Gene expression profiling of planarian heads or cephalic ganglia after inhibition of Hedgehog signaling pathway genes by RNAi

Hedgehog signaling is critical for vertebrate central nervous system (CNS) development, but its role in CNS biology in other organisms is poorly characterized. In the planarian Schmidtea mediterranea, hedgehog (hh) is expressed in medial cephalic ganglia neurons, suggesting a possible role in CNS maintenance or regeneration. We performed RNA sequencing of planarian brain tissue following RNAi of hh and the gene encoding its receptor, patched (ptc). We identified two misregulated genes, intermediate filament-1 (if-1) and calamari (cali), that are expressed in a previously unidentified non-neural CNS cell type. These cells expressed orthologs of astrocyte-associated genes involved in neurotransmitter uptake and metabolism, and extended processes enveloping regions of high synapse concentration. We conclude these are glia-like cells (GLCs). Planarian GLCs exist in two compartments with gene expression programs distinguished by Hh signaling. Planarian GLCs and their regulation by Hedgehog signaling present a novel tractable system for dissection of glia biology.