July 24, 2014

How many times can you say the word “gonad” in a sentence without giggling? If the answer is none, then I congratulate you on turning thirteen. If the answer is many, then you must be a biologist. Biologists appreciate the value of a good gonad, and so should you. The gonad of the worm C. elegans serves as an important model in which to study tissue organization and development, as you’ll see in the paper that accompanies today’s image.

At the end of cell division, cytokinesis typically results in two separate daughter cells. Some cytokinesis, though, is incomplete and leads to two daughter cells sharing cytoplasm. This shared cytoplasm, or syncytium, can be found in the germ cells of many species from worms to humans. The germline of the worm C. elegans is a polarized tube in which germ cells are arranged around the shared cytoplasmic core and move along a conveyer belt of oocyte production. Amini and colleagues recently reported on the formation of the syncytial C. elegans germline throughout development, and the role of the short Anillin family scaffold protein ANI-2. ANI-2 is localized to the intercellular bridges that connect the germ cells to the shared cytoplasm, and loss of ANI-2 results in destabilization of intercellular bridges and sterility. The defects seen in worms lacking ANI-2 are likely due to a loss of the stability and elasticity of the intercellular bridges that is required to compensate for the stress of cytoplasmic streaming during oogenesis. Images above show the germlines of wild-type and ani-2(-) worms at different larval stages (membranes in green; nuclei in red). Worms lacking ANI-2 have abnormal multinucleated germ cells (arrowheads).

Amini, R., Goupil, E., Labella, S., Zetka, M., Maddox, A., Labbe, J., & Chartier, N. (2014). C. elegans Anillin proteins regulate intercellular bridge stability and germline syncytial organization originally published in the Journal of Cell Biology, 206 (1), 129-143 DOI: 10.1083/jcb.201310117

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

April 26, 2013

It’s Worm Week here at HighMag Blog.  Worms are amazing little creatures, and the species C. elegans is an invaluable model system for studying cell and developmental biology.  Their genome is sequenced, their development is precise and well-documented, and their bodies and embryos are translucent (making them photogenic under a microscope).  Today’s image is from the same lab that brought Tuesday’s image…worm gonads rock!

Blurb and image from Christian R. Eckmann:
The image is an immuno-stained part of an extruded C. elegans hermaphrodite gonad; germ cell nuclei (magenta) and the apical membrane (green). The germ stem cells reside at the closed end of this tube like tissue. In wild type, the germ stem cells exit the mitotic zone, entering meiosis further away from the closed tip and start differentiating into sperm or oocytes. 

The image posted earlier this week is from the Gracida and Eckmann paper that identifies a nuclear receptor that protects germ stem cell integrity, and in turn fertility, after dietary perturbations.

Gracida, X. & Eckmann, C. (2013). Fertility and Germline Stem Cell Maintenance under Different Diets Requires nhr-114/HNF4 in C. elegans Current Biology, 23 (7), 607-613 DOI: 10.1016/j.cub.2013.02.034 

April 23, 2013

I’m thankful that my body knows how to handle days when I feed it wonderful things, like a banana and a giant bowl of strawberries, then follow it up with a few gut-busting mini-doughnuts.  Although worms and other organisms don’t have access to doughnuts like I do, their bodies still have protections in place to handle changes in their diet.  Today’s image is from a paper describing how the germline is protected from a changing diet.

Organisms consume a variety of food options, yet their bodies know how to regulate these changes to maintain homeostasis, all the way down to the cellular level.  A recent paper shows how an organism’s germline stem cells (GSCs), the source of eggs and/or sperm, are protected from food intake.  Gracida and Eckmann found that the nuclear receptor NHR-114 protects GSCs from dietary perturbations in worms, possibly through a detoxifying response to certain food intake.  Without NHR-114, worms on certain bacterial diets become sterile due to germ cell division defects during development.  The dietary sensitivity is based on intake of the amino acid tryptophan.  In the images above, gonads of worms fed a certain bacterial diet are stained to see individual germ cells (cell cortex staining in green in merged; DNA is purple).  Compared to wild-type worms (left), worms depleted of NHR-114 (right) have germ cell defects, notably cells with multiple nuclei (arrowhead).

