Fruit Fly Embryo Montage

The image presented below features a triple-labeled Drosophila embryo at the cellular blastoderm stage. The specimen was immunofluorescently tagged with antibodies to the hairy protein in red, Kruppel repressor in green and the giant protein in blue. A variety of color combinations were produced by "channel surfing" in Photoshop.

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  Fruit Fly Embryo Montage

  Specimen: Drosophila Embryo
  Technique: Fluorescence (Triple Label) and Photoshop Channels
  

  Although the general population may not appreciate the fruit fly, this insect is a favorite for scientific research, and has made enormous contributions in the field of genetics. Initially, Drosophila were utilized almost exclusively as specimens in genetic research, but more recently, the fruit fly has been used in the study of developmental biology, with particular emphasis on the embryonic phase. There is also a growing body of research that focuses on the adult fruit fly, with the compound eye being of particular interest.

Butterfly Wing Scale in Autofluorescence

Confocal microscopy, especially in combination with fluorescent probes, is often used to examine optical sections from fairly thick biological specimens. The digital image presented below features autofluorescence of a butterfly wing scale (illustrating the striated surface structure) captured in a thin optical section with a confocal laser scanning microscope.

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  Butterfly Wing Scale in Autofluorescence

  Specimen: Butterfly Wing
  Technique: Confocal Autofluorescence
  

  Optical sectioning enables serial portions of the butterfly's wing to be examined under the microscope to the exclusion of other parts of the wing. In confocal microscopy, the image-forming light from a given focal point can be seen through the microscope, while any out-of-focus light is excluded by a pinhole aperture. This "slice" is termed an optical section.

Islands of Color

Cells in tissue culture exhibit a dazzling array of colors when stained with multiple fluorescent probes and imaged with a confocal laser scanning microscope. The digital image presented below illustrates a cluster of living cells captured with the aid of fluorescent probes and laser scanning confocal microscopy.

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  Islands of Color

  Specimen: Cell Culture
  Technique: Fluorescence (Multiple Labels)
  

  Two major classes of cells are prokaryotes and eukaryotes, which are similar in that they both contain DNA, RNA, ribosomes, a similar metabolism, and they are both protected from the outside environment by a thin membrane. Eukaryotes, however, are generally about ten times the size of prokaryotes, and they are also equipped with a nucleus, and membrane-bound organelles that perform specialized functions within the cell.

Fruit Fly Embryo Nervous System

Featured below is the central nervous system of a Drosophila (fruit fly) embryo captured in a serial optical section by confocal laser scanning microscopy. This double-labeled fluorescent specimen reveals peripheral neurons in green and glial cells in red.

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  Fruit Fly Embryo Nervous System

  Specimen: Drosophila Embryo Nervous System
  Technique: Fluorescence (Double Label)
  

  The fruit fly is a favorite laboratory organism for a wide range of biological and medical research. Scientists at the Howard Hughes Medical Institute have recently isolated a protein in the nervous system of the fruit fly that is said to be closely related to the receptor that cocaine targets in the human brain. Researchers hope that by genetically altering this protein in the fruit fly, they might gain a better understanding of how cocaine and other mind-altering substances affect the human brain and point the way towards new therapies.

Salt Crystals and Cells

Reflected light microscopy captured this beautiful digital image that features a combination of salt crystals and cells on an electron microscope specimen grid. The display of color on the surface of the salt crystals is due to interference patterns from surface reflections.

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  Salt Crystals and Cells

  Specimen: Salt Crystals and Cells on EM Grid
  Technique: Reflected Light Microscopy
  

  An important characteristic of light waves is their ability, under certain circumstances, to interfere with one another. Most people observe some type of optical interference every day, but do not realize what is occurring to produce this phenomenon. One of the best examples of interference is demonstrated by the light reflected from a film of oil floating on water. The dynamic interplay of colors derives from simultaneous reflection of light from both the inside and outside surfaces of the bubble.

Fruit Fly Embryo Blastoderm

Featured below is a digital image of a triple-labeled Drosophila embryo at the cellular blastoderm stage. The specimen was immunofluorescently labeled with antibodies to the hairy protein in red, Kruppel in green, and giant in blue. This amazing image won the BioTechniques cover of the year award in 1993.

