Growth of Nerve Fibers to Merkel Cells Observed in Co-Culture of Sensory Ganglia and Sinus Hair Follicles

Abstract

Merkel cells have long been assumed to exhibit a function of guiding sensory nerve fibers to the skin and hairs. However, there has been little experimental evidence that supports this hypothesis. In order to test this possibility, we performed co-culture of sinus hair follicles and sensory ganglia in a collagen gel, intending to examine how sensory nerve fibers grow to the Merkel cell-enriched regions of sinus hair follicles. During co-culture with a serum-free medium supplemented with NGF and NT3, nerve fibers from sensory ganglia grew in a manner making convergence to the superior enlargement of hair follicles at which Merkel cells were enriched. Live Merkel cells stained with FM1-43 dye were demonstrated to be present in co-culture preparations. The presence of Merkel cells in this region of hair follicles was also demonstrated by immunostaining against cytokeratin 20. Immunostaining of a co-culture preparation against synaptophysin I showed that the hair follicle was surrounded tightly with synaptophysin I-enriched newly grown sensory nerve fibers. We therefore considered that Merkel cells are likely to have a capability of attracting sensory nerve fibers.