Scientists revealed how skin decides where to grow hair

The arrangement of future hairs on the skin may be shaped by directed cell movement in response to chemical signals. Scientists from the University of Geneva demonstrated that a single mechanism can reproduce entirely different patterns of hair primordia in two species of rodents. The results of the study were published in the journal Proceedings of the National Academy of Sciences.

Long before birth, placodes form on the embryo's skin — tiny regions that eventually develop into fully formed hair follicles. In laboratory mice, new primordia appear in sequential waves, inserting themselves between already existing ones.

The classical explanation of this process attributes it to skin growth and the inhibition of new primordia formation near existing ones. However, this framework struggles to explain the more ordered patterns observed in other animals.

The researchers turned to chemotaxis — directed cell movement along a chemical gradient. In their mathematical model, motile dermal cells interacted with an attracting signal from the epidermis on a growing area of skin.

This mechanism accurately reproduced the pattern of sequential primordia emergence in the common house mouse. The scientists then decided to test the model on the spiny mouse Acomys dimidiatus, in which hair primordia are arranged in a particularly regular pattern with a clearly defined directionality.

To reproduce the second arrangement variant, it was sufficient to merely adjust the directionality of interactions and skin growth parameters in accordance with experimental data. Creating an entirely separate mechanism for each species was not required.

According to the authors of the study, the obtained result clearly demonstrates how local behavior of individual cells can give rise to the complex structure of an entire tissue.