Biological significance of dermal Merkel cells in development of cutaneous nerves in human fetal skin.

We detected epidermal Merkel cells in 12-week fetuses with monoclonal antibodies (MAb) against simple epithelium keratin and epithelial membrane antigen. In 15-week fetuses these Merkel cells began to descend into the dermis and expressed nerve growth factor receptors (NGF-R). At approximately the same time, cutaneous nerves, as detected with an MAb against neurofilaments, extended from the subcutaneous trunk and branched to form the subepidermal nerve plexus. The expression of NGF-R on dermal Merkel cells preceded their connection with immunoreactive small nerves. Initially, most of these fine nerve endings were directed towards dermal Merkel cells. In 23-week fetuses the subepidermal nerve plexus was well developed and immunoreactive dermal Merkel cells began to disappear. At all stage of fetal development the epidermal Merkel cells did not strongly express NGF-R. We postulate that dermal Merkel cells play an inductive and a promotional role in development of the cutaneous nerve plexus in the upper dermis.