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 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 patched (ptc), which encodes the Hh receptor. Two misregulated genes, intermediate filament-1 (if-1) and calamari (cali), 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 if-1 and cali in the neuropil near hh+ neurons. Planarian glia and their regulation by Hedgehog signaling present a novel tractable system for dissection of glia biology.
Highlights
The Hedgehog (Hh) signaling pathway has been implicated in numerous developmental processes across the Metazoa, including limb and midline development in vertebrates and segmentation in Drosophila (Ingham et al, 2011)
To identify roles of Hh signaling in planarian central nervous system (CNS) maintenance, we examined gene expression changes using RNA sequencing of cephalic ganglia following inhibition of hh, ptc, or a control sequence (C. elegans unc-22) not present in the planarian genome
Inhibition of hh does not result in loss of planarian glia 329 To determine whether if-1+/cali+ cells in the neuropil represent a glial subtype that requires constitutive Hh signaling for survival, we examined the persistence of IF-1 protein in hh(RNAi) 331 animals
Summary
The Hedgehog (Hh) signaling pathway has been implicated in numerous developmental processes across the Metazoa, including limb and midline development in vertebrates and segmentation in Drosophila (Ingham et al, 2011). About the role of Hh 30 signaling in the Lophotrochozoa, one of the three superphyla that comprise the Bilateria. Further study and comparison with representatives of the other two Bilaterian superphyla, the Deuterostomes and the Ecdysozoa, is required to understand the evolution of this signaling pathway and its roles in metazoan biology. Schmidtea mediterranea, is a model system for the study of stem cell biology, wound response, 35 and tissue patterning (Reddien et al, 2005a; Sanchez Alvarado and Newmark, 1999). Planarians are free-living platyhelminthes capable of regenerating essentially any lost tissue, a process involving the maintenance of a pluripotent stem cell population throughout adulthood (Morgan, 1898; Reddien, 2011; Reddien and Sánchez Alvarado, 2004; Wagner et al, 2011; Witchley et al., 2013). Inhibition of Hh signaling in planarians perturbs regeneration of the anteroposterior (AP)
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