December 18, 2014

You might not want the dreaded tube socks in your Christmas stocking this year, but you do appreciate the actual tubes that your body depends on in just about every organ system. A recent paper in PLOS Biology describes tube formation in the fly renal system and the signals that regulate it.

Tubes generally start as buds that dramatically elongate during development, but the cell rearrangements that occur during tubulogenesis are not completely understood. Saxena and colleagues recently used the developing fly renal system to track cell movements during tube formation. Tubule elongation primarily occurs through convergent extension, during which cells intercalate along the length of the tube. During these rearrangements, the number of cells around the circumference of the tube drops as the number of cells along the tube increases. Saxena and colleagues show that epidermal growth factor localized at the tip cells of the distal end of the tube guides the polarity of cell rearrangements, via polarization of Myosin II within individual cells. Finally, without proper tube elongation, animals have abnormal excretory function and osmoregulation, leading to lethality. In the images above, the top row shows failure of tube elongation after laser ablation of the distal tip cells (arrowheads). Bottom row shows normal tube elongation without laser ablation of tip cells (arrowheads).

Saxena, A., Denholm, B., Bunt, S., Bischoff, M., VijayRaghavan, K., & Skaer, H. (2014). Epidermal Growth Factor Signalling Controls Myosin II Planar Polarity to Orchestrate Convergent Extension Movements during Drosophila Tubulogenesis PLoS Biology, 12 (12) DOI: 10.1371/journal.pbio.1002013

October 24, 2014

There is a party going on at the ends of microtubules, but I wasn’t invited. That won’t stop me, or countless cell biologists out there, from peeping in the window to check out all of the microtubule shenanigans. Today’s image is from a paper describing how Doublecortin binds to microtubule ends.

The plus end of a microtubule is the primary site for growth and shrinkage, and interaction with several microtubule-associate proteins. Different microtubule end-binding proteins may interact with microtubules using different mechanisms: the end-binding protein EB1 relies on the nucleotide state of the tubulin at the microtubule end, while a recent paper shows how another protein, Doublecortin (DCX), relies on the curvature of microtubule ends for binding. DCX is a neuronal microtubule-associate protein that plays an important role throughout development, yet how it interacted with microtubule ends was previously unclear. Bechstedt and colleagues used single-molecule microscopy to show that DCX (images above, green in merged) binds with higher affinity to curved microtubules (magenta) than to straight microtubules. DCX mutations, which are found in patients with double cortex syndrome, prevent the protein from binding to curved regions of microtubules.

Bechstedt, S., Lu, K., & Brouhard, G. (2014). Doublecortin Recognizes the Longitudinal Curvature of the Microtubule End and Lattice Current Biology, 24 (20), 2366-2375 DOI: 10.1016/j.cub.2014.08.039
Copyright ©2014 Elsevier Ltd. All rights reserved.

October 17, 2014

For years, the prettiest cells to image were flat cells in a dish. Thanks to the tireless work of many, beautiful high-resolution images can now come from tissue within a living organism. Today’s image is from a paper showing improved techniques for imaging fine cellular processes within large volumes, from the lab of recent Nobel prize winner, Eric Betzig. 

A material’s refractive index refers to how light travels through it; the simplest example being how light bends when passed through water. The refractive index heterogeneities stemming from the many cell types, morphologies, and subdomains within a living organism are a challenge to microscopists. As described in a paper from earlier this year, Wang and colleagues improved on previous techniques for imaging within large volumes. Wang and colleagues use adaptive optics (AO), which corrects for the microscope’s aberrations that limit image resolution, in a mode fast enough to correct for the various aberrations within a large sample, without inducing photodamage or photobleaching. The image above shows a 3D rendering from deep within a living zebrafish brain, with oligodendrocytes (magenta) and neuronal nuclei (green) visible.

Wang, K., Milkie, D., Saxena, A., Engerer, P., Misgeld, T., Bronner, M., Mumm, J., & Betzig, E. (2014). Rapid adaptive optical recovery of optimal resolution over large volumes Nature Methods, 11 (6), 625-628 DOI: 10.1038/nmeth.2925
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

October 9, 2014

As Tom and Jerry have proven time and time again, repulsive forces are serious business and highly entertaining. Today’s image is from a paper describing how different cell types repel one another to help create boundaries between tissues. 

