Cells move forward with lamellipodia and filopodia supported by networks and bundles of actin filaments. Proper, controlled cell movement is a complex process. Recent research has shown that an actin-polymerizing factor called the Arp2/3 complex is the key component of the actin polymerization engine that drives amoeboid cell motility. ARPC3, a component of the Arp2/3 complex, plays a critical role in actin nucleation. In this photo, the ARPC3-/- fibroblast cells were fixed and stained with Alexa 546 phalloidin for F-actin (red), mDia1 (green), and DAPI to visualize the nucleus (blue). In ARPC3-/- fibroblast cells, mDia1 is localized at the tips of the filopodia-like structures. Related to images 3328, 3329, 3330, 3332, and 3333.

A crystal of porcine trypsin protein created for X-ray crystallography, which can reveal detailed, three-dimensional protein structures.

A Trigonium diatom imaged by a quantitative orientation-independent differential interference contrast (OI-DIC) microscope. Diatoms are single-celled photosynthetic algae with mineralized cell walls that contain silica and provide protection and support. These organisms form an important part of the plankton at the base of the marine and freshwater food chains. The width of this image is 90 μm.

More information about the microscopy that produced this image can be found in the Journal of Microscopy paper “An Orientation-Independent DIC Microscope Allows High Resolution Imaging of Epithelial Cell Migration and Wound Healing in a Cnidarian Model” by Malamy and Shribak.

C. elegans, a tiny roundworm, with a ribosomal protein glowing red and muscle fibers glowing green. Researchers used these worms to study a molecular pathway that affects aging. The ribosomal protein is involved in protein translation and may play a role in dietary restriction-induced longevity. Image created using confocal microscopy.
View group of roundworms here 6582.
View closeup of roundworms here 6583.

Yeast cells with endocytic actin patches (green). These patches help cells take in outside material. When a cell is in interphase, patches concentrate at its ends. During later stages of cell division, patches move to where the cell splits. This image was captured using wide-field microscopy with deconvolution.

Related to images 6791, 6792, 6794, 6797, 6798, and videos 6795 and 6796.

RNA interference or RNAi is a gene-silencing process in which double-stranded RNAs trigger the destruction of specific RNAs. See 2559 for a labeled version of this illustration. Featured in The New Genetics.

The receptor is shown bound to an antagonist, compound-24

Rendering of the surface of an endothelial cell; membrane curvature is color coded. This is an example of NIH-supported research on single-cell analysis. Related to 2798 , 2799, 357, 2801, and 2802.

Yeast cells with nuclear envelopes shown in magenta and tubulin shown in light blue. The nuclear envelope defines the borders of the nucleus, which houses DNA. Tubulin is a protein that makes up microtubules—strong, hollow fibers that provide structure to cells and help direct chromosomes during cell division. This image was captured using wide-field microscopy with deconvolution.

Related to images 6791, 6792, 6793, 6794, 6797, and videos 6795 and 6796.

Structure of a magnesium transporter protein from an antibiotic-resistant bacterium (Enterococcus faecalis) found in the human gut. Featured as one of the June 2007 Protein Sructure Initiative Structures of the Month.

A model of the molecule himastatin, which was first isolated from the bacterium Streptomyces himastatinicus. Himastatin shows antibiotic activity. The researchers who created this image developed a new, more concise way to synthesize himastatin so it can be studied more easily.

More information about the research that produced this image can be found in the Science paper “Total synthesis of himastatin” by D’Angelo et al.

Related to image 6850 and video 6851.

Wound healing requires the action of stem cells. In mice that lack the Sept2/ARTS gene, stem cells involved in wound healing live longer and wounds heal faster and more thoroughly than in normal mice. This confocal microscopy image from a mouse lacking the Sept2/ARTS gene shows a tail wound in the process of healing. Cell nuclei are in blue. Red and orange mark hair follicle stem cells (hair follicle stem cells activate to cause hair regrowth, which indicates healing). See more information in the article in Science.

Like a strand of white pearls, DNA wraps around an assembly of special proteins called histones (colored) to form the nucleosome, a structure responsible for regulating genes and condensing DNA strands to fit into the cell's nucleus. Researchers once thought that nucleosomes regulated gene activity through their histone tails (dotted lines), but a 2010 study revealed that the structures' core also plays a role. The finding sheds light on how gene expression is regulated and how abnormal gene regulation can lead to cancer.

