lecture 1: introduction to stem cells

Question 1

What is the functional definition of a stem cell?

Answer 1

• cell either in the body or in the embryo
• sit in a tissue/environment in which they sit
• any cell in the body is bathed by fluid: extracellular/interstitial fluid
• tissues are complex: nerves, blood vessels, immune cells
• little stem cell sitting in a tissue surrounded by all of these other types of tissue
• yet it has this incredibly remarkable ability to stay undifferentiated while everything around it is receiving 100s of signals – why is it that that cell can stay undifferentiated?
• when asked to, it can divide into two cell types: stem cell and progenitor cell (i.e. this cell has developed the ability to perhaps become a specialised/differentiated cell)

Question 2

What are properties of a stem cell?

Answer 2

1. it is not differentiated (specialised)
2. when it divides, each daughter cell has a choice:
   a. it can either remain a stem cell i.e. the property to self-renew
   b. or it can begin a pathway to become differentiated i.e. the property to generate differentiated cells, also potency

Question 3

Where do stem cells come from?

Answer 3

• embryonic/foetal 
– blastocyst - embryonic stem cells 
– umbilical cord blood - stem cells 
→ cord blood bank, easy to collect and match with patients
→ ~70% of childhood leukaemias can be treated with cord blood or bone marrow transplant, but cord blood is easier to access 
→ can also save cord blood for future use 
• adult tissues 
– poorly understood:
→ origin
→ low numbers and location 
– successful stem cells
→ blood

Question 4

From where can pluripotent stem cells also be derived?

Answer 4

primordial germ cells (pgcs)

→ foetus → primordial germ mass → cultured pluripotent stem cells

Question 5

What is the difference between ESCs and EGCs?

Answer 5

• stem cells derived from Inner Cell Mass are known as Embryonic Stem Cells (ESCs)
• stem cells derived from pgcs are known as Embryonic Germ Cells (EGCs)
• EGCs are diploid and derived from pgcs that have not yet reached the gonads
• ESCs and EGCs are positive for Oct4, Sox 2 and Nanog (core pluripotency transcription factors)

Question 6

What is cell culture?

Answer 6

• cells in a culture dish
• e.g. petri dish, flask, wells
• media containing vitamins, amino acids, fats, proteins etc; all the things that these cells need to grow in a solution
• e.g. embryonic stem cells growing on a feeder layer
• cells grown in nutrient rich solution (media)
• housed in incubator at 37º with 5-20% oxygen
• cells grow, divide and can be induced to become differentiated cells
• this is what is meant by In Vitro or Cultured Cells

Question 7

What is an important consideration about stem cells?

Answer 7

• stem cells that are studied in vitro have been stabilised by culture conditions but have been removed from their normal environment or niche signals that exist in vivo
• studying stem cells in vitro is vitally important but how they behave and are regulated in vitro may be simplistic snapshots of their behaviour and regulation in vivo

Question 8

What are characteristics of embryonic versus adult stem cells?

Answer 8

• not the same

common to both stem cell types:
• self-renews
• generates differentiated cells
• i.e. functionally the same

embryonic:
• generates all cells of embryo both in vivo and in vitro (pluripotent)
• clonogenic
• maintain normal karyotype
• extensive proliferation in vitro under defined culture conditions

adult:
• restricted potency (multipotent)
• but may be due to culture conditions
• stem cells removed from tissue to study in vitro – could lead to removal from niche signals or reprogramming by culture conditions

Question 9

What is potency?

Answer 9

• stem cells are categorised by potency, which denotes the potential of the cell to derive other cell types – how many and what cell types
• potency = the range of developmental options available to a cell
• totipotent: ability to form the entire organism. In a mammal only the zygote, and the blastomeres are totipotent. Not demonstrated for any other mammalian stem cell type
• pluripotent: ability to form all the lineages of the body. Example: embryonic stem cells and embryonic germ (EG) cells
• multipotent: ability to form multiple cell types from one lineage. e.g. haematopoietic stem cells which form all the blood type cells
• unipotent: ability to form one cell type. e.g. spermatogonia which can only form sperm

Question 10

What does ‘stemness’ mean?

Answer 10

refers to:
• the common molecular processes underlying the core properties of self-renewal and the generation of differentiated cells
• through transcriptional profiling (i.e. the gene transcripts expressed in stem cells)
• many gene transcripts expressed in common in ESC, BMSC and NSC were identified
• this has led to the idea that there are genetic characteristics specific to and shared by all stem cells OR a molecular signature or fingerprint that could be used as a molecular definition

Question 11

What has transcriptional profiling suggested stem cells share?

Answer 11

1. ability to sense a broad range of signals (extrinsic signals)

intrinsic

1. express signal transduction pathways for these signals
2. establish specialised cell cycles (not the same as in any other cell types)
3. high level telomerase activity
4. capable of remodelling chromatin
5. resistance to stress

but bear in mind that stem cell types have different microenvironments or niches and physiological demands

Question 12

What are the key questions in stem cell biology today?

Answer 12

How are stem cells identified, isolated, characterised and judged to be ready for cell transplantation therapy?