Expression, but failing maturation of procholecystokinin in cerebellum

The cerebellum is the only region of the central nervous system which has been found to be devoid of cholecystokinin (CCK). The assays used, however, have been directed against the alpha-amidated C-terminus of fully processed CCK peptides. Using Northern blot analysis and a library of radioimmunoassays specific for different sequences of proCCK in combination with chromatography and enzyme cleavage, we have now examined the expression and processing of proCCK in fetal, neonatal and adult cerebellar tissue from man, pig and rat. In rat cerebellum CCK mRNA was present already in the fetal state. Two weeks after birth the concentrations declined. Also proCCK was found in significant concentrations in the fetal human and rat cerebellum (approximately 20 pmol/g); but already before birth the expression began to decrease towards low concentrations in adults. The adult porcine cerebellum contained 3.2 pmol proCCK and glycine-extended processing intermediates per gram (range less than 0.1-10.4 pmol/g), and 0.8 pmol carboxyamidated CCK per gram (range 0.1-4.1 pmol/g) varying in size from CCK-58 to CCK-5. For comparison, the adult porcine cerebral cortex contained 757 pmol carboxyamidated CCK/g, 20 pmol glycine-extended CCK/g and no proCCK. We conclude that cerebellum expresses proCCK with the highest level of expression in fetal life. In comparison with other regions of the brain, the maturation to transmitter-active, carboxyamidated CCK peptides is, however, attenuated in both fetal and adult cerebellar tissue.