Primordial Germ Cells were Created from Human Stem Cells to Potentially Crack the Genetic Inheritance Code
The recent discovery of a newfound role of a gene called SOX17 led scientists from University of Cambridge and Weizmann Institute to create primordial germ cells (PGCs)—egg and sperm predecessors—from human stem cells. Previously, PGCs were created using rat and mice stem cells, and a few scientists have created germ cells from human stem cells, but this is the first time where primordial germ cells were refashioned from human stem cells efficiently. With this new tool in their arsenal, the researchers are hoping to shed light on the mechanisms that regulate transmission of genetic material from one generation to the next.
During the early stages of embryo development, after an egg cell is fertilized by a sperm cell, the new entity (called a zygote) undergoes a series of cell division until it forms a bundle of cells known as a blastocyst. It consists of an inner cell mass, which develops further until it eventually forms the fetus, and an outer wall that later forms the placenta. Cells in the inner cell mass are rebooted to become stem cells, in which a handful are “specified” into becoming primordial germ cells, which then become germ cells (sperm or egg). Sperm and egg cells are responsible for handling the genetic information that is to be passed down to the next generation.
Scientists knew SOX17 played a role in directing stem cells to become endodermal cells which later form the gut, pancreas, and lungs. Further study led the researchers to discover SOX17’s role in PGC specification from human stem cells and also ascertained that primordial germ cells can be made from reprogrammed adult skin cells, opening doors to new insights on infertility issues and germline tumors, and possibly epigenetic inheritance process.
It’s been known the environment, such as smoking and dietary habits, can impact our genes by methylating, or adding chemical particles, to DNA, which act as dimmer switches that increase or decrease the activity of genes. Methylation patterns can be passed down to offsprings. The researchers conveyed during PGC specification, a de-methylation program commences and virtually resets the primordial germ cells. Nevertheless, traces of these patterns might still be inherited, in which why they occur remain a mystery. Unlocking the reason behind epigenetic inheritance can give scientists clues to comprehending age-related diseases and uncover the secret to eternal youth.
Researchers at A*STAR’s Institute of Molecular and Cell Biology (IMCB) in Singapore have discovered a technique to produce induced pluripotent stem cells (iPSCs) from a single drop of blood. Current methods for harvesting stem cells are invasive, which are generally collected from bone marrow or skin, and may put off potential donors. Other methods require large quantities of blood. Scientists at IMCB demonstrated the efficiency of their stem cell harvesting technique by converting cells from a drop of blood into functional cardiac cells.
Stem cells are essentially “blank slates” that can specialize into any type of cell, when given specific cellular “instructions,” and serve the organ or organ system it was “destined” to service. As a result of their nonspecific nature, stem cells have high regenerative properties. Majority of stem cells exist in 3-5 day old embryos called blastocysts that differentiate into specialized tissues that make up the body. In adults, bone marrow, muscle, and brain tissue have cells that can replace damaged cells that have been lost through everyday wear and tear, injury, or disease.
Induced pluripotent stem cells are genetically reprogrammed to imitate a stem cell-like state. A sample of one drop of blood from a finger stick is stable for 48 hours and lasts up to 12 days in culture. The finger stick does not have to be performed in a medical facility but at the comfort of home and then sent to a laboratory for reprograming.
Stem cells have the potential to shed light on a variety of diseases and are currently being used in regenerative medicine. New drugs to effectively combat chronic disorders, like diabetes and heart disease, can be discovered with stem cell research.
Currently, human and animal, such as those derived from mice, embryonic stem cell research is sanctioned in most countries, but they are not very accessible. Several induced pluripotent stem cell bank initiatives have arisen in Japan, UK, US to make iPSCs available for research and medical studies. With the finger-stick method, IMCB scientists are hoping stem cell research will break scientific barriers and endorse exciting new discoveries.
In vitro fertilization (IVF) is the process of combining the nuclei of an egg cell and a sperm cell outside the Fallopian tubes and then implanting the subsequent embryo into the woman’s uterus for regular gestation. It is one method of assisted reproductive technology (ART) adopted by couples or single women with fertility issues, which affects about 15 percent of the world’s population. However, there may be several failed attempts before a healthy baby is produced. Recently, scientists at Peking University, China in conjunction with Harvard University have developed a method to expose genetic defects in eggs prior to joining them with sperm for up to 50 percent increase in IVF success.
The new technique identifies both chromosomal abnormalities and DNA sequence variations linked to genetic disorders in polar bodies—side products of egg cell division that naturally degrade later in the body—via whole genome egg sequencing. A similar approach is already established for detecting genetic anomalies in sperm cells, though chromosomal abnormalities are more common in egg cells. Currently, genetic tests are typically performed on embryos prior to implantation, which involve the removal of cells and can harm the developing mass, and do not simultaneously uncover chromosomal abnormalities and DNA sequence changes.
There are many factors affecting the fertility of egg cells that are associated with women, such as age, weight, the number of miscarriages, certain medications, exposure to environmental hazards, or current disease state, such as cancer. In vitro fertilization gives these women the chance to experience childbirth. And, with the new technique IVF success rate is supposed to increase from 30 percent to 60 percent, possibly more. Since chromosomal abnormalities and DNA sequence variations linked to genetic disorders are tested in one sitting, the new method is cost-effective and less time-consuming.
The scientists are utilizing the new technique in clinical trials and are optimistic about bolstering in vitro fertilization success rates.