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  Fruit Fly Embryo Blastoderm

  Specimen: Drosophila Embryo
  Technique: Fluorescence (Triple Label)
  

  Drosophila is the scientific name for the common fruit fly, which has proven to be a cornerstone in the field of eukaryotic genetics, both at the cellular and molecular level. This insect is approximately three millimeters long and has two wings. However, many of the most interesting genetic mutations render the fruit fly unable to fly, so the afflicted flies move around by climbing or hopping. An ideal habitat for the fruit fly is a warm climate, rich in vegetation that will provide the insect with a wide variety of fruit and vegetables, which often serve as a temporary home when the fly burrows into the plants during feeding. The fruit fly is a common household pest during spring and summer and can prove to be a menace to agricultural crops, resulting in extensive economic consequences.

Compact Disc

Lands and pits dotting the surface of a compact disc are revealed in this confocal reflected light digital image. Each of the tiny "dots" in the disc is designed to deflect light from a laser to create the necessary binary code for deciphering the information encoded on the disc.

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  Compact Disc

  Specimen: Compact Disc
  Technique: Confocal Reflected Light
  

  The compact disc is a small, plastic form of optical data storage, which is popular in both the music and computer technology industries because of its superior storage capacity. A single disc can hold about twice as much audio information (about 650 megabytes) as the LP, or long-playing record, and the range of sound that is created is about twice the dynamic range as that produced in a live performance. Even the most musically and technically unsophisticated consumer can appreciate the crisp, clear quality of the audio that the compact disc delivers.

Image Processed Compact Disc

Using the power of digital image processing, Dr. Paddock translates the pit and land pattern from the two-dimensional reflected light image of a compact disc into the spiral arrangement actually utilized on the disc. To go a step further, he also adds some special touches to create a masterpiece of digital imaging.

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  Image Processed Compact Disc

  Specimen: Compact Disc
  Technique: Confocal Reflected Light
  

  In the 1980's, the compact disc was popularized as the preferred form of audio information storage and playback because of the crisp, clear quality of the sound produced, as well as the superior storage capacity. Today, with homes and businesses increasingly relying on digital communication systems, the compact disc is often the preferred medium for saving, exchanging, and moving large digital files from one computer to another. Not only does the disc's small size make it quite handy, its storage capacity is significantly greater than that of the archaic floppy.

Fruit Fly Imaginal Discs - Leg, Haltere, and Wing

Featured below is a fluorescence digital image of three imaginal discs: a leg, haltere, and wing, from a third instar Drosophila (fruit fly), all labeled with a green fluorescent dye attached to the Cubitus interruptus (Ci) protein. Imaginal discs are larval tissue structures that develop into adult appendages.

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  Fruit Fly Imaginal Discs : Leg, Haltere, and Wing

  Specimen: Drosophila Imaginal Discs
  Technique: Fluorescence
  

  The life span of the fruit fly is approximately fourteen days. One day after fertilization, a fruit fly egg is hatched into a worm-like larva approximately one millimeter long. During this stage, the larva eats continuously, and molts one, two, four, and six days after hatching. A fruit fly in the larval stage is also equipped with a breathing tube at its tail end.

Butterfly Wing Scales (Phalloidin)

Presented in the digital image below is a whole mount of the wing epithelium from a pupal butterfly, labeled with phalloidin. Note the fluorescently-stained wing scales, which emit a green fluorescence when excited by light from the microscope illuminator.

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  Butterfly Wing Scales (Phalloidin)

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Phalloidin Label)
  

  Mimicry is a fascinating adaptive mechanism wherein one organism takes on the physical characteristics of another organism for the purpose of confusing predators. In Mullerian mimicry, the mimic is as equally defended as the model. For example, the queen butterfly has a colorful similarity to the monarch. Both of these butterfly species are foul tasting, but the monarch is also poisonous to predators. In Batesian mimicry, the mimic is not as well defended as the model. An example of this is the viceroy butterfly, another mimic of the monarch. In this instance, however, the viceroy is neither foul tasting nor poisonous, so it is not as equally defended from predators.

Butterfly Wing Scales

A whole mount of wing epithelium from a pupal butterfly, labeled with phalloidin, is featured in this section. Although stained with phalloidin, this digitally processed image was not provided a green color channel in Photoshop, so the wing scales appear colorless.