The study of how cells adhere to or repel one another is an important field of study in developmental biology. Ephrin ligands and their respective Eph receptors trigger repulsive cues between cells of different types. Many different tissue types express the same ephrins and Eph receptors, yet only those cells at the tissue interface repel one another. A recent study tests how these signals are integrated to provide repulsion at only the tissue interface, and not between cells of the same tissue. Rohani and colleagues used the dorsal ectoderm-mesoderm boundary of early frog embryos to find Eph-ephrin pairs that are expressed in complementary tissues. The cells at the boundary of the tissues have a combined Eph-ephrin repulsive signal that is sufficient for a repulsive force, suggesting a simple model of repulsion based on relative concentrations and binding affinities of Eph receptors and ephrins at tissue boundaries. The image above shows the higher concentration of EphB receptors (green) at the ectoderm-mesoderm boundary.

Rohani, N., Parmeggiani, A., Winklbauer, R., & Fagotto, F. (2014). Variable Combinations of Specific Ephrin Ligand/Eph Receptor Pairs Control Embryonic Tissue Separation PLoS Biology, 12 (9) DOI: 10.1371/journal.pbio.1001955

September 11, 2014

As your therapist likely tells you, understanding where you came from is key to accepting where you are now. Take that therapist’s task and multiply it by several million—you now understand the tough job ahead of developmental biologists trying to track cell lineages in complex organisms. Today’s colorful image is from a paper describing a new computational framework for reconstructing cell lineages. 

The successful tracking of cell position, division, and movement in a developing organism has been a goal for countless developmental biologists. Reconstructing cell lineages in organisms like fruit flies and mice, however, is difficult due to the complexity of cell organization and behavior, poor image quality of thick embryos, the enormous size of the data sets, and an uncompromising need for accuracy. A recent paper by Amat and colleagues describes the development and use of a new open-source framework that reconstructs cell lineages with high accuracy and speed. Their system uses four dimensional and terabyte-sized image data sets of nuclei-tracked embryos, imaged using three different types of fluorescence microscopy. The images above show the first reconstruction of early fruit fly nervous system development (S1 neuroblasts), with precursor cell tracks color-coded for time (purple to yellow).

Amat, F., Lemon, W., Mossing, D., McDole, K., Wan, Y., Branson, K., Myers, E., & Keller, P. (2014). Fast, accurate reconstruction of cell lineages from large-scale fluorescence microscopy data Nature Methods, 11 (9), 951-958 DOI: 10.1038/nmeth.3036
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

August 19, 2014

Think of life without tubes for a moment. Not only would our huge bodies cease to exist, but our homes’ plumbing would be a mess and my 5-year old’s marble run would be pretty boring. The formation of tubes during development is a fascinating topic. Today’s image is from a paper describing the role of endocytosis in seamless tube formation.

The trachea of the fruit fly is a simple tubular system that functions as the respiratory system of the fly. The star-shaped tracheal terminal cells form seamless tubes that extend the length of long cellular extensions. Schottenfeld-Roames and colleagues recently published a study investigating the mutations in the braided gene. Tracheal terminal cells in braided mutants have tubular cysts and fewer branches, as seen in the images above (top is wild-type; bottom is mutant). braided encodes Syntaxin7, a endocytosis protein that promotes fusion of vesicles to early endosomes. Schottenfeld-Roames and colleagues found that mutations in other early endosome proteins cause similar terminal cell tube defects. Additional data showing increased levels of the apical protein Crumbs in braided terminal cells suggests that early endocytosis regulates levels of Crumbs, which in turn affects tube formation through actin cytoskeleton modulation. The images above show the luminal membrane (green) and an apical protein (magenta) in tracheal tubes. The tubes in braided mutants are cystic and abnormal, and the tube tips are disorganized (higher magnified views of the boxed regions are on the left).

Schottenfeld-Roames, J., Rosa, J., & Ghabrial, A. (2014). Seamless Tube Shape Is Constrained by Endocytosis-Dependent Regulation of Active Moesin Current Biology, 24 (15), 1756-1764 DOI: 10.1016/j.cub.2014.06.029
Copyright ©2014 Elsevier Ltd. All rights reserved.

All the images were acquired by Dr. Jodi Schottenfeld-Roames.