Gracida, X., & Eckmann, C. (2013). Fertility and Germline Stem Cell Maintenance under Different Diets Requires nhr-114/HNF4 in C. elegans Current Biology, 23 (7), 607-613 DOI: 10.1016/j.cub.2013.02.034 
Copyright ©2013 Elsevier Ltd. All rights reserved. 

March 7, 2013

DNA is not just shoved into the nucleus of a cell like a college boy’s clothes jammed into his closet (maybe that was just my husband?).  The organization of the nucleus has been getting more attention lately, and the results are pretty fascinating.  Today’s image is from a recent paper showing the association of a promoter to nuclear pores.

The organization of the nucleus may depend on the tethering of chromatin, or packaged DNA, to the nuclear envelope.  While some past results have suggested that actively expressed regions of chromatin are associated with the nuclear envelope in some organisms, other results have shown localization of actively expressed genes at internal nuclear speckles in other organisms.  A recent paper shows a link between the nuclear pore and a promoter, which is a region of DNA that initiates the expression of a nearby gene.  Rohner and colleagues found that the heat shock promoter hsp-16.2 interacts with the nuclear pore after heat shock, a type of stress, in worms.  Without heat shock, the promoter still maintained a perinuclear localization.  Using super-resolution structured illumination microscopy (SR-SIM) to achieve 100-nm resolution, Rohner and colleagues found that after heat shock, the promoter’s localization to the nuclear pore complex increased.  These results suggest that this stress-activated promoter may direct chromatin to the nuclear pores, where genes can be more easily accessed by transcription machinery.  In the image above, a 200-cell stage worm embryo is stained to show the localization of the hsp-16.2 promoter (green) at the nuclear envelope (red, DNA is in blue) under normal circumstances.

BONUS!!  Click here for a video of a 3D reconstruction of super-resolution images showing nuclear pores (green) and nuclear envelope (lamina, red).  

Rohner, S., Kalck, V., Wang, X., Ikegami, K., Lieb, J., Gasser, S., & Meister, P. (2013). Promoter- and RNA polymerase II-dependent hsp-16 gene association with nuclear pores in Caenorhabditis elegans originally published in the Journal of Cell Biology, 200 (5), 589-604 DOI: 10.1083/jcb.201207024

August 20, 2012

When you watch a cell going through mitosis, it looks like a smooth ballet performance—grace with impeccable timing and synchrony. In reality, there is a lot going on within the cell to make mitosis progress so smoothly, just like the ballet dancers’ actual physical exertion and concentration. Today’s image is from a paper that describes the timely removal of proteins from the nuclear envelope during mitosis.

The nuclear envelope (NE) is a double membrane that separates the cell’s genome from the rest of the cell, and permits transport of material into and out of the nucleus through multi-protein complexes called nuclear pores. During mitosis, the NE breaks down in order to allow chromosomes to attach to the mitotic spindle. Prior to NE breakdown, the nucleoporins that make up the nuclear pore complexes must be dissociated from the NE. A recent paper describes the timely removal of the nucleoporin NPP-3 near centrosomes at the onset of mitosis in early worm embryos. Hachet and colleagues found that centrosomes and the Aurora-A kinase AIR-1 are both required for removal of NPP-3 from the NE. In the images above, NPP-3 (right column, red in merged) is localized on the NE and is removed as mitosis progresses. NPP-3 removal begins near centrosomes (microtubules in green). 

Hachet V, Busso C, Toya M, Sugimoto A, Askjaer P, & Gönczy P (2012). The nucleoporin Nup205/NPP-3 is lost near centrosomes at mitotic onset and can modulate the timing of this process in Caenorhabditis elegans embryos. Molecular biology of the cell, 23 (16), 3111-21 PMID: 22740626

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

May 21, 2012

Whenever we go on a trip, my long-suffering husband quietly puts our luggage next the car and slinks away, trembling and twitching.  He knows a mad-woman is ready to pack the trunk, playing luggage-Tetris until it all fits and speaking in tongues.  Seriously, though, I’m freaking awesome.  That said, I don’t envy the insane packing that a cell must accomplish to jam all of that DNA into neat little chromosomes ready for their own cell division road trip.  A recent paper helps us understand how that happens at the centromere.