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  Butterfly Wing Scales

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Phalloidin Label)
  

  A caterpillar, a butterfly in its larval phase, uses its silk to attach itself to a host plant. After attachment, mobility and feeding cease, and a new pupal skin forms beneath the caterpillar's cocoon. The pupal stage of development, or chrysalis stage, lasts approximately one month for most butterfly species. Some species, however, have pupal phases that last as long as two years because of their hibernation process, or diapause. Once organs have matured, the larval skin dismantles, and a newly hatched butterfly emerges with wings that are moist and uninflated. The butterfly hangs upside down and pumps blood into the wings to inflate them before taking flight for the first time.

Fruit Fly Imaginal Discs - Haltere and Wing

Featured below are fluorescence digital images of triple-labeled Drosophila (fruit fly) haltere and wing imaginal discs, labeled with fluorescent antibodies to apterous (wingless mutant) in red, vestigial (short winged mutant) in blue, and Cubitus interruptus (Ci) in green.

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  Fruit Fly Imaginal Discs : Haltere and Wing

  Specimen: Drosophila Imaginal Discs
  Technique: Fluorescence (Triple Label)
  

  After the fourth larval molt of the fruit fly, an immobile pupa emerges. The pupal fruit fly is brown, with two horn-like protrusions, and it takes an additional four to six days at this stage for the fruit fly to achieve its adult form where it has reached its full size, and has a fully developed reproductive system. The female fruit fly drops eggs until she dies, producing hundreds of offspring. Eight days later, the cycle begins again and her offspring are off to the races, making them very effective pests.

Fruit Fly Imaginal Disc - Wing

Featured below is composite series of images of a Drosophila (fruit fly) wing imaginal disc. Different color combinations of this double-labeled sample reveal the location of wingless genetic mutants: achaete genes in red/yellow, yellow/white, purple/white, or blue/white and apterous genes in green, blue, green, and red, respectively.

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  Fruit Fly Imaginal Disc : Wing

  Specimen: Drosophila Imaginal Discs
  Technique: Fluorescence (Triple Label)
  

  In fruit flies, imaginal discs are the developmental tissues from which many adult structures, including eyes, wings, and halteres, are formed.

Fruit Fly Imaginal Disc - Third Instar Wing

Presented below is a fluorescence digital image of a Drosophila third instar wing imaginal disc labeled with apterous (a wingless mutant) in blue, vestigial (a small winged mutant) in red and Cubitus interruptus (Ci) in green. This image won 18th place in the Nikon Small World competition in 1997.

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  Fruit Fly Imaginal Disc : Third Instar Wing

  Specimen: Drosophila Imaginal Discs
  Technique: Fluorescence (Triple Label)
  

  Research in the area of genetics has frequently focused on the various mutations common to the fruit fly. Defects in eye and limb formations have been particularly well documented.

Fluorescent DNA in Tissue Culture Cells

By injecting multiply-labeled DNA into tissue culture cells, Dr. Paddock was able to produce this beautiful image using a confocal laser scanning microscope. The various fluorescent colors each represent different target genes for the probes utilized in the experiment.

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  Fluorescent DNA in Tissue Culture Cells

  Specimen: Fluorescent DNA in Tissue Culture Cells
  Technique: Fluorescence (Multiple Probes)
  

  DNA is a very unusual molecule that is shaped like a very long piece of string. The diameter of the DNA molecule is about 2-3 nanometers (about a billionth of an inch) while the length can exceed a thousand micrometers (0.025 inch) in some organisms. One of the major challenges in molecular biology is how this giant molecule can be packaged into a cell or virus that is far smaller than the length of the DNA molecule. In addition, a number of investigations are concerned about how the cell is able to access the DNA molecule for the purposes of genetic control, routine cellular maintenance, and reproduction.

Fruit Fly Imaginal Disc - Third Instar Wing Montage

In fruit flies, imaginal discs are developmental tissues from which many adult structures, such as eyes, wings, and halteres, are formed. In the third instar phase, a larva has molted three times, and it will do so once more to emerge as an immobile pupa. The image presented below is a composite montage prepared from a digital image of a tripled labeled fruit fly imaginal disc.

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  Fruit Fly Imaginal Disc : Third Instar Wing Montage

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence Montage
  

  Although the general population may not appreciate the fruit fly, some of its more esoteric features have made it a favorite among scientific researchers. Initially, the fruit fly (Drosophila) was used as the primary specimen, in the fields of cellular and molecular biology, for determining the basics of eukaryotic genetics. More recently, the fruit fly has been utilized in developmental biology, with particular interest in the embryonic phase. There is also a growing body of research focusing on the adult fruit fly.

