Ribosomes and polyribosomes are present in the squid giant axon: An immunocytochemical study

Ribosomes and polyribosomes were detected by immune-electron microscopy in the giant axon and small axons of the squid using a polyclonal antibody aga inst rat brain ribosomes. The ribosomal fraction used as antigen was purifi ed by ultracentrifugation on a sucrose density gradient and shown to contai n ribosomar RNAs and native ribosomes. The polyclonal antibody raised in ra bbits reacted with at least ten proteins on immunoblots of purified rat bra in ribosomes as well as with a set of multiple ribosomal proteins prepared from the squid giant fiber lobe. Immunoreactions were performed on cryostat sections of the stellate nerve cut at a distance of more than 3 cm from th e stellate ganglion, using pre-embedding techniques. Ribosomes and polyribo somes were identified within the giant axon and small axons using electron microscopic methods, following binding of peroxidase-conjugated anti-rabbit IgG secondary antibody. Polysomes were more frequently localized in periph eral axoplasm, including the cortical layer of the giant axon, and were gen erally associated with unidentified cytoskeletal filaments or with dense ma trix material. The immunochemical demonstration of ribosomes and polyribosomes in the gian t axon and small axons of the squid confirms similar observations in the sq uid and the goldfish obtained with the method of electron spectroscopic ima ging, and strongly supports the view that a local system of protein synthes is is present in axons. The immunochemical method here described offers an alternative tool for the selective identification of ribosomes, and is like ly to prove of value in the analyses of other axonal systems. (C) 1999 IBRO . Published by Elsevier Science Ltd.