February 20, 2015

Even the simplest and most elegant song or painting still has a complicated story behind it. That’s what I’m thinking about as I read about cilia today. Cilia are simple and beautiful, but the axonemal structure of cilia is far more complex than one might first appreciate. Today’s image is from a paper describing a protein required for one of the ciliary radial spokes. 

Motile cilia are structures on the surface of some microscopic organisms and certain types of cells, and function in locomotion or the movement of fluid over the cell. Inside each of these cilia is a microtubule-based axoneme structure—9 outer doublets of microtubules form a circle around a central microtubule pair, with radial spokes connecting the center pair with the outer microtubules. These radial spokes are important for regulating ciliary motility. The cilia of most species have three radial spokes, but these spokes are not identical to one another, suggesting that each spoke has a unique functional role. In a recent collaboration between the Nicastro and Gaertig labs, Vasudevan and colleagues found that the ciliary protein FAP206 likely serves as a microtubule docking protein for one of the radial spoke proteins (RS2) and dynein c. In the top images above, FAP206-GFP can be seen exclusively in the cilia of interphase (left) and dividing (right) Tetrahymena cells. In the absence of FAP26, the axoneme lacked proper assembly of the radial spoke RS2. Cryo-electron tomography images (bottom) show a wild-type axoneme (left), with RS2 connecting to the A-tubule of an outer microtubule doublet, compared to an axoneme lacking FAP206, which lacks RS2 (right, arrowhead).

Vasudevan, K., Song, K., Alford, L., Sale, W., Dymek, E., Smith, E., Hennessey, T., Joachimiak, E., Urbanska, P., Wloga, D., Dentler, W., Nicastro, D., & Gaertig, J. (2014). FAP206 is a microtubule-docking adapter for ciliary radial spoke 2 and dynein c Molecular Biology of the Cell, 26 (4), 696-710 DOI: 10.1091/mbc.E14-11-1506

March 1, 2013

There are a handful of major signaling modules in development, and I’m fascinated every time a paper comes out showing a new role for one of these pathways, or how multiple pathways interact.  I admire the resourcefulness of cells in using a limited number of proteins to get an unlimited number of things done.  Today’s image is from a paper showing the role of PCP signaling in primary cilia assembly.

The PCP (polar cell polarity) signaling pathway is important in establishing cell polarity throughout development.  PCP signaling has also been linked to the formation and function of cilia, microtubule-based organelles, and a recent study investigates the mechanism between the two.  Primary cilia are solitary cilia that reside on most vertebrate cells and function in signaling, and Zilber and colleagues found that Fuzzy, a PCP signaling effector protein, is involved in primary cilium formation.  Fuzzy localizes to the basal body of cilia, and is necessary to drive Golgi-derived vesicles to the primary cilium.  Fuzzy regulates the localization of Dishevelled, a core PCP protein, to the basal body, and without Fuzzy, PCP signaling is inhibited (while activating the canonical Wnt pathway).  The images above show migrating mammalian cells at the edge of a wound in control (left) and Fuzzy mutant cells (right).  Wound-healing is controlled by PCP signaling in vertebrates, but the role of Fuzzy was unknown.  In control cells, the Golgi network (green) is polarized in front of the nucleus in most migrating cells.  In Fuzzy mutants, the Golgi network is oriented randomly in most cells (asterisks), and cell migration covered less of the initial wound area than in control cells (direction of migration indicated by white arrow).

Zilber, Y., Babayeva, S., Seo, J., Liu, J., Mootin, S., & Torban, E. (2013). The PCP effector Fuzzy controls cilial assembly and signaling by recruiting Rab8 and Dishevelled to the primary cilium Molecular Biology of the Cell, 24 (5), 555-565 DOI: 10.1091/mbc.E12-06-0437

November 30, 2012

I didn’t pay enough attention to primary cilia in my earlier years, and that is one of life’s big regrets (well, regret is a strong word). They are very fascinating little sensory organelles, and the thought of primary cilia carrying the weight of neuron migration on their little basal body shoulders is impressive. Check out today’s image, from a paper showing the role of primary cilia in brain development.

