1-stem cells

Define stem cells

• A type of cell that has the unique ability to develop into many different types of cells

  • Can divide and renew to repair tissue

Fundamental abilities of stem cells

• Can proliferate and produce progeny exactly like the original cell

  • Unlike cancer cells, stem cells can produce progeny that can differentiate into specialised cell types

• Can grow in vitro - can manipulate their genome before being introduced into a host

  • By inserting exogenous DNA = creating transgenic cells

  • By editing endogenous DNA of the cells

Stem cell classification

1. Totipotent

2. Pluripotent

3. Multipotent

4. Oligopotent

5. Unipotent

Totipotent and pluripotent cells

• A morula is formed after the sperm and egg have fused and undergone a few rounds of cell division

  • Any of these cells can produce a full embryo (including embryo and extra membrane)

• Only the zygote and blastocysts are TOTIPOTENT

• The cells of the blastocysts seperate into an outer layer and inner mass

  • Inner mass = embryo

  • Outer layer = extracellular membrane (e.g/ placenta)

• Innermost cells = embryonic stem cells —> can be put in culture and differentiate to form all types of tissue to form an adult

  • Can’t differentiate to form extracellular membrane = PLURIPOTENT

Multipotent and oligopotent

• MULTIPOTENT cells (found in bone marrow) can differentiate into cells that are similar

  • Can differentiate into oligopotent stem cells

    • Lymphoid progenitor = makes lymphocytes

    • Myeloid progenitor = makes RBC

Unipotent stem cells

• Epidermal stem cells

  • Everyday generation of the different layers of the epidermis

  • Found in the basal layer of the epidermis

• Hair follicle stem cells

  • Ensures constant renewal of the hair follicles

    • Can also regenerate the epidermis & sebaceous glands if the tissues are damaged

  • Found throughout the hair follicles

• Melangocyte stem cells

  • Responsible for regeneration of melanocytes - a type of pigment cell

    • Produce melanin

  • Not certain where in the human body they are found

Layers of the skin

3 layers:

1. Epidermis

2. Debris

3. Subcutic

   • Epidermis contain layers of cells called keratinocytes

     • Basal layer

     • Spinous layer

     • Granular layer

     • Stratinum corneum

Which stem cells are best for therapy

• Adult/somatic stem cells are:

  • Scarce

  • Hard to isolate

  • Have limited growth in vitro

• But pluripotent stem cells like ESCs grow indefinitely in vitro and can differentiate into any type of cell in the organism

Cloning of individuals by somatic nuclear transfer (SNT) —>[The frog/tadpole experiment]

1. Took a nucleus from differentiated intestinal cells of a tadpole

   • Transplanted this nucleus into an enucleated egg (egg with the nucleus removed)

2. The egg cell with the new nucleus was then allowed to develop

• Some tissues would form, others wouldn’t

• Some tadpoles would die

• Occasionally a frog would be produced

• From some malformed tadpoles, he took cells and repeated the experiment

• DNA in a mature differentiated cell contains all the genetic info needed to develop into a complete organism

  • Cells dont loose the genetic info; its just frozen

How to induce pluripotent in somatic cells

1. Introduce 4 specific genes (transcription factors) into mouse skin cells

2. The genes were introduced using a retrovirus to activate embryonic-like gene expression

3. These cells were reverted to a pluripotent state - behaving like embryonic stem cells

   • Induced pluripotent cells

     • Can divide indefinitely

     • Can differentiate into any of the germ layers:

       • Ectoderm

       • Mesoderm

       • Endoderm