Why does a human pregnancy last 9 months, in mice 20 days and in rhinos 17 months?

Researchers from the European Molecular Biology Laboratory (EMBL) in Barcelona (northeast of Spain) created a library of mother cells record of six species of mammals -human, mouse, monkey, rabbit, cow and rhinoceros- to compare them and study why they differ in the time they take to develop.

The work, published today in the Cell Stem Cell magazine, was carried out by the group led by the EMBL Barcelona researcher, Miki Ebisuya, who has been studying for some time why there are differences in the speed of embryonic development if almost all Mammals follow the same growth stages to form their backbones.

According to the researchers, the formation of the body segments that give rise to vertebrae and ribs, called somites, is controlled by a mechanism called the ‘segmentation clock’ and this work revealed to them that both the segmentation clock and the different evolutionary histories of mammals have an influence on development times between species.

In humans, pregnancy lasts nine months, in mice just 20 days, and in rhinos up to 17 months, and although many mammalian species go through the same stages during embryonic development, the speed of development is different, from one to another. other things because the expression of the segmentation clock genes oscillates with different frequencies, for example, it is two to three times slower in humans than in mice.

“The segmentation clock is an ideal system to study the differences between species”according to the researchers from the Ebisuya group.

Their research recently revealed that differences in the speed of biochemical reactions are responsible for the differences in mouse and human clocks, but to establish whether this is a general principle of embryonic development, the researchers needed to expand the species studied, which until now were only humans and mice.

For this reason, Ebisuya’s group, in collaboration with researchers from Europe, Japan and the US, added to the laboratory the segmentation clock of four new species of mammals: marmoset, rabbit, cow and rhinoceros.

The researchers collected induced pluripotent and embryonic stem cells from these four animals, which added to the existing human and mouse library, to form a general platform for comparing developmental processes.

“We wanted to create a platform of cells from various mammalian species to study why their development time is different, and to have as wide a range of diversity as possible, we chose species with body weights ranging from 50 grams to 2 tons, durations gestation from 20 days to 17 months and three different evolutionary histories or phylogenies: primates (human and marmoset), glires (mouse and rabbit) and ungulates (cow and rhino)”explained the researcher Jorge Lázaro.

The EMBL scientists studied the differences in the segmentation clock of the four new species to differentiate the stem cells that would later give rise to the vertebral column, ribs and skeletal muscles.

“It is an ideal platform to investigate the cause of interspecies differences and determine if there is any general relationship between segmentation tempo and organism characteristics,” Ebisuya pointed out.

Although it was known that the length of gestation, like many other body parameters, depends on the weight of the animal, the researchers found no correlation between the average weight of each species and the period of its segmentation clock.

However, they did see that the segmentation clock correlates with the length of the embryogenesis stage, the time between fertilization and the end of organogenesis, when all the organs of an embryo are formed.

Furthermore, they found that the three different evolutionary histories—primates, glires, and ungulates—correspond to slow, fast, and intermediate segmentation clock periods, respectively, pointing to a relationship between developmental tempo and evolutionary groups.

They also found that genes related to biochemical processes show an expression pattern that correlates with the period of the cleavage clock, providing clues to a possible molecular mechanism underlying the different rates of development between species.

Source: EFE