In Vitro Fertilization and Cloning

Learning Objectives

  1. Define In Vitro Fertilization (IVF) and explain how this biotechnology can result in offspring
  2. Compare and contrast therapeutic, reproductive, and molecular cloning
  3. Define stem cells and explain their relationship to therapeutic cloning
  4. Know what can be achieved by these methods and reflect on the bioethical implications

Infertility

Infertility is the inability to conceive a child. Male infertility is typically due to decrease in sperm count/motility resulting from medical conditions (radiation, chemotherapy, diabetes, cystic fibrosis), unhealthy habits (heavy alcohol or illicit drug use, anabolic steroids), and environmental toxins (lead, pesticides). Female infertility may result from complications with fallopian tube (blockage, damage or removal), and disorders of the ovaries or uterus that may be affected by age, smoking, heavy alcohol or illicit drug use, and extreme weight loss/gain. Currently, 20% of US women have their first child after age 35, and about a third of couples in which the woman is older than 35 years have fertility problems. (References: https://www.cdc.gov/reproductivehealth/infertility/)

 

In Vitro Fertilization

In vitro fertilization (IVF) is a series of procedures used to treat fertility or genetic problems and assist with the conception of a child. The process is in vitro (Latin for in glass), in contrast to in vivo (Latin for in something alive), because fertilization occurs outside the body. One cycle of IVF involves 1) administration of follicle stimulating hormone (FSH) to stimulate follicle production in the ovaries 2) extraction of mature eggs from a woman’s ovaries, 3) retrieval of a sperm sample from a man, and then 4) manual fertilization of the egg by sperm to produce an embryo in a laboratory dish. One or more embryo(s) are implanted in the uterus. The IVF cycle takes about two weeks. Eggs and embryos from an IVF procedure can also be frozen. Because inter-gamete contact occurs and fertilization takes place, the offspring still has DNA derived from both male and female parents. The first human conceived as a result of IVF (the first “test tube baby”) was born in 1978. The CDC now estimates that 1.5% of babies born in the US are conceived using Assisted Reproductive Technologies (ARTs).

Watch this video on IVF

Intracytoplasmic sperm injection (ICSI) is a specialized IVF procedure in which a single sperm is injected directly into an egg. IVF (and ICSI) can be performed with a woman’s own eggs and a male’s sperm, or can involve eggs, sperm or embryos from a donor that may be known or anonymous. In some cases, a woman who is not the egg donor can serve as a carrier or surrogate by having an embryo implanted in her uterus. (Reference: https://www.cdc.gov/art/artdata/index.html).

Intracytoplasmic sperm injection (ICSI) into an egg 

Therapeutic and Reproductive Cloning

One definition of a clone is an identical copy of an organism. Identical twins are genetic copies that arise when a single zygote splits in two soon after fertilization. Both halves contain the same DNA and eventually form two fetuses. Identical twins are technically natural clones. However, organismal clones can also be generated artificially. One commonly used technique for cloning is Somatic Cell Nuclear Transfer (SCNT). The nucleus is removed from a healthy egg (germ cell). This egg with its nucleus removed becomes the host for a nucleus that is transplanted from another cell, such as a skin cell (somatic cell).

Cloning by Somatic Cell Nuclear Transfer (SCNT)

The resulting embryo, which has the identical chromosomal DNA as the nucleus donor, can be used to generate pluripotent embryonic stem cells in tissue culture. This process is called therapeutic cloning because the goal is to harvest stem cells that can be used to study human development and to potentially treat diseases. Stem cells are undifferentiated (unspecialized) cells that can both differentiate into specialized cells  (such as a liver or heart cell) and can also divide to produce more stem cells. Alternatively, the embryo can be implanted into a surrogate mother to create a new multicellular organism, with chromosomal DNA as the nuclear donor. This method, reproductive cloning, is an asexual method of reproduction, where no fertilization or inter-gamete contact takes place.

 

In 1999, a private company successfully used SCNT to generate a human/animal hybrid clone that was cultured for several days in a dish and destroyed (http://news.bbc.co.uk/2/hi/science/nature/371378.stm). Soon after, in 2001, the US House of Representatives passed a bill to ban both reproductive and therapeutic cloning, which the president indicated he would sign, but a Senate vote was not taken. President Bush passed a ban on federal funding for both reproductive and therapeutic cloning, which permits federal funding for research on ~20 human embryonic stem cells created prior to 2001. At this time, there are currently no federal statutes against cloning in the US, although several states including Georgia legally prohibit reproductive cloning. Bans in other countries vary. Reference:  http://www.geneticsandsociety.org/article.php?id=305)

 

Recombinant DNA Technology and Molecular Cloning

Our understanding of the nature of the gene along with genomic discoveries has led to the development of techniques to engineer genes collectively called recombinant DNA technology. This process involved the joining together of different DNA molecules and then inserting this DNA into a host organism to produce new genetic combinations. The development of Recombinant DNA technology arose in the last 50 years because scientists needed to generate sufficient amounts of specific DNA, for example to study the protein coded by that DNA. To obtain large quantities of DNA, the desired DNA fragment of interest is cut out of the surrounding DNA and copied millions of times. Then microbial cells can be engineered to use the cell machinery to produce the foreign protein.

