Precursor Egg, Sperm Cells Shed Light on Human Development

Scientists have created precursor egg and sperm cells in a lab, shedding light on human development, a new study says.

"The creation of primordial germ cells is one of the earliest events during early mammalian development," Dr. Naoko Irie, first author of the paper from the Wellcome Trust/Cancer Research UK Gurdon Institute at the University of Cambridge, said in a statement.

"It's a stage we've managed to recreate using stem cells from mice and rats," he added, "but until now few researches have done this systematically using human stem cells. It has highlighted important differences between embryo development in humans and rodents that may mean findings in mice and rats may not be directly extrapolated to humans."

When a sperm fertilizes an egg cell, it divides into a ball of cells - called a blastocyst - consisting of inner and outer cells. Some cells in the inner cell mass are "reset" to become stem cells that can turn into any type of cell in the body. And a small number of these cells become primordial germ cells (PGCs), which have the potential to become germ cells (sperm and egg).

Described in the journal Cell, during a process called "specification," researchers found that a gene known as SOX17 is critical for directing human stem cells to become PGCs. Based on prior studies in mice, the team was surprised to find that the mouse equivalent of the SOX17 gene is not involved in the process, suggesting a key difference between mouse and human development.

SOX17 has previously been associated with transforming stem cells into cells in the lung, gut and pancreas, but this is the first time it has been seen in PGC specification.

The research has potential implications into understanding the human germline infertility and germ cell tumors, as well as "epigenetic" inheritance, or the idea that our environment can affect our genes and effect our offspring.

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