This video shows an instance of abnormal mitosis where chromosomes are late to align. The video demonstrates the spindle checkpoint in action: just one unaligned chromosome can delay anaphase and the completion of mitosis. The cells shown are S3 tissue cultured cells from Xenopus laevis, African clawed frog.

Macrophages (green) are the professional eaters of our immune system. They are constantly surveilling our tissues for targets—such as bacteria, dead cells, or even cancer—and clearing them before they can cause harm. In this image, researchers were testing how macrophages responded to different molecules that were attached to silica beads (magenta) coated with a lipid bilayer to mimic a cell membrane.

Find more information on this image in the NIH Director’s Blog post "How to Feed a Macrophage."

A mosquito larva with genes edited by CRISPR. The red-orange glow is a fluorescent protein used to track the edits. This species of mosquito, Culex quinquefasciatus, can transmit West Nile virus, Japanese encephalitis virus, and avian malaria, among other diseases. The researchers who took this image developed a gene-editing toolkit for Culex quinquefasciatus that could ultimately help stop the mosquitoes from spreading pathogens. The work is described in the Nature Communications paper "Optimized CRISPR tools and site-directed transgenesis towards gene drive development in Culex quinquefasciatus mosquitoes" by Feng et al. Related to image 6770 and video 6771.

Molecular model of the struture of heme. Heme is a small, flat molecule with an iron ion (dark red) at its center. Heme is an essential component of hemoglobin, the protein in blood that carries oxygen throughout our bodies. This image first appeared in the September 2013 issue of Findings Magazine. View side view of heme here 3539.

Cell division is an incredibly coordinated process. It not only ensures that the new cells formed during this event have a full set of chromosomes, but also that they are endowed with all the cellular materials, including proteins, lipids and small functional compartments called organelles, that are required for normal cell activity. This proper apportioning of essential cell ingredients helps each cell get off to a running start.

This image shows an electron microscopy (EM) thin section taken at 10,000x magnification of a dividing yeast cell over-expressing the protein ubiquitin, which is involved in protein degradation and recycling. The picture features mother and daughter endosome accumulations (small organelles with internal vesicles), a darkly stained vacuole and a dividing nucleus in close contact with a cadre of lipid droplets (unstained spherical bodies).  Other dynamic events are also visible,  such as spindle microtubules in the nucleus and endocytic pits at the plasma membrane.

These extensive details were revealed thanks to a preservation method involving high-pressure freezing, freeze-substitution and Lowicryl HM20 embedding.

Cells move forward with lamellipodia and filopodia supported by networks and bundles of actin filaments. Proper, controlled cell movement is a complex process. Recent research has shown that an actin-polymerizing factor called the Arp2/3 complex is the key component of the actin polymerization engine that drives amoeboid cell motility. ARPC3, a component of the Arp2/3 complex, plays a critical role in actin nucleation. In this photo, the ARPC3+/+ fibroblast cells were fixed and stained with Alexa 546 phalloidin for F-actin (red), mDia1 (green), and DAPI to visualize the nucleus (blue). mDia1 is localized at the lamellipodia of ARPC3+/+ fibroblast cells. Related to images 3328, 3329, 3331, 3332, and 3333.

An axolotl—a type of salamander—that has been genetically modified so that its developing nervous system glows purple and its Schwann cell nuclei appear light blue. Schwann cells insulate and provide nutrients to peripheral nerve cells. Researchers often study axolotls for their extensive regenerative abilities. They can regrow tails, limbs, spinal cords, brains, and more. The researcher who took this image focuses on the role of the peripheral nervous system during limb regeneration.

This image was captured using a stereo microscope.

Related to images 6927 and 6928.

Cilia (cilium in singular) are complex molecular machines found on many of our cells. One component of cilia is the doublet microtubule, a major part of cilia’s skeletons that give them support and shape. This animated video illustrates the structure of doublet microtubules, which contain 451 protein chains that were mapped using cryo-electron microscopy. Image can be found here 6548.

Superresolution microscopy work on endoplasmic reticulum (ER) in the peripheral areas of the cell showing details of the structure and arrangement in a complex web of tubes.
The ER is a continuous membrane that extends like a net from the envelope of the nucleus outward to the cell membrane. The ER plays several roles within the cell, such as in protein and lipid synthesis and transport of materials between organelles. The ER has a flexible structure to allow it to accomplish these tasks by changing shape as conditions in the cell change. Shown here an image created by super-resolution microscopy of the ER in the peripheral areas of the cell showing details of the structure and the arrangements in a complex web of tubes. Related to images 5856 and 5857.

