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General Laboratory Techniques

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Basic Methods in Cellular and Molecular Biology

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Model Organisms I

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Model Organisms II

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JoVE Science Education Model Organisms I: yeast, Drosophila and C. elegans An Introduction to Drosophila melanogaster

An Introduction to Drosophila melanogaster

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Drosophila melanogaster, also known as the "fruit fly," is a small insect that is commonly found near ripening fruit. Drosophila is a widely used model organism for scientific research and the study of this organism has provided insight into eukaryotic genetics and human disease.

To begin, let’s get to know Drosophila as an organism. Drosophila have three main body segments--the head, thorax, and abdomen--as well as a single pair of wings, and three pairs of legs. They are between 2-4 mm long and weigh about 1 mg. Females are typically larger than males. Wild-type fruit flies have large red eyes, and pale yellow or light brown bodies with black stripes on the abdomen.

The Drosophila life cycle is about 2 weeks long, and is comprised of 4 major stages: the embryo, larva, pupa, and adult. The average lifespan of Drosophila is between 60-80 days, however lifespan can be affected by factors such as temperature or overcrowding.

Fruit flies are present on every continent except Antarctica. More often they are found in tropical climates, but they can adapt to colder climates by moving indoors.

Drosophila can survive in a range of 12-35 °C. In the lab, we store flies in incubators set to 25 °C and 60% humidity for ideal survival and fertility.

The typical diet for Drosophila are the microorganisms, sure as yeast, that inhabit very ripe and rotting fruits and vegetables. However in the lab, we use food composed of cornmeal, molasses, agar, sugar, yeast, and water.

Now that we’ve learned a bit about Drosophila the organism, let’s discuss why researchers have decided to study it. First, the small size of the fly makes them easy to both handle and anesthetize.

Flies are also appealing to work with because they require inexpensive equipment to maintain and house in the laboratory.

Thanks to their short life cycle, it takes approximately 2 weeks from when mating is set up to generate new adult progeny. Females are extremely fertile and can lay hundreds of eggs per day. Therefore, experiments with flies can be conducted quickly and with very high sample numbers.

Drosophila are easy to study, because their genetics are simple in comparison to mammals. The Drosophila genome is comprised of only four chromosomes with approximately 14,000 genes. Flies also have limited genetic redundancy. Genetic redundancy means that more than one gene is responsible for a certain biological function. For example, mice may have three copies of a gene causing a particular phenotype. When one gene is mutated, the others can compensate leading to no observable developmental or physiological change. Thus, the mutagenesis experiment in mice is less informative. In contrast, flies may only have one version of a gene, so when that gene is mutated it causes a change in phenotype, giving insight into that particular gene’s function.

Furthermore, several methods have been developed to induce genetic mutations, including X-rays, or UV irradiation, and homologous recombination. Lastly, many years of research yielded a friendly community of Drosophila scientists, which makes it easy to access the vast number of mutant lines and genetic tools.

Finally, flies are an excellent model organism because of their striking genetic similarities to humans and other mammals. Approximately 50% of fly genes are homologous to mammalian genes, meaning the gene originates from a common ancestor. Furthermore, 75% of human disease-related genes have orthologs, or genes with similar functions, in the fly.

So now that we’ve heard a bit about what makes Drosophila so great for experimental study, let’s check out some of the great research that has been done on flies. In the early 20th century, flies first emerged as a model organism in the lab of Thomas Hunt Morgan. In 1910, Morgan discovered a white-eyed fly among a collection of red-eyed flies. Using microscopy, he observed the banding patterns of chromosomes, and saw that the same pattern was always observed in white-eyed flies. With these experiments he established the chromosomal theory of inheritance for which he won the Nobel Prize in 1933.

In 1927, one of Thomas Hunt Morgan’s students, Hermann Muller, discovered x-rays can induce genetic mutations. Muller won the Nobel Prize in 1946 for his discovery.

During the ’70s and ’80s, Ed Lewis, Christiane Nusslein-Volhard, and Eric Wieschaus performed screens to identify a number of genes that are essential during development. They identified some of the genes that establish the dorsal-ventral and anterior-posterior axes of the embryo, as well as the genes involved in segmentation, which specify the body plan. They won the Nobel Prize in 1995.

In the 1990’s, Jules Hoffmann used Drosophila for research on innate immunity, the first line of defense against pathogens, like bacteria. He discovered Toll receptors and demonstrated their importance for sensing and defending against pathogens. Here are embryonic hemocytes, cells that can recognize and respond to pathogens in the Drosophila embryo. Hoffman won the Nobel Prize in 2011 for his work on the Drosophila innate immune system, and shared the prize with Bruce Beutler and Ralph Steinman for their work on innate immunity in mammals.

