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Uncovering the Mechanisms of Mammalian Nose Formation

A recent study led by researchers at the University of Geneva (UNIGE) has provided insights into the intricate patterns observed in the noses of various mammals, including dogs, ferrets, and cows. Utilizing advanced 3D imaging techniques and computer simulations, the team examined the embryonic development of these unique nasal structures. Their findings indicate that the differential growth of skin layers plays a crucial role in the emergence of polygonal grooves, supported mechanically by underlying blood vessels. This research represents a pioneering effort to describe this morphogenetic process, potentially illuminating the development of other blood vessel-related biological structures. The study has been published in the journal Current Biology.

Exploring Nature’s Patterns

The natural world showcases an array of fascinating shapes, each identifiable by specific coloration or three-dimensional configurations. For instance, zebras are known for their distinct stripes, while cheetahs are easily recognized by their spots. In addition to animal traits, natural formations like pine cones reveal unique spiral patterns. These striking designs result from different morphogenetic processes, which encompass the shaping and structuring that occurs during embryonic growth.

On one hand, morphogenesis can emerge from self-organizing chemical interactions, as outlined by Alan Turing’s reaction-diffusion theory. This model explains how certain chemical responses lead to patterns like stripes and spots in the skin of various species. Conversely, other biological shapes arise due to mechanical constraints, exemplified by the foldings in the human brain, where faster growth of the cortex leads to the formation of complex convolutions.

The Study of Life’s Complexity

Professor Michel Milinkovitch, who leads a research group in the Department of Genetics and Evolution at UNIGE, aims to unravel the developmental mechanisms that contribute to the vast complexity of life on Earth. He observes, “Identifying stunning patterns in living beings is straightforward; they surround us in our environment. Our current research shines a spotlight on the distinctive polygonal designs found in the noses of mammals like dogs, ferrets, and cows.”

Specifically, the rhinarium—exposed skin covering the nose—exhibits a polygonal pattern created by skin grooves. These grooves serve an essential function by maintaining moisture in the nose, facilitating the detection of pheromones and other scent molecules. The Geneva research team collaborated with institutions such as the Université Paris-Saclay, the École Nationale Vétérinaire d’Alfort, and the Institute of Neurosciences de San Juan de Alicante to gather embryonic samples from various mammals.

Advanced Imaging Techniques

The collected samples underwent analysis via light sheet fluorescence microscopy, a cutting-edge imaging method allowing for three-dimensional visualization of biological structures. The investigation revealed that as embryonic development progresses, dogs, cows, and ferrets all exhibit similar networks of epidermal folds that are accurately aligned with the rigid blood vessel structures found in the dermis, the deeper skin layer. Notably, researchers identified a pattern of faster proliferation in the epidermal cells compared to their dermal counterparts.

Blood Vessels: The Structural Framework

Building on these observations, scientists constructed a mathematical model to simulate tissue growth dynamics. This model considers the differential growth rates of the dermis and epidermis, their material stiffness, and crucially, the spatial presence of blood vessels in the dermis. “Our simulations indicate that the mechanical stress from rapid epidermal growth concentrates at the locations of the supporting blood vessels, acting like strong architectural pillars,” explains Paule Dagenais, a post-doctoral fellow at UNIGE and the first author of the study. “This pressure prompts the epidermis to bulge outward, resulting in dome-like formations that echo the structure of arches.”

Significantly, the positioning of the epidermal polygonal features appears to be dictated by the arrangement of the underlying dermal blood vessels. These vessels impose localized constraints as the epidermis expands, leading to the precise formation of grooves and raised structures. “This groundbreaking mechanism, which we term ‘mechanical positional information,’ is a new explanatory framework for understanding embryonic development, and we are optimistic it will shed light on the creation of additional biological forms associated with blood vessels,” concludes Milinkovitch.

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