Overview stem cells

An overview Stem Cells

Gunjan Mehta,

M.Sc. (Ph.D)

Dept. Biotechnology,

VSC, Rajkot

Outline:I. Introduction

A. Definition of Stem Cell

B. History and Discovery of SCs

II. Therapeutic Applications of SCs

A. Methods for studying Stem Cells

B. Problems with cloning

C. Alternatives to cloning

III. Policy

IV. Nuclear Reprogramming

Properties of Stem Cells• Self-renewal

• Potency･ Totipotent: Includes fertilized zygote and first few divisions of the fertilized egg. These cells can differentiate into embryonic and extraembryonic cell types.･ Pluripotent: SC’s are the descendants of totipotent cells and can differentiate into cells derived from any of the three germ layers.･Multipotent: SC’s 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: SC’s 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).

How do SC arise?

Where do SC come from?

Embryonic

Fetal

Adult

BerashisStem Cells

When do SC arise?

Major Types of Stem Cells

Embryonic Stem Cells• Totipotent : cell can develop into all cell

types

• “Immortal”: can self-renew indefinitely

• Plentiful

Adult Stem Cells• Multipotent: cell can develop into a few

cell types but not all

• Located in few organs or may be unidentified

• Hard to find

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Embryonic Stem cells

Embryos are formed in labs that help couples get pregnant. An egg and sperm fertilize a zygote and are inserted into a woman’s uterus to develop into an embryo and then

fetus. http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=HUMN150B&File_type=GIF

Embryonic Stem Cells

This process creates multiple embryos that will not be used to make a baby. Many donors wish to donate these unused embryos to scientific research instead of having the lab throw them away. http://en.wikipedia.org/wiki/Polar_bodies

First stages of segmentation of a mammalian ovum. Semidiagrammatic. z.p. Zona striata. p.gl. Polar bodies. a. Two-cell stage. b. Four-cell stage. c. Eight-cell stage. d, e. Morula stage.

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Embryonic Stem Cells

The embryo used in research is 4-5 days old and is a microscopic ball of about 150 cells.

The ball as thick as a hair is called a Blastocyst and has three layers called germ layers. Each layer has special stem cells that makes a part of the body.

http://en.wikipedia.org/wiki/Image:Blastocyst.svg

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Blastocyst: Source of Embryonic Stem

Cells Blastocyst under the microscope

Germ Layers The embryo develops three

germ layers of cells called the ectoderm, mesoderm and

endoderm

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Embryonic Stem Cell These embryos not

used in IVF will not grow into a fetus or baby because an embryo like the one in the picture needs to be implanted inside a woman’s uterus to develop into a human fetus. Fetuses and babies are not aborted for stem cell research.AuthorPhotograph by Ed Uthman, MD.PermissionPD Public domain

http://en.wikipedia.org/wiki/Image:Tubal_Pregnancy_with_embryo.jpg.

Embryonic Stem Cells Embryos can also be used

for cloning research. The process called Somatic Nuclear Transfer (SNT) removes an embryo’s nucleus and replaces it with another person’s adult cell nucleus. The embryo would then have the ability to develop into a clone or genetic copy of the nucleus donor if the embryo were implanted into a woman’s uterus.

http://en.wikipedia.org/wiki/Image:Icsi.JPG

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Dolly the Sheep was first cloned using SNT. An adult

sheep body cell nucleus was implanted into an embryo and

then implanted in a mother sheep’s uterus.

http://en.wikipedia.org/wiki/Image:Dollyscotland.JPG

Adult Stem Cells Adult stem cells are

called somatic or body stem cells. Some people call these adult because they are found after an embryo develops into a fetus and are no longer an embryonic stem cell. Not only adults have adult stem cells! Some organs are believed to lack stem cells and these cells grow and replace dead cells with mitosis.

http://en.wikipedia.org/wiki/Image:Mitosis-flourescent.jpg

Adult Stem Cells

Adult stem cells develop into a few cell types. These multipotent cells are used in bone-marrow transplants and will develop into all the blood cells. These cells are important, but some organs may not have adult stem cells and these cells can be difficult to find.

http://www.ulb.ac.be/sciences/biodic/homepage2.htm red corpuscles figurel

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All Stem Cells Are Important• All stem cells can help scientists learn how

cells regenerate or repair injured cells, tissues and organs.