Centromeres are the regions on chromosomes that bind sister chromatids together and serve as the sites of kinetochore assembly during mitosis.  The presence of the protein CENP-A is a hallmark of centromere location, as it is a histone H3 variant that helps package and compact centromeric DNA.  It was previously presumed that CENP-A was passed down to daughter cells epigenetically, inherited from previous cell divisions, but a recent paper shows that this is not the case in the nematode worm C. elegans.  According to Gassmann and colleagues, pre-existing CENP-A is not required for CENP-A localization to centromeres in subsequent divisions.  In fact, CENP-A is unloaded from centromeres at one point in oogenesis, the production of eggs, and later reloaded onto centromeres.  By mapping the location of CENP-A in the genome, Gassmann and colleagues found that regions of transcribed genes are regions where CENP-A is excluded, a pattern that changes when germline gene transcription switches to embryonic gene transcription.  In the images above, the C. elegans germline is labeled to show chromosomes (top image) and the location of CENP-A (bottom).  CENP-A is lost from chromosomes during the pachytene stage of meiosis and later reloaded onto chromosomes during diplotene, and is not found in sperm.  

Gassmann, R., Rechtsteiner, A., Yuen, K., Muroyama, A., Egelhofer, T., Gaydos, L., Barron, F., Maddox, P., Essex, A., Monen, J., Ercan, S., Lieb, J., Oegema, K., Strome, S., & Desai, A. (2012). An inverse relationship to germline transcription defines centromeric chromatin in C. elegans Nature, 484 (7395), 534-537 DOI: 10.1038/nature10973
Adapted by permission from Macmillan Publishers Ltd, copyright ©2012

February 20, 2012

Full disclosure: today’s image is near and dear to me. Today’s image is from a paper written by members of my former graduate lab, with some very close friends as the co-first authors. This is not to say that this paper isn’t utterly fascinating with sparkling images and fantastic experiments designed by some of the brightest scientists around (enough superlatives for you?), because it is all of the above and more. I’m just disclosing my bias so if today’s post sounds like a love letter, you’ll let it slide.

During development, it is necessary for cells to change their shape—it allows cells and sheets of cells to form into specific structures and tissues. Apical constriction drives cell shape changes in many cell types by contracting the actin-myosin network on the apical side of the cell, causing that side of the cell to shrink. After apical constriction, cells are shaped more like wedges, and a whole sheet of apically constricting cells can result in dramatic changes. For example, apical constriction drives the folding and closing of neural plate cells to form the neural tube, which later becomes our brain and spinal cord. A recent paper looks at apical constriction during gastrulation in the worm embryo, at the start of which two cells on the outside of the embryo apical constrict and are internalized into the middle of the embryo. Roh-Johnson and colleagues found that the actin-myosin networks were dynamic and contracting long before the cells showed any type of shape change, functioning as a molecular “clutch.” The cells were internalized only after the actin-myosin contractions appeared to have been mechanically linked to the cell-cell contact zone. Roh-Johnson and colleagues found this same molecular clutch in apically constricting cells in the developing fruit fly, suggesting that this mechanism might be a key component of apical constriction across the board. The images above show two timepoints of a worm embryo in the process of internalizing the two cells at the start of gastrulation (bottom image is about 6 minutes after the top image). Green is myosin, red is membranes, and blue marks the surfaces of the internalizing cells. Image credit: Chris Higgins and Liang Gao.

BONUS!! Check out a fancy little blurb about this paper in The Scientist here (complete with movie!).

BONUS!! Do you like worms? Of course you do! Mosey over to the Goldstein Lab’s site for more movies here.

Roh-Johnson, M., Shemer, G., Higgins, C., McClellan, J., Werts, A., Tulu, U., Gao, L., Betzig, E., Kiehart, D., & Goldstein, B. (2012). Triggering a Cell Shape Change by Exploiting Preexisting Actomyosin Contractions Science DOI: 10.1126/science.1217869

September 29, 2011

Would you rather solve a 302-piece or a 100 billion-piece puzzle? This is a question I like to throw out when I explain the power of model organisms at family gatherings. Worms have 302 neurons, while the human brain has about 100 billion (give or take a few). Today’s image is from a great example of how informative model organisms can be in understanding key processes in our bodies.

