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BISC 219/2009: Mod 1 C. elegans General Information: Difference between revisions
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BISC 219/2009: Mod 1 C. elegans General Information (view source)
Revision as of 10:00, 20 May 2009
, 20 May 2009→Introduction to Caenorhabditis elegans
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Many aspects of gene function that have been studied extensively in prokaryotes pertain to eukaryotes as well. However, prokaryotic cells cannot be used to investigate the many questions specific to the biology of higher organisms. Chromosome structure and the development of a complex anatomy are key examples. The small, free-living soil nematode, ''C. elegans'', is a convenient model system in which to approach basic questions concerning the genetic control of development and behavior in multicellular organisms. The animal's short life cycle is advantageous for genetic study, and at the same time it is small enough to allow complete anatomical studies at the ultrastructural level. A synopsis of the major attributes of ''C. elegans'' is given below. The two worm/web meccas are: [http://elegans.swmed.edu/ Leon Avery's ''C. elegans'' server] it’s perfect for virtually any worm detail you would need and [http://www.wormbase.org/ Wormbase] an interactive web site for all your worm gene needs. <br> | Many aspects of gene function that have been studied extensively in prokaryotes pertain to eukaryotes as well. However, prokaryotic cells cannot be used to investigate the many questions specific to the biology of higher organisms. Chromosome structure and the development of a complex anatomy are key examples. The small, free-living soil nematode, ''C. elegans'', is a convenient model system in which to approach basic questions concerning the genetic control of development and behavior in multicellular organisms. The animal's short life cycle is advantageous for genetic study, and at the same time it is small enough to allow complete anatomical studies at the ultrastructural level. A synopsis of the major attributes of ''C. elegans'' is given below. The two worm/web meccas are: [http://elegans.swmed.edu/ Leon Avery's ''C. elegans'' server] it’s perfect for virtually any worm detail you would need and [http://www.wormbase.org/ Wormbase] an interactive web site for all your worm gene needs. <br> | ||
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''C. elegans'' is easily and inexpensively grown in the laboratory in liquid medium or on the surface of agar-filled petri dishes, feeding on ''Escherichia coli''. Adults are about 1 millimeter in length, with a tubular body consisting of a hypodermal wall and an underlying musculature that encloses the digestive and reproductive organs. Although ''C. elegans'' has most major types of differentiated tissue (nerve, muscle, hypodermis, intestine, and gonad), adults contain only | ''C. elegans'' is easily and inexpensively grown in the laboratory in liquid medium or on the surface of agar-filled petri dishes, feeding on ''Escherichia coli''. Adults are about 1 millimeter in length, with a tubular body consisting of a hypodermal wall and an underlying musculature that encloses the digestive and reproductive organs. Although ''C. elegans'' has most major types of differentiated tissue (nerve, muscle, hypodermis, intestine, and gonad), adults contain only 959 somatic cells. <br> | ||
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'''Nematode Anatomy'''<br> | |||
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Embryogenesis occurs in about 12 hours, development to the adult stage occurs in 2.5 days, and the life span is 2-3 weeks. The development of ''C. elegans'' is known in great detail because this tiny organism (1 mm in length) is transparent and the developmental pattern of all 959 of its somatic cells has been traced.<br> | |||
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The hypodermal body wall is covered by an external cuticle composed primarily of modified forms of collagen. The body cavity (or pseudocoelom) is maintained at a high hydrostatic pressure relative to the outside, and this pressure on the elastic cuticle gives the animal rigidity and structural integrity. The hypodermis consists of four longitudinal ridges (dorsal, ventral, left and right lateral) joined circumferentially by thin sheets of cytoplasm which separate the muscle cells from the cuticle. The hypodermal cells secrete cuticular components and display a periodic activity associated with molting. The body muscles are organized into four longitudinal rows of 24 cells each, located between the hypodermal ridges. When the animal moves, the two subventral muscle strips are coordinated together as are the two subdorsal strips, producing a sinusoidal wave motion in the dorsal-ventral plane. The alimentary canal includes a muscular pharynx, which takes up food (bacteria), grinds it, and pumps it into the intestine. The intestine consists of 30 to 34 cells and is lined with microvilli leading to an anal sphincter valve that is operated by a pair of muscles.<br> | |||
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The nervous system of ''C. elegans'' consists of approximately 300 neurons, including a circumpharyngeal nerve ring, dorsal and ventral nerve cords, and a variety of sensory receptors and ganglia. About 70% of the neurons are located in the head. Sense organs (sensilla) are arranged in two concentric rings around the mouth and include both chemoreceptors and mechanoreceptors. ''C. elegans'' exhibits chemotaxis to a number of compounds. It also responds to a tap on the head by moving backwards, and then turning to move forward in a different direction.<br> | |||
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''C. elegans'' generally reproduces as a self-fertilizing hermaphrodite, with each animal producing BOTH sperm and eggs. Two reflexed gonadal arms, each of which contains an ovary, oviduct, spermatheca, and uterus, terminate at the vulva, located midway along the ventral side. The mature hermaphrodite is effectively a female in which the gonad has earlier made and stored sperm before turning to the production of oocytes. Eggs (developing embryos) are fertilized by endogenous sperm and undergo some of their development inside the parental hermaphrodite. Embryos are arranged in sequence along the uterus with the most developed ones nearest the vulva. Fertilized eggs are covered with a chitinous shell and deposited on the agar surface. The entire life cycle takes about 3 1/2 days at 20°C with each adult hermaphrodite producing 250-350 progeny. | |||
