Primary cilia control hedgehog signaling during muscle differentiation and are deregulated in rhabdomyosarcoma

Abstract

The primary cilium acts as a cellular antenna, transducing diverse signaling pathways, and recent evidence suggests that primary cilia are important in development and cancer. However, a role for cilia in normal muscle development and rhabdomyosarcoma (RMS) has not been explored. Here we implicate primary cilia in proliferation, hedgehog (Hh) signaling, and differentiation of skeletal muscle cells. Cilia and Hh signaling are highly dynamic during the differentiation of myoblasts. We show that cilia are assembled during the initial stages of myogenic differentiation but disappear as cells progress through myogenesis, concomitant with the destruction of proteins critical for cilia assembly and shortly after the Hh effector, Gli3, leaves the cilium. Importantly, we show that ablation of primary cilia strongly suppresses Hh signaling and myogenic differentiation while enhancing proliferation. Interestingly, our data further indicate that both cilia assembly and Hh signaling are deregulated in RMS, and cilia respond to Hh ligand in certain subsets of RMS cells but not others. Together, these findings provide evidence for an essential role for both primary cilia assembly and disassembly in the control of Hh signaling and early differentiation in muscle cells. We suggest that the temporally orchestrated destruction of centrosomal and ciliary proteins is a necessary antecedent for removal of the primary cilium and cessation of Hh signaling during myogenic differentiation. Additionally, our results further stratify RMS populations and highlight cilia assembly and disassembly as potential RMS drug targets.centrosome | ciliogenesis | myotube

Cilium assembly and disassembly

“…Assembly of the primary cilium begins when cells exit the mitotic cycle in response to mitogen deprivation or differentiation cues, although certain differentiated cell lineages (including lymphocytes, hepatocytes, mature adipocytes and skeletal muscle) lack primary cilia 14–18 . Ciliation can be recapitulated in cell culture through serum withdrawal, and the use of mouse 3T3 fibroblasts and human retinal pigment epithelial (RPE1) cells 19–21 , in particular, has been instrumental for the analysis of factors required for cilium assembly.…”

Role for the IFT-A Complex in Selective Transport to the Primary Cilium

“…The primary cilium, an antenna-like structure protruding from the cell surface, is essential for multiple signaling pathways and development (Fu et al, 2014; Nozawa et al, 2013). The primary cilium is derived from centrosomes and is maintained by intraflagellar transport (IFT) particles, including two protein sub-complexes, IFT-A and IFT-B (Engel et al, 2012; Hao and Scholey, 2009).…”

The primary cilium undergoes dynamic size modifications during adipocyte differentiation of human adipose stem cells

“…Marion et al have shown that the cilium disappears during adipocyte differentiation [5]. More recently, Fu et al showed that the cilium disappears during myogenic differentiation [6].…”