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DBLecture9posted

DBLecture9posted - Caenorhabditis elegans(C elegans An...

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Caenorhabditis elegans (C. elegans) An elegant worm
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Why study worms? Sydney Brenner “Thus we want a multicellular organism which has a short life cycle, can be easily cultivated, and is small enough to be handled in large numbers, like a micro-organism. It should have relatively few cells, so that exhaustive studies of lineage and patterns can be made, and should be amenable to genetic analysis.” -- Excerpts from Proposal to the Medical Research Council, 1963
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C. elegans : the chosen one! Photo credit: Ian D. Chin-Sang (Queen's University, Kingston, ON, Canada). Short generation time : 3 days Easily cultivated : can grow thousands on a petri dish, feed on non-hazardous bacteria, and cheap to maintain Small : 1 mm (about the size of a pinhead) Few cells : The adult has 959 hermaphrodrodite (XX) or 1031 (XO) cells Amenable to genetic analysis : maintained as hermaphrodites, but males exist for genetic studies, The genome is small- 100 Mb Transparency : allows for development to be analyzed from a single cell and all cells to be lineage
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Life cycle of C. elegans Photo credit: http://www.scq.ubc.ca/genetic-studies-of-aging-and-longevity-in-model-organisms/
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Anatomy of C. elegans Pharynx Intestine (yellow) Gonad (pink) Vulva Rectum Anus Epidermis head tail anterior posterior ~1 mm Fig. 5.42
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Hermaphrodite (XX) Males (X0) Hermaphrodites do it by themselves Photo credit: http://homepages.ucalgary.ca/~dhansen/worms.gif
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The C. elegans gonad : an extremely efficient reproductive system Fig. 5.42
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Within this lineage is the secret of embryonic development John Sulston
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All neural synapses have been mapped
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Learn to read a lineage diagram! = Cell death Line ending = differentiated cell Branching = cell division Increasing age of worm 1st stage larva 2nd stage larva embryo An entire C. elegans hermaphrodite worm consists of exactly 959 cells EVERY SINGLE TIME, allowing one to follow the cell lineage.
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Cleavage Events Lineage P0 zygote 2 cell stage 4 cell stage 8 cell stage Fig. 5.42
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Most lineages consist of multiple tissue types but the P4 , E and D cells gives rise to a single tissue type Fig. 5.42
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Mutations can alter lineages in many ways
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