IFT is mediated by the bidirectional movement of large protein particles, referred to as the IFT trains, along a microtubule-based structure called the axoneme

IFT is mediated by the bidirectional movement of large protein particles, referred to as the IFT trains, along a microtubule-based structure called the axoneme. and GPCRs and IFT-B accumulation at the bulged tips. These observations demonstrate the distinct roles of the core and peripheral IFT-A subunits: IFT139 is dispensable for IFT-A assembly but essential for retrograde trafficking of IFT-A, IFT-B, and GPCRs; in contrast, IFT144 is essential intended for functional IFT-A assembly and ciliary entry of GPCRs but dispensable for anterograde IFT-B trafficking. Thus the data presented here demonstrate that the IFT-A complex mediates not only retrograde trafficking but also entry into cilia of GPCRs. == INTRODUCTION == Cilia are microtubule-based appendages projecting from the surfaces of various eukaryotic L,L-Dityrosine hydrochloride cells. Cilia play essential roles in sensing extracellular stimuli and transducing developmental signals, such as Hedgehog (Hh) signaling (Ishikawa and Marshall, 2011; Sung and Leroux, 2013). Therefore a L,L-Dityrosine hydrochloride number of proteins are specifically localized in cilia, such as some G-proteincoupled receptors L,L-Dityrosine hydrochloride (GPCRs) and ion channels. Defects in ciliary assembly and functions cause a variety of hereditary disorders, generally called ciliopathies, with a broad spectrum of symptoms, including retinal degeneration, polycystic kidney, morbid obesity, and brain and skeletal malformations (Schwartzet al., 2011; Madhivanan and Aguilar, 2014). These disorders include Joubert syndrome, nephronophthisis, Meckel syndrome, BardetBiedl syndrome, short-rib thoracic dysplasia (SRTD), and cranioectodermal dysplasia (CED); note that SRTD has phenotypic overlaps with CED. The assembly and maintenance of cilia by intraflagellar transport (IFT) were first demonstrated inChlamydomonas reinhardtii(Rosenbaum and Witman, 2002) and subsequently intensively studied L,L-Dityrosine hydrochloride in metazoans (Ishikawa and Marshall, 2011; Sung and Leroux, 2013). IFT is mediated by the bidirectional movement of large protein particles, referred to as the IFT trains, along a microtubule-based structure called the axoneme. The IFT train contains the IFT-B complex, which comprises 16 subunits and mediates anterograde trafficking from the ciliary base to the tip with the aid of kinesin-2 motor proteins, and the IFT-A complex, which comprises at least six subunits and mediates retrograde trafficking powered by dynein-2 (Ishikawa and Marshall, 2011; Taschneret al., 2012; Sung and Leroux, 2013; also see Figure7Klater in this article). We and others recently demonstrated the overall architecture of the IFT-B complex, which can be divided into the core subcomplex (composed of 10 subunits) and the peripheral subcomplex (composed of six subunits), which are connected by composite interactions involving the IFT38, IFT52, IFT57, and IFT88 subunits (Boldtet al., 2016; Katohet al., 2016; Taschneret al., 2016). == FIGURE 7: == IFT144-KO cells demonstrate defects in the ciliary localization of SSTR3 and MCHR1. Control RPE1 cells (A, F), theIFT139-KO cell lines 139-2-6 (B, G) and 139-2-8 (C, H), and theIFT144-KO cell lines 144-2-1 L,L-Dityrosine hydrochloride (D, I) and 144-2-5 (E, J) stably expressing SSTR3-EGFP (AE) or MCHR1-EGFP (FJ) were serum-starved intended for 24 h and double immunostained intended for Ac–tubulin (AJ) and -tubulin CALN (AJ). (AD) Merged images. Insets, enlarged images of the boxed regions. Scale bars, 10 m. (K) Schematic representation of the phenotypes of control, IFT139-KO, andIFT144-KO cells. In control cells, the IFT-A complex is required for ciliary entry of GPCRs and anterogradely trafficked along with the IFT-B complex. Then the IFT-B complex and GPCRs undergo IFT-Adependent retrograde trafficking. In the absence of IFT139 (IFT139), other IFT-A subunits can be assembled, mediate ciliary entry of GPCRs, and are anterogradely trafficked along with the IFT-B complex. However , the IFT139-deficient IFT-A complex cannot mediate retrograde trafficking. In the absence of IFT144 (IFT144), GPCRs cannot enter cilia because functional IFT-A complex cannot be formed. On the other hand, the IFT-B complex can be trafficked anterogradely, although it cannot undergo IFT-Adependent retrograde trafficking. In contrast, relatively little is known about the IFT-A.