Fig. 4. Testing NT-3/TrkC-dependent competition.
(A) β-Gal staining reports NT-3 expression patterns in a NT-3lacZneo/+ knock-in mouse (green).
Left: coronal section of the mouse medulla at postnatal day 7. FoxP2 staining labels inferior olive neurons (red). β-Gal is present in a subset of neurons in the inferior olive principal nucleus
(IOPr), but not in the medial or dorsal nuclei (IOM, IOD). Middle and right: At P7, β-Gal is enriched in granule cells of posterior folia. By P10, β-Gal is present in all folia. No signal was detectable in the external granular layer (EGL, bracket), which contains granule cell precursors. Likewise, no signal was detectable in Purkinje cells or the deep cerebellar nuclei (DCN, dashed line), the postsynaptic targets of Purkinje cells. (B) Schematic of a viral approach to test relative NT-3/TrkC signaling in dendrite morphogenesis. Viruses encoding either tdTomato (AAV-tdT) or a dominant negative TrkC together with GFP (AAV-trkCDN-2A-GFP) were co-injected into math1-Cre;NT-3flox/flox, math1-Cre;NT-3flox/+, or control math1-Cre mice at P1. tdT or GFP/TrkCDN-expressing Purkinje cells were analyzed 21–24 days post-injection. (C) Dendrite arbors of tdT or GFP/TrkCDN-expressing Purkinje cells. In math1-Cre;NT-3+/+ or math1-Cre;NT-3flox/+ mice, TrkCDN-expressing cells exhibited decreased arbor complexity much like MADM trkC−/− cells (Fig. 1). However, in math1-Cre;NT-3flox/flox animals, dendrite defects were rescued to WT levels. (D) Quantification of height deficiency index. * p<0.05, one-way ANOVA with Tukey’s multiple comparisons test. (E) Quantification of tdT and GFP/TrkCDN dendritic branch number (top) and cumulative length (bottom). Boxes indicate the mean (middle line) and 25–75% range, while whiskers indicate maximum and minimum values. ***p<0.001, two-way ANOVA with Sidak’s multiple comparisons test. Also see Table S1.