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Drosophila

(Redirected from Fruit fly)
Drosophila

|- | style="text-align:center;" | Image:Drosm3.gif
Male Drosophila melanogaster |- style="text-align:center;" ! style="background: pink;" | Scientific classification |- style="text-align:center;" |

|- valign=top |Kingdom:||Animalia |- valign=top |Phylum:||Arthropoda |- valign=top |Class:||Insecta |- valign=top |Order:||Diptera |- valign=top |Family:||Drosophilidae |- valign=top |Genus:||Drosophila |} |- style="text-align:center; background:pink;" !Species |- | Drosophila melanogaster
Drosophila subobscura |}

Drosophila (modern scientific Latin adaptation from Greek δρόσος, drósos, "dew", + φίλη phílē, "a female friend" + Latin femenine suffix -a) is a genus of fruit fly; however, members of Drosophila are more appropriately termed vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies. One species in particular, Drosophila melanogaster, has been heavily used in research in genetics and is a common model organism in developmental biology. This species has undergone speciation events under laboratory conditions.

Drosophila is part of the phylum Arthropoda, a phylum of segmented animals with paired, jointed appendages and a hard exoskeleton made of chitin. They have an open circulatory system with a dorsal heart, hemocoel occupies most of the body cavity, and coelom is reduced.

Contents

Physique

Drosophila (also known as vinegar flies) are striped in "yellow and dark gray with red eyes, and are probably familiar to everyone. They appear on over-ripe fruit in kitchens, they swarm in thousands about the residue produced by the pressing of grapes or apples for wine. They nibble on marmalade and other preserves, and wherever vinegar is standing open, they are there." (Pomance Flies, 1969)

Typically Drosophila are an orange-brown color and range approximately from 3.2 mm to 4.2 mm in length. Most species have red eyes. The adults are "yellowish, with dark crossbands on abdomen; the feathered arista is characteristic of the family. A female lays up to 2000 pearly white eggs, each with a pair of "wings" or respiratory "horns" near the anterior end; the eggs of all known Drosophila have one or more of these horns, the tips of which extend above the surface of the moist media in which the eggs develop." (Swan, 1972)

Lifecycle and ecology

Male (left) and female fruit flies.
Enlarge
Male (left) and female fruit flies.

Habitat

Sometimes called the wine fly or vinegar fly, the Drosophila is found primarily in tropical regions. "The fruit fly, is a cosmopolitan holometabolous insect, that is found in all warm countries, while in cooler regions, it is established by migrants during the summer or can over winter in warm places." (Weigmann, 2003) These flies are "found in all warm countries in abundance of overripe soft fruits like grapes, bananas and plums. Adult flies as well as larvae feed on the fruit juices and the yeast growing on rotting fruit." (Weigmann, 2003). Most eggs live inside of the fruit along the peel of the fruit. "Some feed on other decaying organic matter or on plant exudations; a few are leaf miners, parasites, or predators." (Swan, 1972)

Respiration

The insect respired by means of air-filled internal tubes, the tracheae. This ectoderm-derived organ forms a highly branched tubular network which provides the organs with oxygen.

Reproduction

Drosophila melanogaster egg
Drosophila melanogaster egg

"The female fruit fly lays batches of between 15 and 20 white eggs each day." (Burton) A female lays up to 2000 pearly white eggs, each with a pair of “wings” or respiratory “horns” near the anterior end; the eggs of all known Drosophila have one or more of these horns, the tips of which extend above the surface of the moist media in which the eggs develop.

Generation time is about 10 days (at 23 °C), this will vary with temperature. During that time viable eggs will develop larvae, which then hatch to feed on the available food supply. After about 7 days they will form pupae, at this point they form a hard case around themselves and change their body form in to the adult stage. After the adult flies hatch, they are infertile for approximately 14 hours. This is important for their scientific usefulness as it allows virgin flies to be collected and separated according to sex before they are able to mate, allowing genetic crosses to be studied when they are paired with flies that have other variations.

Development and embryogenesis

Main article: Drosophila embryogenesis

Embryogenesis in Drosophila has been extensively studied, the small size, short generation time, and large brood size makes it ideal for genetic studies. It is also unique among model organisms in that cleavage occurs in a syncytium. About 5000 nuclei accumulate in the unseparated cytoplasm of the oocyte before they migrate to the surface and are encompassed by plasma membranes to form cells surrounding the yolk sac. Early on, the germ line segregates from the somatic cells through the formation of pole cells at the posterior end of the embryo.

