cells can only form one cell type e.g. spermatogonial stem cells can only generate sperm

Question 13

How is the process of differentiation tightly controlled?

Answer 13

• controlled by gene changes and how these genes influence one another as the cells make decisions on the path to differenation
• embryo is well protected form environmental affects in the womb

Question 14

What determined cell fate in general?

Answer 14

cytoplasmic factors (intrinsic, driven by transcription factors) and cell-cell interactions (other cells, hormones)

Question 15

What happens to mice eggs with Oct4 knockouts?

Answer 15

• cells are unable to form a blastocyst and are stuck before so
• shows Oct4 must be central in the development of the blastocyst

Question 16

What happens to mice eggs with Nanog knockouts?

Answer 16

• growth of the egg occurs
• germ layers do not form

Question 17

What happens when Oct4, Sox2 and Nanog are actvive?

Answer 17

activation of genes involved in pluripotency and ES cell transcription

Question 18

What happens when Oct4, Sox2 and Nanog are inactive

Answer 18

genes related to germ layer formation are activated

Question 19

What other genetic factors other than transcription factors can be involved in signalling pathways related to pluripotency and differentiation?

Answer 19

-chromatin regulation (epigenetics)
- miRNA

Question 20

How are embryonic stem cells isolated and cultured?

Answer 20

• isolate and transfer inner cell mass into a plastic culture dish
• medium contains feeder cells (mouse embyronic skin cells) to allow the ES cells to attach
• need to keep changing the medoum to ensure autodifferentiation doesnt occur
• can use cytokines and other chemicals to trigger specific differentiation for use in research and therapy

Question 21

What is one way to use mouse models to trace the tissue destinations of stem cells?

Answer 21

• add markers to a line of stem cells
• add them to a fertilised egg at the blastocyst stage
• cells in the egg will be a mixture of embyronic labelled cells and de novo egg cells
• mouse born from the egg will show the marker in any of the cells that were dervied from the stem cells added
• also shows that ES cells are still able to function normally after being reproduced in the lab

Question 22

Why are xeno-free cultures important?

Answer 22

• human ES cells are usually grown with animal serum and mouse-derived feeder layers
• animal contaminations could contian certain pathogens or xenogens that could trigger immune reactions after transfer to a host

Question 23

What are the risks/barriers to consider in the use of human ES cells?(6)

Answer 23

• need for xeno-free cultures
• risk of tumours
• genetic instability
• transplant rejection
• chromosomal abnormalities during prolonged culture
• ethical considerations