August 7, 2014

No matter how many brilliant discoveries are made by countless brilliant scientists, there will always be a lot of unknowns out there. These unknowns are what keep our mental wheels turning, our imaginations running, and our labs busy. Today’s image is from a paper that describes a newly-discovered process of vascular development called “canalogenesis.”

Schlemm’s canal (SC) is a flattened tube that encircles the anterior portion of the eye and drains fluid from the area. Abnormal drainage contributes to glaucoma, a disease that causes vision loss, yet a description of SC development and SC endothelial cells (SECs) is incomplete. In a recent study, Kizhatil and colleagues developed a new whole-mount procedure and used high-resolution confocal microscopy to study large regions of the SC during development. Kizhatil and colleagues found that the phenotype of SECs is a blend of blood and lymphatic endothelial cells, and that the SC develops through by a newly-discovered process called “canalogenesis.” Canalogenesis has features that are similar to, yet different from, the three well-studied vascular development programs—vasculogenesis, angiogenesis, and lymphangiogenesis. The image above was acquired using the new whole-mount procedure that protects the delicate ocular drainage structures. The SC (blue) is visualized in 3D relative to nearby blood vessels (magenta).

Kizhatil, K., Ryan, M., Marchant, J., Henrich, S., & John, S. (2014). Schlemm's Canal Is a Unique Vessel with a Combination of Blood Vascular and Lymphatic Phenotypes that Forms by a Novel Developmental Process PLoS Biology, 12 (7) DOI: 10.1371/journal.pbio.1001912

July 31, 2014

Do you ever feel nostalgic for a specific paper? Maybe this paper inspired your own research, or maybe it was a paper you immediately knew would be game-changing. Maybe, like today’s TBT paper, it was a great paper about solidly executed research with a memorable giggle-inducing technique. Thanks to a nostalgic HighMag reader and friend, Omar Quintero, we are being re-introduced to gonad sandwiches. 

In mammals, sex determination refers to the changes during early development that lead to the formation of either the testis or ovary. A gene on the Y chromosome called Sry initiates testis formation from the early bipotential gonad, including organizing Sertoli cells into the testis cord structure. In a 1997 paper, Martineau and colleagues investigated the early cell movements that occur after Sry expression, specifically the movement of nearby mesonephric cells to the genital ridge. To see these cell movements, Martineau and colleagues grafted a “blue” mesonephros from a mouse ubiquitously expressing β-galactosidase next to a “white” gonad from a different mouse. The movement of blue cells into the white gonad in these gonad sandwiches revealed that this movement is dependent on a signal induced by the male (XY) gonad that acts as a chemoattractant. Migration does not occur if an XX gonad is used in the sandwich, yet migration can occur whether an XY or XX mesonophros is used. The images above show the different XX and XY combinations used in these experiments, with XY gonads leading to extensive migration of blue cells. 

Martineau, J., Nordqvist, K., Tilmann, C., Lovell-Badge, R., & Capel, B. (1997). Male-specific cell migration into the developing gonad Current Biology, 7 (12), 958-968 DOI: 10.1016/S0960-9822(06)00415-5

Copyright ©1997 Elsevier Ltd. All rights reserved.

June 30, 2014

Which came first, the primordial germ cell or the gamete? Unlike the old chicken or egg philosophical dilemma, we know for certain that the primordial germ cell came first. And, thanks to a recent paper about primordial germ cells in sea urchins, we now know that they can migrate across the urchin embryo.

During development, germ cells produce gametes (eggs or sperm). In many organisms, including mammals, primordial germ cells (PGCs) are born far from the eventual location of gametes and must migrate across the embryo while dividing. In sea urchins, small cells called micromeres are PGCs and precisely segregate along the left-right axis of the embryo. A recent paper by Campanale and colleagues describes the use of live-cell imaging of small micromeres in urchin embryos to test whether the precise segregation of these eight micromeres is due to passive translocation or active migration. Images show that the micromeres are, in fact, motile cells with features such as cortical blebs and filopodia that direct migration across the sea urchin embryo, towards the coelomic pouches. In the images above, sea urchin embryos express micromere (red) and apical membrane (green) markers before (left) and during (middle, right) gastrulation.