Multiphoton fluorescence image of HeLa cells with cytoskeletal microtubules (magenta) and DNA (cyan). Nikon RTS2000MP custom laser scanning microscope. See related images 3518, 3519, 3521, 3522.

Sensory organs have cells equipped for detecting signals from the environment, such as odors. Receptors in the membranes of nerve cells in the nose bind to odor molecules, triggering a cascade of chemical reactions tranferred by G proteins into the cytoplasm.

A global "map of the protein structure universe." The Berkeley Structural Genomics Center has developed a method to visualize the vast universe of protein structures in which proteins of similar structure are located close together and those of different structures far away in the space. This map, constructed using about 500 of the most common protein folds, reveals a highly non-uniform distribution, and shows segregation between four elongated regions corresponding to four different protein classes (shown in four different colors). Such a representation reveals a high-level of organization of the protein structure universe.

E. coli bacteria normally live harmlessly in our intestines, but some cause disease by making toxins. One of these toxins, called Shiga toxin (green), inactivates host ribosomes (purple) by mimicking their normal binding partners, the EF-Tu elongation factor (red) complexed with Phe-tRNAPhe (orange).

Find these in the RCSB Protein Data Bank: Shiga toxin 2 (PDB entry 7U6V) and Phe-tRNA (PDB entry 1TTT).

More information about this work can be found in the J. Biol. Chem. paper "Cryo-EM structure of Shiga toxin 2 in complex with the native ribosomal P-stalk reveals residues involved in the binding interaction" by Kulczyk et. al.

Stereo triplet of a sea urchin embryo stained to reveal actin filaments (orange) and microtubules (blue). This image is part of a series of images: 1047, 1048, 1050, 1051 and 1052.

Green and yellow fluorescence mark the processes and cell bodies of some C. elegans neurons. Researchers have found that the strategies used by this tiny roundworm to control its motions are remarkably similar to those used by the human brain to command movement of our body parts. From a November 2011 University of Michigan news release.

Myelinated axons in a rat spinal root. Myelin is a type of fat that forms a sheath around and thus insulates the axon to protect it from losing the electrical current needed to transmit signals along the axon. The axoplasm inside the axon is shown in pink. Related to 3397.

Featured in the March 15, 2012 issue of Biomedical Beat. Related to Hsp33 Figure 2, image 3355.

Multiple actin filaments (magenta) are organized around a dynamin helical polymer (rainbow colored) in this model derived from cryo-electron tomography. By bundling actin, dynamin increases the strength of a cell’s skeleton and plays a role in cell-cell fusion, a process involved in conception, development, and regeneration.

This illustration shows vesicle traffic inside a cell. The double membrane that bounds the nucleus flows into the ribosome-studded rough endoplasmic reticulum (purple), where membrane-embedded proteins are manufactured. Proteins are processed and lipids are manufactured in the smooth endoplasmic reticulum (blue) and Golgi apparatus (green). Vesicles that fuse with the cell membrane release their contents outside the cell. The cell can also take in material from outside by having vesicles pinch off from the cell membrane.

Muscles stretch and contract when we walk, and skin splits open and knits back together when we get a paper cut. To study these contractile forces, researchers built a three-dimensional scaffold that mimics tissue in an organism. Researchers poured a mixture of cells and elastic collagen over microscopic posts in a dish. Then they studied how the cells pulled and released the posts as they formed a web of tissue. To measure forces between posts, the researchers developed a computer model. Their findings--which show that contractile forces vary throughout the tissue--could have a wide range of medical applications.

3D image of Caulobacter bacterium with various components highlighted: cell membranes (red and blue), protein shell (green), protein factories known as ribosomes (yellow), and storage granules (orange).

The enzyme Dicer generates microRNAs by chopping larger RNA molecules into tiny Velcro^®-like pieces. MicroRNAs stick to mRNA molecules and prevent the mRNAs from being made into proteins. See image 2556 for an unlabeled version of this illustration. Featured in The New Genetics.

The three neurons (red) visible in this image were derived from human embryonic stem cells. Undifferentiated stem cells are green here. Image and caption information courtesy of the California Institute for Regenerative Medicine.

