EVALUATION OF RNAS PRESENT IN SYNAPTODENDROSOMES - DENDRITIC, GLIAL, AND NEURONAL CELL BODY CONTRIBUTION

''Synaptodendrosomes'' are subcellular fractions that contain pinched- off axon terminals and dendrites. These fractions are a potential sour ce of RNAs that are localized in dendrites. However, these fractions m ay also contain RNAs that are seen in situ in neuronal cell bodies and glia. To evaluate whether synaptodendrosomes could be used as a sourc e of dendritic RNA, we studied the RNA content of this fraction as com pared with RNA isolated from total forebrain and a cell body-enriched fraction. RNA was analyzed by gel electrophoresis, oligo-dT chromatogr aphy, and northern blot hybridization. RNA from synaptodendrosomes con tained a greater proportion of low-molecular-weight nonpolyadenylated RNAs. RNAs known to be present in dendrites (mRNA for the alpha subuni t of the calcium/calmodulin-dependent protein kinase II and the polyme rase III transcript BC1) were detected in synaptodendrosomes; RNAs tha t are restricted to neuronal and glial cell bodies (mRNAs for the 68-k Da neurofilament protein, 43-kDa growth-associated protein, beta-tubul in, and beta-actin) were present only at low levels. However, the mRNA for glial fibrillary acidic protein (seen in situ in glial cell bodie s and processes) was present at high levels in the synaptodendrosomes. These results support and extend previous studies indicating that a l imited subset of mRNAs is present in neuronal and astrocyte processes and reveal that both of these types of mRNAs are present in synaptoden drosomes. Thus, synaptodendrosomes may be useful as a source of dendri tic RNAs, but it will be necessary to develop strategies to subtract m RNAs present in astroglial processes.