Campanale, J., Gökirmak, T., Espinoza, J., Oulhen, N., Wessel, G., & Hamdoun, A. (2014). Migration of sea urchin primordial germ cells Developmental Dynamics, 243 (7), 917-927 DOI: 10.1002/dvdy.24133

Febrary 26, 2014

Not all stem cells are created equally. Some are totipotent, meaning they can divide and differentiate into any cell type, while some are unipotent, meaning they can differentiate into one specific cell type. Understanding the potenty of various stem cells is an important step towards understanding how tissues are developed, remodeled, and maintained. Today’s beautiful images are from a study of stem cells in the mammary gland.

Mammary glands go through a lot of changes during both puberty and adulthood, and are made up of two main cell lineages—myoepithelial and luminal. The function of mammary stem cells was previously unclear—in one model, bipotent stem cells contribute to the development and maintenance of adult mammary glands, while in the other model, those stem cells are unipotent and separately control mammary gland lineages. A recent cell fate mapping study by Rios and colleagues featured the use of multicolor reporters and 3D imaging. Rios and colleagues found that mammary stem cells are indeed bipotent, and function in ductal remodeling and homeostasis in the adult mammary gland. In the image above, the sea of colorful cells seen in the mid-puberty mouse mammary gland (top) indicates the presence of multiple progenitors. The arrow and arrowhead in the inset image point to myoepithelial and luminal cells, respectively. As puberty progressed (bottom), discreet regions of similarly-colored cells indicate clonal expansion and a shift towards adulthood.

Rios, A., Fu, N., Lindeman, G., & Visvader, J. (2014). In situ identification of bipotent stem cells in the mammary gland Nature, 506 (7488), 322-327 DOI: 10.1038/nature12948
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

February 19, 2014

It will take cell biologists an eternity to understand how cells function in a dish. It will take developmental biologists even longer to understand how cells function within a developing organism. Today’s image is from a paper describing the use of liquid droplets as cell biological crash test dummies to determine cell-generated forces within living tissue.

The development of an organism and the generation of its organs depend on mechanical forces that can move cells and groups of cells. There are many techniques that have been helpful in understanding these forces, but these techniques have not been applicable for measuring forces in three dimensional living tissue (or, in the case of laser ablation, have only provided relative force measurements). Campàs and colleagues have just published a paper describing the clever use of oil microdroplets to measure force within living tissues and organs. These spherical microdroplets are a similar size as cells, are fluorescently labeled, and display cell surface adhesion receptors. After these microdroplets are injected into tissue, their deformation by surrounding cells exerting mechanical stress can be measured and quantified. The images above show a microdroplet (white arrow, top) embedded in an incisor tooth bud of a mouse embryo (E13.5). Higher magnification views of the microdroplet (bottom row) show the pixel-resolution contour of the droplet (middle). The higher curvature regions (arrows, right image) correlate with cell-cell junctions of adjacent cells. 

Campàs O, Mammoto T, Hasso S, Sperling RA, O'Connell D, Bischof AG, Maas R, Weitz DA, Mahadevan L, & Ingber DE (2014). Quantifying cell-generated mechanical forces within living embryonic tissues. Nature methods, 11 (2), 183-9 PMID: 24317254
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

February 13, 2014

Whenever I’m lucky enough to make it down the road to the amazing Georgia Aquarium, I find myself glued to the jellyfish tanks. I have always loved watching the graceful movements of the jellies, and as a cell biologist my fluorescently-tagged appreciation runs deep. Today’s image is from a paper describing the molecular pathways in jellyfish development.

The phylum Cnidaria are made of organisms that cycle through two completely different stages—polyps and jellyfish. The polyp-to-jellyfish transition is dramatic, as seen in the images above, and begins with a shift in water temperature. During strobilation, segment-like disks (white arrows) are formed progressively down the polyp. Each disk detaches from the strobila and becomes an ephyra, or young jellyfish, which then quickly matures to an adult jellyfish. A recent paper in Current Biology describes the molecular pathways important in the polyp-to-jellyfish transition in translucent moon jellies. Fuchs and colleagues found that two pathways are important—one relying on retinoic acid, and the other involving secreted proteins that are upregulated following shifts in temperature. One of these secreted proteins (CL390) serves as the precursor of the strobilation hormone in moon jellies.

