FORMATION OF HUMAN GERM CELLS FROM ADULT CELLS: A BREAKTHROUGH

A joint Israeli-British research group yesterday announced a breakthrough in reverting human embryonic cells into primordial germ cells (PGCs) which can produce sperm and ova in laboratory. The study led by a group of scientists from University of Cambridge and Weizmann Institute of Science demonstrates that human cells can be programmed to “go back in time” into early developmental stage for the first time, though this had already been shown in rodent stem cells.

PGCs are diploid cells, formed in early stages of embryogenesis. They are the precursors of spermatozoa and ovum. The researchers identified a gene known as SOX17, which plays critical role in conversion of human stem cells to become PGCs. Earlier studies have shown the involvement of SOX17 gene in directing stem cells to become endodermal cells. These endometrial cells are the precursors of any type of cells of our body including cells of the lung, gut and pancreas.

The group also showed that PGCs could be made from any type of reprogrammed adult cells. This would no doubt help in knowledge advancement and treatment of problems related to human germline, infertility and germ cell tumours.  Thus this understanding would one day help to revert adult cells to sperm or ova in test tube, which theoretically could enable women who have undergone chemotherapy or premature menopause to conceive.

This study also has potential implications on understanding the process of ‘epigenetic’ inheritance. Epigenetic inheritance goes against the idea that inheritance happens only through the DNA code that passes from parent to offspring. It means that a parent’s experiences from the environment (may be by diet and or smoking etc.), in the form of epigenetic tags, can be passed down to future generations. Methylation of DNA occurs as a result of epigenetic changes, by which molecules attach themselves to our DNA, acting like dimmer switches to increase or decrease the activity of genes. The group have also observed that during the PGC specification stage, a programme is initiated to erase these methylation patterns acting as a ‘reset’ switch. However, traces of these patterns might be inherited.

Experts think that germ cells are ‘immortal’ in the sense that they provide an enduring link between all generations. The comprehensive removal of epigenetic information ensures that most, if not all, epigenetic mutations are wiped out, which promotes revival of the lineage and allows it to give rise to endless generations. These mechanisms are of wider interest towards understanding age-related diseases, which in part might be due to cumulative epigenetic mutations.

 

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Arunima Maiti

Arunima Maiti

Biomedical scientist with special interest in reproductive biology.

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