Calretinin and other CaBPs in the nervous system.

At least three CaBPs are abundant in various types of nerve cells: calbindin-D28, calretinin, and parvalbumin. The sequence of chick calretinin, from cDNA clones, is 60% homologous to that of chick calbindin. The genomic calretinin gene has also been partially sequenced. Calretinin is a protein of 29-30 kilodaltons. Antisera have been raised against beta-galactosidase-calretinin fusion proteins, and used to compare the distribution of calretinin with that of calbindin by two-colour immunofluorescence. Some sections have also been stained for parvalbumin. In chick brain and retina, the three proteins are largely in different neurons. Calbindin and calretinin are particularly abundant in some sensory nuclei, and co-expression is more common in peripheral sensory neurons. In rat brain, and in retinae of rat, cat, and salamander, some of the expression patterns are conserved, but some are not. In the chick embryonic retina, some cells show a transient phase of calbindin immunoreactivity during development.