The cover image of the March 18 issue of Biophysical Journal shows two mouse embryos at the eight-cell stage and two doublets of cells coming from dissociated mouse embryos. The embryo and doublet on the top have small cell-cell contacts, and the bottom ones have large cell-cell contacts. During the eight-cell stage, mouse embryos undergo compaction, and cells grow their cell-cell contacts because of increased contractility at the contact-free interface, which pulls at the edges of the contact. This is expected to stabilize cell-cell contacts.

In our paper, we took advantage of the ability of doublets to compact just like intact embryos to pull contacts apart by using a dual micropipette setup. With this we can measure the force necessary to separate contacts before and after compaction. In addition to quantitatively measuring the increase in mechanical stability of cell-cell contacts after compaction, we could also use mutant mouse embryos to disrupt the cell-cell adhesion machinery and measure the effect on adhesion strength. This constitutes a new physiological system to study the mechanics of cell-cell adhesion strength.

Understanding how cells of early mammalian embryos adhere to one another is key to fighting infertility. Indeed, in vitro fertilized human embryos produced via Assisted Reproductive Technologies can sometimes fail to compact, which will prevent further development and lower the chances of live birth.

Our lab studies the mechanics of mammalian development, and more information can be found at https://institut-curie.org/team/maitre.

­—Ludmilla de Plater, Julie Firmin, and Jean-Léon Maître