• Scientists need both types of stem cells for their research.

• Each cell type can help inform scientists on how we develop and how some diseases affect our cells.

Stem Cell Debate

Some people oppose stem cell research because they believe that the 4-5 day old ball of cells is a living human being. What some do not understand is that unused embryos are trashed regardless. Many people, religious and non-religious, believe it is better to use these embryos for research on how to cure human diseases rather than to just trash them without purpose. The underlying issue is the personal belief when life actually begins.

Misconceptions

• Pregnancy, fetuses or babies are aborted or harmed in stem cell research.

Fact: Fertilized Blastocysts donated from IVF labs are used and no pregnancy is aborted.

• The fertilized embryos are removed from women’s bodies and used for research.

Fact: The embryos are left over from IVF and are frozen and are not implanted for pregnancy.

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Misconceptions

• A clone is grown in a lab without an embryo or born from a mother and is the same age and personality as you, and has no belly button.

Fact: a clone would need a fertilized embryo and would have to be implanted in a woman’s uterus. If you were cloned at 14, the clone would be 14 years younger than you (a baby you) and would have to have a mother to be born, so yes, it would have a belly button.

http://en.wikipedia.org/wiki/Image:Femnavel.jpg

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Harvard College.

Misconceptions

• If the embryos were not used in stem cell research they would have been used to make children.

Fact: The embryos left over from IVF are discarded.

• Men and women who donate their embryos do not know that their embryos are used for research.

Fact: The embryos used in scientific research are donated with written and informed consent (permission) by the donors.

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Harvard College.

Stem Cell Research

Some scientists want to identify the genes and processes used in embryo development to figure out how to make new cells in damaged or diseased cells and organs or fix old cells by reprogramming them to be young cells again.

Cell-Based Therapies

Science has known for a long time that certain organisms and organs can regenerate or re-grow themselves after being damaged or injured. For example, planaria can regenerate after being cut up into small pieces and certain lizards can regenerate limbs and tails. Scientists want to know “How do they do it?” and study these animals in the lab. Using cells to medically regenerate or replace dead or injured cells is an example of a cell-based therapy.

Cell-Based Therapy• If your skin was burned in an accident,

there would be layers of skin cells that die. Using stem cell techniques, scientists could take a skin cell from another area on your body or stem cell and grow new plates of skin tissue in a lab tissue culture dish to regenerate new skin cells for you.

http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=HUMN164B&File_type=GIF

Future Applications

Stem Cells may one day help scientists to regenerate cells lost in diseases like:

• Repair heart muscle after a heart attack• Pancreas cells lost in diabetes• Neurons lost in Alzheimer’s• Retinal cells causing blindness• Understand the cell growths of cancers • Help organ transplantation

Therapeutic Cloning

• Nuclear Transfer: Method is the same as was used to clone Dolly the sheep in February 1997

Therapeutic Cloning

Problems with Therapeutic Cloning

• Cost• Destruction of embryos• Inefficiency – 277 cells taken from

Dolly’s “mother,” but only 30 became blastocysts. (13.21%)

III. Policy Issues

• No federal law criminalizing destruction of embryos, though some states have these laws

• Proposition 71 in California – explicitly permits research using somatic cell nuclear transfer

• 2008 presidential election could bring about a significant change in current policy

• What’s your opinion?

• Current policy only allows federal funding for existing embryonic stem cell lines (21 in all), not new ones

Stem Cell Video

http://youtube.com/watch?v=mUcE1Y_bOQE