2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Chinese scientists have sent more than 1,000 mouse embryos into space at the two-cell stage to track their development. It turned out that in orbit, embryonic cells divide and differentiate worse than on Earth. Apparently, the matter is in radiation: if the embryos on Earth are irradiated with the same dose as in space, then they accumulate double-strand DNA breaks and develop worse. Perhaps this explains why rats have so far failed to reproduce in space experiments. The research is published in the journal National Science Review.
Scientists have repeatedly sent a variety of animals into space, including those at embryonic stages. Although many invertebrates and vertebrates continued to thrive even in zero gravity, it is still not known about mammals how this is possible. Attempts to force male and female rats to reproduce in orbit have so far failed. Apparently, the point is not in the production of germ cells - at least, after returning from space, rodents are able to become fathers. Sperm quality also does not change in space.
A group of scientists led by Enkui Duan of the Institute of Zoology of the Chinese Academy of Sciences suggested that problems may arise during the early embryonic stage. To test this, the researchers developed an incubator for space travel. Under terrestrial conditions, it made it possible to cultivate embryos to the preimplantation stage (blastocysts): about a third of the embryos grown in it, after replanting to females, developed into full-fledged mice.
In April 2016, China launched the SJ-10 satellite, and 12 hours before launch, an incubator with mouse embryos at the two-cell stage was installed on it. The microscope camera took pictures of them every 4 hours, and after 64 hours they were fixed in order to stop development and analyze gene expression after returning to Earth.
On Earth, scientists have collected 1184 recorded embryos from an incubator. Of these, 856 have developed to the stage of morula (multicellular dense ball) or blastocyst (ball with a cavity inside). However, blastocysts in space turned out to be almost two times less than in the same incubator on Earth (34, 3 percent versus 60, 2). Thus, the transition from morula to blastocyst in space was disrupted.
When researchers began to study the quality of the resulting blastocysts, they noticed that they had fewer cells than similar terrestrial embryos (an average of 41.5 versus 51.6). In addition, it turned out that they differ in the expression of the main markers characteristic of this stage. Among the surface cells of blastocysts that developed in space, there were twice as many of those that were stuck in the process of differentiation: they expressed the Oct4 and Cdx2 proteins characteristic of the inner cell mass. This means that problems in embryos began at the level of cell division and differentiation.
In the causes of these problems, the researchers suspected cosmic radiation. To find out if it had an effect on the DNA of embryos, they measured the number of double-strand breaks in blastocyst cells: those that flew into space had almost twice as many of them.
Then the authors of the work decided to find out what affects the development of mouse embryos more strongly: radiation or the absence of gravity. Already on Earth, they collected a new set of embryos and some were exposed to a dose of radiation (which was approximately equal to that which the embryos received during the flight - 0.5-2 mGy), while others were cultivated in a rotating vessel. It turned out that under zero gravity, slightly fewer embryos survived to the blastocyst than usual (65.4 percent versus 72.9 percent), but under the influence of radiation the effect was stronger - only 45.7 percent survived at the maximum dose. In addition, under conditions of weightlessness, the embryos did not develop double-strand breaks, but under the action of radiation they appeared throughout the blastocyst. As a result, the irradiated embryos took root in the mothers' bodies worse: the birth rate dropped to 7-21 percent (depending on the dose) compared to 32.6 percent in the control group.
Double-stranded breaks in blastocyst cells in control and under the influence of different doses of radiation. Red - double-strand break marker, blue - cell nuclei.
Based on their data, the researchers concluded that radiation prevents mammals from reproducing in space, which reduces the already low survival rate of embryos. Nevertheless, the authors of the work note that it is unlikely that radiation alone is to blame for all the troubles of developing embryos: the number of full-fledged blastocysts that formed in orbit was still lower than on Earth under the influence of an appropriate dose of radiation. This means that changes in gravity also play some role in the development of embryos, they just do not have such a strong effect.
Earlier we wrote that for the brain of rats, radiation, apparently, was harmless. But the mice, once in space, began to describe strange circular paths.