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 25, 2011

Sometimes you read a sentence in a paper and it feels like Babe Ruth’s “called shot” in the 1932 World Series. There’s my favorite line from Watson and Crick’s 1953 Nature paper describing the DNA double helix:

It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.

While reading a recent paper on a new EM technique from Roger Tsien’s lab, I stopped in my tracks when I read the following:

MiniSOG may do for EM what Green Fluorescent Protein did for fluorescence microscopy.

The power of electron microscopy (EM) comes from its ability to visualize structures that are smaller than the limit of resolution in light microscopy. However, the EM techniques used for optimal visualization require such heavy-duty fixation that antibodies and gold particles, both used to label target proteins, can’t get very far in the cell. A recent paper introduces “miniSOG,” a very small protein that can be genetically fused to nearly any protein of interest. After illumination by blue light and fixation of a tissue, miniSOG generates singlet oxygen which results in the creation of a precipitate that can be clearly imaged at high resolution using EM. MiniSOG can also be visualized using fluorescent light microscopy techniques, allowing for correlative fluorescent AND EM visualization. Images above show the fluorescent and EM images of miniSOG being used to label different proteins, such as α-actinin (an actin cross-linker, top), histone 2B (a protein used for packaging DNA, middle), and mitochondria (bottom).

Shu, X., Lev-Ram, V., Deerinck, T., Qi, Y., Ramko, E., Davidson, M., Jin, Y., Ellisman, M., & Tsien, R. (2011). A Genetically Encoded Tag for Correlated Light and Electron Microscopy of Intact Cells, Tissues, and Organisms PLoS Biology, 9 (4) DOI: 10.1371/journal.pbio.1001041

April 21, 2011

I just couldn’t help myself…today’s image is taken from the same paper as Monday’s image. Such stunning high magnification images of microtubules are a testament to the amazing technology available to biologists and the talented microscopists taking the images.

As mentioned on Monday, a recent paper found that different levels of a specific tubulin isotype can affect microtubule behavior. Mammalian cells with increased levels of this isotype, called β5-tubulin, had many fragmented microtubules. After finding this, Bhattacharya and colleagues tested possible explanations for these fragments and found that in cells with increased β5-tubulin, microtubules frequently detached from centrosomes, which are microtubule organizing centers. As seen in the time-lapse series of images above, microtubules do detach from centrosomes (asterisk) in normal cells (arrows mark the minus ends of detached microtubules). However, the frequency of microtubule detachment increased more than ten-fold in cells with high β5-tubulin levels (bottom series of images).

Bhattacharya, R., Yang, H., & Cabral, F. (2011). Class V -tubulin alters dynamic instability and stimulates microtubule detachment from centrosomes Molecular Biology of the Cell, 22 (7), 1025-1034 DOI: 10.1091/mbc.E10-10-0822

April 18, 2011

It’s no secret, but I’ll say it anyway…I love microtubules. Really, several qualities of microtubules are ones we all inspire to have ourselves…dynamic, elegant, organized, photogenic, and essential. The image above is from a recent paper discussing how different tubulin isotypes may play bigger roles in microtubule behavior than once believed.

Microtubules are hollow tubes of linear protofilaments that are composed of α- and β-tubulin heterodimers. Most organisms have multiple isotypes of α- and β-tubulin, some of which are expressed in the same cells. It was not clear if some of these isotypes could be used interchangeably in the assembly and function of microtubules, but a recent paper describes how one specific β-tubulin isotype affects microtubule behavior. The altered dynamics of microtubules when this isotype, called β5-tubulin, is either overexpressed or reduced results in cell division defects. In seen in the images above, mammalian cells with too much β5-tubulin (left) had many short microtubules (arrowheads) and indicators of cell division defects (compare fragmented nucleus to neighboring cell’s nucleus). Cells with reduced levels of β5-tubulin (right) had normal looking microtubules despite defects in cell division.

Bhattacharya, R., Yang, H., & Cabral, F. (2011). Class V -tubulin alters dynamic instability and stimulates microtubule detachment from centrosomes Molecular Biology of the Cell, 22 (7), 1025-1034 DOI: 10.1091/mbc.E10-10-0822

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 11, 2011

Mitosis has always been near and dear to my heart, and there are enough proteins at the kinetochore to keep me fascinated for eternity. A recent study teases apart the roles of two proteins in mediating the attachment between microtubules and kinetochores.

Kinetochores are multi-protein complexes on chromosomes that serve as sites for microtubule attachment during mitosis. Other jobs of the kinetochore include relaying signals for mitotic progression and generating force that drives chromosome movement during anaphase. The Ndc80 complex is a group of proteins essential to providing stable microtubule-kinetochore interactions, and a recent paper adds to our understanding of two of these proteins, Hec1 (aka Ndc80) and Nuf2. Sundin and colleagues found that two specific domains of the Hec1 protein (the CH and tail domains, for those keeping track) are important for generating these stable microtubule-kinetochore attachments, while the CH domain of Nuf2 is not. Images above are of mitotic spindles in normal mammalian cells (top row) and Hec1 mutants (bottom two rows). Spindles with either of the domains in Hec1 mutated had many unaligned chromosomes (left column). Kinetochores (middle left, green in merged) and spindle microtubules (middle right, red in merged) can also be seen.

Sundin, L., Guimaraes, G., & DeLuca, J. (2011). The NDC80 complex proteins Nuf2 and Hec1 make distinct contributions to kinetochore-microtubule attachment in mitosis Molecular Biology of the Cell, 22 (6), 759-768 DOI: 10.1091/mbc.E10-08-0671

April 7, 2011

What do you have in common with a worm? A lot, and you should be thankful! The worm C. elegans is used as a model system that allows researchers to learn an amazing amount about the genetic pathways and development in many systems, including our own. Thankfully for HighMag, the worms are quite photogenic too.

Our germ line is the line of cells that are responsible for passing on our genetic material to the next generation. The germline is composed of gametes (eggs and sperm), as well as the cells that divide to give rise to gametes. The cytoplasm of germ cells contain special aggregates of proteins and RNA called germ granules, yet their formation and function are not completely understood. A recent paper was published describing work on the germ granules, called P-granules, in the nematode C. elegans. Updike and colleagues probe further into the comparison of P-granules to nuclear pores and provide new information on the roles of different P-granule proteins. Interestingly, P-granules establish a size-exclusion barrier and are held together by hydrophobic interactions, similar to nuclear pores. Images above show the germ lines of a wild-type worm (left) and a worm with decreased levels of the P-granule protein GLH-1 (right). Without normal levels of GLH-1, the P-granules (green) were not able to localize to the surface of the nuclei (blue).

Updike, D., Hachey, S., Kreher, J., & Strome, S. (2011). P granules extend the nuclear pore complex environment in the C. elegans germ line originally published in The Journal of Cell Biology, 192 (6), 939-948 DOI: 10.1083/jcb.201010104

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