Fruit Fly Imaginal Disc - Haltere

The haltere, a club-shaped balancing structure supported by the thorax muscles, is one of the fruit fly's many limbs. Fruit flies typically have a single pair of these appendages. The digital image featured below was recorded on a confocal laser scanning microscope using a fluorescently labeled specimen.

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  Fruit Fly Imaginal Disc : Haltere

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Triple Label)
  

  The fruit fly has a single pair of wings, but crawling, hopping, and climbing also serve as primary forms of mobility. Abnormal limb formation in fruit flies, due to induced and natural mutations, has been the subject of a substantial body of research in genetics and biology. In particular, the formation of legs that protrude from the head in place of antennae is a perplexing phenomenon that scientists found to be a result of a defect in the Antennapedia gene. Investigations of this mutation is led to the discovery of the hox genes, a group of genes responsible for regulating body formation in vertebrates.

Nuclei in Butterfly Wing Epithelium

Cellular nuclei present in the butterfly pupal wing epithelium tissue are the subject of the digital image presented below. The nuclei were imaged with a confocal laser scanning microscope and color-mapped with digital image processing software.

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  Nuclei in Butterfly Wing Epithelium

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Color Mapping)
  

  The colored scales on a butterfly's wing serve a variety of purposes, from camouflaging the butterfly to attracting a mate. In fact, the male butterfly's scales even emit a pheromone that aids in the mating process. Some butterflies also have large spots of color that mimic eyes and deceive predators into thinking that they are bigger than they actually are, thus scaring the predators away and saving the butterfly to live another day. Dark-colored scales also help with heat absorption and thermoregulation for these flying cold-blooded insects.

Ordered Nuclei in Butterfly Wing Epithelium

The orderly arrangement of nuclei in the wing epithelium of a pupal butterfly is evident in the digital image presented below. The image was captured using a confocal laser scanning microscope and enhanced with digital image processing techniques.

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  Nuclei in Butterfly Wing Epithelium

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Color Mapping)
  

  Butterflies belong to the order Lepidoptera. In Latin, lepido translates roughly to scale, and ptera is a term for wings. The tiny ridges covering each butterfly wing scale cause light to reflect from different angles resulting in interference, which gives butterfly wings their iridescent quality. These beautiful, cold-blooded insects are most active during the spring and summer, when ample sunlight is available. There are an estimated 12,000 to 15,000 butterfly species in North America alone. More than 20 butterfly and moth species are listed as endangered by the U.S. Fish and Wildlife Service.

Fruit Fly Imaginal Disc - Second Instar

The fruit fly is a favorite specimen for biological research, and it has been utilized in the studies of a vast array of subjects ranging from sleep disorders to cocaine addiction. The digital image presented below features a double-labeled fluorescence image of a Drosophila imaginal disc from the second larval instar stage of development.

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  Fruit Fly Imaginal Disc : Second Instar

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Double Label)
  

  In a recent study conducted at the University of Connecticut, researchers found that modifying a particular fruit fly chromosome, of which humans have a comparative counterpart, resulted in mutated flies whose life spans were up to double that of normal fruit flies. Not only was the lifespan increased, but also quality of life appeared to be maintained. In addition, female mutants continued to reproduce until death, often producing as many as two hundred offspring.

Fruit Fly Imaginal Disc - Eye (Low Magnification)

Presented below is digital image captured with a confocal laser scanning microscope of a Drosophila (fruit fly) eye imaginal disc from the third instar larval stage that has been has been double-labeled using green and red fluorophores (the Hairy gene is labeled in green and Cubitus interruptus (Ci) in red).

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  Fruit Fly Imaginal Disc : Eye (Low Magnification)

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Double Label)
  

  The fruit fly's normal eye color is reddish-brown, but genetic mutations produce a wide variety of defects that are helpful to geneticists in tracing genes and following their developmental patterns. As an example, a mutation that has been mapped to a defect on the X-chromosome, results in flies having yellow eyes. Some mutations cause the flies to have eyes that turn out pink, green, or white, while other mutations can produce flies that express an eyeless gene.

Fruit Fly Imaginal Disc - Eye (Higher Magnification)

The Drosophila (fruit fly) eye has been the subject of extensive research, ranging from mutations that cause eye discolorations to the fascinating compound structure, which is built into a formation of 800 individual eyes termed ommatidia. The digital image presented below features a double-labeled fluorescence image of an imaginal disc from the Drosophila second larval instar development stage.