Neurons are frequently born far from their final home in the brain, and this migration is key to healthy nervous system development and function. A recent paper shows the importance of primary cilia in the migration of interneurons (neurons that connect one neuron to another) in the cerebral cortex. Primary cilia are microtubule-based sensory organelles that project out of a cell’s membrane. Higginbotham and colleagues imaged migrating interneurons in the developing cerebral cortex and found a correlation between primary cilia dynamics and interneuron mobility. This process requires the ciliary protein Arl13b, a GTPase in the Arf/Arl family. Arl13b ensures correct localization and movement of guidance cue receptors in primary cilia. In the images above, interneurons (green chamber in cartoon, green cells in images) migrate along tracks toward a signal secreted by dorsal cortical cells (blue chamber in cartoon). The migration of Arl13b mutant interneurons (right panel) was drastically reduced when compared to control interneurons (left, same scale).

Higginbotham, H., Eom, T., Mariani, L., Bachleda, A., Hirt, J., Gukassyan, V., Cusack, C., Lai, C., Caspary, T., & Anton, E. (2012). Arl13b in Primary Cilia Regulates the Migration and Placement of Interneurons in the Developing Cerebral Cortex Developmental Cell, 23 (5), 925-938 DOI: 10.1016/j.devcel.2012.09.019
Copyright ©2012 Elsevier Ltd. All rights reserved.

August 16, 2012

One of the most fascinating and terrifying things about human health is how a single mutation in a single gene can cause such dramatic disorders and diseases. A person may have a lifetime of adjustments that their disorder or handicap requires, a constant looking-over-your-shoulder for that increased cancer risk (BRCA, I’m looking at you), or far worse. One mutation can affect one small part of a cell that, in no small way, affects everything. Today’s image is from a paper on primary cilia, and discusses applications of the research into understanding human ciliopathies.

Cilia are microtubule-based protrusions that function in sweeping material across a tissue (motile cilia) or as sensory orgnanelles (primary cilia). The link between several disorders and ciliary defects has driven more research towards understanding how cilia are formed and how they function. Specifically, certain disorders that cause blindness result from defective or dying photoreceptor cells in the retina, which have the largest primary cilia found in mammals—rod and cone photoreceptors. In a recent paper, Zhang and colleagues identified the roles of a novel protein, Ttc26, in ciliogenesis. Zebrafish with reduced levels of Ttc26 had ciliary defects both in kidneys and photoreceptor cells. Without Ttc26, cells produced cilia that were short and defective. In the images above of rat photoreceptor cells (green), Ttc26 (red) is seen in the transition zone of cilia. Zhang and colleagues suggest that based on the importance of Ttc26 in ciliogenesis, patients with ciliary disorders should be screened for ttc26 gene mutations.

Zhang Q, Liu Q, Austin C, Drummond I, & Pierce EA (2012). Knockdown of ttc26 disrupts ciliogenesis of the photoreceptor cells and the pronephros in zebrafish. Molecular biology of the cell, 23 (16), 3069-78 PMID: 22718903

March 19, 2012

If you are a scientist (trained or at heart) reading this blog, you are likely a tinkerer. As a kid, you likely pulled apart all of your toys to figure out how they worked—maybe it was your basic water gun, your Etch-a-Sketch, or poor Teddy Ruxpin. Most biologists still do this today, but without their parents yelling at them about it. Today’s image is from a study identifying the components of primary cilia, which starts out with enough tinkering around to yank the cilia off of cells.

