treatment fails to induce dendritic differentiation in early RORa-deficient staggerer PCs in organotypic cultures. (A-D) PCs in organotypic cultures from wild-type (A,C) or RORα-deficient Rorasg/sg (B,D) P0 mice were revealed by CaBP immunolabeling after 7 DIV without T3 (A,B) or with 30 nM T3 (C,D). PCs from wild-type mice responded to T3 treatment: without T3, PCs were mostly in stage II (PCs with regressive-atrophic dendrites all around the soma) whereas they were in stages II, III (empty arrows) and IV (empty arrowheads) after 30 nM T3 treatment (C). PCs from Rorasg/sg mice were unresponsive to T3 treatment since they remain in stage I (fusiform PCs with long processes of bipolar shape) in the absence (B) or in the presence (D) of 30 nM T3 treatment. Note the bipolar or fusiform shape of the PCs with long processes but no dendritic arborization in (B,D). Scale bar = 20 μm.