Predators

One predator is the orchid mantis which feeds on free living insects, primarily fruit flies.

The Drosophila research project

Drosophila is one of the most studied organisms in biological research, particularly genetics. Their short generation time (about 2 weeks), high reproductively rate (females can lay 500 eggs in 10 days), small size (1/8" to 1/15" long), and multitude of genes for study make them an ideal specimen for studying genetic mutations. Charles W. Woodworth is credited with being the first to breed Drosophila in quantity and for suggesting to W. E. Castle that they might be used for genetic research during his time at Harvard University. Fruit flies helped Thomas Hunt Morgan accomplish his studies on heredity. "Thomas Hunt Morgan and colleagues extended Mendel's work by describing X-linked inheritance and by showing that genes located on the same chromosome do not show independent assortment. Studies of X-linked traits helped confirm that genes are found on chromosomes, while stuies of linked traits led to the first maps showing the locations of genetic loci on chromosomes" (Freman 214). Species of Drosophila have migrated with man over history and can now be found all over the world.

The Drosophila genome

The genome of Drosophila contains 4 pairs of chromosomes: an X/Y pair, and three autosomes labeled 2, 3, and 4. The fourth chromosome is so tiny that it is often ignored. The genome contains about 165 million bases and approximately 14,000 genes. The genome has been sequenced and is currently being annotated.1

Genetic nomenclature

Genes named after recessive alleles begin with a lowercase letter, while dominant alleles begin with a uppercase letter. Genes named after a protein product begin with an uppercase letter. Genes are typically written in italics. The convention for writing out genotypes is X/Y; 2nd/2nd; 3rd/3rd.2

Vision in Drosophila

Stereo pair of images as viewed by fly eye
Stereo pair of images as viewed by fly eye

The compound eye of the fruit fly contains 800 unit eyes or ommatidia. Each ommatidium contains 8 photoreceptor cells (R1-8), support cells, pigment cells, and a cornea. Wild-type flies have reddish pigment cells, which serve to absorb excess blue light so the fly isn't blinded by ambient light.

Each photoreceptor cell consists of two main sections, the cell body and the rhabdomere. The cell body contains the nucleus while the rhabdomere is made up of toothbrush-like stacks of membrane called microvilli. Each microvillus is 1 mm to 1.5 mm in length and 50 nm in diameter. The membrane of the rhabdomere is packed with about 100 million rhodopsin molecules, the visual protein that absorbs light. The rest of the visual proteins are also tightly packed into the microvillar space, leaving little room for cytoplasm.

The photoreceptors in Drosophila express a variety of rhodopsin isoforms. The R1-R6 photoreceptor cells express Rhodopsin1 (Rh1) which has absorbs blue light (480 nm). The R7 and R8 cells express a combination of either Rh3 or Rh4 which absorb UV light (345 nm and 375 nm), and Rh5 or Rh6 which absorb blue (437 nm) and green (508 nm) light respectively. Each rhodopsin molecule consists of an opsin protein covalently linked to a carotenoid chromophore, 11-cis-3-hydroxyretinal.3

As in vertebrate vision, visual transduction in invertebrates occurs via a G protein-coupled pathway. However, in vertebrates the G protein is transducin, while the G protein in invertebrates is Gq (dgq in Drosophila). When rhodopsin (Rh) absorbs a photon of light its chromophore, 11-cis-3-hydroxyretinal, is isomerized to all-trans-3-hydroxyretinal. Rh undergoes a conformational change into its active form, metarhodopsin. Metarhodopsin activates Gq, which in turn activates a phospholipase Cβ (PLCβ) known as NorpA.

A diagram of a single microvillus in a Drosophila photoreceptor cell.
A diagram of a single microvillus in a Drosophila photoreceptor cell.

PLCβ hydrolyzes phosphoinositol-4,5-bisphosphate (PIP2), a phospholipid found in the cell membrane, into soluble inositol triphosphate (IP3) and diacylgycerol (DAG), which stays in the cell membrane. DAG or a derivitive of DAG causes a calcium selective ion channel known as TRP (transient receptor potential) to open and calcium and sodium flows into the cell. IP3 is thought to bind to IP3 receptors in the subrhabdomeric cisternae , an extension of the endoplasmic reticulum, and cause release of calcium, but this process doesn't seem to be essential for normal vision.4

Calcium binds to proteins such as calmodulin (CaM) and an eye-specific protein kinase C (PKC) known as InaC. These proteins interact with other proteins and have been shown to be necessary for shut off of the light response. In addition, proteins called arrestin s bind metarhodopsin and prevent it from activating more Gq.