Primary cilia are found on many cells and serve as antenna to extracellular signals. Primary cilia are typically found one to each cell, and are important for many processes. Defects in primary cilia can cause a range of diseases called ciliopathies (polycystic kidney disease, for example). A recent study resulted in the identification of the proteins of primary cilia from mouse kidney cells. In this paper, Ishikawa and colleagues used a calcium-shock method to isolate the cilia from the cells, as seen in the images above. Before shock treatment (top), primary cilia (green) are seen on each cell. After treatment (middle), the isolated cilia (bottom) can be then analyzed for protein identification. From the 195 proteins identified, about 75% were proteins also seen in motile cilia or specialized cilia. About 25% were proteins only found in primary cilia, and will likely provide new insights to primary cilia biology and ciliopathies.

Ishikawa, H., Thompson, J., Yates, J., & Marshall, W. (2012). Proteomic Analysis of Mammalian Primary Cilia Current Biology, 22 (5), 414-419 DOI: 10.1016/j.cub.2012.01.031
Copyright ©2012 Elsevier Ltd. All rights reserved.

June 20, 2011

As you all vacation this summer at the beach, throw a “Thank you!” out to the sea urchins for their amazing contributions to cell and developmental biology research. Today’s image is from a paper showing a role for a major polarity protein in cilia formation in sea urchin embryos.

After a sea urchin’s initial stages of embryogenesis, it hatches out of its eggshell to become a swimming resident of the marine world. It swims using cilia, which beat to push water around. The cilia on this swimming embryo reside in the outer layer of epithelial cells, and emanate from basal bodies just below each cell’s surface. A recent paper shows a role for the polarity protein aPKC (atypical protein kinase C) in the formation of cilia in the sea urchin embryo. aPKC is a member of a protein complex important in asymmetric cell divisions, and Prulière and colleagues found that it has a very asymmetric localization during ciliogenesis. Images above show cilia (red) of sea urchin embryos in the absence (top left) or presence of an aPKC inhibitor. As the levels of the inhibitor increases (concentrations are indicated), the length of cilia decreases.

Pruliere, G., Cosson, J., Chevalier, S., Sardet, C., & Chenevert, J. (2011). Atypical protein kinase C controls sea urchin ciliogenesis Molecular Biology of the Cell, 22 (12), 2042-2053 DOI: 10.1091/mbc.E10-10-0844

April 28, 2011

The rods and cones in our retinas detect light. Thankfully, amazing cameras do the same and have captured images of these photoreceptor cells in today’s image.

The outer segments of photoreceptor cells are modified cilia that detect light at the back of the eye. Like the cilia in many other cell types, these outer segments can’t synthesize their own proteins but instead depend on transport of proteins from the cell body along ciliary microtubules. IFT proteins (intraflagellar transport) are important for this transport of material, and a recent paper describes the roles of the IFT20 protein in the retina. IFT20 is required for transport into the outer segments and is uniquely localized to the Golgi complex. Keady and colleagues conclude that IFT20 functions both as part of and independently of the typical IFT system. Images above show retinal sections of mice with normal IFT20 (top) and IFT20 mutated in cone cells (bottom). The lack of RG opsin (green) in IFT20 mutants indicates an absence of cone cells, while normal rhodopsin staining (red) indicates that rod cells are unaffected in mutants.

Keady, B., Le, Y., & Pazour, G. (2011). IFT20 is required for opsin trafficking and photoreceptor outer segment development Molecular Biology of the Cell, 22 (7), 921-930 DOI: 10.1091/mbc.E10-09-0792

April 14, 2011

Biologists understand how valuable all organisms are, but we each have our own favorites. To a cell biologist studying basal bodies and cilia, Paramecium might be one of the most important organisms around. A recent paper looks at the role of a centriole duplication protein in Paramecium, and reminds us why this little protist is important.

Paramecium tetraurelia is frequently used in studies looking at basal body duplication for a very significant reason—they are covered in cilia. Basal bodies are short structures found at the base of cilia that anchor the cilia to the cell. Basal bodies are related to centrioles, which are found at the center of microtubule-organizing centrosomes. A recent paper describes results showing the roles of Sas4, a centriole duplication protein originally found in worms, in Paramecium. Gogendeau and colleagues found that Sas4 is similarly required for basal body duplication, with additional roles for Sas4 than found in other organisms. Images above show localization of Sas4 to basal bodies in a whole organism (left), with zoomed regions (right) providing a better view of basal bodies (top, red in merged) and Sas4 (middle, green in merged).