Björn Fuchs, Wei Wang, Simon Graspeuntner, Yizhu Li, Santiago Insua, Eva-Maria Herbst, Philipp Dirksen, Anna-Marei Böhm, Georg Hemmrich, Felix Sommer, Tomislav Domazet-Lošo, Ulrich C. Klostermeier, Friederike Anton-Erxleben, Philip Rosenstiel, Thomas C (2014). Regulation of Polyp-to-Jellyfish Transition in Aurelia aurita Current Biology, 24 (3) DOI: 10.1016/j.cub.2013.12.003


Copyright ©2013 Elsevier Ltd. All rights reserved. 

February 5, 2014

The next time you try swatting away that little fruit fly from a neighboring lab while you enjoy your midday coffee break, take a beat and appreciate how stinkin’ purrrty those flies are. Today’s image features the developing egg of the fruit fly, and accompanies a paper describing the important role for prostaglandins in the (very photogenic) process.

Prostaglandins (PGs) are small lipids that act as signaling molecules in various physiological processes such as pain, inflammation, and platelet aggregation. On the cellular level, PGs regulate the organization of the actin cytoskeleton. A recent paper in Molecular Biology of the Cell from the Tootle lab sheds light on the role of PGs in development, and shows that PGs temporally regulate actin cytoskeleton organization during Drosophila oogenesis. Specifically, PGs function at stages 9 and 10 of oogenesis to inhibit, then promote, actin remodeling via the actin elongation factor Ena. Loss of PG signaling at stage 9 triggers early actin filament formation and bundling, while loss of PG signaling at stage 10 triggers a reduction of, or complete loss of, parallel actin filament bundling. As seen in the images above, actin filament organization (white) is abnormal in two different PG mutant follicles (middle, bottom), compared to a wild-type follicle (top).

Andrew J. Spracklen, Daniel J. Kelpsch, Xiang Chen, Cassandra N. Spracklen, & Tina L. Tootle (2014). Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis Molecular Biology of the Cell, 25 (3) DOI: 10.1091/mbc.E13-07-0366

July 2, 2013

 
Timing is everything….from the fluke encounter in a romantic comedy, to your rush to make the bus/train/plane this morning, to the development of an organism. Today’s image is from a paper describing the temporal patterning involved in the development of the fruit fly optic lobe.

In the fruit fly optic lobe, the medulla processes visual information using 40,000 neurons of over 70 different cell types. The medulla develops from a crescent-shaped tissue from which the neuronal progenitors divide, requiring several different transcription factors. A recent paper describes the sequential patterning of five transcription factors as the medulla neuroblasts age. Li and colleagues found that this temporal patterning of transcription factors is necessary for the diversity of cell types found in the medulla. The images of the developing medulla above show the sequential expression of these five transcription factors—Homothorax (Hth), Eyeless (Ey), Sloppy paired 1 and 2 (Slp), Dichaete (D), and Tailless (Tll)—in five consecutive stripes. Hth is found in the youngest neuroblasts. Ey, Slp, and D are required for turning on the next transcription factor in the cascade. Slp and D are also required for turning off the preceding transcription factor.

Li X, Erclik T, Bertet C, Chen Z, Voutev R, Venkatesh S, Morante J, Celik A, & Desplan C (2013). Temporal patterning of Drosophila medulla neuroblasts controls neural fates. Nature, 498 (7455), 456-62 PMID: 23783517 
Adapted by permission from Macmillan Publishers Ltd, copyright ©2013

June 21, 2013

Good things come in small packages.  Maybe I’m referring to the burst of antioxidants jammed into tiny blueberries.  Maybe I’m referring to my tiny three year-old who yells, “Come oooon, THAT was funny!” when I don’t laugh loudly enough at her jokes.  Or maybe I’m referring to C. elegans.  These worms are tiny, but pack a serious punch of significant biology that helps us learn about important cellular processes.  Today’s image is from a paper that serves as an excellent example of this.