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  Fruit Fly Imaginal Disc : Eye (Higher Magnification)

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Double Label)
  

  Ommatidia each have their own miniature lens system, which operate in a somewhat independent manner. At the core of each eye are eight specialized, light-sensitive neurons (R-cells) and four non-neuronal cells. Surprisingly, scientists have found that introducing the fruit fly's eyeless gene into other parts of the organism's anatomy, such as on the wings or legs, results in the formation of numerous eyes in those areas.

Fruit Fly Imaginal Disc - Third Instar Eye (Low Magnification)

The fruit fly (Drosophila) is commonly utilized in laboratory research in a wide variety of scientific disciplines. For example, sleep disorder studies have employed the fruit fly as an experimental model with notable results. Featured below is a fluorescence digital image captured with a confocal laser scanning microscope of a triple-labeled Drosophila eye imaginal disc recovered from the third instar larval developmental stage.

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  Fruit Fly Imaginal Disc : Third Instar Eye (Low Magnification)

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Triple Label)
  

  One group of researchers found that fruit flies and humans share a similar genetic structure that is responsible for controlling sleeping patterns. The fact that the sleeping patterns of the fruit flies are altered when substances such as caffeine and antihistamines are introduced seems to confirm, or at least add evidence for, these conclusions. Scientists hope that by studying the fruit fly, they might continue to make discoveries that will have positive implications for the treatment of a range of sleeping disorders, from narcolepsy to sleep walking and sleep apnea.

Fruit Fly Imaginal Disc - Third Instar Eye (High Magnification)

Featured below is a fluorescence digital image captured with a confocal laser scanning microscope of a triple-labeled Drosophila eye imaginal disc recovered from the third instar larval developmental stage. This image is a higher magnification view of a previous image in the gallery.

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  Fruit Fly Imaginal Disc - Third Instar Eye (High Magnification)

  Specimen: Drosophila Imaginal Disc
  Technique: Fluorescence (Triple Label)
  

  Drosophila was the model organism most widely utilized in genetics experiments prior to the development of advanced fungal genetic techniques in the 1930s. Both models took a backseat to bacteriophage in the 1950s and 1960s when a majority of scientists turned to the field of molecular biology and began to examine genetic concepts on a molecular level. Recombinant DNA technology, which developed into a useful tool in the 1970s and took the field by storm, provided a convenient method to isolate and examine the complex genetic structure of eukaryotes, thus reawakening the scientific community to the lowly fruit fly. Today, because so much is known about Drosophila than any other higher organism, it has become the E. coli of eukaryotic genetics.

Fruit Fly on Butterfly Wing

The colorful scales attached to the butterfly's wings often form beautiful patterns and large, colored spots. These spots serve as an effective survival mechanism in that they make the butterfly appear larger than its actual size to a potential predator by mimicking the eyes of a much larger creature. The digital image presented below features a Drosophila (fruit fly) resting near the eyespot on a butterfly wing.

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  Fruit Fly on Butterfly Wing

  Specimen: Drosophila Resting on Butterfly Wing
  Technique: Reflected Light
  

  Eyespots on the butterfly wing mimic larger eyes that often can defer predators to other prey. Common predators of the butterfly are spiders, baldfaced hornets, and birds, while fruit flies typically fall prey to spiders, ants, and beetles, not to mention specially designed fly traps and quick-handed humans.

Butterfly Wing Scale Montage

Using the color channel feature from Photoshop, Dr. Paddock has assembled a montage image of butterfly wing scales that exhibit a wide spectrum of color. The digital image presented below shows four color-palette selections from this process.

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  Butterfly Wing Scale Montage

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Photoshop Montage)
  

  The butterfly's beautifully colored wings have inspired legends throughout the ages. One legend holds that witches often assumed the form of a butterfly in order to steal milk and honey. Many cultures believed that butterflies were the souls of deceased loved ones, and to some, the butterfly has been seen as a sort of good luck omen. In fact, an old Native American legend states that capturing a butterfly and whispering a secret wish will result in that wish being swooped up to the heavens and granted by the Great Spirit. Legends aside, with its multi-colored wings, the butterfly is considered by many to be one of the most beautiful of insects.

