In Vitro Fertilization and Gene Editing

Learning Objectives

Define In Vitro Fertilization (IVF) and explain how this biotechnology can result in offspring
Compare and contrast therapeutic and reproductive cloning
Define stem cells and explain their relationship to therapeutic cloning
Define and explain how CRISPR can be used for gene editing, and name the key molecules and how they work together.
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.

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

IVF 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.

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 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. Embyronic stem cells are cells from an early stage embryo; the cells have not yet specialized cells into certain cell lines (like liver or heart muscle cells). Because they are unspecialized, or “undifferentiated” in jargon, they have the ability to divide to produce more stem cells…cells that might become any tissue type. In other words, these divided cells are clones of each other. The other type of cloning, reproductive cloning, results in an entire organism instead of a cell line in a petri dish. In reproductive cloning, the embryo is implanted into a surrogate mother to create a new multicellular organism, with chromosomal DNA as the nuclear donor. Reproductive cloning is an asexual method of reproduction because 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. 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. The ban permits federal funding for research on ~20 human embryonic stem cell lines that already existed in the US 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.

CRISPR Gene Editing

While cloning genes of interest in stem cells is fairly restricted legally, the potential for gene therapies depended almost solely up on that technology until recently, when CRISPR/Cas9 was discovered in bacteria. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a “gene editing” technique. These repeats can be cut by an enzyme called Cas9 when the appropriate nucleotide match pairs with it. Imagine you want to edit the sickle cell hemoglobin allele. You’d guide the CRISPR-Cas9 toward the hemoglobin gene using a short piece of RNA called…short guide RNA or sgRNA. Once there, Cas9 will cut the genome there, which allows for editing. Read the article below:

https://www.sciencenewsforstudents.org/article/2020-chemistry-nobel-gene-editing-tool-crispr

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…. 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”