October 31, 2011

All storytellers want to tell their story all the way to its end. Imagine how unsatisfying most movies or books would be without their endings. What if Scout didn’t get to meet Boo Radley? How boring would The Sixth Sense be? How tragic would Toy Story 3 be?! In cell biology, telling a whole story in one paper, from protein to cell to animal, is a rare luxury given the time and difficulty of most techniques. Today’s image is from a paper with a well-rounded story about the role of a cell cycle protein in non-cell cycle-related business.

The cell cycle is driven forward by complexes made up of proteins called cyclins and cyclin-dependent kinases (Cdks). One cyclin called cyclin E functions in the G1 to S phase transition in the cell cycle, marking the start of DNA replication. Because of this role, cyclin E is typically found in only dividing cells. A recent paper describes the important role of cyclin E in non-dividing cells in the adult brain. In this paper, Odajima and colleagues found that cyclin E regulates synapse formation by inhibiting Cdk5. Cyclin E disruption in neurons causes the number of synapses and dendritic spines to drop. Finally, adult mice with cyclin E-deficient brains had impaired learning and memory. In the images above, non-dividing neurons from mouse brain show the presence of cyclin E (red) in both axons and dendrites, along with Cdk5. SynGAP and Synapsin I are post- and presynaptic markers.

Odajima, J., Wills, Z., Ndassa, Y., Terunuma, M., Kretschmannova, K., Deeb, T., Geng, Y., Gawrzak, S., Quadros, I., Newman, J., Das, M., Jecrois, M., Yu, Q., Li, N., Bienvenu, F., Moss, S., Greenberg, M., Marto, J., & Sicinski, P. (2011). Cyclin E Constrains Cdk5 Activity to Regulate Synaptic Plasticity and Memory Formation Developmental Cell, 21 (4), 655-668 DOI: 10.1016/j.devcel.2011.08.009
Copyright ©2011 Elsevier Ltd. All rights reserved.

October 27, 2011

Apoptosis sounds like a brutal death for a cell—all of that blebbing, fragmentation, and destruction just gives me the willies. Most of the time, cells only go through apoptosis when absolutely necessary thanks to proteins such as Bcl-x_L. A recent paper finds a new, non-apoptosis role for Bcl-x_L in cell health and survival.

The Bcl-2 family is made up of proteins that can either drive or inhibit apoptosis, which is programmed cell death. Bcl-x_L is a Bcl-2 family member that inhibits apoptosis by binding Bax, a pro-apoptosis family member, at the outer membrane of mitochondria. There, Bcl-x_L inhibits the release of cytochrome c, which during apoptosis serves to kick-start a cascade that destroys the cell. A recent paper finds an exciting new role for Bcl-x_L outside of apoptosis. Chen and colleagues found Bcl-x_L localized to the inner mitochondrial membrane, contrary to previous opinion that it is only found at the outer mitochondrial membrane. At the inner membrane, Bcl-x_L is important in maintaining the efficiency of the mitochondria by inhibiting excessive flux of ions across the inner membrane. The images above are electron micrographs of mitochondria. Antibodies that label Bcl-x_L are bound to tiny gold beads, which are found at the inner membrane (black arrows), as well as the outer membrane (arrowheads) and adjacent membranes (line arrows).

Chen, Y., Aon, M., Hsu, Y., Soane, L., Teng, X., McCaffery, J., Cheng, W., Qi, B., Li, H., Alavian, K., Dayhoff-Brannigan, M., Zou, S., Pineda, F., O'Rourke, B., Ko, Y., Pedersen, P., Kaczmarek, L., Jonas, E., & Hardwick, J. (2011). Bcl-xL regulates mitochondrial energetics by stabilizing the inner membrane potential originally published in The Journal of Cell Biology, 195 (2), 263-276 DOI: 10.1083/jcb.201108059

October 24, 2011

Breaking up is hard to do. Thankfully for us, breaking up is also very beautiful (in cells). Abscission is the final cleaving of two daughter cells at the end of mitosis, and is really quite stunning to see. So, enjoy today’s images!

Cytokinesis is the physical division of two daughter cells at the end of mitosis. The final step of cytokinesis is abscission, during which the small midbody that connects the two cells is finally cleaved. This process involves precise regulation of cytokinesis proteins; for example, the small GTPase RhoA is required during cytokinesis for the establishment and contraction of the cleavage furrow that develops to divide the cells, yet RhoA must be inactivated for abscission. A kinase protein called CIT-K (citron kinase) was previously shown to function as a downstream effector of RhoA activity, yet a recent paper describes results suggesting the converse—that CIT-K regulates RhoA activity. In addition, Gai and colleagues found that CIT-K also interacts with and regulates anillin, an actin scaffold protein crucial in cytokinesis. The images of midbodies above show the localization of either anillin (left, green) or RhoA (right, green), as well as DNA (blue) and microtubules (red). Compared with control cells (top row), anillin and RhoA were nearly undetectable at late stage midbodies in cells lacking CIT-K (bottom row).

