TY - BOOK

T1 - Characterization of membrane protein trafficking and cellular signaling at the primary cilium

T2 - implications for cardiomyogenesis

AU - Mogensen, Johanne Bay

PY - 2016

Y1 - 2016

N2 - Primary cilia are microtubule-based, non-motile, sensory organelles emerging in a single copyfrom the surface of most quiescent cells in vertebrates. They emanate from the centrosomalmother centriole and are assembled and maintained by a bidirectional transport process termedintraflagellar transport. Specific receptors, ion channels and downstream signaling componentsare localized along the cilium-centrosome axis, enabling the cilium to function as a hot spot forthe balanced coordination of multiple signaling pathways to control cell cycle entry,differentiation and migration during embryonic development and in tissue homeostasis.Consequently defects in ciliary assembly and/or sensory function lead to a plethora of diseasesand syndromic disorders termed ciliopathies, which include congenital heart defects, skeletaldysplasias, retinal degeneration, renal disease, cerebral anomalies, diabetes and tumorigenesis. Aspecialized gate at the proximal end of the cilium, the transition zone, maintains the specificciliary protein composition as well as a specialized membrane lipid structure.This dissertation includes two reviews on ciliary signaling (articles I and II) as well as twooriginal articles (articles III and IV), which focuses on two specific signaling systems,conducted via the primary cilium; the Sonic hedgehog (SHH) and the Transforming growthfactor β (TGFβ) signaling pathways. In article III we show that the motor protein, KIF13B, viaits interaction with the transition zone protein NPHP4, is recruited to the ciliary base. Thecaveolae-enriched protein Caveolin-1 (CAV1) is concentrated at the transition zone of the ciliumand depletion of KIF13B or NPHP4 dramatically alter this localization. In the absence of thisspecialized CAV1 microdomain, SHH-induced ciliary accumulation of Smoothened (SMO) andtranscriptional of expression of GLI1 is impaired. We conclude that KIF13B and NPHP4 inconcert establish a CAV1 rich membrane microdomain at the transition zone in primary cilia toregulate SHH signaling. In article IV we show that Tak1 and Tab2, two modulators of noncanonicalTGFβ signaling operating through the NFκB pathway, localize to the primary cilium.Previous studies showed that mutations in TAB2 and TGFβ receptors lead to congenital heartdisease, and we here demonstrate that Tab2 is upregulated during in vitro cardiomyogenesis andrequired for proper differentiation of mouse stem cells into cardiomyocytes. These resultssupport the conclusion that Tab2 functions at the primary cilium to coordinate specifiedsignaling events, which when defective may lead to congenital heart diseaseCollectively, the results presented in this PhD thesis provide new insights into the currentunderstanding of the mechanisms underlying ciliary signal transduction. Further elucidation ofthis topic may contribute to knowledge leading to prevention and new therapeutic treatmentopportunities against ciliopathies

AB - Primary cilia are microtubule-based, non-motile, sensory organelles emerging in a single copyfrom the surface of most quiescent cells in vertebrates. They emanate from the centrosomalmother centriole and are assembled and maintained by a bidirectional transport process termedintraflagellar transport. Specific receptors, ion channels and downstream signaling componentsare localized along the cilium-centrosome axis, enabling the cilium to function as a hot spot forthe balanced coordination of multiple signaling pathways to control cell cycle entry,differentiation and migration during embryonic development and in tissue homeostasis.Consequently defects in ciliary assembly and/or sensory function lead to a plethora of diseasesand syndromic disorders termed ciliopathies, which include congenital heart defects, skeletaldysplasias, retinal degeneration, renal disease, cerebral anomalies, diabetes and tumorigenesis. Aspecialized gate at the proximal end of the cilium, the transition zone, maintains the specificciliary protein composition as well as a specialized membrane lipid structure.This dissertation includes two reviews on ciliary signaling (articles I and II) as well as twooriginal articles (articles III and IV), which focuses on two specific signaling systems,conducted via the primary cilium; the Sonic hedgehog (SHH) and the Transforming growthfactor β (TGFβ) signaling pathways. In article III we show that the motor protein, KIF13B, viaits interaction with the transition zone protein NPHP4, is recruited to the ciliary base. Thecaveolae-enriched protein Caveolin-1 (CAV1) is concentrated at the transition zone of the ciliumand depletion of KIF13B or NPHP4 dramatically alter this localization. In the absence of thisspecialized CAV1 microdomain, SHH-induced ciliary accumulation of Smoothened (SMO) andtranscriptional of expression of GLI1 is impaired. We conclude that KIF13B and NPHP4 inconcert establish a CAV1 rich membrane microdomain at the transition zone in primary cilia toregulate SHH signaling. In article IV we show that Tak1 and Tab2, two modulators of noncanonicalTGFβ signaling operating through the NFκB pathway, localize to the primary cilium.Previous studies showed that mutations in TAB2 and TGFβ receptors lead to congenital heartdisease, and we here demonstrate that Tab2 is upregulated during in vitro cardiomyogenesis andrequired for proper differentiation of mouse stem cells into cardiomyocytes. These resultssupport the conclusion that Tab2 functions at the primary cilium to coordinate specifiedsignaling events, which when defective may lead to congenital heart diseaseCollectively, the results presented in this PhD thesis provide new insights into the currentunderstanding of the mechanisms underlying ciliary signal transduction. Further elucidation ofthis topic may contribute to knowledge leading to prevention and new therapeutic treatmentopportunities against ciliopathies

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122120723205763

M3 - Ph.D. thesis

BT - Characterization of membrane protein trafficking and cellular signaling at the primary cilium

PB - Department of Biology, Faculty of Science, University of Copenhagen

ER -