In vitro detection of calretinin immunoreactivity in chicken embryo dorsal root ganglion neurons: a possible developmental marker.

Calretinin, a cytosolic calcium-binding protein, is widely expressed in mammalian and chicken neurons, including subpopulations of dorsal root ganglion neurons. In chicken embryo spinal ganglion cells, calretinin first appears on the 9th day of incubation. To determine whether the expression of this protein is maintained in vitro and depends on the developmental stage, dissociated dorsal root ganglion cultures from chick embryos at E6 and E10 (before or after establishing connections) were processed for calretinin immunohistochemistry. Cultured neurons from E6 embryos never showed calretinin immunoreactivity at any culture duration, whereas neurons from E10 embryos displayed strong immunostaining immediately after attaching to the culture dish. Quantitative evaluation revealed that the percentage of calretinin-positive neurons increased until day 3 in culture and afterwards declined in parallel the total cell number. These results indicate that primary sensory neurons express calretinin in vitro similarly as in vivo and the gene expression depends from the establishment of connections with peripheral targets.