Fig. 1. HuD protein colocalizes with tau mRNA in RNP granules. (A) Confocal image analysis of HuD protein localization in differentiated P19 cells. (a) Phase image of a differentiated P19 cell. (b) Expression of GFP-tau protein. (c) Staining with HuD antibodies. (d) In situ hybridization analysis with the GFP probe (which detects the transfected tau mRNA). (e) Merged confocal image of b, c and d (x2500 magnification). The solid arrowheads denote axons; empty arrowheads denote dendrites; and small solid curved arrowheads denote neuronal cell bodies. Bar, 10 µm. (B) Confocal merged image of a growth cone. An enlarged merged image from the growth cone of the cell shown in A. The merged staining includes the GFP-tau fluorescence (green), HuD immunostaining (cyan) and GFP in situ hybridization (red) to yield a white area of colocalization. Aggregation of tau granules is marked by a solid white arrowhead; free HuD protein (cyan) is marked by an asterisk. Bar, 1 µm (x20000 magnification).