Some nerve cells (neurons) in the brain keep track of the daily cycle. This time-keeping mechanism, called the circadian clock, is found in all animals including us. The circadian clock controls our daily activities such as sleep and wakefulness. Researchers are interested in finding the neuron circuits involved in this time keeping and how the information about daily time in the brain is relayed to the rest of the body. In this image of a brain of the fruit fly Drosophila the time-of-day information flowing through the brain has been visualized by staining the neurons involved: clock neurons (shown in blue) function as "pacemakers" by communicating with neurons that produce a short protein called leucokinin (LK) (red), which, in turn, relays the time signal to other neurons, called LK-R neurons (green). This signaling cascade set in motion by the pacemaker neurons helps synchronize the fly's daily activity with the 24-hour cycle. To learn more about what scientists have found out about circadian pacemaker neurons in the fruit fly see this news release by New York University. This work was featured in the Biomedical Beat blog post Cool Image: A Circadian Circuit.

A tomographic reconstruction of the colon shows the location of large pools of HIV-1 virus particles (in blue) located in the spaces between adjacent cells. The purple objects within each sphere represent the conical cores that are one of the structural hallmarks of the HIV virus.

T cells are white blood cells that are important in defending the body against bacteria, viruses and other pathogens. Each T cell carries proteins, called T-cell receptors, on its surface that are activated when they come in contact with an invader. This activation sets in motion a cascade of biochemical changes inside the T cell to mount a defense against the invasion. Scientists have been interested for some time what happens after a T-cell receptor is activated. One obstacle has been to study how this signaling cascade, or pathway, proceeds inside T cells.

In this video, researchers have created a T-cell receptor pathway consisting of 12 proteins outside the cell on an artificial membrane. The video shows three key steps during the signaling process: phosphorylation of the T-cell receptor (green), clustering of a protein called linker for activation of T cells (LAT) (blue) and polymerization of the cytoskeleton protein actin (red). The findings show that the T-cell receptor signaling proteins self-organize into separate physical and biochemical compartments. This new system of studying molecular pathways outside the cells will enable scientists to better understand how the immune system combats microbes or other agents that cause infection.

To learn more how researchers assembled this T-cell receptor pathway, see this press release from HHMI's Marine Biological Laboratory Whitman Center. Related to image 3787.

Multiphoton fluorescence image of cultured HeLa cells with a fluorescent protein targeted to the Golgi apparatus (orange), microtubules (green) and counterstained for DNA (cyan). Nikon RTS2000MP custom laser scanning microscope. See related images 3518, 3519, 3520, 3521.

The light organ (~0.5 mm across) of a juvenile Hawaiian bobtail squid, Euprymna scolopes, stained blue. The two pairs of ciliated appendages, or “arms,” on the sides of the organ move Vibrio fischeri bacterial cells closer to the two sets of three pores at the base of the arms that each lead to an interior crypt. This image was taken using a confocal fluorescence microscope.

Related to images 7017, 7018, 7019, and 7020.

Stereo triplet of a sea urchin embryo stained to reveal actin filaments (orange) and microtubules (blue). This image is part of a series of images: 1047, 1048, 1049, 1050 and 1052.

Floral pattern emerging as two bacterial species, motile Acinetobacter baylyi (red) and non-motile Escherichia coli (green), are grown together for 48 hours on 1% agar surface from a small inoculum in the center of a Petri dish.

See 6557 for a photo of this process at 24 hours on 0.75% agar surface.
See 6555 for another photo of this process at 48 hours on 1% agar surface.
See 6556 for a photo of this process at 72 hours on 0.5% agar surface.
See 6550 for a video of this process.

A three-dimensional representation of the structure of E2, a key antigen protein involved with hepatitis C virus infection.

Stereo triplet of a sea urchin embryo stained to reveal actin filaments (orange) and microtubules (blue). This image is part of a series of images: 1047, 1048, 1049, 1050 and 1051.

Cells function within organs and tissues, such as the lungs, heart, intestines, and kidney.

Model of the enzyme nicotinic acid phosphoribosyltransferase. This enzyme, from the archaebacterium, Pyrococcus furiosus, is expected to be structurally similar to a clinically important human protein called B-cell colony enhancing factor based on amino acid sequence similarities and structure prediction methods. The structure consists of identical protein subunits, each shown in a different color, arranged in a ring.

A scanning electron microscope picture of a nerve ending. It has been broken open to reveal vesicles (orange and blue) containing chemicals used to pass messages in the nervous system.

Sketch of an egg cell.