Fig. 2. Dendritic transport of microinjected BC1 RNA. Sympathetic neurons in culture were injected with the radiolabeledin vitro transcripts as follows (with the respective numbers of analyzed cells/dendrites given inparentheses). A, B, Full-length BC1 RNA (128/612). Cell bodies and dendrites (including medial and distal segments) of neurons injected with full-length BC1 RNA were labeled strongly.
Open arrows point to clusters of autoradiographic silver grains over some dendritic segments. C, D, Nuclear U4 RNA (33/154). No specific labeling was observed in medial or distal dendritic regions (arrowheads), whereas a low labeling signal was apparent in proximal regions of some dendrites. In such cases, scattering from the soma may also have contributed to the signal in proximal dendritic regions. E, F, A random irrelevant RNA (144 nt), generated from the polylinker sequence of plasmid pSL300 (27/122). As with U4 RNA, no specific labeling was evident in medial and distal dendritic regions. G, Full-length BC1 RNA, low-amount injection routine. Arrows indicate labeling in distal dendritic segments. Although the overall labeling signal was significantly lower than in A, the somatodendritic distribution of the injected RNA was the same. Curved arrow indicates a noninjected cell. H, U4 RNA, low-amount injection routine. No dendritic labeling was observed.I, Chimeric GFP-BC1 RNA (21/99); J, Nonchimeric GFP mRNA (16/71). The chimeric RNA was targeted to dendrites (arrows in I indicate labeling in distal dendritic regions), whereas the nonchimeric RNA was not (arrowheads in J indicate lack of labeling in dendrites). Curved arrow in Iindicates a noninjected cell. Equivalent results were obtained with BC1-bcd RNA and with bcd mRNA, respectively, and in experiments in the low-amount injection routine (data not shown). Microinjection of 35S-UTP (12/44 cells/dendrites analyzed) did not result in any significant dendritic labeling after 4 hr of incubation (data not shown). A, C, E, G-J, Dark-field optics; B, D, F, Nomarski (DIC) optics. Scale bar, 100 μm.