The Revolution in Cell Technology The Living World Fifth Edition George B. Johnson Jonathan B. Losos Chapter 16 The Revolution in Cell Technology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16.1 Proving That Reproductive Cloning is Possible Hans Spemann proposed in 1938 that cloning might be possible by removing the nucleus from an egg cell and replacing with a nucleus from another cell early attempts in cloning were unsuccessful unless the transplanted nucleus was from a very early stage of development the theory of irreversible determination suggested that animal cells become irreversibly committed after the first cell divisions

Figure 16.1 A cloning experiment.

16.1 Proving That Reproductive Cloning is Possible geneticists working in Scotland made a key breakthrough in animal cloning Keith Campbell suggested they conduct nuclear transfers between a donor and recipient cell that were at identical stages of the cell cycle the cells were starved so that they were at the beginning of the cell cycle at the G1 checkpoint Neil First in 1994 and Campbell and Ian Wilmut in 1995 successfully cloned farm animals from advanced embryos using this method

16.1 Proving That Reproductive Cloning is Possible Wilmut progressed with the method to transfer successfully a nucleus from an adult cell into an enucleated egg Wilmut used an adult sheep’s mammary gland as the nuclear donor both the donor mammary cells and the enucleated eggs were first starved and a brief electrical shock allowed the contents to fuse together the resulting embryos developed into blastulae and were implanted into a surrogate mother “Dolly” the cloned lamb was born on July 5, 1996

Figure 16.2 Wilmut’s animal cloning experiment.

Figure 16.3 A parade of cloned critters.

16.3 Problems with Reproductive Cloning many problems have been encountered with reproductive cloning since Dolly most transplanted cloned embryos die late in pregnancy large offspring syndrome describes the oversized condition of many of these transplants among surviving cloned offspring, their development into adults goes unexpectedly haywire most do not survive to live a normal life span for example, Dolly died prematurely in 2002

16.3 Problems with Reproductive Cloning reprogramming by parent males and females of the sperm and eggs may affect cloning success genomic imprinting involves chemical changes to DNA that alters when genes are expressed without changing the sequences genes can be locked on or off normal animal development depends on precise genomic imprinting

16.3 Problems with Reproductive Cloning genomic imprinting occurs at different stages gametic imprinting takes place in adult reproductive tissue requires months for sperm and years for eggs zygotic imprinting the egg cell cytoplasm acts to reprogram the DNA introduced by the sperm donor DNA to be cloned may be less efficient at doing this reprogramming

Figure 16.4 Two forms of genomic imprinting.

16.4 Embryonic Stem Cells embryonic stem cells are totipotent this means that they have the ability to form any body tissue, and even an adult animal later in development the embryonic stem cells differentiate into adult stem cells these cells produce only one kind of tissue the genes needed to produce other types of tissues are turned off

Figure 16.5 Human embryonic stem cells (x20).

16.4 Embryonic Stem Cells embryonic stem cells offer the possibility of restoring damaged tissues embryonic stem cells grown in culture could be induced to form any type of tissue in the body this healthy tissue can be injected into a patient where it will grow and replace damaged tissue

Figure 16.6 Using embryonic stem cells to restore damaged tissue.

16.5 Therapeutic Cloning the possibility for immune rejection of transplanted stem cells must be addressed in order to make stem cell therapy work in therapeutic cloning, DNA from adult cells are used to create an embryo from an individual stem cells are then harvested from the embryo, which is subsequently destroyed the tissue developed from these stem cells can be injected into the damaged host there is no issue of immunological tolerance because the donor and recipient of the stem cell therapy are the same individual

Figure 16.8 How human embryos might be used for therapeutic cloning.

16.6 Grappling with the Ethics of Stem Cell Research the use of embryonic stem cells raises a number of important ethical concerns, including should human embryos be destroyed? how can the potential for future abuse be avoided? are there alternative sources to using embryonic stem cells?

16.7 Initial Attempts at Gene Therapy gene transfer therapy involves transferring healthy versions of a gene into cells that lack them while the research is promising, problems remain in finding an appropriate vector for gene transfer adenovirus vector was used to piggyback healthy genes but was both subject to immune attack and prone to introduce mutations that lead to cancer

Figure 16.7 Initial Attempts at Gene Therapy.

16.8 More Promising Vectors adeno-associated virus (AAV) is a more promising choice for vector this parvovirus needs adenovirus to replicate but is a good gene carrier once its two genes are removed it infects easily but, when the AAV genes are removed, does not produce an immune response or introduce cancerous mutations

Figure 16.10 Using gene therapy to cure a retinal degenerative disease in dogs.

16.9 Ethical Issues Raised by Gene Therapy ethicists prefer the term gene intervention in lieu of gene therapy to describe any procedure that deliberately alters a person’s genes it is important to consider the permanence of these changes changes to somatic tissue are not inherited changes to germ-line tissues are inherited

16.9 Ethical Issues Raised by Gene Therapy beneficence principle ethicists use this to weigh the risks versus the benefits when making decisions about potential therapy respect-for-persons principle ethicists respect the right of persons affected by the procedure to make their own informed decisions

Inquiry & Analysis Judging by visual similarity, which adult dog is the closer relative of Snuppy? What evidence would you accept that Snuppy is indeed a clone? Photo of Snuppy, with his Clone Dad and Surrogate Mom