10.4 Cell Differentiation

Key Concepts

• How do cells become specialized for different functions?

• What are stem cells?

• What are potential benefits and issues with stem cell research?

Vocabulary

• Embryo • Pluripotent

•Totipotent • Differentiation

• Multipotent • Blastocyst

• Stem cell

Cell Differentiation

• An adult human body can be made up from 1 trillion to 100 trillion cells depending on height, weight, etc…

• Humans start from 1 cell and end up with many different types of cells (e.g. muscle cells, skin cells,) with different functions

Cell Differentiation

• As cell goes through multiple cell divisions, it is going through various developmental stages (e.g. zygote, embryo)

• Each developmental stage, cells begin to differentiate and become specialized

• DIFFERENTIATION: process of cells becoming specialized in structure and function (e.g. nerve cell)

What are Stem Cells?

Stem Cells are extraordinary because:

1. They can divide and make identical copies of themselves over and over again through mitotic cell division (Self-Renewal)

2. They have the potential to differentiate into a diverse range of specialized cell types (Potency)

The Major Types of Stem Cells

A. Embryonic Stem Cells

• From blastocysts left over from In-Vitro Fertilization (IVF) in the laboratory

B. Adult Stem Cells

• Have been found in the blood, bone marrow, liver, kidney, cornea, dental pulp, umbilical cord, brain, skin, muscle, salivary gland . . .

- Function: repair system for the body, replenishing specialized cells, but also maintaining the normal

turnover of regenerative organs, such as blood, skin or intestinal

Potency Definitions

•Totipotent cells - can develop into any type of cell found in body

•Pluripotent - are the descendants of totipotent cells and can differentiate into most but not all cell types

Potency Definitions• Multipotent - can produce only cells of a closely related family

of cells • (e.g. hematopoietic stem cells differentiate into red blood

cells, white blood cells, platelets, etc.).

• Unipotent - cells can produce only one cell type, but have the property of self-renewal which distinguishes them from non-stem cells

• (e.g. muscle stem cells).

http://commons.wikimedia.org/wiki/Image:Stem_cells_diagram.png

Advantages and Disadvantages to Embryonic and Adult Stem Cells

Embryonic S.C. Adult S.C.

“Pluripotent” “Multipotent”

Stable. Can undergo many cell divisions.

Less Stable. Capacity for self-renewal is limited.

Easy to obtain but blastocyst is destroyed.

Difficult to isolate in adult tissue.

Possibility of rejection?? Host rejection minimized

Reprinted with permission of Do No Harm. Click on image for link to website.

Why is Stem Cell Research So Important to All of Us?

•Allow us to study how organisms grow and develop over time.

•Can replace diseased or damaged cells that cannot heal or renew themselves.

•Can test different substances (drugs and chemicals) on stem cells.

•Can get a better understanding of our “genetic machinery.”

Reprinted with permission from the Univ. of Kansas Medical Center. Click on image for link to originating website.

What Human Diseases are Currently Experimentally Being Treated with Stem Cells?

•Parkinson’s Disease

•Leukemia (Bone Marrow Transplants)

•Skin Grafts resulting from severe burns

Stem Cell Therapy has the Potential to:

•Regenerate tissues/organs

•Cure diseases like diabetes, multiple sclerosis, etc.

Why the Controversy Over Stem Cells?

•Embryonic Stem cells are derived from extra blastocysts that would otherwise be discarded following IVF.

•Extracting stem cells destroys the developing blastocyst (embryo).

For further information: http://bioethics.gov/cgi-bin/bioeth-counter

A Way Around the Controversy??

•Induced Pluripotent Stem Cells (iPS cells)•are derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state

• enables the development of an unlimited source of any type of human cell needed for therapeutic purposes.

• Examples• iPSC can be prodded into becoming beta islet cells to treat

diabetes

• blood cells to create new blood free of cancer cells for a leukemia patient

• neurons to treat neurological disorders.