A powerful study in embryology by a team from European Molecular Biology Labs (EMBL), Heidelberg, Germany and Institut Curie, Paris reveals what drives cells in becoming the fetus rather than the placenta very early in mouse embryo development.
Soon after the sperm and egg meet forming an embryo, it divides into a mass of cells. According to the lead author at Institut Curie, Dr. Jean-Leon Maître, "In the very first days of our development, cells make their very first decision of either becoming part of the placenta or of the embryo."
But there are some rules about which cells becomes what part of the embryo. "We knew this decision is based on the position of the cell within the embryo: if the cell is at the surface, it will become placenta; if it is buried inside the embryo, it will be part of the embryo," says Maître.
Therefore based on the above reasoning, the fate of the cells should be obvious, right?
However, the scientists wanted to go a step further, reasoning out how cells acquire that particular position. Now for cells to acquire a position, they have to move. As general laws of physics would dictate, for any cell to be mobile it has to exert a force. But here's where it could get tricky. How do you estimate it?
"Measuring forces of cells is not trivial. The forces are small, so you need to be quite sensitive. Scientists know how to do that with atoms of course, but we don't want to put our embryos through the same instruments because that would smash them into pieces," cautions Maître.
Therefore what the scientists needed to do was a very gentle arm wrestling with the cells. They measured these forces and figured that the cells moving around are the ones exerting the strongest force. However, there was still the matter of quantifying under what conditions could the cell, move into the embryo. This is where mathematical equations from 'soft matter physics' came in handy.
"[Since] the embryo formed by the mass of cells is analogous to a foam formed by bubbles, I used similar mathematical and computing techniques that have been used to understand the shape and arrangement of bubbles," says Dr. Herve Turlier, a co-author in the study, at EMBL.
Maître adds, "I am amazed by how complex the mammalian embryo is and yet, how a very simple equation can recapitulate its architecture on a computer." And just like that, it appears that interdisciplinary sciences could have the strangest and most unpredictable intersections!
"What's funny is that this equation was formalized in the 19th century by a scientist, called Athanase Dupré, working on the effect of heat on the meniscus formed by liquids in tubes. Little did he know that the very same equation would be used 250 years later to explain how mammalian embryos are formed!" says Maître.
The researchers also made another curious observation. The stronger cells start a surface wave (or a 'dance') making the cell beat every 80 seconds. The scientists could use this 'dance' move to see which cell was going to be an embryo and not that of a placenta. "In other words, the cells that made it as embryo are the ones that carried on dancing," comments Maître.
These are spectacular results, albeit they were established in the mouse model. So a natural question then is how well do they translate to human embryos? A confident Maître adds, "Before their implantation into the maternal uterus, the mouse and human embryos are very similar, especially when it comes to their architecture."
In fact, he says if you see pictures of each embryos, you may not spot the difference!
In future, the scientists hope to uncover the mystery behind functionality of the 'waves' that persist in cells that form the embryos. They would also like to further explore the idea that mechanical forces influence the first decision of mammalian embryos.
But for the time being, are there implications of this study for human healthcare?
Such studies could come in very handy in fertility clinics to better diagnose the embryos from in vitro fertilization. With an increase in Europe's graying population and a decline in birth rates this is particularly a critical area of medicine that currently concerns millions of Europeans.
Image credit: Unsplash.com (Lesly B. Juarez)