Neurons are made of axons and dendrites – axons transmit information, while dendrites receive it. While both processes are key to the formation of a healthy nervous system, very little is known about dendrite formation. A recent paper describes dendrite development, using an oxygen-sensing neuron in the worm C. elegans. Kirszenblat and colleagues showed that dendrite formation in the oxygen sensory neuron is dependent on Wnt signaling, which is frequently used throughout development. Specifically, the LIN-44/Wnt signal and its associated LIN-17/Frizzled receptor trigger the initiation and guidance of the dendrite independently of axon development. Images and cartoons above show the oxygen sensory neuron (green) in normal worms (top left) and Wnt mutants (all others). Arrows point to axons while the arrowheads point to dendrites, which are either absent or incorrectly formed in the mutants.

Kirszenblat, L., Pattabiraman, D., & Hilliard, M. (2011). LIN-44/Wnt Directs Dendrite Outgrowth through LIN-17/Frizzled in C. elegans Neurons PLoS Biology, 9 (9) DOI: 10.1371/journal.pbio.1001157

September 15, 2011

There is something so gratifying about a light switch. My two-year old will pull a chair to our kitchen light switch to turn it on and off. Over. And over. And over again. Maybe that’s why I find phosphorylation so satisfying (and maybe why I have a headache). It’s a molecular switch, and the vast combinations of where, when, and how different proteins are phosphorylated can provide mind-numbing levels of regulation within a cell. Combine my appreciation for phosphorylation with my absolute love for early worm embryos, and you have today’s lovely images.

The one-cell stage worm embryo divides like many cells throughout development—asymmetrically. Asymmetric cell division results in two daughter cells with different developmental fates and frequently different sizes. For asymmetric cell division to take place in the early worm embryo, the entire mitotic spindle apparatus is moved towards one end of the cell, the posterior. A complex of polarity proteins (made of PAR proteins and the aPKC homolog PKC-3) functions upstream of an evolutionary conserved pathway of proteins (made of the NuMA homolog LIN-5 and G-protein signaling), and a recent paper finds the well sought-after link between these two pathways. In Galli and colleagues’ paper, they show that LIN-5 is phosphorylated by PKC-3. The position of PKC-3 at only one side of the cell results in the phosphorylation of LIN-5 only in that region, which in turns allows the mitotic spindle to position itself correctly. In the images above, one-cell stage worm embryos show staining for phosphorylated LIN-5 (top row, red in bottom row) during mitosis (spindle is in green, chromosomes in blue). Phosphorylated LIN-5 is enriched at higher levels at the anterior cortex (the left-hand side in each image) during earlier stages of mitosis.

Galli, M., Muñoz, J., Portegijs, V., Boxem, M., Grill, S., Heck, A., & van den Heuvel, S. (2011). aPKC phosphorylates NuMA-related LIN-5 to position the mitotic spindle during asymmetric division Nature Cell Biology, 13 (9), 1132-1138 DOI: 10.1038/ncb2315
Adapted by permission from Macmillan Publishers Ltd, copyright ©2011

August 22, 2011

There are some images that just stick with you. They might be beautiful, fascinating, or terrifying. For example, I’ll never forget when my former labmates told me to Google pictures of a teratoma. Seriously, don’t do it…wait, you just did, didn’t you? Unless you are a C. elegans worm, you won’t find today’s images terrifying…instead, you are likely to be utterly fascinated.

C. elegans are small 1mm-long roundworms that are used extensively in biology research. When the head of one of these worms is touched, its immediate response is to quickly back away from the touch. A recent paper describes how a fungus may have shaped the evolution of this behavior. Maguire and colleagues found that a predacious fungus called D. doedycoides capture larval stage worms by forming rings that constrict the worm passes through. There is a delay between when the fungus senses a worm passing through its ring and when it constricts to trap the worm. During this delay, the worm’s touch response can trigger the worm to quickly back out of the trap. However, there are some worms with mutations in its touch response—these worms are caught more efficiently by the fungus. Images above are electron micrographs of larval stage worms caught by the constricting rings of the fungus (left) and close-up images of the fungus’ rings before (top) and after (bottom) they are constricted.

