GFP-GABARAP, but little LC3, is enriched in the axonal initial segments of neurons.

(A–L) Distribution patterns of GFP-GABARAP (green) and endogenous LC3 (red) in the pyramidal neurons of the CA1 region of the hippocampus (A–D) and cerebellar Purkinje cells (E–L) of GFP-GABARAP transgenic mice. Boxed areas in E–H are enlarged and shown in I-L. Nuclei were stained with DAPI (blue). Immunopositive signals for GFP and LC3 co-localized in the dendrites of hippocampal pyramidal and cerebellar Purkinje cells located in the stratum radiatum (sr) and the molecular layer (m), respectively (arrowheads). Intense immunopositivity for GFP, but not for LC3, was present along the axonal initial segments of these neurons (arrows). (M–P) Fluorescence intensity of GFP (M, O) and LC3 (N, P) immunoreactivity in the somata (S), dendrites (D) and axon initial segments (A) of pyramidal neurons in the hippocampus (Hp) (M, N) and Purkinje cells in the cerebellum (Cb) (O, P). Intensities are normalized relative to those of somata. Vertical bars represent means ± SEMs (n = 10 and 7 for hippocampal neurons and cerebellar Purkinje cells, respectively). Both in the hippocampal neurons and cerebellar Purkinje cells, the intensity of GFP immunoreactivity was highest in the axonal initial segments, whereas the highest immunoreactivity for LC3 was detected in the dendrites (*P<0.01, one-way ANOVA followed by Tukey's post hoc test). The intensity of LC3 immunoreactivity in the axon initial segments was almost negligible. Abbreviations: so, stratum oriens; sp, stratum pyramidale; p, Purkinje cell layer; g, granular cell layer. Bars indicate 30 µm in (A–H) and 60 µm in (I–L).