Expression of the cholecystokinin gene in rat brain during development

The expression of the gene encoding for cholecystokinin (CCK) was studied pre- and postnatally in rat brain with a preproCCK-specific cDNA probe to quantitate mRNA. In addition, a C-terminal-specific radioimmunoassay was used to measure CCK-immunoreactive peptides. Poly(A)+-enriched RNA from rat brain was analyzed for the presence of CCK mRNA by agarose gel electrophoresis, followed by transfer to nitrocellulose and hybridization to a 32P-labeled CCK cDNA probe. An RNA of approximately 700 nucleotides was observed and there were no obvious CCK mRNA differences between samples taken at the different developmental stages. Brain preproCCK mRNA was detectable by embryonic day 14 and increased continuously until postnatal day 14 when it reached maximal concentrations. In young adult rats, levels were slightly decreased. CCK-immunoreactive peptides began to be detected in the samples from embryonic day 21, but marked development was seen only postnatally with a rapid increase occurring during the first 2 weeks after birth. The highest content of the peptide was present in young adult rats.