Researchers at Newcastle University in England report they have coaxed the first human sperm cells from embryonic stem cells, in a remarkable demonstration of how quickly the field of stem-cell science is moving.
The achievement, described in the journal Stem Cells and Development, comes just 11 years after the first human-embryonic-stem-cell line was created — an eyeblink in scientific terms — in the lab of James Thomson at the University of Wisconsin.
Although the development once again raises the specter of creating humans in a petri dish or custom-designing egg and sperm cells for reproduction, lead author Karim Nayernia says that was not his team's intention. Rather, the experiment was a proof of concept that stem cells can generate any cell in the body — not only the dozens of tissues that make up the human body but also those egg and sperm cells that may give rise to altogether new bodies. "Other cell types don't generate the next generation," says Nayernia, a professor of stem-cell biology at Newcastle University. "This makes a very big difference between our study and the study of other cell types from embryonic stem cells."
Nayernia's in vitro–derived sperm, or IVD sperm, are not exactly like naturally occurring sperm, though they do bear four important similarities to the cells created in the testes. They contain half the number of chromosomes of other human cells (somatic cells contain 46 chromosomes, but egg and sperm cells have only 23, since they combine their genetic payloads during fertilization); they possess a head and a tail; they contain proteins essential for activating the egg during fertilization; and they swim, or move as sperm do in seeking out eggs to fertilize.