The whorls, arcs, and loops that make fingerprints unique are created during fetal development by waves of tiny ridges that form at the tip of the finger, widen, and then bump into each other a process similar to what gives a zebra its stripes or a cheetah’s spots.
The precise location of these areas and the collisions between waves provide a unique fingerprint pattern. “To come up with these different patterns of arcs, loops and whorls, the key is not just the molecular components,” says study co-author Denis Headon, a developmental biologist at the University of Edinburgh, UK. “It’s the way they’re fitted to the anatomy of the hand.”
Identification signs
Fingerprints are believed to provide greater grip and sensitivity to the fingertips, and their patterns have long been used to identify individuals and diagnose certain developmental conditions. Last year, Headon and colleagues published a paper2 describing the genes that influence fingerprint patterns, many of which are involved in limb development. These genes appeared to lay the groundwork for fingerprint formation, but many were inactive during the process, suggesting that they were not directly involved in ridge formation.
To learn more about fingerprint patterning, Headon and his colleagues looked at how fingerprints form during fetal development. Anatomical studies and analyzes of gene activity showed that the cells that make up the fingerprint ridges followed a developmental path that initially mimicked that of a hair follicle. But unlike the follicle’s pattern of gene activity, the ridge cells failed to incorporate cells deeper below the skin’s surface.
The analyzes supported the presence of a “Turing reaction-diffusion system” that can be created when a molecule that activates a developmental process stimulates both itself and an inhibitory molecule. The result is a self-organizing system that creates periodic patterns, says Marian Ros, a developmental biologist at the Institute of Biomedicine and Biotechnology of Cantabria in Santander, Spain.
The mathematics patterns
Such systems were proposed3 by the mathematician Alan Turing in 1952 as a chemical explanation of developmental processes, such as the arrangement of leaves on a plant or the tentacles on small aquatic organisms called hydras. Since then, the Turing reaction and diffusion mechanisms have been described as instrumental in producing a wide variety of familiar biological sights, including the brightly colored scales of some tropical fish and the feather patterns of birds.
To find the molecules that control fingertip patterning, Headon and his collaborators studied mouse toe ridges and human cells grown in 3D cultures. They found that a protein called WNT, which is important for the development of hair follicles, stimulates the formation of ridges. Another molecule, called BMP, inhibits them, forming a Turing reaction-diffusion system.
The ridges come from three areas: the tip of the finger; the middle of the fingertip; and the crease at the base of the fingertip where the finger bends (see “How fingerprints are patterned”). In the simulations, Headon and his team changed the timing, angle, and exact location of the wave origins at these three locations, creating arcs, loops, and whorls. “These waves collide,” says Cheng-Ming Chuong, a developmental biologist at the University of Southern California in Los Angeles. “And when they collide, they create turbulence that helps create the diversity of fingerprint patterns.”
The findings are a significant advance in our understanding of fingerprint patterning, says Ros. Chuong notes that past studies of skin ridges, like fingerprints, have tended to focus more on theoretical and modeling approaches than experimental data. But the latest study uses advances in cell culture techniques and other methods to advance the field: “Their work opens up the field,” says Chuong. “Now people can look more closely at these hidden patterns in our skin.”
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