Developmental origin of avian Merkel cells

We have investigated the developmental origin and ultrastructure of avian M erkel cells by electron microscopy and chick/quail transplantation experime nts. On embryonic day 3, chick leg primordia were homotopically grafted onto Jap anese quail host embryo. Fourteen days later, quail cells that had migrated into grafted chick legs were identified according to the masses of heteroc hromatin associated with the nucleolus that are characteristic for quail. B oth in chick and quail, Merkel cells are usually located in the dermis just below the epidermis. They are placed between nerve terminals either indivi dually or in small groups wrapped in sheaths that are formed by glial cell processes. Occasionally, some Merkel cells appear in nerve fascicles and wi thin Herbst corpuscles. Merkel cells, as well as glial cells, in grafted ch icken legs were of quail origin. This finding provides evidence against the epidermal origin of avian Merkel cells and indicates that Merkel cells are derived from neural crest cells that colonise, together with glial cells a nd melanocytes, the developing limb primordium.