Making Sperm, No Men Necessary

early embryos called blastocysts

These early embryos, called blastocysts, were developed from eggs fertilized by sperm created from embryonic stem cells. George Q. Daley/Nature hide caption

itoggle caption George Q. Daley/Nature
A primitive spermatid derived from mouse embryonic stem cells.

A primitive spermatid derived from mouse embryonic stem cells. George Q. Daley/Nature hide caption

itoggle caption George Q. Daley/Nature

Men's ability to produce sperm makes them an invaluable resource for the human species. But what if you could produce sperm without men? As NPR's Joe Palca reports in part two of his series The End of Men, that may soon be possible.

Part 1 of This Report

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Making Sperm in the Lab: A Primer

The secret of producing sperm without men appears to lie in embryonic stem cells. Under the right conditions, these cells can replenish themselves indefinitely in the laboratory, and they can, in theory, turn into any type of cell in the body.

But for a long time, many questioned whether embryonic stem cells could turn into sperm — a highly specialized cell that's only formed after puberty. The smallest cells in the male body, sperm are programmed to find and fertilize an egg.

Last year, scientists proved that they could not only create sperm in a petri dish, but also use that sperm to fertilize a mouse egg.

Led by George Daley of Children's Hospital in Boston, the researchers began their process by culturing mouse embryonic stem cells to form globular clusters called embryoid bodies.

Cells in these embryoid bodies differentiated into primitive germ cells (the precursors of eggs and sperm). The germ cells were tagged with a fluorescent chemical that allowed the scientists to isolate and track the germ cells as the body developed.

Those embryoid bodies that were allowed to grow contained cells that became mature male sex cells similar to sperm, minus the tails. Those tail-less sperm were injected directly into mouse egg cells, essentially fertilizing them. The fertilized eggs then developed into early embryos called blastocysts.

So What's This Mean for Men?

Although embryonic stem cells can make primitive spermatids, it's not known yet whether these resulting tail-less sperm will be able to do all the things that regular sperm are supposed to do.

Daley's team has not yet proved that eggs fertilized with sperm derived from embryonic stem cells will grow into a mouse pup when implanted in a mouse mom. But he's confident he'll be able to do that.

Daley also believes that what works with mouse embryonic stem cells will also work with human embryonic stem cells. But he's not trying to put men out of business — he simply wants to study sperm cell development and infertility.

"The implications for being able to make sperm in a dish allows you to ask questions about normal sperm development, and abnormal sperm development," Daley says.

Besides, Daley notes, there's still one thing that makes men indispensable: "It's clear to make a sperm cell, you do need the Y chromosome. So insofar as men are the only ones who harbor the Y chromosome, you still need a male cell."

Of course, once embryonic stem cells start producing sperm, they can keep doing so forever.

—- Joe Palca

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