The group of Michel Milinkovitch has recently published a study showing how hair follicle morphogenesis has been altered during the evolution of the spiny mouse (Acomys dimidiatus), resulting in a shift from ancestral hair follicles to enlarged asymmetrical spines.
Indeed, spiny mice have concave spines involved in avoidance of both predators and aggressive conspecifics. Individuals escape aggression thanks to the easy loss of spines, leaving the aggressor with a tuft of spines in its mouth.
This study shows that Acomys spines are large awl hairs that originate from enlarged placodes resulting in voluminous follicles.
Moreover, the off-centered dermal papilla generates two waves of anisotropic proliferation, first of the follicle posterior matrix, then of the anterior inner root sheath.
This study, performed by combining developmental biology and numerical modeling approaches, contributes to a better understanding of the evolutionary developmental mechanisms that generated the great diversity of skin appendages observed in mammals.