Dr. Saswati Sengupta
M.Tech, Ph.D (Jadavpur University) EMail: saswatis.biologics@gmail.com
Introduction:
investigation such models can be either computer models, theoretical models or living models. Scientific investigations in any area require some model systems. Depending on the field of Scientists perform experiments or analysis with these models and try to get some clues from their findings. Living organisms are used as models to address questions in biological science spanning from fundamental biological and medical research to application oriented research for developing n treatments for diseases. It is well known that before marketing a newly discovered drug, its efficacy and safety are tested on some model animals. Animals are also used as disease models to learn how the disease affects the body and what could be the cure. Nonetheless, model organisms have long been used in the classroom to help students learn important concepts in various disciplines of biology.
An attempt has been made in this article to introduce some of these living model organisms which are extensively used in biological and medical research. It includes a diverse array of organisms ranging from unicellular bacterium to multicellular organisms, plants and even human cell line. In this context let us commemorate the father of genetics, Gregor Mendel, who used cross pollinating pea plants to understand the genetic inheritance pattern in the middle of the nineteenth century. Probably this was the first successful use of a model to understand a basic phenomenon in biology.
Escherichia coli:
The bacterium E. coli was discovered by the German paediatrician and bacteriologist, Theodor Escherich in 1885. It is a natural inhabitant of human colon and usually harmless. However some of its cousins cause serious food-borne diseases in humans. It also occurs in soil and water. Because of its rapid growth and small amount of genetic material present in the cell, it is extensively used in studying genetic engineering.
Dictyostelium discoideum (Slime Mold):
Dicyostelium discoideum, commonly referred to as slime mold, occurs in soil. During its life cycle it undergoes a transition from unicellular amoebae to a multicellular organism. A number of its genes have similar counterparts in human cells. Its life cycle i simple. For these reasons, D. Discoideum is a valuable model organism to study genetic, cellular, and biochemical processes in other organisms.
Saccharomyces cerevisiae (Baker's Yeast):
Saccharomyces cerevisiae is the yeast that we use for making bread and wine. Almost 30% of the genes implicated in human diseases have counterparts in yeast. Therefore, it is being used as a model to study different biological processes such as aging, regulation of gene expression, signal transduction, cell cycle, metabolism, apoptosis (programmed cell death), neurodegenerative disorders and so on.
Neurospora crassa (Bread Mold):
The bread mold Neurospora, is used as a model organism for genetic and biochemical studies and have been very helpful for our understanding of several basic and fundamental aspects of biology.
Drosophila melanogaster:
Drosophila is a fruit fly that shares highly homologous gene sequence with human. Hence it is one of the most preferred organisms for studies in human genetics. It is easy to maintain, grows quickly from embryo to adult within 12 days. Drosophila has been widely used for the study of several diseases, including Parkinson's disease, Alzheimer's and various types of cancer and more recently as a tool to study human diseases and to screen compounds for therapeutic use.
Caenorhabditis elegans:
Caenorhabditis elegans (Caeno, recent; rhabditis, rod; elegans, nice) is a very small soil nematode (1 mm length), transparent for ease of manipulation and observation, feeds on bacteria. It grows very easily in large numbers (10,000 worms/Petri plate) and is very cheap to breed. It has been used in many frontier research areas in biology such as programmed cell death (Nobel Prize awarded to Sydney Brenner and associates in 2002) and RNA interference process (Nobel Prize awarded to Andrew Fire and Craig C Mello in 2006).
Arabidopsis thaliana:
Arabidopsis thaliana is a flowering plant with a small genome. Some of its notable advantages are that it reproduces relatively quickly, produces numerous progeny through self pollination, require limited space, and is easily grown in a greenhouse or indoor growth chamber with simple growth requirement like only light, air, water and a few minerals to complete its life cycle. Therefore, it is being used as a model system for more than several decades to understand the genetics and molecular biology of flowering plants.
Xenopus laevis:
Xenopus laevis is a bizarre looking frog, native to Sub-Saharan Africa. The eggs and embryos of X. laevis can be produced in large numbers by means of a simple hormone injection and are, like other amphibian embryos, can be easily manipulated. It was introduced as a model system in 1950s. Earlier it was used to understand many physiological processes. Recently it is also used as amodel system in molecular biology.
Fugu rubripes (Puffer fish):
This pufferfish also known as Fugu is a great delicacy in Japan. Even though men and fish diverged from their common ancestor over 450 million years ago, the Fugu genome contains roughly the same number of genes as its human counterpart, which is eight times larger. The compactness of the pufferfish genome simplifies the detection and analysis of genes and their regulatory elements. Hence it is used as a model system in studying human genetics.
Mus musculus (Mouse):
A mouse is an agricultural and household pest creating a whole lot of menace in our everyday life. But the scientists have appreciated immense potential of this organism as the model for understanding human biology and disease. It bears similarities in terms of tissue structure and organization. It is also susceptible to many of the common diseases that we suffer from. Another advantage of this model system is its low maintenance cost and its short reproduction time (nine weeks). Models of different human diseases can be created in mice by genetic manipulation. Needless to say, these models are highly useful for testing the efficacy of new drugs.
Nude mouse:
A nude mouse is a laboratory mouse with a genetic mutation that causes a defective or absent thymus. This organ plays a key role in protecting an animal from foreign organisms. Because of absence or malfunctioning of the thymus the nude mice have a non-functional immune system. They can receive different types of tissue and tumour grafts since their body fails to reject the foreign tissues. Due to lack of body hair these animals are nicknamed as "nude mouse".
Danio rerio (Zebrafish):
The zebrafish (Danio rerio) occurs in northern India, northern Pakistan, Nepal, and Bhutan. It is a showpiece in household aquariums. Due to the small size and ease of culture, zebrafish has occupied an important position in the catalogue of model organisms. The embryos of the fishes develop outside the mother's body and remain transparent until most of the organs have fully developed. Hence they are widely used for the study of embryonic
development and gene function. Thus zebrafish permits scientists to follow the formation of tissues and organs in microscopic detail as the organism grows. Thus this small fish may be the key to understanding how vertebrates, including, human beings, develop.
A number of variants of zebrafish mutants have been so far been generated and are good models of human diseases such as Alzheimer's disease,
congenital heart disease, polycystic kidney disease and cancer.
HeLa cells:
HeLa cell is an immortal cultured cell line used in scientific research. It is the oldest of all the cell lines. This cell line was derived from cervical cancer cells from a cancer patient Henrietta Lacks who eventually died of cancer at Johns Hopkins Hospital (Maryland, USA) on October 4, 1951. This cell line is remarkably durable and prolific and the ease of use makes HeLa a genetically manageable model.
Conclusion:
It is evident from the foregoing discussion that biological models are one of the pillars of research in life science. They provide insight into the mysteries of life and offer clues to the medical problems. Scientists are indebted to them for the significant achievements in life science research witnessed during the past few decades. The list of model organisms is expected to be longer during the decades to come.