A potassium-dependent sodium/calcium exchanger known as NCKX30C pumps the calcium out of the cell. It uses the inward sodium gradient and the outward potassium gradient to extrude calcium at a stoichiometry of 4 Na+/ 1 Ca++, 1 K+.5

TRP, InaC, and PLC form a signaling complex by binding a scaffolding protein called InaD. InaD contains five binding domains called PDZ domains which specifically bind the C termini of target proteins. Disruption of the complex by mutations in either the PDZ domains or the target proteins reduces the efficiency of signaling. For example, disruption of the interaction between InaC, the protein kinase C, and InaD results in a delay in inactivation of the light response .

Unlike vertebrate metarhodopsin, invertebrate metarhodopsin can be converted back into rhodopsin by absorbing a photon of orange light (580 nm).

Approximately two-thirds of the Drosophila brain (about 200,000 neurons total) is dedicated to visual processing. Although the spatial resolution of their vision is significantly worse than that of humans, their temporal resolution is approximately ten times better.

Drosophila flight

The wings of a fly are capable of beating at up to 250 times per second. Flies fly via straight sequences of movement interspersed by rapid turns called saccades. During these turns, a fly is able to rotate 90 degrees in less than 50 milliseconds.

It was long thought that the characteristics of Drosophila flight were dominated by the viscosity of the air, rather than the inertia of the fly body. However, recent research by Michael Dickinson and Rosalyn Sayaman has indicated that flies perform banked turns, where the fly accelerates, slows down while turning, and accelerates again at the end of the turn. This indicates that inertia is the dominant force, as is the case with larger flying animals.

Similarity to humans

Genetically speaking, people and fruit flies are very similar. About 61% of known human disease genes have a recognizable match in the genetic code of fruit flies, and 50% of fly protein sequences have mammalian analogues. As a result, fruit flys are commonplace in genetic research labs. They can be good substitutes for people. They reproduce quickly, so that many generations can be studied in a short time, and their genome has been completely mapped. Drosophila is being used as a genetic model for several human diseases including Parkinson's and Huntington's.

External links

  • A quick and simple introduction to Drosophila melanogaster http://ceolas.org/VL/fly/intro.html
  • Flybase http://flybase.harvard.edu:7081/
  • FlyMove http://flymove.uni-muenster.de/
  • The Interactive Fly - A guide to Drosophila genes and their roles in development http://www.sdbonline.org/fly/aimain/1aahome.htm
  • NASA-supported researchers are going to send fruit flies to the International Space Station to learn what space travel does to the genes of astronauts http://www.nasa.gov/vision/earth/livingthings/03feb_fruitfly.html

Further reading

  • K. Haug-Collet, et al. (1999). "Cloning and Characterization of a Potassium-dependent Sodium/Calcium Exchanger in Drosophila". J. Cell Biol. 147(3):659-669.
  • P. Raghu, et al. (2000). "Normal Phototransduction in Drosophila Photoreceptors Lacking an InsP3 Receptor Gene". Molec. & Cell. Neurosci. 15:4289-445.
  • R. Ranganathan, et al. (1995). "Signal Transduction in Drosophila Photoreceptors". Annu. Rev. Neurosi. 18:283–317.
  • S. Fry and M. Dickinson (2003). "The Aerodynamics of Free-Flight Maneuvers in Drosophila". Science. 300:495-498.

References

  1. Burton, Maurice. "Fruit Fly." International Wildlife Encyclopedia. 2002 ed.
  2. Freeman, Scott. Biological Science. New Jersey: Prentice-Hall, Inc., 2002.
  3. "Pomace Flies". Grzimek's Animal Life Encyclopedia, First Edition, 1969.
  4. Swan, Lester A., and Charles S.Papp. 1972. The Common Insects of North America: Fitzhenry & Whiteside Limited, Toronto. pp. 629
  5. Weigmann, K., Klapper, R., Strasser, T., Rickert, C., Teachnau, G.M., Jackle, H., Janning, W. and Klambt, C. (2003). FlyMove- A new way to look at development of Drosophila. pp. 19,310-311.



Last updated: 02-05-2005 15:14:58
Last updated: 03-18-2005 11:16:12