BIOTIN-CONTAINING PROTEINS OF THE INSECT NERVOUS-SYSTEM, A POTENTIAL SOURCE OF INTERFERENCE WITH IMMUNOCYTOCHEMICAL LOCALIZATION PROCEDURES

When the biotinylated Manduca sexta adipokinetic hormone gene was used as a probe for in situ hybridization, the intrinsic neurosecretory ce lls were stained with a biotin detection system that contained strepta vidin or avidin. Further experiments showed that the DNA probe was not necessary for staining these cells by streptavidin-alkaline phosphata se, and that they were not stained by alkaline phosphatase alone. Simi larly, the intrinsic neurosecretory cells were stained directly by str eptavidin conjugated to a fluorescent dye. Other parts of the central nervous system could also be stained with streptavidin-alkaline phosph atase but not as readily as the intrinsic neurosecretory cells of the corpora cardiaca. Further analysis demonstrated three biotin-containin g proteins in the intrinsic neurosecretory cells of the corpora cardia ca and in the brain. The most abundant of these proteins, when analyze d by sodium dodecyl sulfate polyacrylamide gel electrophoresis, was fo und to have a molecular weight of 130,000, which is the size of the su bunits of pyruvate carboxylase, a biotin-containing enzyme. The same p rotein was recognized by an antiserum against an insect pyruvate carbo xylase, indicating that this protein is probably pyruvate carboxylase. The results reported here indicate that the intrinsic neurosecretory cells of the corpora cardiaca may contain pyruvate carboxylase in a co ncentration higher that other cells of the central nervous system, We also note that caution is necessary to avoid false positive results if an avidin containing detection system is used for in situ hybridizati on or immunocytochemistry.