Cilia

The Jackson Lab has a longstanding interest in understanding the biology and function of the primary cilium. This stems from our extensive work on interrogating cell cycle checkpoints and elucidating how the quiescence state is regulated. The primary cilium is a sensory, antenna-like organelle found on the apical surface of diverse cell types. It plays an integral and multifaceted role during development and in the adult, which is highlighted by a wide range of human genetic disorders called ciliopathies. These syndromes have underlying ciliary defects and present with a wide range of clinical manifestations, including obesity, polydactyly, retinal degeneration, mental retardation, anosmia, liver fibrosis, and kidney cysts. We have been very successful in identifying novel ciliary proteins and ciliary pathways by performing a combination of localization studies and tandem-affinity purification followed by mass spectrometry (LAP-preps) of known ciliopathy genes in a high-throughput manner¹. This approach has allowed us to build high-confidence ciliary protein networks that can be mapped onto specific regions of the primary cilium². By the tagging more known and newly identified ciliary/centrosomal protein, we are continually expanding our network of ciliary and centrosomal protein complexes and interactors, and uncovering novel ciliary regulatory and signaling pathways. 

Much of the lab’s effort has been in identifying and elucidating the function of pathways regulating entry and exit of proteins into the primary cilium. A gate at the base of the cilium separates the primary cilium from the plasma membrane and the cytoplasm. This barrier is absolutely necessary to create a distinct signaling microenvironment and mutations leading to alterations of the ciliary gate or regulated trafficking across the gate result in ciliopathies. We have uncovered numerous essential trafficking pathways using our proteomics approach followed by a wide array of biochemical, genetic, and molecular techniques, including the only two known complexes involved in trafficking of ciliary GPCRs, the BBSome³ and the Tubby-family of membrane phosphoinositide binding proteins⁴, the UNC119 pathway for trafficking of myristoylated proteins⁵, and the CEP19-RABL2 pathway for ciliary IFT injection⁶.

Another major area of the lab is identifying ciliary receptors. Most ciliary receptors identified to date are GPCRs⁷. Our lab has described several novel ciliary-localization sequences^8,9. This has resulted in the discovery of a number of ciliary GPCRs over the last few years, including a major novel Hedgehog signaling component, GPR161, and a hypothalamic ciliary GPCR, NPY2R, involved in feeding behavior. We are actively working to uncover more novel ciliary GPCRs and examine how localization of these GPCRs to the primary cilium enables their function. Currently, we are focusing on identifying ciliary receptors involved polycystic kidney disease, adipogenesis, and feeding behavior.

1               Torres, J. Z., Miller, J. J. & Jackson, P. K. High-throughput generation of tagged stable cell lines for proteomic analysis. Proteomics 9, 2888-2891, doi:10.1002/pmic.200800873 (2009).

2               Sang, L. et al. Mapping the NPHP-JBTS-MKS protein network reveals ciliopathy disease genes and pathways. Cell 145, 513-528, doi:10.1016/j.cell.2011.04.019 (2011).

3               Nachury, M. V. et al. A core complex of BBS proteins cooperates with the GTPase Rab8 to promote ciliary membrane biogenesis. Cell 129, 1201-1213, doi:10.1016/j.cell.2007.03.053 (2007).

4               Mukhopadhyay, S. et al. TULP3 bridges the IFT-A complex and membrane phosphoinositides to promote trafficking of G protein-coupled receptors into primary cilia. Genes & development 24, 2180-2193, doi:10.1101/gad.1966210 (2010).

5               Wright, K. J. et al. An ARL3-UNC119-RP2 GTPase cycle targets myristoylated NPHP3 to the primary cilium. Genes & development 25, 2347-2360, doi:10.1101/gad.173443.111 (2011).

6               Kanie, T. et al. The CEP19-RABL2 GTPase Complex Binds IFT-B to Initiate Intraflagellar Transport at the Ciliary Base. Developmental cell, doi:10.1016/j.devcel.2017.05.016 (2017).

7               Hilgendorf, K. I., Johnson, C. T. & Jackson, P. K. The primary cilium as a cellular receiver: organizing ciliary GPCR signaling. Current opinion in cell biology 39, 84-92, doi:10.1016/j.ceb.2016.02.008 (2016).

8               Mukhopadhyay, S. et al. The ciliary G-protein-coupled receptor Gpr161 negatively regulates the Sonic hedgehog pathway via cAMP signaling. Cell 152, 210-223, doi:10.1016/j.cell.2012.12.026 (2013).

9               Loktev, A. V. & Jackson, P. K. Neuropeptide Y family receptors traffic via the Bardet-Biedl syndrome pathway to signal in neuronal primary cilia. Cell reports 5, 1316-1329, doi:10.1016/j.celrep.2013.11.011 (2013).