BONUS!! Check out the authors’ video abstract, which includes movies of this predator-prey interaction, here.

Maguire, S., Clark, C., Nunnari, J., Pirri, J., & Alkema, M. (2011). The C. elegans Touch Response Facilitates Escape from Predacious Fungi Current Biology, 21 (15), 1326-1330 DOI: 10.1016/j.cub.2011.06.063
Copyright ©2011 Elsevier Ltd. All rights reserved.

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

November 4, 2010

Back when I was a budding little scientist, I joined the first lab that showed me glowing cells in a whole living organism. It wasn’t a rule I made for myself and my research had nothing to do with those particular cells called seam cells, but I knew that a lab with glowing worms would be a cool place to be.

Seam cells are hypodermal cells that are aligned along the left and right sides of the worm C. elegans. They serve an important purpose in postembryonic development—after the worm hatches, seam cells undergo stem-cell-like divisions that produce several different types of cells. A recent paper describes the role of spindle checkpoint proteins, which ensure proper chromosome segregation during mitosis, in the postembryonic divisions of seam cells. When one of these checkpoint proteins, MDF-2 (Mad2), is missing, the number and alignment of seam cells is disrupted. Images above show seam cells (green) in normal (top) and mdf-2 mutant (bottom) worms. The mutant worms frequently have extra or clustered seam cells (box) instead of the ordered alignment seen in normal worms.

Reference: Maja Tarailo-Graovac, Jun Wang, Jeffrey SC Chu, Domena Tu, David L Baillie and Nansheng Chen. Authors’ BMC Cell Biology paper can be found here.

September 6, 2010

Strong cell-cell adhesion is crucial for tissue organization during development. A complex of three proteins—cadherin, α-catenin, and β-catenin—play an important role in adhesion by organizing and regulating the actin cytoskeleton. A recent paper demonstrates how α-catenin functions within this complex and with actin in the developing worm embryo, and shows that this complex is regulated differently from the mechanism in mammals. Image is a C. elegans embryo with a mutant form of α-catenin (blue and green) and actin (yellow and magenta). Both are localized at cell junctions in normal embryos, but in this mutant there is reduced α-catenin and gaps of actin localization at cell-cell junctions.

Reference: Image is by Stephanie L. Maiden, and is the cover image cover for the August issue of PNAS, which can be found here. Accompanying paper is by Adam V. Kwiatkowski, Stephanie L. Maiden, Sabine Pokutta, Hee-Jung Choi, Jacqueline M. Benjamin, Allison M. Lynch, W. James Nelson, William I. Weis, and Jeff Hardin, and can be found here.

July 8, 2010

A neuron’s dendrites are responsible for relaying signals from a stimulus or other neuron, and their branched patterns are important for the specific function of each type of neuron. In the worm C. elegans, the PVD neurons are mechanoreceptors that trigger an avoidance response after a touch stimulus. The dendrites of PVDs are repetitive structures that look like candelabras or menorahs. Image above shows a worm with a fluorescent signal in PVD neurons. A recent paper describes the role of a cell fusion protein called EFF-1 in regulating the formation of these menorahs, showing that EFF-1 sculpts the branching of the menorahs.

Reference: Meital Oren-Suissa, David H. Hall, Millet Treinin, Gidi Shemer, and Benjamin Podbilewicz. Similar images can be found in their Science paper, which can be found here.

May 17, 2010

In endocytosis, material is taken into the cell and is transported around the cell in vesicles, or endosomes, with different functions and associated proteins. A recent paper has shown the transition of an early endosome into a late endosome, using live imaging of a scavenger cell called a ceolomocyte, in the worm C. elegans. Image above shows this transition, with early endosomes in green and late endosomes in red. The arrow is pointing to one particular endosome as it transitions into a late endosome.

Reference: Dmitry Poteryaev, Sunando Datta, Karin Ackema, Marino Zerial, and Anne Spang. Cell 141, 497-508. ©2010 Elsevier Ltd All rights reserved. Paper can be found here.