Fruit Fly Embryo Color Depth

Presented below is a color mapped image of a Drosophila embryo, featuring stripes of the engrailed gene, which circle the embryo. The engrailed gene helps to direct fruit fly wing development, and mutations in this gene can affect how the wings appear in adult flies.

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  Fruit Fly Embryo Color Mapped

  Specimen: Drosophila Embryo
  Technique: Fluorescence (Color Mapped)
  

  Presented below is a color mapped image of a Drosophila embryo, featuring stripes of the engrailed gene, which circle the embryo. The engrailed gene helps to direct fruit fly wing development, and mutations in this gene can affect how the wings appear in adult flies.

Cell Outlines in Butterfly Wing Epithelium

The beautiful digital image presented below is a color-mapped fluorescence rendition of cell outlines in butterfly pupal wing epithelium tissue. The image was captured on a confocal laser scanning microscope and manipulated using digital image processing software.

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  Cell Outlines in Butterfly Wing Epithelium

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Color Mapping)
  

  Butterflies have two forewings and two hind wings. Strong thoracic muscles move these wings up and down in a figure-eight motion during the butterfly's graceful flight. While in flight, each pair of fore and hind wings functions together as a single unit. In most species, these couplings are made using lobes located on the hind wings. At rest, the butterfly's wings are held vertically.

Butterfly Wing Scales and Nuclei

Fluorescent labeling with dual probes (green and red) reveals both cellular nuclei and wing scales in the digital image presented below. Taken with a confocal laser scanning microscope, the wing tissue shows nuclei in green and developing scales in red.

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  Butterfly Wing Scales and Nuclei

  Specimen: Butterfly Pupal Wing Epithelium
  Technique: Fluorescence (Double Label)
  

  A network of scales covers most of the butterfly wing, giving it a beautiful array of colors produced either by pigmentation or through optical interference. The iridescent colors usually associated with butterfly wings arise from the small ridges on the scales, which interact with light causing constructive and destructive interference, much like that produced by a soap bubble. Other coloration in the wing is caused by clusters of dehydrated blood cells, leading to a wide spectrum of colors that we see as distinct patterns in the wings.

Stress Fibers in 3T3 Cells

Reflected light confocal microscopy can reveal details not visible using standard transmitted light techniques. Dr. Paddock utilized this technique to capture stress fibers in Swiss mouse embryo (3T3) fibroblast cells grown in monolayer cell culture.

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  Stress Fibers in 3T3 Cells

  Specimen: 3T3 Cells
  Technique: Confocal Reflected Light
  

  The 3T3 tissue culture cell line is composed of fibroblasts from an albino Swiss mouse embryo. Fibroblasts are cells that develop into connective tissue and display a distinct morphology when grown in culture. This well-known cell line was established in 1962, and throughout the 1960's and 1970's, the cell line was widely used in oncogenic virus studies. Now these contact-inhibited fibroblasts are used more extensively as feeder cells for other rodent or human cells.

Fibroblasts in Reflected Light

Living cells in culture can be examined by a variety of optical techniques, but reflected light microscopy can reveal details not afforded by other methods. The image presented in this section reveals differences in a fibroblast cell that are observed with two different reflected light modes.

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  Fibroblasts in Reflected Light

  Specimen: Fibroblasts in Culture
  Technique: Reflected Light (Fluorescence)
  

  Reflected light microscopy is often referred to as incident light, epi-illumination, or metallurgical microscopy, and is the method of choice for fluorescence and for imaging specimens that remain opaque even when ground to a thickness of 30 micrometers. The range of specimens falling into this category is enormous and includes most metals, ores, ceramics, many polymers, semiconductor wafers, integrated circuits, slag, coal, plastics, paint, paper, wood, leather, glass inclusions, and a wide variety of specialized materials. Because light is unable to pass through these specimens, it must be directed onto the surface and eventually returned to the microscope objective by either specular or diffused reflection. As mentioned above, such illumination is most often referred to as episcopic illumination, epi-illumination, or vertical illumination (essentially originating from above), in contrast to diascopic (transmitted) illumination that passes through a specimen.

Muscle Tissue

Striations in muscle tissue are revealed with phalloidin-stained specimens when imaged with confocal laser scanning microscopy. The digital image presented below illustrates an alternating red, green, black, and blue pattern that represents the striations characteristic of this type of tissue.

