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Fig. 2 The centrosome occupies a progressively basal position during RB development. (A) Schematic showing how centrosome position (yellow circle) was measured relative to the apical-basal axis. (B) Quantification of average centrosome position and its distribution about the mean (± 2 s.e.m.) during stages of RB development. Mean percentages are: phase 0, 70.0±10.2% (n=13); phase I, 36.1±8.6% (n=12); phase II, 19.3±3.4% (n=14); phase III, 12.7±3.6% (n=11). A total of 36 neurons were analyzed in live zebrafish embryos. (C,D) RB neurons labeled by transient expression of TagRFP-CAAX in GFP-Xcentrin mRNA-expressing wild-type embryos. Images shown are z-projections and optical cross-sections through the centrosome-containing region (indicated with yellow hatch marks). (C) Centrosome position during central axon initiation (phase 0). The open arrowheads indicate central axons. z-projection and xy view show centrosome (yellow circle) localized apically in the cell body. (D) Centrosome position during peripheral extension (phase III). White arrowheads indicate central axons. The centrosome is localized basally, near the PAS (asterisk). Scale bars: 5 μm.