Table 1.

Molecular characters of touch dome keratinocyte and Merkel cell.

Marker	Note	Ref
K18	A type I cytokeratin expressed by MCs. Usually expressed in single layer epithelial tissues with its partner K8.	(9)
K20	A type I cytokeratin expressed by MCs. K20+ MCs cells are negative for K17.	(25)
K8	At E15, K8 is restricted to scattered immature MCs in developing tylotrich follicles and the adjacent epidermis. By E16-E17, the K8+ MCs form a disc-shaped TD.	(21)
Math1/Atoh1	A basic helix-loop-helix transcription factor expressed by MCs and necessary for MC specification.	(17)
FM 1-43	Small fluorescent styryl dye taken up by MCs after systemic administration.	(17)
VGLUT2	Presynaptic protein. VGLUT2 immunoreactivity is most intense on the side of the MCs that abut sensory nerve terminals. The ionotropic receptor GluR2 that monitors glutamate release is also enriched in MCs.	(57)
Cav2.1	MCs have functional L-type and P/Q–type voltage-gated calcium channels.	(57)
Rab3c, SNAP25, piccolo, CCK8, synaptotagmin13, cholecystokinin 26-33, Synaptic vesicle protein	Among 362 MC-enriched transcripts, this list is confirmed by immunostaining. These features demonstrate that MCs are excitable cells.	(57)
Vasoactive intestinal peptide (VIP)	A neuropeptide hormone expressed by MCs. VIP can enhance keratinocyte proliferation and reduce inflammation.	(32, 38, 52)
Serotonin	A monoamine hormone expressed by MCs. Serotonin plays important roles in many biological process including neurotransmission, stress responses, and the regulation of inflammation.	(35, 36)
Sox2	All MCs express Sox2, a transcription factor expressed in adult stem cells that plays a crucial role in tissue regeneration in various organs.	(22)
CD200	A membrane glycoprotein expressed in TD KCs and MCs. CD200 attenuates inflammatory reactions and promotes immune tolerance.	(12, 58)
Tbc1d10c	Marks TD KCs.	(12)
K17	A type I cytokeratin. TD KCs prominently express K17 and show reduced K15 expression. K17 can regulate cutaneous inflammation.	(5, 55)