Developmental Timing of Hair Follicle and Dorsal Skin Innervation in Mice

The study investigated the developmental timing of hair follicle and dorsal skin innervation in C57BL/6 mice using immunofluorescence and neuronal markers. It found that skin innervation occurred in successive waves, starting at embryonic day 15 (E15) before hair follicle development. By embryonic day 16 (E16), nerve fibers were associated with developing hair follicles, and by embryonic day 18 (E18), additional nerve fibers formed around the isthmus and bulge region of stage 5 hair follicles. The innervation pattern observed in newly formed hair follicles at E18 and postnatal day 1 (P1) was similar to the first wave. Epidermal innervation peaked just before hair shaft penetration at postnatal day 5 (P5) and decreased afterward. The study concluded that the sequence of innervation closely correlated with hair follicle development, indicating an interdependence between neuronal and epithelial morphogenesis.