Hedgehog signaling regulates gene expression in planarian glia.

Abstract

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 <i>Schmidtea mediterranea, hedgehog (hh</i>) 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 <i>hh</i> and <i>patched (ptc)</i>, which encodes the Hh receptor. Two misregulated genes, <i>intermediate filament-1 (if-1</i>) and <i>calamari (cali</i>), were 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 propose that these cells are planarian glia. Planarian glia were distributed broadly, but only expressed <i>if-1</i> and <i>cali</i> in the neuropil near <i>hh</i>⁺ neurons. Planarian glia and their regulation by Hedgehog signaling present a novel tractable system for dissection of glia biology.