A new study from the Milinkovitch-Tzika lab, published in PNAS, reveals how simple cellular interactions can generate the diverse spatial arrangements of mammalian hair follicles during embryonic development.
The article, revisits a classical question in developmental biology: how do new hair follicle precursors appear at specific positions in the growing skin?
In the laboratory mouse, new follicles form progressively and at regular distances from pre-existing ones. This behaviour has long been described by an “expansion–induction” rule, in which existing follicles prevent nearby new ones from forming as the skin expands. However, more recent developmental data suggest that skin appendage precursors—such as hairs, feathers, and scales—emerge through self-organizing interactions between epidermal and dermal tissues, establishing a Turing reaction-diffusion system.
Instead, our study shows that chemotaxis, the directed movement of cells toward chemical cues, dominates this patterning process. Using numerical simulations, mathematical analysis, and comparisons with experimental developmental data, we show first that a chemotaxis-based model reproduces the effective geometric rule observed in the laboratory mouse. Second, we apply the same framework to the spiny mouse, Acomys dimidiatus, which forms a strikingly regular hair follicle pattern with long-range order, specific orientation, and anisotropies. In this species, the pattern cannot be explained by an expansion–induction mechanism. On the other hand, it is recapitulated by our anisotropic chemotaxis model combined with experimentally observed anisotropic skin growth.
Together, these findings show that chemotaxis is a major component of the hair self-organized patterning process in mammals. Our analyses suggest that variation in the chemotactic component of the reaction-diffusion-chemotactic system may be a key driver of interspecific differences in hair follicle patterning, showing how simple cellular behaviours can produce complex and diverse tissue architectures across mammals.
Explore a 3D volumetric model of the spiny mouse embryo here, as well as the corresponding video here.
Read the article in PNAS:
Chemotactic self-organization captures the dynamics of mammalian hair follicle patterning
Ibrahimi, Jahanbakhsh, Tzika & Milinkovitch
PNAS, 123 (27) e2530407123, https://doi.org/10.1073/pnas.2530407123 (2026)