13.1. Stem Cells and Differentiation

Question 1

Stems cells…

Answer 1

Undifferentiated cells that can differentiate to give rise to other cell types.

Have the ability for quiescence.

Can asymmetrically divide to self-renew (dividing into two cell types, one new and one original).

Question 2

Types of stem cells…

Answer 2

Totipotent: have the ability to give rise to all the embryonic and extraembryonic cell types. The only time this can occur is in the zygotic stage.

Pluripotent: have the ability to give rise to all the cell types in adult organisms. Embryonic stem cells (a type of pluripotent) are found in the blastocyst.

Multipotent: have the ability to give rise to multiple, but not all, cell types found in adult organisms. The differentiation ability is restricted in certain cell types.

Question 3

Differentiation…

Answer 3

Cells switch on and off genes which causes differentiation.

However, cells retain all DNA content.

The cell that ultimately forms is due to gene expression within the cell.

Transcription factors can stimulate or inhibit transcription of specific genes, leading to differentiation.

Errors in expression can change the fate of the cell.

Question 4

Satellite cells…

Answer 4

MyoD switches the genes on to become a muscle fibre.

This produces a specific myosin protein and the mature cell is a myocyte.

Question 5

Mesenchymal stem cells…

Answer 5

Chondrocytes… sox9… collagen type 2.

Osteocytes… runx2… osteocalcin.

Adipocytes… Ppary… fatty acid binding protein 4.

Question 6

Rules…

Answer 6

Cell division must be shut down for differentiation to occur.

This is mediated in muscles by MyoD though upregulation of the cell cycle inhibitor P21.