aspirateComing face to face with a powerful alligator might scare the living daylights out of most people, but Michelle Milinkovic I think they are beautiful. Milinkovitch, a biophysicist at the University of Geneva, studies the development and evolution of vertebrate skin in crocodiles, with a focus on the biomechanics of scale growth and evolution. In 2012, he and his team discovered that: scales of crocodile head Although they are generated through physical processes rather than regulated by genetic drivers, the exact mechanisms of their development have been unclear.1
Michel Milinkovitch, a biophysicist at the University of Geneva, studies the development of vertebrate skin using unconventional models: crocodiles.
Gregory Loichot, University of Geneva
now, new researchMilinkovitch and his team reported that polygonal head scales form due to growth and compression of the skin, creating a self-organized pattern of wrinkles.2 The results of this study are nature, We reveal a simple evolutionary mechanism for changes in scale shape and size seen in various crocodile species.
Most vertebrate skin appendages (fur, feathers, scales) develop in patterns determined by the interaction of functionally opposing molecules. This creates spots of high protein concentration interspersed with areas of low protein concentration, regulating the growth of precursors from which skin appendages can grow. The scales on a crocodile’s body develop through this mechanism. about 10 years agoMilinkovitch discovered that the scales of a reptile’s jaw and face are different from the scales of its body. He speculated that mechanical processes may underlie its formation.
Testing this theory was a long and arduous journey. This is because accessing crocodiles for experiments is not easy. It took the team more than 10 years to gather a sufficient number of animals. In the new study, researchers first examined how head scales develop in embryos. They imaged Nile crocodile embryos using light-sheet fluorescence microscopy over several days. What they observed was that long, rectangular scales appeared on the upper jaw, while smaller, polygonal scales appeared on the sides and bottom of the jaw. The team also found that as the embryos grew and more scales formed, the stiffness of the skin and the number of wrinkles increased.
Like other vertebrates, the skin is connected to additional layers underneath, such as connective tissue, muscle, and bone. Milinkovic hypothesized that if the skin grew faster and became stiffer than the underlying tissue, it would bend and fold inward. To investigate this theory, he and his colleagues injected epidermal growth factor (EGF), a protein that stimulates skin growth, into crocodile embryos and watched what happened to their head scales. These embryos showed a greater number of thin scales on the upper jaw, while the scales on the underside of the jaw displayed a maze-like pattern, showing that the skin folds more inward as its stiffness increases. The researchers hatched some EGF-treated embryos to see if the temporary increase in skin growth had lasting effects. This crocodile’s head scales were somewhere between partially polygonal and labyrinth-shaped, and were similar in shape and size to the scales of another species, the caiman crocodile. The team also hatched some embryos that had been injected with EGF for long periods of time and observed that these crocodiles had only labyrinth-like scales.
Using light-sheet fluorescence microscopy, the researchers discovered that, unlike the scales on the crocodile’s body, the growth and physical properties of the skin drive the formation of scales on the crocodile’s head.
Grigorii Timin & Michel Milinkovitch, University of Geneva
To investigate whether skin growth and stiffness also play a role in the development of head scales in other crocodile species, Milinkovic created a computer model that allowed input of growth, physical properties, and location parameters of the tissue layers of the crocodile’s head. We test whether scale output is similar to patterns observed in other wild species. This model faithfully mimicked the development of the head scale pattern of the Nile crocodile and the labyrinth scales of EGF-treated embryos and juveniles. The researchers also adjusted the mechanical properties of the skin in their models and observed head scale patterns in marsh crocodile, spectacled caiman, and American alligator species.
“These computer simulations show that tissue dynamics can easily explain the variation in the morphology of specific anatomical structures in different species without involving complex molecular and genetic factors,” he said. Ebrahim Jahanbakhshis a computer engineer at the University of Geneva and a co-author of the study. press release.
