How mammals get their fur?

A new study from the Milinkovitch‑Tzila laboratory, published in Proceedings of the National Academy of Sciences (PNAS), demonstrates how simple cellular interactions can generate the diverse spatial arrangements of mammalian hair follicles during embryonic development. 

The work revisits a classic 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 at regular distances from pre‑existing ones. This behavior has long been described by an “expansion–induction” rule, in which existing follicles inhibit nearby new ones as the skin expands. More recent data, however, suggest that skin‑appendage precursors (hairs, feathers, scales) emerge through self‑organizing interactions between epidermal and dermal tissues, consistent with a Turing‑type reaction‑diffusion system. 

In the present study, the authors show that chemotaxis—the directed movement of cells toward chemical cues—dominates this pattern‑forming process. Using numerical simulations, mathematical analysis, and comparisons with experimental developmental data, they demonstrate that: 

• A chemotaxis‑based model accurately reproduces the effective geometric rule observed in the laboratory mouse. 
• Applying the same framework to the spiny mouse (Acomys dimidiatus), which displays a strikingly regular hair‑follicle pattern with long‑range order, specific orientation, and anisotropies, the model remains successful. In this species, the pattern cannot be explained by an expansion‑induction mechanism; instead, it is recapitulated by an anisotropic chemotaxis model coupled with experimentally observed anisotropic skin growth.

These findings identify chemotaxis as a major component of the self‑organized hair‑follicle patterning process in mammals. The authors propose that variation in the chemotactic component of the reaction‑diffusion‑chemotaxis system may drive inter‑specific differences in hair‑follicle patterning, illustrating how simple cellular behaviours can produce complex and diverse tissue architectures across mammals. 

Read the full article in PNAS:

Chemotactic self‑organization captures the dynamics of mammalian hair follicle patterning 
Ibrahimi, Jahanbakhsh, Tzika & Milinkovitch
PNAS 123 (27): e2530407123, 2026. DOI: https://doi.org/10.1073/pnas.2530407123