During cell invasion, a cell is able to breach and cross over the basement membrane that underlies a sheet of epithelial cells.  Cell invasion occurs throughout development and in the spread of cancer, yet biologists studying cell invasion have been challenged by the difficulty of visualizing the event.  A recent paper describes the development of live-cell imaging methods for studying cell invasion, using the worm’s anchor cell.  The anchor cell in the developing worm’s uterus breaches the basement membrane in order to link uterine and vulval tissues, and its transmigration is precisely timed.  Hagedorn and colleagues followed the interactions between the invading anchor cell and the basement membrane, and found very dynamic actin-based invadopodia that first breach the basement membrane.  These protrusions then stabilize to expand the breach and cross into the vulval tissue.  Anchor cell invasion depends on the netrin receptor UNC-40 (DCC) at the interface between the anchor cell and basement membrane.  In the time-lapse images above, the invading protrusion (cyan in top, grayscale in bottom) can be seen breaching the basement membrane (purple) and invading the vulval tissue underneath.

Hagedorn, E., Ziel, J., Morrissey, M., Linden, L., Wang, Z., Chi, Q., Johnson, S., & Sherwood, D. (2013). The netrin receptor DCC focuses invadopodia-driven basement membrane transmigration in vivo originally published in the Journal of Cell Biology, 201 (6), 903-913 DOI: 10.1083/jcb.201301091

June 18, 2013

The study of how cells move in development is not just about development.  Understanding cell migration can also help researchers understand how tumors spread and invade other tissues.  So, the next time you see someone roll their eyes at your fruit fly egg chambers (or worm vulva, or culture dishes), take pity at their ignorance and explain to them how they should thank you instead.

The movement of cells during development drives the shape changes and organization of an embryo.  In the fruit fly ovary, a small cluster of border cells migrates across a region of the egg chamber in order to reach the oocyte.  This collective migration of these border cells depends on polarization of the actin cytoskeleton.  A recent paper describes the role of the Hippo signaling pathway in driving the polarization of actin to the outer rim of the migrating border cell cluster.  Lucas and colleagues found that upstream Hippo pathway components localize to the contacts between border cells within the cluster in order to link polarity signaling with actin cytoskeleton organization.  In the images above, the actin cytoskeleton (red) can be seen at the outer rim of the migrating cluster of border cells (arrows) as it moves across the egg chamber towards the oocyte (top to bottom, chronologically).  Higher magnification views of the cluster are on the right.

 Lucas, E., Khanal, I., Gaspar, P., Fletcher, G., Polesello, C., Tapon, N., & Thompson, B. (2013). The Hippo pathway polarizes the actin cytoskeleton during collective migration of Drosophila border cells originally published in the Journal of Cell Biology, 201 (6), 875-885 DOI: 10.1083/jcb.201210073

April 12, 2013

I think I speak for many when I say that dinosaurs were the first objects of our life-long science obsessions.  Their size, history, and ferocious good looks fascinate even the youngest preschoolers.  Although my obsession turned to microscopic things, some folks remained true to their love of dinosaurs and history.  Today’s image is a treat, and a great example of how the basic questions in developmental biology know no timeline.

The study of dinosaur embryos at the cellular levels helps scientists understand the growth patterns of dinosaurs.  Despite this, little is known about dinosaur embryos, as they are rare and typically still inside of their eggshells.  A recently discovered dinosaur embryo bone bed in China is the oldest dinosaur embryo find in fossil record, from the Lower Jurassic about 190-200 million years ago.  These embryos represent several different nests, and are at different developmental stages.   In addition, these embryos are likely that of a Lufengosaurus, from the sauropodomorph clade of dinosaurs known for long necks and gigantism.  Because of the variation of age of these found embryos, Reisz and colleagues were able to track development through several different stages, including very early embryonic stages.  In the images above, thin sections from three different femur (thigh) bone samples (of 24 discovered total) show changes in the bone tissue formation as the embryos age from youngest (left) or oldest (right).  Two different regions of the femora are shown for each sample (top and bottom).

BONUS!  More thin sections are shown below.

Reisz, R., Huang, T., Roberts, E., Peng, S., Sullivan, C., Stein, K., LeBlanc, A., Shieh, D., Chang, R., Chiang, C., Yang, C., & Zhong, S. (2013). Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains Nature, 496 (7444), 210-214 DOI: 10.1038/nature11978 
Adapted by permission from Macmillan Publishers Ltd, copyright ©2013 

April 2, 2013

As I write this, I have dirt underneath my fingernails and I love it.  Spring is here, and I have begun playing in the dirt and cheering for my budding vegetable garden seedlings.  I love the food plants provide us, but they’re also fascinating models for understanding cell biology and developmental biology.  Today’s image is from a paper identifying a player in the development of stomata, which are important plant organs.

