Stem Cells

What are Stem Cells?

• Stem cells possess two key characteristics:

  • Self-renewal: The ability to copy themselves, creating more stem cells.

  • Differentiation: The ability to specialize into different types of cells (e.g., muscle cells, nerve cells).

• Function:

  • Provide new cells for the body as it grows.

  • Replace specialized cells that are damaged or lost.

• Stem cells can divide repeatedly to produce new cells.

• As they divide, they can differentiate into various cell types that make up the body.

Self-Renewal and Differentiation

• Self-renewal maintains the stem cell pool.

• Differentiation replaces dead or damaged cells throughout life.

• Stem cells both self-renew and differentiate to maintain the stem cell pool while also replacing damaged cells.

A Life Story: Human Development

• Human development begins with a single fertilized egg (zygote).

• This cell divides to produce two daughter cells, which further divide repeatedly.

• Many steps are required to form an adult body or even a baby.

• Different cell types must be made along the way.

Types of Stem Cells During Development:

• Totipotent Stem Cells

  • Found in the zygote and early embryo.

  • Can divide into all cell types in an organism.

  • Have the potential to create an entire, complete organism.

  • "Toti" = whole, "potent" = ability to differentiate

• Embryonic Stem Cells

  • Found in the inner cell mass of the blastocyst (a very early embryo).

• Tissue Stem Cells

  • Found in the fetus, baby, and throughout life.

Embryonic Stem (ES) Cells

• Location: Inner cell mass of the blastocyst.

• Embryonic stem cells are taken from the inner cell mass and cultured in the lab to grow more cells using fluid with nutrients.

Capabilities of Embryonic Stem (ES) Cells

• Embryonic stem cells are pluripotent, meaning they can differentiate into all possible types of specialized cells.

  • "Pluri" = several, "potent" = ability to differentiate

• Function: Supply new cells for an embryo as it grows and develops into a baby.

Tissue/Adult Stem Cells

• Multipotent: Can only change into some cells in the body, not any cell.

• Example: Blood stem cells found in bone marrow can differentiate into red blood cells, white blood cells, and platelets.

• Function: Supply new cells as an organism grows and replace cells that get damaged.

Blood Stem Cells

• Most adult stem cells are multipotent.

• Multipotent stem cells can self-renew by dividing.

• They develop into multiple specialized cell types within a specific tissue or organ.

Epidermal Stem Cells

• Function: Replace older skin cells that are shed with new skin cells.

• Location: Deep under the first layer of skin.

• Unipotent: Can only make one type of cell (mature, already specialized skin cells).

• They renew and differentiate to replace the shedding skin cells.

Induced Pluripotent Stem Cells (iPS Cells)

• Stem cells that scientists create in the laboratory.

• Induced pluripotent stem (iPS) cells behave like embryonic stem cells.

• Advantage: No need for embryos.

• Can differentiate into all possible types of specialized cells.

• Process:

  • Normal adult cells (e.g., skin or blood cells) are taken and reprogrammed to become pluripotent stem cells.

  • 'Induced' means they are made in the lab.

Stem Cell Hierarchy and Differentiation

• Totipotent

  • Oocyte → Zygote → Morula → Blastocyst

• Pluripotent

  • Embryonic Stem Cells from the Blastocyst

  • Induced Pluripotent Stem Cells

  • Can differentiate into:

    • Endoderm Line → Lung, Pancreas

    • Mesoderm Line → Heart, Red Blood Cell, Muscle

    • Ectoderm Line → Skin, Neuron

• Multipotent

  • Adult stem cells from bone marrow, skin, cord blood, or deciduous teeth.

• Transcription factors are important in iPS.