EXPRESSION OF A LOW-MOLECULAR-WEIGHT (10 KDA) CALCIUM-BINDING PROTEININ GLIAL-CELLS OF THE BRAIN OF THE TROUT (TELEOSTEI)

Calcium-binding proteins of the EF-hand family are widely distributed in the vertebrate central nervous system. In the present study of the trout brain, immunocytochemistry with a monoclonal antibody against ch ick gut calbindin-28k and a polyclonal antibody against bovine S100 pr otein specifically stained ependymocytes and radial glia cells with id entical patterns. Western blot analysis of trout brain extracts with t he antibodies to S100 and calbindin stained the same low-molecular-wei ght (10 kDa) protein band. In rat brain extracts, however, the monoclo nal antibody to calbindin recognized a major protein band with molecul ar weight corresponding to that of calbindin-28k. This indicates that the trout protein is a new calcium-binding-like (calbindin-like) molec ule that is immunologically related to both S100 and calbindin. Immuno cytochemical studies of the trout brain using the antibodies to CaB an d S100 showed that ependymocytes were stained in most ventricular regi ons, except in a few specialized ependymal areas of the ventral telenc ephalon, epithalamus, hypothalamus (including the paraventricular orga n and saccus vasculosus) and brain stem. Immunocytochemistry also indi cated the presence of calbindin-like protein in radial glia cells of s everal regions of the brain (thalamus, pre tectal region, optic tectum , and rhombencephalon). Differences in immunoreactivity between neighb ouring ependymal areas suggest that this protein may be a useful marke r of different territories. All immunoreactive glial cells were nicoti n-adenin-dinucleotide-phosphate diaphorase-positive, although this enz ymohistochemical reaction is not specific for these glial cells since it reveals oligodendrocytes and some neurons. Immunoreactivity appears at different developmental stages in the different brain regions, wit h a broadly caudorostral gradient, suggesting that the expression of t his protein is developmentally regulated. Comparison of the distributi on of the calbindin-like protein with that of glial acidic fibrillary protein indicates that calbindin-like immunocytochemistry is a specifi c technique for revealing radial glia and ependymocytes in the trout.