Stomata are pore organs on leaves that regulate gas and water vapor exchange in plants.  They are made of pairs of guard cells that regulate the size of the stomata openings to let air in and oxygen out.  A recent paper describes the identification of a protein that regulates the maturing and functioning of stomatal guard cells.  Negi and colleagues identified SCAP1, a transcription factor, that when mutated results in irregularly-shaped guard cells.  These mutants also lack the ability to control stomatal opening and closing.  SCAP1 regulates the transcription of known guard cell development genes.  The images above show a wild-type plant (top) with normal developing stomata at all stages (mature stomata is right-most image).  In a scap1 mutant (bottom), however, later stages of stomata development are defective and result in stomata with a floppy or irregular appearance.

Negi, J., Moriwaki, K., Konishi, M., Yokoyama, R., Nakano, T., Kusumi, K., Hashimoto-Sugimoto, M., Schroeder, J., Nishitani, K., Yanagisawa, S., & Iba, K. (2013). A Dof Transcription Factor, SCAP1, Is Essential for the Development of Functional Stomata in Arabidopsis Current Biology, 23 (6), 479-484 DOI: 10.1016/j.cub.2013.02.001
Copyright ©2013 Elsevier Ltd. All rights reserved.

February 4, 2013

The brain needs blood like Beyonce needed pants at last night’s SuperBowl Halftime show.  (Side note, I think she was and looked amazing, but seriously…pants!)  Today’s image is from a paper describing the development of the blood vessel network in the brain.

The brain depends on an intricate network of blood vessels to supply the brain with oxygen and nutrients, but how the network forms during development is not well-understood.  A recent paper describes how radial glial cells play an important role in blood vessel formation and growth.  Radial glial cells are a type of stem cell in the developing brain and function in neurogenesis.  Ma and colleagues ablated radial glial cells during late embryonic development of the brain’s cerebral cortex and found that blood vessels regressed.  Radial glial cells interact with and stabilize new blood vessels, through use of the Wnt signaling cascade.  The images above show the cortical plate of a developing mouse’s brain at different stages.  Increasing blood vessel growth (green) can be seen from E14.5 (embryonic day 14.5) through E17.5.

Ma S, Kwon HJ, Johng H, Zang K, & Huang Z (2013). Radial glial neural progenitors regulate nascent brain vascular network stabilization via inhibition of wnt signaling. PLoS biology, 11 (1) PMID: 23349620

January 31, 2013

I like to think of early embryos as kicking ass and asking questions later.  Once fertilization happens, embryos undergo rapid, synchronous cell divisions.  Next, the cell divisions slow down as cells begin to move around and form the different germ layers, then organs, within the growing embryo.  Today’s image is from a paper describing this transition in fruit flies, and how gene transcription in the embryo plays a role.

In fruit fly embryos, early development begins with synchronous nuclear divisions, which are divisions in which the nuclei divide without going through cytokinesis.  After 13 rounds of mitosis, the large multinucleate syncytium pauses in cycle 14 and undergoes cellularization to form plasma membranes around nuclei.  During this transition, the transcription of the embryo’s own genes begins as the maternally-contributed genetic material (RNA) is degraded.  A recent paper describes evidence that this switch to zygotic transcription is the trigger for the pause in cycle 14 and cellularization.  Sung and colleagues found a novel mutation in the RNPII215 gene that results in a reduced number of nuclear divisions, as well as premature zygotic transcription and cellularization.  The number of nuclear divisions in this mutant depends on zygotic transcription and Vfl, a transcription factor that controls many early zygotic genes.  In the images above, a mutant early fly embryo (bottom) has fewer cells due to the reduced nuclear divisions, compared to a normal embryo (top).  A nuclear protein is in green, and the pair-rule protein Eve is in red.

Sung, H., Spangenberg, S., Vogt, N., & Großhans, J. (2013). Number of Nuclear Divisions in the Drosophila Blastoderm Controlled by Onset of Zygotic Transcription Current Biology, 23 (2), 133-138 DOI: 10.1016/j.cub.2012.12.013
Copyright ©2013 Elsevier Ltd. All rights reserved.