original version Of this story appeared in Quanta Magazine.
Sip a glass of wine and you will see liquid flowing continuously into the wet part of the glass. In 1855, James Thomson, brother of Lord Kelvin, explained philosophical magazine These “tears” or “feet” of the wine result from surface tension differences between the alcohol and water. Thomson wrote, “This fact provides an explanation of many very curious motions.” Little did they realize that the same effect, later named the Marangoni effect, could also shape fetal development.
In March, a group of biophysicists in France reported that the Marangoni effect is responsible for the critical moment when a homogeneous blob of cells grows and develops a head and tail axis—what will become the first defining features of the organism.
The discovery is part of a trend that rejects the norm in biology. Typically, biologists attempt to characterize growth, development, and other biological processes as the result of chemical signals generated by genetic instructions. But that picture often seems incomplete. Researchers are now appreciating the role of mechanical forces in biology: forces that push and pull tissues in response to their physical properties, driving growth and development in ways that genes cannot.
Modern imaging and measurement techniques have opened scientists’ eyes to these forces by bringing a flood of data to the field that invite mechanical explanations. “What has changed in the last decades is the possibility to actually see live, and to see the mechanics in terms of cell movement, cell rearrangement, tissue growth,” said Pierre-François Lane of Aix-Marseille University, one of the researchers behind the recent study.
The shift toward mechanical explanations has revived interest in pre-genetic models of biology. For example, in 1917 the Scottish biologist, mathematician and classics scholar D’Arcy Thompson published on development and formWhich highlighted the similarity between the shapes found in living organisms and those emerging in inanimate matter. Thompson wrote this book as an antidote to the excessive tendency to explain everything in terms of Darwinian natural selection. His thesis – that physics also shapes us – is coming back into vogue.
“The hypothesis is that physics and mechanics can help us understand biology at the tissue scale,” said Alexandre Kabala, a physicist and engineer at the University of Cambridge.
The task now is to understand the causal interplay, where genes and physics somehow work together to shape organisms.
go with the flow
Mechanical models of embryonic and tissue development are not new, but biologists have long lacked ways to test these ideas. It is difficult to see only the fetus; They are small and diffuse, scattering light in all directions like frosted glass. But new microscopy and image analysis techniques have opened a clearer window on evolution.
Lenne and his colleagues applied some new techniques to observe the movement of cells inside mouse gastruloids: bundles of stem cells that, as they grow, mimic the early stages of embryonic development.