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  Muscle Tissue

  Specimen: Muscle Tissue
  Technique: Fluorescence (Phalloidin)
  

  For millions of years, the human diet has included the edible portion of animal tissues, or meat. Meat is an excellent source of protein, providing all nine essential amino acids in addition to vitamins and minerals. There are three types of muscle: smooth, cardiac, and skeletal, but skeletal muscles make up most meats and meat products. Other components include the connective tissue, fat, nerves, and blood vessels that surround and are embedded within the muscles. Lean muscle, regardless of the animal, usually consists of approximately 21 percent protein, 73 percent water, 5 percent fat, and 1 percent ash (the mineral component of muscle).

Processed Muscle Tissue

Using the power of digital image processing, Dr. Paddock has transformed a remarkable confocal microscopy image of muscle tissue into a work of art. The concentric rings in the image represent striated fibers in the tissue.

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  Processed Muscle Tissue

  Specimen: Muscle Tissue
  Technique: Fluorescence (Digital Image Processed)
  

  As the meat cooks, there is a physical unfolding and denaturation of the proteins in animal muscle tissue as a direct response to thermal agitation. Unstained meat goes from deep red to pale gray or brown as it cooks and the myoglobin degrades to the point at which it can no longer bind oxygen (82 degrees Celsius). As heat is applied to the raw meat, muscle fibers shorten and toughen, until the muscle structure eventually breaks down in fully cooked meat. When meat is overcooked, the connective tissue (primarily composed of collagen) undergoes complete denaturation into a gelatin-like mass. Overall, cooked meat becomes less structured and easier to chew. Because of worries with bacterial contamination and harmful parasites in undercooked meats, color is not sufficient to judge degree of cooking, and therefore, a meat thermometer or an image captured by the light microscope may be far more reliable (although sometimes not practical). Staining for some types of bacteria will also highlight potential health problems.

Cells on a Glass Fiber

Living tissue culture cells are captured growing on a glass fiber with the aid of reflected light microscopy. This unusual image reveals a single cell in the center of the image that appears to display fibroblast morphology.

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  Cells on a Glass Fiber

  Specimen: Cells Growing on Glass Fiber
  Technique: Reflected Light Microscopy
  

  Cells are often cultured in hollow glass fibers to enable histologists to grow cells in a more in vivo-like environment. The glass fiber is first coated with a hydrophilic polymer that enhances cell adhesion, then the cells are plated in media and allowed to attach. Carbon dioxide, oxygen, and fresh media can be pumped through the fibers to provide the cells with a continuous supply of fresh nutrients and carry the metabolic waste products away. This system is ideal for introduction of therapeutic drugs or other biochemicals in a controlled and sustained manner.

Darkfield Cell

Edges of the cell membrane are revealed in this darkfield image of a living fibroblast growing in monolayer tissue culture. This technique is useful for capturing details in difficult specimens that cannot be imaged using other methods.

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  Fibroblast Cell (Darkfield)

  Specimen: Fibroblast in Culture
  Technique: Darkfield
  

  Darkfield illumination requires blocking out of the central light which ordinarily passes through and around (surrounding) the specimen, allowing only oblique rays from every azimuth to "strike" the specimen mounted on the microscope slide. The top lens of a simple Abbe darkfield condenser is spherically concave, allowing light rays emerging from the surface in all azimuths to form an inverted hollow cone of light with an apex centered in the specimen plane. If no specimen is present and the numerical aperture of the condenser is greater than that of the objective, the oblique rays cross and all such rays will miss entering the objective because of their obliquity. The field of view will appear dark, while the specimen will appear in bright contrast.

Endoplasmic Reticulum

Utilizing a double fluorescent label, Dr. Paddock has managed to capture dynamic endoplasmic reticulum structures in living plant cells with the confocal laser scanning microscope.

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  Endoplasmic Reticulum

  Specimen: ER in Plant Cells
  Technique: Fluorescence (Double Label)
  

  The endoplasmic reticulum consists of a network of membranes called cisternae, and is the part of the cell that is responsible for the biosynthesis of lipids, proteins, and complex carbohydrates. This organelle typically accounts for more than half the total membrane in a cell. The two types of endoplasmic reticulum are rough and smooth. Rough endoplasmic reticulum contains ribosomes, and performs the function of protein synthesis, while smooth endoplasmic reticulum contains no ribosomes, and is primarily responsible for carbohydrate metabolism.