Transient expression of calretinin during development of chick cerebellum. Comparison with calbindin-D28k.

Calcium ions play a critical role in neural development. Insights into the ontogeny of Ca2+ homeostasis were gained by investigating the developmental expression of two E-F hand calcium-binding proteins. Calretinin and calbindin were monitored through their immunoreactivity in the developing chick cerebellum (from E6 to E20). Calbindin was detected from E13 and in Purkinje cells only. Intensity of labelling increased with Purkinje cell development. Calretinin presented a transitory immunoreactivity between E11 and E20 in the internal granular cell layer. This cell layer contains cells which will differentiate into Golgi and granular cells which are calretinin-negative in adult chick cerebellum. Calretinin immunoreactivity presented a peak (both in number of cells and in intensity) at E15 and fell dramatically after E20 while calbindin immunoreactivity was restricted to the Purkinje cells and increased with the development of these cells.