Gai, M., Camera, P., Dema, A., Bianchi, F., Berto, G., Scarpa, E., Germena, G., & Di Cunto, F. (2011). Citron kinase controls abscission through RhoA and anillin Molecular Biology of the Cell, 22 (20), 3768-3778 DOI: 10.1091/mbc.E10-12-0952

October 20, 2011

One man’s trash is another man’s treasure. Photobleaching is an unavoidable side effect of imaging that leads to weakened fluorescent signals. Most of us pooh-pooh photobleaching, but some clever cell biologists use photobleaching as a fantastic tool instead. Today’s image is my new favorite use of photobleaching.

Glial cells function in the nervous system to support neurons and their signal transmission. Schwann cells are glial cells found at the neuromuscular junction (where neurons signal to muscles), and monitor the neurotransmission exchanged. Schwann cells can even function to form and regenerate the neuromuscular junction. A recent paper describes how Schwann cells establish their arrangement around the neuromuscular junction. In this paper, Brill and colleagues labeled individual Schwann cells and used live imaging to monitor their positioning. Schwann cells are dynamic during development, finding their appropriate position by competing for space with other Schwann cells. Schwann cells in adult animals, however, are much more static. In the images above, individual Schwann cells (pseudo-colored yellow, blue, white, and purple) were labeled by sequentially photobleaching one cell at a time, leading to distinct levels of fluorescence in each cell. The axon of the neuromuscular junction is in green. The Schwann cells are very dynamic in young mice (left) compared with adult mice (right), seen as the frequent formation and retraction of cell protrusions (arrowheads in the images of the boxed regions).

Brill, M., Lichtman, J., Thompson, W., Zuo, Y., & Misgeld, T. (2011). Spatial constraints dictate glial territories at murine neuromuscular junctions originally published in The Journal of Cell Biology, 195 (2), 293-305 DOI: 10.1083/jcb.201108005

October 17, 2011

A cell biologist’s most valuable asset is his or her toolbox…the collection of techniques and methods they can use to ask a question about a cell. For example, to figure out how important a given protein is in a specific process, there are many options…good old fashioned deletion or mutation of its gene, chemical inhibition, imaging its localization, finding binding partners, etc. Varying results from each of these approaches can lead to confusion, but a good scientist can turn that confusion into a more fully developed understanding.

Angiogenesis is the formation of blood vessels off of existing vessels, and is a key process in development and tumorigenesis. VEGF (vascular endothelial growth factor) is a potent activator of angiogenesis, and Notch is a protein that converts endothelial cells into tip and stalk cells, which are cell types required for vessel formation. A research group found that function-blocking antibodies for VEGFR-3, a VEGF receptor protein, caused a decrease in angiogenesis in developing mice and in tumors. However, this same research group more recently found that complete deletion of the VEGFR-3 gene caused excessive branching and sprouting during angiogenesis, as well as decreased Notch signaling. By finding varying results with similar, but subtly different approaches, Tammela and colleagues were able to distinguish bimodal functions of VEGFR-3 during angiogenesis. In the images above, blood vessels lacking the gene for VEGFR-3 (left) have more branching than wild-type vessels (right). Vessels lacking VEGFR-3 also have more filopodia (yellow dots, bottom row), actin-rich protrusions used by tip cells to guide branching.

Tammela, T., Zarkada, G., Nurmi, H., Jakobsson, L., Heinolainen, K., Tvorogov, D., Zheng, W., Franco, C., Murtomäki, A., Aranda, E., Miura, N., Ylä-Herttuala, S., Fruttiger, M., Mäkinen, T., Eichmann, A., Pollard, J., Gerhardt, H., & Alitalo, K. (2011). VEGFR-3 controls tip to stalk conversion at vessel fusion sites by reinforcing Notch signalling Nature Cell Biology, 13 (10), 1202-1213 DOI: 10.1038/ncb2331
Adapted by permission from Macmillan Publishers Ltd, copyright ©2011

October 13, 2011

I started on my biology journey with my Ranger Rick subscription as a tiny kid (quickly followed by my Fisher-Price microscope). I loved wildlife, and felt heartbreak for declining populations of so many species. Now that I’m trying to pass along this conservation concern and love of animals to my F1, I’m excited to talk about how stem cells may help save the animals!