 

Molecular cloning refers to the replication of a fragment of DNA placed in an organism so that there is enough to analyze or use in protein production. Molecular cloning exploits the rapid growth of bacterial cells for producing large amounts of identical DNA fragments. A DNA fragment to be amplified is first inserted into a cloning vector, such as a small circular DNA molecule called a plasmid that is naturally replicated by the bacterial cell machinery.

Insertion of foreign DNA into a plasmid. The plasmid contains an antibiotic resistance gene (blue) to select only bacteria carrying the plasmid. A promoter sequence (green) may be present if the goal is to express a gene in the DNA fragment of interest.

After insertion of the foreign DNA in vitro, the recombinant plasmid is re-introduced into a bacterial cell. A growing culture of bacterial replicates the plasmid with its foreign DNA to yield multiple, identical clones of the original recombinant molecule. This technology is so efficient for cloning DNA that a liter of bacterial cells engineered to amplify a single fragment of human DNA can produce 10 times the amount of that specific DNA segment than could be purified from all the cells of an entire human body! 

Whole Genome Sequencing

Determining the order of bases in a DNA sequence is called sequencing. We can determine the sequence of a single gene, a short piece of DNA or RNA, and even of an entire genome. Sequencing an entire genome can help identify genes of interest, such as those with mutations that cause disease. Whole genome sequencing is a laboratory procedure that determines the order of bases in the entire genome of an organism in one process. The cost of sequencing the first human genome in 2001 was $1 billion dollars and took 13 years to complete. Technologies have advanced rapidly to determine the entire genome sequence of an individuals organism. Progress has been made possible by advances in high speed computing and the development of the field of bioinformatics for analyzing the large data sets generated. Currently, a human genome can be sequenced for about $3000 in about 1 day!

Here are some benchmark firsts, by year, in the complete genome sequencing of different organisms:

  • 1995 Haemophilus influenzae Rd (1st bacterium, and also first free living organism)
  • 1995 Methanococcus jannaschii (1st archaea)
  • 1996 Saccharomyces cerevisiae 1996 (1st eukaryote)
  • 1998 Caenorhabditis elegans (1st animal)
  • 2000 Arabidopsis thaliana (1st plant)
  • 2001 Homo sapiens (1st human)

Molecular cloning and genetic engineering have provided detailed fundamental knowledge of gene structure, organization, and regulation and also produced new genetic combinations that are of value to industry, agriculture, medicine and the environment.

  • Industry: useful compound and products (enzymes, vitamins, amino acids)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3026452/

  • Medical advancement: pharmaceuticals (antibiotics, cancer and heart attack drugs), disease diagnostics and treatments, genetic testing, and gene therapy

https://www.scientificamerican.com/biotech/

  • Agriculture: transgenic animals and plants

http://www.nature.com/nbt/journal/v18/n10s/full/nbt1000_IT59.html

  • Environment: bioremediation

http://journal.frontiersin.org/researchtopic/3787/new-and-emerging-trends-of-biotechnology-in-bioremediation

 

Bioethical implications of IVF and cloning biotechnologies

What are the bioethical implications of these technologies? Do all IVF and cloning procedures warrant the same concern? Who should be involved in discussions about what procedures are permitted and banned? Who is affected by these decisions? Some prominent early and current quotations on this topic:

“One egg, one embryo, one adult – normality. But a bokanovskified egg will bud, will proliferate, will divide . . . becoming anywhere from eight to ninety-six embryos – a prodigious improvement, you will agree, on nature. Identical twins – but not in piddling twos and threes . . . Standard men and women; in uniform batches.”Aldous Huxley (writer and philosopher). 1932. Brave New World. 

There is nothing to suggest any particular difficulty about accomplishing this in mammals or man […] If a superior individual (and presumably then genotype) is identified, why not copy it directly, rather than suffer all the risks of recombinational disruption.” Joshua Lederberg (1958 Nobel Laureate for discovery of genetic recombination). 1966. American Naturalist essay.

“We didn’t want people running away with the idea of being able to manipulate genes,” Beckwith said. “We were worried about the technology being used for profiling people or intervening in the human genome.” – Jon Beckwith (Harvard professor who cloned the first gene). 1969. Press conference after cloning study published.

“If I can provide a glimpse of, ‘Where did we come from? What happened to us, for us to get here?’ I think that, to me, is a strong enough rationale to continue pushing this,” – Ali Brivanlou (Rockefeller University professor of embryology). March 2 2017. National Public Radio story “Embryo Experiments Reveal Earliest Human Development, But Stir Ethical Debate”

Finally, listen to this short article on current research on embryos and the laws and ethics surrounding the research: