Between the high number of breast cancer patients and the pink ribbons seen all over, breast health is and will always be a hot topic. The breast is a fascinating system of different cell and tissue types, and today’s image is from a paper looking at a population of epithelial cells in the breast.
Breast tissue contains two layers of epithelial sheets—an outer layer of myoepithelial cells (MECS) and an inner layer of luminal epithelial cells (LECs). The LECs greatly expand during certain events, such as pregnancy and tumorigenesis, which results in either thinner or discontinuous coverage by the outer layer of MECs. Because of this, the MEC layer serves as an epithelial “gatekeeper,” by generating boundaries that help organize breast tissue. A recent paper looks at this gatekeeper function of MECs and finds that two proteins, SLIT and ROBO2, are important in regulating the proliferation of MECs. And, in turn, the growth of the MEC layer regulates the branching of mammary tissue. Image above shows mammary tissue in normal (left) or Robo mutant (right) mice. The loss of Robo leads to excessive branching (close-up views of boxed regions on bottom).
Macias, H., Moran, A., Samara, Y., Moreno, M., Compton, J., Harburg, G., Strickland, P., & Hinck, L. (2011). SLIT/ROBO1 Signaling Suppresses Mammary Branching Morphogenesis by Limiting Basal Cell Number Developmental Cell, 20 (6), 827-840 DOI: 10.1016/j.devcel.2011.05.012
Copyright ©2011 Elsevier Ltd. All rights reserved.
In my grad school days, I was an asymmetric cell division aficionado. I loved the asymmetric cell division that I studied for those years, the one-cell stage worm embryo. With that statement out of the way, I can admit that I secretly coveted the extremely asymmetric divisions of ooctyes. Check out today’s lovely image of a mouse oocyte, from the cover of Current Biology.
Rather than dividing to produce two identical daughter cells, an oocyte divides to produce a large egg ready for fertilization and a very small polar body. This extreme asymmetric division allows the egg to retain all of the crucial cytoplasm to support a future early embryo. This asymmetry is necessary for fertility and development, but the mechanisms required for this event are not completely understood. A recent paper describes the importance of two novel actin nucleators called Spire1 and Spire2 in mouse meiotic divisions. These Spire proteins drive the assembly of an actin network that acts as a substrate for positioning of the meiotic spindle, and promotes the cytokinetic cleavage furrow that results in polar body extrusion. Image above shows a mouse oocyte undergoing a meiotic division—chromosomes are cyan, microtubules are blue, and cortical actin is red.
BONUS!! Check out this great movie showing spindle positioning in normal (left) and Spire-deficient (right) ooctyes.
To see the cover of Current Biology for this issue, which features the above image, click here.
Pfender, S., Kuznetsov, V., Pleiser, S., Kerkhoff, E., & Schuh, M. (2011). Spire-Type Actin Nucleators Cooperate with Formin-2 to Drive Asymmetric Oocyte Division Current Biology DOI: 10.1016/j.cub.2011.04.029
Copyright ©2011 Elsevier Ltd. All rights reserved.
Life is a balance of giving and taking, and this starts with our cells. I’ve written about cells taking in material (endocytosis) plenty of times, but it’s time to talk about cells secreting material out of the cell. Check out today’s stunning image of salivary gland cells in the fruit fly larva.
All cells undergo some base level of secretion, but there are many cell types with specialized “regulated” secretion. For example, our endocrine cells secrete the hormones that regulate our bodies and throw teenagers into crazed states. Cells with regulated secretion store high concentrations of certain proteins in dense organelles called secretory granules, until there is a signal that triggers the release of these proteins. A recent paper asks how secretory granules are formed, and finds that two vesicle coat proteins, called AP-1 and clathrin, are required. Burgess and colleagues looked at secretory granules in larval fruit fly salivary glands, and found that AP1 and clathrin are localized at newly synthesized secretory proteins, Golgi structures (where the proteins are sorted), and maturing secretory granules. Images show salivary gland cells with AP1 (red) colocalizing with Golgi structures (green).
Burgess, J., Jauregui, M., Tan, J., Rollins, J., Lallet, S., Leventis, P., Boulianne, G., Chang, H., Le Borgne, R., Kramer, H., & Brill, J. (2011). AP-1 and clathrin are essential for secretory granule biogenesis in Drosophila Molecular Biology of the Cell DOI: 10.1091/mbc.E11-01-0054
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
Glutamate is such an abundant and important neurotransmitter that I may just eat my weight in MSG-filled Chinese takeout tonight to get extra (honestly, I don’t recommend this). Today’s image is from a paper using kick-ass techniques to show how glutamate plays a role in dendritic spine formation.
Our neurons have dendritic spines that receive input signals. These spines are small protrusions that are formed and remodeled throughout development and as a result of learning and sensory experiences. A recent paper describes the identification of glutamate as a biochemical signal able to induce spine growth. In this paper, Kwon and Sabatini took high-resolution images of specific mouse neurons and then uncaged, or activated, a form of glutamate at specific spots on the neuron. At these spots of uncaged glutamate, dendritic spines formed de novo and were rapidly functional. Images above show two examples of mouse neurons on which glutamate was uncaged (yellow dots), leading to the appearance of new spines (arrowheads).
Hyung-Bae Kwon, & Bernardo L. Sabatini (2011). Glutamate induces de novo growth of functional spines in developing cortex
Nature, 474, 100-104 : doi:10.1038/nature09986
Adapted by permission from Macmillan Publishers Ltd, copyright 2011
It’s true that yeast isn’t considered the most photogenic organism around because of their tiny size, but I shudder to think how far behind we’d all be if it weren’t for the amazing discoveries made using yeast. Today, please enjoy these stunning images of fission yeast from a paper describing actin polymerization during endocytosis.
Endocytosis is the process during which a cell takes in material from the outside. Membrane-bound vesicles form within the cell to transport material to its final destination. Like most things dynamic in a cell, actin plays a very important role. In yeast, actin patches form at sites of endocytosis to help in membrane invagination and scission, key processes that result in the formation of a vesicle. A recent paper found that a protein called dip1p is a crucial switch to initiate the formation of actin patches at sites of endocytosis in fission yeast. Images above show a reduction in the number of actin patches in yeast without dip1p (right), compared to wild-type yeast (left).
Roshni Basu, & Fred Chang (2011). Characterization of Dip1p Reveals a Switch in Arp2/3-Dependent Actin Assembly for Fission Yeast Endocytosis Current Biology, 21 (11), 905-916 : doi:10.1016/j.cub.2011.04.047
Copyright ©2011 Elsevier Ltd. All rights reserved.
There are a lot of great horror movies around, but not a single one features GIANT MITOCHONDRIA! I’m going to call Hollywood directly and suggest a movie about giant mitochondria. Or, I could suggest you check out today’s image and fascinating paper on giant mitochondria in fruit fly sperm.
Sperm can grow quite long in the testes of male fruit flies, with some reaching 6 cm long. These elongated sperm have better success at fertilizing female fruit flies than shorter sperm. A recent paper looks at the cellular mechanisms that allow developing spermatids to grow to such great lengths, and the authors find that giant mitochondria play a very important role. Noguchi and colleagues found that growing mitochondria provide a platform for microtubules to grow in the elongating spermatids, and this combined structure serves as a template for cell shape. Image above shows microtubules (green) and mitochondria (red) in a fruit fly spermatid.
Tatsuhiko Noguchi, Michiko Koizumi, & Shigeo Hayashi (2011). Sustained Elongation of Sperm Tail Promoted by Local Remodeling of Giant Mitochondria in Drosophila Current Biology, 21 (10), 805-814 : doi:10.1016/j.cub.2011.04.016
Copyright ©2011 Elsevier Ltd. All rights reserved.
The human body is amazing, but cannot hold a candle to many organisms when it comes to limb regeneration. Zebrafish are able to regenerate amputated fins, including the sensory axons in the fin that sense touch. Today’s image is from a paper discussing the signals required for this process.
When tissue is regenerated, there are several different cell types that must be involved in order to heal the entire tissue. A recent paper looks at the regeneration of skin cells and sensory neuron axons in zebrafish to determine how the process of wound healing requires the coordination of several cell types. Zebrafish larvae can regenerate both the skin tissue and sensory axons of an amputated tail fin, and Rieger and Sagasti found that the reactive oxygen species hydrogen peroxide (H2O2) plays an important role in this coordination. Injured skin cells release the H2O2 signal, and this signal then promotes robust regeneration of the sensory axons. Images above show the sensory axons in uninjured (top) and amputated (bottom) tail fins over time. Axons were regenerated into the amputated region (dotted line, shaded region), as seen as the red trajectories of axon tips (left-most image). Rieger, S., & Sagasti, A. (2011). Hydrogen Peroxide Promotes Injury-Induced Peripheral Sensory Axon Regeneration in the Zebrafish Skin PLoS Biology, 9 (5) DOI: 10.1371/journal.pbio.1000621
Alphabet soup is not tasty, but must be devoured by any researcher. Some of the acronyms in biology, though, stand out for their importance and FRAP is one of them. FRAP is a very handy technique for studying the dynamics of proteins in a cell, and the paper from today’s image is a great example of how elegant and informative FRAP can be.
Titin is an abundant muscle protein that provides structural support for the sarcomere, which is the basic contracting unit in muscle. There are many isoforms of titin that allow structural and mechanical changes of the muscle tissue throughout development and during disease. The sturdiness that titin provides muscles may give an impression of a lack of dynamics, but a recent paper shows exactly the opposite. The authors in this study use a technique called fluorescence recovery after photobleaching (FRAP). In this case, fluorescently labeled titin was photobleached using a high power laser. By watching if and how the photobleached region recovers new fluorescent titin over time, da Silva Lopes and colleagues concluded that titin is very mobile and dynamic. Titin maintains unrestricted movement around sarcomeres, and this movement is dependent on calcium. In the images above, two different sized regions (top, bottom) of fluorescently-tagged titin within sarcomeres were photobleached. In both cases, the bleached regions (arrowheads in middle images) quickly recovered the titin fluorescent label (right) to levels similar to pre-bleach images (left).
da Silva Lopes, K., Pietas, A., Radke, M., & Gotthardt, M. (2011). Titin visualization in real time reveals an unexpected level of mobility within and between sarcomeres originally published in The Journal of Cell Biology, 193 (4), 785-798 DOI: 10.1083/jcb.201010099