Some species have too few individuals to allow successful breeding and genetic diversity. For example, the drill is an endangered primate of Africa and the northern white rhinoceros is a critically endangered species with only 7 known individuals (that’s right…not 7 million or 7 thousand, just 7). A recent method paper describes the generation of induced pluripotent stem cells (iPSCs) from both of these endangered species. Ben-Nun and colleagues generated fully reprogrammed iPSC lines from cryopreserved fibroblasts. These cell lines had characteristics of pluripotent cells in other species (ie, alkaline phosphatase activity, Oct4, Sox2, and Nanog). Images above show differentiated embryoid bodies developed from the northern white rhinoceros’ iPSCs. These differentiated cells have markers for all three developmental germ layers, as indicated at the bottom of the image (SMA = smooth muscle actin). Future applications of these iPSCs are truly exciting. In addition to therapeutic uses for sick captive animals, iPSC-derived germ cells can help increase species numbers and diversity (in combination with assisted reproduction).

Friedrich Ben-Nun, I., Montague, S., Houck, M., Tran, H., Garitaonandia, I., Leonardo, T., Wang, Y., Charter, S., Laurent, L., Ryder, O., & Loring, J. (2011). Induced pluripotent stem cells from highly endangered species Nature Methods, 8 (10), 829-831 DOI: 10.1038/nmeth.1706
Adapted by permission from Macmillan Publishers Ltd, copyright ©2011

October 10, 2011

If you are a fellow child of the 80s, you probably visualize a fried egg when you think of drug addiction. Fried eggs are delicious, but the reality about drug use is much more devastating and sobering…all the way to the level of the dendrites on our neurons. A recent paper describes the use of psychoactive drugs to help identify regulators of dendrite morphology.

MicroRNAs (miRs) are RNA structures that regulate gene expression by preventing the translation of specific mRNA sequences into proteins. miRs function throughout development, notably in the morphology and function of dendritic spines, which are small neuronal processes important in the transmission of a neuron’s signals. Psychoactive drugs such as nicotine, cocaine, and amphetamines can trigger changes in neuronal structure and function, and a recent paper identifies miRs as regulators of these changes. Lippi and colleagues found altered levels of miR-29a/b after exposing mice to psychostimulants. Altered levels of these miRs affect synaptic transmission and dendritic spine morphology, as seen in the images above. Healthy dendrites (top, left) have a mix of spine morphologies (top, right). After transfection with miR-29a (bottom, left) or miR-29b (bottom, right), the proportion of mushroom-shaped dendrites dropped significantly. miR-29a/b increases the number of filopodial protrusions through its targeting of the Arp2/3 actin nucleation complex.

Lippi, G., Steinert, J., Marczylo, E., D'Oro, S., Fiore, R., Forsythe, I., Schratt, G., Zoli, M., Nicotera, P., & Young, K. (2011). Targeting of the Arpc3 actin nucleation factor by miR-29a/b regulates dendritic spine morphology originally published in The Journal of Cell Biology, 194 (6), 889-904 DOI: 10.1083/jcb.201103006

October 6, 2011

Plants are underrepresented on this blog. Thankfully, this isn’t a food blog with only carnivorous cholesterol-thickened readers. But still, plants need representing (woot woot!) and today’s lovely images should help.

Plant cell communication is accomplished through the direct cell-to-cell transport of transcription factors, which are proteins that regulate gene expression. Just as in animal cells, plant development depends on these signals being relayed correctly. A recent paper describes how one transcription factor called SHR (SHORT-ROOT) is trafficked. Koizumi and colleagues identified a SHR-interacting protein called SIEL, which also associates with endosomes. Without SIEL, plant embryos arrest in early development. The images above are cross-sections of roots. Top root is normal, with one layer each of 8 endodermis (E) and 8 cortex (C) cells. SIEL mutants (middle, bottom) had multiple endodermis and cortex layers, each with more cells than in wild-type. The double arrows indicate the thickness of these tissue layers combined.

Koizumi, K., Wu, S., MacRae-Crerar, A., & Gallagher, K. (2011). An Essential Protein that Interacts with Endosomes and Promotes Movement of the SHORT-ROOT Transcription Factor Current Biology, 21 (18), 1559-1564 DOI: 10.1016/j.cub.2011.08.013
Copyright ©2011 Elsevier Ltd. All rights reserved.