By Deborah Grainger
The primary cilium acts as a sensory organelle that transfers information from the environment to the cell interior. Once thought of as an evolutionary artefact, this organelle is now understood to be crucial for regulating important cellular processes, including the cell cycle, cytoskeletal organization, intraflagellar transport and signaling pathways such as hedgehog, notch and canonical and non-canonical Wnt/planar call polarity (PCP) pathways. Proteintech has over 70 antibodies recognizing cilia-related proteins in its catalog. This article reviews a selection of these targeting proteins involved in cilia development, or ciliogenesis...
IFT88 (intraflagellar transport protein 88; also known as TG737 or TTC10) is a component of IFT particles required for cilium biogenesis. Along with other molecular motors and IFT particles, IFT88 helps mediate intraflagellar transport, an important process essential for the assembly and maintenance of both primary and motile cilia, and flagella, in many organisms. IFT88 also localizes to spindle poles during mitosis and is required for spindle orientation. Defects in IFT88 lead to polycystic kidney disease, characterized by progressive cyst development and bilaterally enlarged kidneys.
Proteintech’s polyclonal IFT88 antibody (13967-1-AP) has appeared in over 40 publications to date, recently appearing in Nature Cell Biology in June 2014. The paper looks at the role of another protein, Kif7, in mammalian Hedgehog (Hh) signaling and cilium tip organization, but utilizes anti‑IFT88 as a marker for cilium retraction along with acetylated tubulin in immunofluorescence staining; IFT88 signal outlines the original shape of the cilium, while acetylated tubulin marks the shrinking microtubules of the retreating cilium.
The Proteintech polyclonal IFT88 antibody was raised against the C-terminal region of human IFT88 and can detect endogenous levels of IFT88.
CP110, also named CCP110 or KIAA0419, is a 110 kDa centriolar protein, not to be confused with CEP110 (centriolin). CP110 positively regulates centriole duplication while restricting centriole elongation and ciliogenesis. It acts as a key negative regulator of ciliogenesis in collaboration with CEP97 by capping the mother centriole, thereby preventing cilia formation.
The Proteintech antibody anti-CP110 (12780-1-AP) has appeared in several publications since its first appearance in Nature Cell Biology in mid-2012. In this paper the authors describe CP110’s regulation by the microRNA miR-129-3p (M129). The Proteintech anti-CP110 antibody was utilized for Western blotting (WB) and immunofluorescence studies looking at the impact of blocking or upregulating M129 on ciliogenesis and cilia elongation. Cilia formation was inhibited when M129 levels were depleted, and, conversely, potently upregulated with M129 overexpression. Correspondingly, WB experiments showed that CP110 protein levels were depleted in the presence of overexpressed M129. Several other Proteintech antibodies were also used by the authors for this work, including those targeting housekeeping protein GAPDH (60004-1-Ig), the actin nucleation protein ARP2 (10922-1-AP) and actin binding LIM protein 1 (ABLIM1, 15129-1-AP).
ARL13B, (also named ARL2L1), is a small ciliary G protein of the Ras superfamily. Localized to cilia, it is required for cilium biogenesis as well as sonic hedgehog signaling and antibodies targeting ARL13B can be used to mark the cilium (PMID:22072986). Defects in ARL13B lead to Joubert syndrome (JBTS), an autosomal recessive disorder characterized by malformation of the cerebellum. Consequentially JBTS patients lack muscle control and tone, among other defects.
Proteintech’s anti-ARL13B antibody (17711-1-AP) has featured in 30 peer-reviewed publications to date, including one that further investigates its interaction with the phosphatase inositol polyphosphate-5-phosphatase E (INPP5E) – another JBTS-causing protein when mutated. Along with a C-terminal motif and prenylation signals, ciliary targeting of INPP5E is facilitated by ARL13B. ARL13B missense mutations that cause JBTS in humans disrupt the ARL13B–INPP5E interaction. The paper, which appeared in PNAS at the end of 2012, identifies several more centrosomal and ciliary proteins involved in ARL13B–INPP5E interactions, and found that this functional network of proteins is also involved in JBTS and the related ciliopathy nephronophthisis.
The acetylation of K40 on α-tubulin is a hallmark of stable microtubules, and anti-acetylated α‑tubulin (anti-ace tubulin) is the antibody of choice for researchers wishing to perform control immunofluorescence staining of stable cilia. The acetylated residue of α-tubulin is K40, which is catalyzed by α-tubulin acetyl-transferase (α-TAT).
Proteintech's anti-ace tubulin (K40) antibody (66200-1-Ig) can be used to reliably mark the cilium; as mentioned previously, it can also be used to gauge cilium retraction in tandem with IFT88.
No information is available regarding the specific function of Bardet–Biedl syndrome (BBS) protein 2, but it is known to be one of the seven BBS proteins that form the stable core of the BBSome. The BBSome is a component of the ciliary basal body and is integral to the formation of a functional primary cilium as mutations in BBS proteins, as well as several others, lead to their eponymous syndrome BBS. BBS is a heterogeneous, pleiotropic human disorder characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, hypogenitalism, and an increased incidence of diabetes and hypertension.
Proteintech’s BBS2 antibody (11188-2-AP) has appeared in several publications since its addition to the catalog. One of these appearances, in the Journal Cell, describes how the BBSome establishes an electron-rich coat complex that sorts membrane proteins to primary cilia, including the somatostatin receptor 3 (SSTR3) signaling molecule. The BBSome coat model suggested by the authors could explain the variety of symptoms found in BBS patients: likely resulting from the failure to transport signaling receptors to the cilium through the lack of a stable BBSome – though in the case of SSTR3, its exact role in BBS is unclear.