Work in Drosophila has many important applications, ranging from genetics to human disease. For example, the genetics of development are often homologous, so the identification and characterization of genes that regulate development in flies has been important for understanding human development. The Drosophila "eyeless" gene is essential for development in the fly. The mammalian homologs of eyeless have many functional similarities, thus understanding Drosophila eye development could have implications in understanding human eye development and disease.

Drosophila research can also have implications in understanding human neurological diseases. For example, expression of a human gene involved in Parkinson’s disease in the fly, leads to a loss of neurons over time and an accumulation of protein aggregates culminating in decreased locomotor ability.

Research in the fly has lead to important knowledge of human heart development and function. Many genes associated with cardiac function are conserved between flies and humans, and, similar to humans, exercise training can greatly improve performance with physical tasks.

You’ve just watched JoVE’s introduction to Drosophila melanogaster. In this video we reviewed the characteristics of Drosophila, the reasons why it makes such a powerful model organism, as well as important discoveries and applications. Although they may seem very different from humans, Drosophila research has been an important source of understanding human development and disease. Only time will tell what the future of Drosophila research holds.

Summary

Drosophila melanogaster, also known as the fruit fly, is a powerful model organism widely used in biological research that has made significant contributions to the greater scientific community over the last century. First, this video introduces the fruit fly as an organism, including its physical characteristics, life cycle, environment, and diet. Next, the reasons why fruit flies make an excellent model organism are discussed. For example, fruit flies are inexpensive to maintain in the laboratory, have simplified genetics, and short generation times allow for quick experiments with high sample numbers. Then, key discoveries and important Drosophila researchers, such as Thomas Hunt Morgan are profiled. Finally, applications of Drosophila research, ranging from genetics to cardiac and neurological development and disease, are provided. This video serves as an overview of the highly-important and influential model organism that is Drosophila melanogaster.

Cite this Video

JoVE Science Education Database. Model Organisms I: yeast, Drosophila and C. elegans. An Introduction to Drosophila melanogaster. JoVE, Cambridge, MA, doi: 10.3791/5082 (2014).

Applications

 JoVE Biology

Live Imaging Of Drosophila melanogaster Embryonic Hemocyte Migrations


JoVE 1696 2/12/2010

1Department of Biology and Biochemistry, University of Bath, 2Randall Division of Cell and Molecular Biophysics, King's College London

This video presents a protocol for the live imaging of fluorescently labeled hemocytes, which are embryonic immune cells during embryogenesis. Embryonic hemocytes are often used as a model to understand the mechanisms that govern cell migrations.

 JoVE Neuroscience

Assessing Neurodegenerative Phenotypes in Drosophila Dopaminergic Neurons by Climbing Assays and Whole Brain Immunostaining


JoVE 50339 4/24/2013

1Department of Biomolecular Genetics, University of Rochester Medical Center

This video describes two neurodegeneration assays to demonstrate that expression of a human Parkinson’s disease gene in dopaminergic neurons leads to progressive loss of neurons and locomotor deficits in the fly, which are both characteristics of the human disease. This demonstrates that Drosophila can be used as a model organism to study neurological diseases such as Parkinson’s disease.

 JoVE Biology

Visualizing the Beating Heart in Drosophila


JoVE 1425 9/28/2009

1Development and Aging Program, The Sanford Burnham Institute for Medical Research

The Drosophila heart shares many similarities with humans and it can be used to understand the cellular, molecular, and genetic mechanism of heart development and function. Methods to visualize the beating heart of larval and adult Drosophila are described in order to observe and quantify Drosophila heart physiology, development, and function.

 JoVE Biology

Measurement of Lifespan in Drosophila melanogaster


JoVE 50068 1/07/2013

1Department of Molecular and Integrative Physiology, University of Michigan, 2Cellular and Molecular Biology Program, University of Michigan

Due to their short lifespan, Drosophila makes an ideal model to study aging and longevity, which may lead to a greater understanding of age-related diseases. This video describes an optimized method to measure longevity in Drosophila, which reduces the influence of genetic and environmental artifacts that often complicate aging experiments.

 JoVE Biology

Paraffin-Embedded and Frozen Sections of Drosophila Adult Muscles


JoVE 2438 12/27/2010

1Gene Expression and Signaling Research Group, Max Planck Institute for Biophysical Chemistry

Drosophila adult multi-fiber muscles resemble striated muscles in vertebrates, thus flies can be used to study the genetic and molecular mechanisms of muscle development and damage. Here, a technique to prepare paraffin-embedded and frozen sections of Drosophila thoracic muscles is presented. These tissues can be visualized via classic histology or immunohistochemistry and differences in morphology, structure and localization of proteins can be assessed.


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