Cloning and Stem Cells How are animals cloned, especially mammals? What is the difference between...

Cloning and Stem Cells

• How are animals cloned, especially mammals?

• What is the difference between reproductive cloning and therapeutic cloning?

• What is the difference between embryonic stem cells and adult stem cells?

• What legal and ethical issues revolve around cloning and stem cell technologies?

Hello, Dolly!

Dolly and her surrogate mother Dolly’s lamb, Bonnie

Mammalian cloning

Somatic nuclear transfer

Totipotency (the ability to differentiate into all different cell types) was regained when somatic cells were arrested in the cell cycle before DNA synthesis.

Why has cloning mammals become possible now?

• In vitro fertilization technology has come of age. Louise Brown the first “test tube baby” was born in the 1970s.

• Nuclear transfer into human eggs is possible for males with defective sperm.

• Embryo transfer is routinely used for reproduction of livestock (cattle)

How easy (efficient) is animal reproductive cloning?

Dolly was the only lamb from 277 fused eggs

Mice, cows, pigs, sheep, cat, monkey, mule successfully cloned.

Tetra – rhesus monkey

CopycatIdaho Gem

Are cloned animals healthy?

Dolly gave birth to a healthy lamb named Bonnie.

Dolly was put down because she was suffering from premature arthritis and other ailments.

What would a human clone be like?

A. The clone will not have a mother.

B. The clone will be essentially an identical twin of the original, offset in time.

C. The clone will have the memories of the original.

D. All of the above.

E. None of the above.

Complications in reproductive cloning

• Cloned offspring syndrome– Placental abnormalities– Fetus too large– High rate of spontaneous abortions– Early death

• Shorter telomeres?

• Genes not imprinted properly– Genes that control placental growth, fetal

growth inactivated in maternal chromosomes

Human development from egg to morula

oocyte 2-cell

4-cell 8-cell

Human blastocyst and post- implantation fetal development

The blastocyst implants into the uterine wall for further development

5 weeks, 5 mm 9 weeks, 30 mm

Cloning to produce embryonic stem cells:“therapeutic cloning”

Create a cloned embryo from the patient’s own genetic material as a source of genetically matched embryonic stem cells.

Involves destruction of the embryo to create a stem cell culture.

Q: What does the law say about human cloning?

A. No legal restrictions.

B. Research with human fetal tissues prohibited.

C. Research restricted to a limited set of pre-existing embryonic stem cell lines.

D. The 13th Amendment prohibits creation of human clones.

E. Individual states ban reproductive cloning

Alternatives to embryonic stem cells?

• Adult stem cells• Induced pluripotent stem cells

– Aoi et al. 2008, Generation of Pluripotent Stem Cells from Adult Mouse Liver and Stomach Cells, Science 321:699-702

– Retroviral vectors used to transduce 4 transcription factors, incl. c-Myc (proto-oncogene)

– ES-like cells in gene expression profile, pluripotency (form tumors containing different cell types, form all 3 major tissue types in chimaeras, germline transmission)

Q: Which of these pose ethical issues when applied to human reproductive cloning?

A. Cloning is still inefficient – only a few percent of somatic cell transfers are successful.

B. Cloning requires surrogate mothers

C. Human egg donors are required

D. Human clones will have the memories of the original

E. All of the above are ethical difficulties for human cloning

Q: In your opinion, when does a human embryo acquire personhood, deserving of legal protection?

A. At the time of fertilization or nuclear transferB. At the time of first cell divisionC. At the time of implantation into uterusD. At 40 days after conceptionE. When fetus becomes viable outside the

wombF. At birth