Neuronal properties in cultured ultimobranchial C cells of chick embryos: process outgrowth and expression of TuJ1 and enkephalin.

We have analyzed the neuronal properties in cultured ultimobranchial C cells isolated from embryonic chicks at different developmental stages (12--16 days of incubation) by immunohistochemistry and electron microscopy. The ultimobranchial glands mostly consist of C cell solids. In 13-day-old embryos, many C cells cultured for 7 days on laminin-coated slides extended long neurite-like processes, reaching 300 microm in length. Neuritic outgrowth of C cells was regulated developmentally and virtually unaffected by nerve growth factor (NGF). The cultured C cells expressed intense immunoreactivity for calcitonin and enkephalin. It was also confirmed by confocal laser-scanning microscopy that almost all C cells were intensely immunostained by both the calcitonin antiserum and the monoclonal antibody TuJ1, a neuron-specific marker. Scanning electron microscopy identified the outgrowth of long, branching neuritic processes emerging from C cell soma. The processes had numerous varicosities along their course and ended in growth cones. The C cells with processes were usually monopolar and less frequently bipolar or multipolar. Transmission electron microscopy revealed the presence of membrane-bounded secretory granules in the cultured C cells. The neuritic processes of C cells contained aggregations of microfilaments, intermediate filaments and microtubules arranged in parallel to the long axis. In addition, synaptic-like contacts showing desmosome-like membrane-thickenings and accumulations of small clear vesicles and dense-cored vesicles were formed between the endings of the processes and the surface of C cells. These results indicate that the C cells cultured from early chick embryos (12- and 13-day-old) maintain the neuronal characteristics for long periods in vitro.