Subcellular distribution of patched and smoothened in the cerebellar neurons

The Sonic hedgehog (Shh) signaling pathway carries out a wide range of biological functions such as patterning of the embryonic neural tube and expansion of cerebellar granule cell precursors. We previously have found that the Shh signaling receptors, Patched1 (Ptch1) and Smoothened (Smo), are expressed in hippocampal neurons of developing and adult rats, suggesting the continued presence of Shh signaling in postmitotic, differentiated neurons. Here, we report that Ptch1 and Smo are present in the processes and growth cones of immature neurons in the developing cerebellum, and that, in the mature cerebellum, Ptch1 and Smo are expressed by several types of neurons including Purkinje cells, granule cells, and interneurons. Within these neurons, Ptch1 and Smo are predominantly localized in the postsynaptic side of the synapses, a distribution pattern similar to that found in hippocampal neurons. Our findings provide morphological evidence that Shh signaling events are not confined to neuronal precursors and are likely to have ongoing roles within the postmitotic neurons of the developing and adult cerebellum.