Why does the gestation period vary so much between species? – 06/21/2023 – Science

Researchers from the European Molecular Biology Laboratory (EMBL) in Barcelona (ESP) have created an unprecedented archive of stem cells from six mammals: human beings, mice, monkeys, rabbits, cows and rhinos. The purpose was to compare them to understand why the time they need to develop differs. The results were published on Tuesday (20) in the journal Cell Stem Cell.

The group is led by scientist Miki Ebisuya, who has long studied why there are different speeds of embryonic development, if almost all mammals go through the same stages of growth to form their backbone.

His conclusion was that the formation of mesomeres, the body segments that result in vertebrae and ribs, is controlled by the so-called “segmentation clock”: both this and the different evolutionary histories of species influence the pace of development.

While in humans gestation lasts nine months, in mice it is only 20 days, and in rhinos, up to 17 months. Despite going through the same embryonic stages, the expression of the segmentation clock genes oscillates at different frequencies. For example: in humans it is two to three times slower than in mice.

Weight doesn’t explain everything

The research led by Ebisuya had already revealed that the differences in the speed of biochemical reactions determine the variations between the “clocks” of mice and humans. To establish whether this was a general principle of embryonic development, however, the scientists had to expand the number of species examined.

So, in collaboration with colleagues in Europe, Japan, and the US, the group added titi monkey, rabbit, cow, and rhino targeting clocks. Embryonic and pluripotent stem cells were included, composing a general comparative platform.

“To have as wide a range of diversity as possible, we chose species with body weights from 50 grams to two tons, gestation times from 20 days to 17 months, and diverse evolutionary histories, or phylogenies: primates (human and titi), glires (mouse and rabbit) and ungulates (cow and rhinoceros)”, explains researcher Jorge Lázaro.

The EMBL group in Spain studied the differences between the “clocks” of the four new species, in order to distinguish the stem cells that will generate the spine, ribs and skeletal muscle tissue. “It’s an ideal platform to investigate whether there is any general relationship between segmentation time and organism characteristics,” notes Ebisuya.

Although it is known that, like many other body parameters, the duration of gestation depends on the weight of the animal, the scientists did not find any correlation between the average weight of the six species studied and the period of their segmentation clock.

However, they found that the clock is correlated with the duration of embryogenesis —the stage between fertilization and the end of organogenesis, when all the organs of an embryo are formed.