July 30, 2012

It may appear that chromosomes are just floating around inside of the nucleus, but that couldn’t be further from the truth. Inside that double membrane of the nucleus is a lot of chromosome choreography, and this is especially true during meiosis. Today’s image is from a paper showing the interaction between two nuclear envelope proteins and their regulation of chromosome dynamics and pairing.

Meiosis is a type of cell division that reduces the number of chromosomes down to one copy of each in the resulting daughter cells, called gametes (eggs and sperm). During meiosis, the pairing of homologous chromosomes (matching chromosomes) is important for recombination and chromosome segregation later in meiosis. Recombination is the exchange of DNA regions between two paired chromosomes, and is key in generating genetic variation. In yeast and worms, KASH domain proteins and SUN domain proteins of the nuclear envelope interact to ensure proper chromosome pairing and positioning within the nucleus. Mammals were known to have a SUN domain protein, SUN1, and a recent paper identified its KASH domain binding partner, KASH5. Morimoto and colleagues found that KASH5 and SUN1 both localize at telomeres, regions at the ends of chromosomes, during meiosis in mice. In addition, KASH5 interacts with the microtubule-associated dynein-dynactin complex to regulate chromosome movement. In the images above, chromosomes from mouse spermatocytes have both KASH5 and SUN1 localized at telomeres throughout meiosis (chromosomes are blue).

Akihiro Morimoto, Hiroki Shibuya, Xiaoqiang Zhu, Jihye Kim, Kei-ichiro Ishiguro, Min Han, & Yoshinori Watanabe (2012). A conserved KASH domain protein associates with telomeres, SUN1, and dynactin during mammalian meiosis originally published in the Journal of Cell Biology, 198 (2), 165-172 DOI: 10.1083/jcb.201204085

July 26, 2012

Ahhh…I remember the first time I saw worms under the microscope. I was an undergrad attending my future graduate school’s recruitment weekend, during which a kick-ass scientist showed me beautiful worms with glowing green seam cells down their bodies and matter-of-factly told me that “Worms rock.” I silently agreed with her, and found myself a few months later in that lab and spreading the gospel of the awesome rocking ability of worms. So, whenever I see a worm paper I feel like I’m part of the family…using genetic nomenclature that makes fly biologists roll their eyes (right back at you, sillies) and waxing nostalgic about beers in front of Royce Hall at the big worm meetings. Today, stunning images of worm muscles serve as a great example of the power of worms to show scientists some fascinating biology.

A sarcomere is the basic unit of muscle that contracts and relaxes. The fine balance of the proteins involved in a functional sarcomere is achieved by degradation of damaged proteins and production of new proteins. This balance is tipped during muscle atrophy in humans, caused by disease, disuse, starvation, or old age. The small nematode worm C. elegans has been a great model for muscle development and function, and a recent paper describes how protein degradation in muscle is regulated. Wilson and colleagues found that the sarcomeric protein UNC-89 (obscurin) binds to another protein called MEL-26 in C. elegans. MEL-26 is an adaptor protein that plays an important role in the ubiquitin proteasome system that degrades damaged or old proteins. Mutations in the mel-26 gene cause disorganization of the sarcomere structure, and some of this disorganization is due to an increase in the activity of a microtubule-severing protein called MEI-1 (katanin). These results suggest that normally UNC-89 inhibits the MEL-26 degradation complex toward MEI-1 in muscle. In the images above, adult body wall muscle from C. elegans is stained for UNC-89 (left, purple in merged) and MEL-26 (middle, green in merged). Some MEL-26 is found at the M-line of the sarcomere, where UNC-89 predominantly sits (arrow).

Kristy J. Wilson, Hiroshi Qadota, Paul E. Mains, & Guy M. Benian (2012). UNC-89 (obscurin) binds to MEL-26, a BTB-domain protein, and affects the function of MEI-1 (katanin) in striated muscle of Caenorhabditis elegans Molecular Biology of the Cell, 23 (14), 2623-2634 DOI: 10.1091/mbc.E12-01-0055

July 5, 2012

I’ve never run a marathon, but I’d imagine that it is a rollercoaster of feelings that finishes with a life “high” that is unbeatable. That’s how I feel when I read a paper from the journal Cell. They’re long, exhausting, sweat-inducing, and frequently some of the most rewarding paper-reading experiences a biologist can have. Today’s image is from a Cell paper that is so extensive in data, with a story that starts with protein localization and ends with a behavior study in mice.

Fibroblast growth factors (FGFs) are proteins that regulate several processes during development, such blood vessel growth and neurogenesis. A research group recently investigated the developmental role of FGF13, a growth factor believed to be connected to X-chromosome-linked mental retardation. Wu and colleagues found that FGF13 interacts with and stabilizes microtubules in cerebral cortical neurons during development. Through this interaction, FGF13 is required to polarize neurons—an event necessary for proper neuron migration and brain development. Finally, Wu and colleagues tracked the behavior of mice lacking FGF13, and found a reduced learning ability similar to that seen in X-chromosome-linked mental retardation patients. Images above show control (left) and FGF13-silenced (right) neurons in cerebral cortical slices. Without FGF13, neurons could not complete their radial migration in the tissue.

Wu QF, Yang L, Li S, Wang Q, Yuan XB, Gao X, Bao L, & Zhang X (2012). Fibroblast growth factor 13 is a microtubule-stabilizing protein regulating neuronal polarization and migration. Cell, 149 (7), 1549-64 PMID: 22726441

 Copyright ©2012 Elsevier Ltd. All rights reserved.

July 2, 2012

Microscopy can truly be a religious experience for some of us. We get to see the beauty of life unfold before our eyes, often in a dark room with the white-noise hum of equipment, all while being humbled by the mysteries in front of us. No matter your education, your amazing research pedigree, or the fancy-shmancy technology in front of you, you still don’t know how the heck it all happens…even in the tiniest of organisms. I’ll drink a bottle of immersion oil if that doesn’t bring your ass down a peg. Today’s image is from a paper describing the identification of a microtubule-like cytoskeleton in a bacteriophage.

Bacteriophages are viruses that infect bacteria. They are very common, found in dirt, sea water, and any place bacteria are found, and are very diverse. While bacteria are known to have cytoskeletal structures similar to our own cells, actin- or tubulin-like structures were not previously described in bacteriophages. A research group recently identified a tubulin-like protein called Phu-Z. Like the microtubules formed from tubulin in our own cells, Phu-Z assembles into filaments that surround the bacteriophage DNA and helps to position it within the infected bacterial cell. In the image above, Phu-Z is expressed in a bacterium and is able to assemble into filaments.

Kraemer JA, Erb ML, Waddling CA, Montabana EA, Zehr EA, Wang H, Nguyen K, Pham DS, Agard DA, & Pogliano J (2012). A Phage Tubulin Assembles Dynamic Filaments by an Atypical Mechanism to Center Viral DNA within the Host Cell. Cell, 149 (7), 1488-99 PMID: 22726436
Copyright ©2012 Elsevier Ltd. All rights reserved.