Dendritic transport of ID-chimeric α-tubulin mRNAs under basal conditions. Sympathetic neurons in primary culture (nonstimulated) were microinjected with chimeric reporter mRNAs as noted in the images. Chimeric mRNAs contained the α-tubulin protein-coding sequence, an ID element, and an A98 poly(A) tail, as indicated. (A–H) Photomicrographs show subcellular localization of injected RNAs. In this figure (and in most of the following figures showing photomicrographs), dark-field images are on the left, and corresponding phase-contrast photomicrographs are depicted on the right. RNA signal appears as white silver grains in dark-field photomicrographs. Chimeric mRNAs containing ID1 or ID2 elements (A–D) were targeted to distal dendritic domains, whereas chimeric mRNAs containing ID3 or ID4 elements (E–H) were not. Number of cells analyzed: (A and B) 12 neurons, 41 dendrites; (C and D) 15 neurons, 49 dendrites; (E and F) 21 neurons, 79 dendrites; (G and H) 17 neurons, 58 dendrites. Bar, 50 µm. (I) Quantitative analysis. One-way analysis of variance (ANOVA), Dunnett’s post hoc analysis (comparison of levels of ID1-chimeric α-tubulin mRNA with levels of other ID-chimeric α-tubulin mRNA forms): comparison with ID2-chimeric α-tubulin mRNA (C and D), P > 0.5 for interval points 50 µm; comparison with ID3-chimeric α-tubulin mRNA (E and F), P < 0.001 for all interval points; comparison with ID4-chimeric α-tubulin mRNA (G and H), P < 0.001 for all interval points. Quantitative data in this and the following figures are given in the format means ± SEM; error bars indicate SEM.