How rat sperm grown in mice can revive an extinct species

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Here’s your dose of weird science for the day: A team of Zurich-based researchers turned sterile mice into rat sperm factories using stem cell injections. They hope that the research, published on Thursday in Stem Cell Reportswill open the door to new fertility treatments, especially for animals at risk of extinction.

“In the future, if there is a critically endangered mouse species and we just have a skin biopsy and it goes extinct, we might be able to produce stem cells and maybe generate gametes from such critically endangered animals,” Ori Bar-Nur, a biologist at ETH Zurich in Switzerland and a co-author of the new study told The Daily Beast.

Bar-Nur and his team used a technique that allowed them to inject stem cells derived from rat embryos, or their skin, into a very early stage mouse embryo. The organism then evolved into a mouse-rat chimera, meaning it contained cells from both mice and rats.

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But more importantly, its sperm-producing cells all came from the rat, so the chimera produced exclusively rat sperm.

Previous research had successfully led to the opposite result – mouse-rat chimeras that produced mouse sperm. Joel Zvick, a biologist at ETH Zurich who led the new study, told The Daily Beast that both research projects complement each other nicely, even though their methods were different.

However, the researchers were unsuccessful in using the chimeric rat sperm to fertilize rat eggs and produce viable baby rats. According to the study, the sperm of the mouse-rat chimera was inferior to naturally produced rat sperm.

Bar-Nur said this method seems to work best in species that are closely related by evolution. In addition, the two species in the chimera must have similar gestation periods for fertilization to work.



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Fluorescent staining of rat semen.

With permission of the authors

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Fluorescent staining of rat semen.

With permission of the authors

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Fluorescent staining of rat semen.

Courtesy of the authors

The researchers are now trying to go a step further and grow living rats with mouse-rat-chimera sperm. They are also looking at adapting their methods for egg production, which Bar-Nur said should operate under the same principles as sperm. But we won’t be able to do IVF or other fertility treatments in human-mouse chimeras anytime soon—and maybe that’s for the best.

“If you get a heart or a pancreas, which has been grown through a chimera, it’s just an organ,” Zvick said. “But if you generate sperm and eggs, of course for many people this will be much more difficult to accept.”

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Other studies have also used this stem cell-based method to grow a rat pancreas inside a mouse – but more research into both the technology and ethics is needed before researchers can go around growing human organs in animals for use as transplants.

“It may raise many questions, and this is not the purpose of our research,” Bar-Nur said. “We want to try to save very cute little endangered mice and rats, not generate human gametes inside animals.”

Read more at The Daily Beast.

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