Gogendeau, D., Hurbain, I., Raposo, G., Cohen, J., Koll, F., & Basto, R. (2011). Sas-4 proteins are required during basal body duplication in Paramecium Molecular Biology of the Cell, 22 (7), 1035-1044 DOI: 10.1091/mbc.E10-11-0901

April 4, 2011

Cilia are found on nearly every cell in our bodies, and many genetic multi-system diseases are caused by defects in cilia formation and function. A recent paper describes the roles for several ciliary proteins, with fantastic images of cilia cross-sections to help tell the story.

Cilia are long microtubule-based organelles that project from cells, and nearly every cell has one single primary cilium that is important for sensory processes. Mutations that disrupt the formation and function of these primary cilia affect nearly all cell types and can cause a variety of different diseases. Despite the importance of primary cilia, the functions of many proteins involved weren’t completely understood. Thankfully, a recent paper describes the functions of eight cilia disease proteins that function at the cilia’s transition zone, a site adjacent to the cilia’s organizing center (called the basal body). Images above show cross sections of the transition zone of cilia from different genetic backgrounds. The wild-type (left) cilium has an ordered structure, with the important Y-links connecting microtubules and membrane. These Y-links are still present when one cilia disease gene called mks-6 is mutated (middle), but these Y-links are not present when two cilia disease genes, mks-6 and nphp-4, are mutated at the same time (right).

Williams, C., Li, C., Kida, K., Inglis, P., Mohan, S., Semenec, L., Bialas, N., Stupay, R., Chen, N., Blacque, O., Yoder, B., & Leroux, M. (2011). MKS and NPHP modules cooperate to establish basal body/transition zone membrane associations and ciliary gate function during ciliogenesis originally published in The Journal of Cell Biology, 192 (6), 1023-1041 DOI: 10.1083/jcb.201012116

September 20, 2010

Cilia are beating hair-like projections protruding from the surface of some cells, and can function in propelling single-cell organisms or moving fluid over fields of cells with many cilia. The structure of cilia is precise and remarkable due to the arrangement of microtubules, the microtubule motor dynein, and associated proteins. Mutations in a protein called CEP290 cause cilia-related diseases in humans, and a recent paper uses the flagella, structures similar to cilia, of the single cell algae Chlamydomonas reinhardtii to understand the role of CEP290 in ciliary function. Image above shows a cross-section of the transition zone at the base of the flagella in normal or cep290 mutant cells. While the normal cells had Y-shaped connectors joining the microtubules to the flagellar membrane (arrowheads), the mutant cells did not.

Reference: Branch Craige, Che-Chia Tsao, Dennis R. Diener, Yuqing Hou, Karl-Ferdinand Lechtreck, Joel L. Rosenbaum, and George B. Witman, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201006105. Paper can be found here.

July 12, 2010

Cilia are microtubule-based cellular protrusions, and there are two types – motile and non-motile. Non-motile, or “primary,” cilia function in sensory reception and signaling. This signaling role of primary cilia means that signaling receptors must be sorted to their elongated plasma membrane. A recent paper shows the ability of a complex of proteins called the BBSome to assemble a coat complex that can transport and sort membrane proteins to cilia. Image above is of artificial vesicles called liposomes mixed with members of the BBSome, and the arrowheads are pointing to surfaces coated with the BBSome complex.

Reference: Hua Jin, Susan Roehl White, Toshinobu Shida, Stefan Schulz, Mike Aguiar, Steven P. Gygi, J. Fernando Bazan and Maxence V. Nachury. Cell 141, 1208-1219. ©2010 Elsevier Ltd. All rights reserved. Paper can be found here.