Understanding Assisted and Artificial Reproduction Techniques
Assisted and Artificial Reproduction Techniques
Assisted reproduction, also known as artificial reproduction, involves the insertion of sperm into a woman’s uterus, timed to coincide with ovulation.
In Vitro Fertilization (IVF)
In in vitro fertilization (IVF), eggs are removed from the woman after hormone treatment to stimulate the ovaries. The eggs are then fertilized by sperm. When the sperm count is low, a single sperm can be injected directly into the oocyte using intracytoplasmic sperm injection (ICSI). The resulting embryos, typically consisting of 6-16 cells, are then implanted in the uterus.
Preimplantation Genetic Diagnosis
Preimplantation diagnosis involves genetic testing of the embryo at the 8-cell stage. This allows for the selection of embryos that do not carry genes for specific diseases. The Commission on Assisted Human Reproduction typically authorizes these procedures on a case-by-case basis. In some instances, this technique is used to select healthy embryos that can serve as donors for sick siblings, treating diseases where a suitable match has not been found.
Reproductive Cloning
Reproductive cloning differs from molecular cloning. Molecular cloning refers to creating many identical copies of a molecule, such as a gene. In contrast, reproductive cloning aims to create a genetically identical individual. This technique involves removing the nucleus of an egg cell and replacing it with a somatic cell from the animal to be cloned. This method, called nuclear transplantation, creates an artificial embryo that is then implanted into the uterus of a female of the same species to complete its embryonic development. The resulting individual is genetically identical to the donor of the somatic cell nucleus.
Stem Cells
Stem cells are undifferentiated cells that can divide indefinitely to produce new stem cells. Under appropriate conditions, they can differentiate into one or more specialized cell types. Stem cells possess three key characteristics:
- Undifferentiated: They lack specialization, preventing them from performing specific functions.
- Self-renewal (division): They have the ability to divide and create more stem cells.
- Differentiation: They can generate specialized cells with specific functions and features.
Totipotent: Capable of generating a complete organism.
Pluripotent: Capable of generating any tissue type.
Multipotent: Capable of generating various tissues of a specific cell type.
Not all stem cells are the same; they differ in origin and differentiation capacity.
Types of Stem Cells:
Embryonic stem cells – Adult stem cells – Induced pluripotent stem cells – Fetal stem cells – Umbilical cord blood stem cells
Embryonic Stem Cells
Embryonic stem cells (ESCs) are derived from the inner cell mass of the blastocyst. At this early embryonic stage (around day 5 after fertilization), two groups of cells are present: those forming the surface layer (which will become the placenta) and those occupying the interior (the inner cell mass). Under normal conditions, these inner cell mass cells would continue their differentiation process, leading to the three primary embryonic tissues (ectoderm, endoderm, and mesoderm in the gastrula stage). However, when removed and placed in a suitable culture medium, they can potentially develop into any cell type. Due to this differentiation ability, embryonic stem cells are considered pluripotent cells. While they cannot give rise to a whole organism, they are the origin of all cell types and tissues within an individual.
Challenges with Embryonic Stem Cells
Several challenges are associated with the use of embryonic stem cells:
- Rejection: To avoid rejection issues, embryonic cells are ideally sourced from the same individual who will receive them. The only way to achieve this is through therapeutic cloning, which involves creating an embryo clone (with the patient’s genetic material) that is then destroyed to obtain stem cells.
- Tumor Formation: Embryonic stem cells frequently degenerate into tumor cells, posing a significant drawback.
- Ethical Concerns: Obtaining embryonic stem cells requires the destruction of embryos, raising ethical dilemmas regarding their use.
- Efficiency: Many embryos are needed to obtain a suitable cell line.
Adult Stem Cells
Adult stem cells (ASCs) are stem cells obtained from various adult tissues. Their primary function is to replace dying cells within a tissue or organ. These cells have been discovered in numerous tissues, including bone marrow, fat, skin, and even tissues with low cell renewal rates, such as neural tissue. Interestingly, some cells initially categorized as multipotent may be able to generate many types of tissues.