The nerve-dependency of merkel cell proliferation in cultured human fetal glabrous skin

Merkel cells are thought to function as slowly adapting mechanoreceptors an d are known as targets for sensory nerves. However, the nerve-dependency of Merkel cells remains controversial. In this respect, some investigators ha ve found interregional differences between hairy and glabrous skin and othe rs have shown intraregional differences within denervated rat touch domes. Differences between species have also been reported. This study was performed to determine whether Merkel cells proliferate in v itro in the absence of the systemic factors, blood vessels and the intact n erves in human skin. Suspension organ culture was performed using fetal dig its to investigate their in vitro proliferation. Merkel cells and cutaneous nerves were identified using antibodies to cytokeratin 20 and protein gene product 9.5 (PGP 9.5), respectively. Fetal digits of 56-82 day gestational age were cultured in serum free medium in a high O-2 (45%) environment. Ti ssues were harvested before starting culture (D0) and 1,4,7,14, 28d after c ulture; Merkel cells were observed in the volar pads and dorsal nail matric es at DO. After 28d of suspension organ culture, digits looked healthy stru cturally and the number of Merkel cells had increased. However, PGP 9.5-imm unoreactive nerves were markedly diminished after 1 day of culture and almo st disappeared after 4 days. Merkel cell proliferation in vitro suggested that Merkel cell development i s probably nerve-independent in human fetal glabrous skin.