Primary Cilia as Switches in Brain Development and Cancer

Abstract

The primary cilium plays key roles in regulating the cell cycle. This specialized organelle grows from the basal body, a modified centriole that during mitosis functions as part of the centrosome organizing the mitotic spindle. The primary cilium is essential for neural stem cell specification and neural progenitor expansion. Growing evidence indicates that several brain tumors arise from progenitor or stem cells. Recent work has demonstrated that the primary cilium is a sensory organelle that concentrates receptors and second messenger components for the hedgehog (Hh) signaling pathway. Several types of cancers show oncogenic activation of Hh signaling, yet the role for primary cilia in cancer has only recently been addressed. Interestingly, the primary cilium appears to have dual and opposing roles in cancer; depending on the underlying oncogenic event, primary cilia can either promote or prevent tumor formation. Here, we suggest that primary cilia function as ON or OFF switches to regulate cell proliferation and as such could have important implications in the diagnosis and treatment of cancer.