Cloning – In the Eyes of the Beholder

Ida Chow, Ph.D.Society for Developmental Biology

Bethesda, Maryland

Society for Developmental Biology

The Society for Developmental Biology declares a voluntary five-year moratorium on cloning human beings, where ‘cloning human beings’ is defined as the duplication of an existing or previously existing human being by transferring the nucleus of a differentiated, somatic cell into an enucleated human oocyte, and implanting the resulting product for intrauterine gestation and subsequent birth. Sept. 1997. Extended Jan. 2003

Cloning

• Greek klon = twig (cuttings from one original plant)

• Molecular biology: copies of DNA (gene) fragments

• Cell cultures: cell multiplication by cell division (mitosis)

• Bacterial growth• Plants budding• Identical twins• Identical genetic copies

Fundamental Question

How does a single cell, the fertilized egg, transform into a complex organism, with many different types of cells, tissues and organs?

- processes?- genes?- control / regulation?

• Totipotency – Capable of giving origin to all the cell types in the organism, person, e.g., fertilized egg developing into a whole organism

• Gradual loss of the capability for differentiation with the process of development - Pluripotency, multipotency, e.g., superficial skin cell from deep layer skin cell

Definitions• Somatic cells: body cells, full genetic

complement, 2 sets of chromosomes = diploid, 46 in humans

• Germ cells: gametes, oocyte (unfertilized egg) and sperm, one half of genetic complement, 1 set of chromosomes = haploid, 23 in humans

• Fertilization = fusion of sperm and oocyte, full genetic complement, 1 set of chromosome from egg and 1 from sperm, diploid

Somatic Cell Nuclear Transfer

• Removal of the nucleus containing the genes of an unfertilized oocyte

• Fusion of an isolated body cell with the oocyte, or injection of the somatic cell nucleus into the oocyte

• Stimulation of the oocyte to begin the process of cell division and differentiation, producing the blastocyst (a hollowed ball with a mass of about 150 cells)

Fundamental Questions

• Reprogramming of gene expression: How to make the adult somatic cell nuclear DNA (genes) express the same way as in an embryo, that is, following the proper sequence.

• What molecules in the oocyte cytoplasm are capable of

de-differentiating the adult somatic cell nucleus?

Somatic Cell Nuclear Transfer

Conditions

StrokeHeart

attacksType I

Diabetes

Neuraldegenerative

diseases

Diseases of the blood

Muscular dystrophies

Damage to nerve cells

Certain types of cancer

Bone diseases

DifferencesEmbryonic• unlimited capability

for cellular reproduction

• broader pluripotency

• more direct access to stem cells

• large number of available stem cells

• many identified inducing factors

Adult• limited capability for

cellular reproduction

• limited pluripotency

• difficult access and identification of the stem cells

• limited number of available stem cells

• chromosomal defects

Reproductive Cloning• Implantation of the blastocyst into a

prepared womb of a female• Further differentiation and growth of

the cloned product • Delivery of a full-term (or almost)

cloned individual, with nuclear DNA identical to that of the donor of the body cell, and mitochondrial DNA identical to that of the oocyte; no genetic similarity to surrogate female if not oocyte donor

NO CLONING OF HUMAN BEINGS

FOR REPRODUCTIVE

PURPOSES

Figures in this presentation are from publications by the

National Institutes of Health (http://www.nih.gov ):

Stem Cells: a Primer (http://www.nih.gov/news/stemcell/primer.htm)

Stem Cells: Scientific Progress and Future Research Directions

(http://www.nih.gov/news/stemcell/scireport.htm)

Additional Resources• Society for Developmental Biology (SDB): www.sdbonline.org, Focus on

Stem Cells: http://sdb.bio.purdue.edu/publications/focus/index.html

• National Institutes of Health (NIH): www.nih.gov, Stem Cell Information Index: http://www.nih.gov/news/stemcell/index.htm

• National Bioethics Advisory Commission Reports (NBAC): http://www.georgetown.edu/research/nrcbl/nbac/pubs.html. Scrawl done and see the following reports: Ethical Issues in Human Stem Cell Research (Sept. 1999) and Cloning Human Beings (June 1997)

• The President’s Council on Bioethics (PCBE): www.bioethics.gov, and see the Cloning Report: http://www.bioethics.gov/cloningreport/

• The National Academies: www.nas.edu. Scientific and Medical Aspects of Human Reproductive Cloning: http://www.nap.edu/catalog/10285.html?se_side, Stem Cells and the Future of Regenerative Medicine: http://www.nap.edu/catalog/10195.html?se_side

• Federation of American Societies for Experimental Biology (FASEB): www.faseb.org, Cloning, Past, Present and the Exciting Future: http://www.faseb.org/opar/cloning/