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S. purpuratus
(Purple Sea
Urchin)
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A. california
(Aplysia)
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Genome
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haploid
chromosome #
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42
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17
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Size
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800 Mb
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1,000 Mb
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fraction
sequenced
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~3%
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225 cDNAs;
only 125 in DB
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genes/ORFs
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cDNA/EST
sequence
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~2,500
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Characteristics
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cellular
organization
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deuterostome
metazoan; indirect development with pelagic feeding larva; metamorphosing
after 5 weeks; embryogenesis complete at 1800-cell stage in 3 days
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multicellular;
map cell-cell connections easily->cell bodies are peripherally
located and accessible for injection and other mainpulations
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Ploidy
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diploid
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some very large
neurons are up to 7,000 x haploid genome=15 duplications
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generation
time
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~1 year
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4 months to
6 months
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(egg->egg)
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Cultivation
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egg to egg
culture, including large scale embryo, larva and adult maintenance
easily performed
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Transfection/transgenic
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injection of
expression vectors into eggs very efficient
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transfection:
yes, by microinjection; in princiiple: any gene into any cell; transgenic:
no
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gene inactivation
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TKO, other
methods
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by injection
of antisense RNAs or oligonucleotides
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Mutants
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several naturally
occurring under study
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no
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Cell Culture
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yes, primary
only
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Storage
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gametes
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several weeks
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no
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embryos
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no
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intact organisms
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captured from
the wild; no isogenic lines; there is a facility that breeds and
rears Aplysia at U. Miami
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Special Strengths
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gene transfer
simple and efficient; great background knowledge of embryo molecular
and cell biology; large assemblage of clones libraries, probes available;
genomics; advanced technology for molecular biology of gene regulation;
ease of culture of embryo and adults; enormous fecundity; rapid,
simple embyogenesis; long-lived; hardy adult form.
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relatively
simple nervous system; only 20,000 neurons; big neurons/few cells;
well defined circuitry that can be reconstituted in culture; demonstrates
multiple forms of synaptic plasticity; relating individual cells
to behavior easy; functional characterization of genes, relating
genes to specific neuronal function and neuronal placticity in individual
indentified cells that are causally related to behavior and learning
possible; genes important for memory and for motivational state
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Weaknesses
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long egg to
egg life cycle; no cell culture
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no isogenic
strains; no classical whole animal genetics
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Resources
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SUMS at Cal
Tech; arrayed libraries
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U. of Miami
Marine Facility
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Databases
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Stowers Genome
Project (in preparation); EST database
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Database of
Identified Cell Anatomy, Physiology, and Behavior (Dan Gardner;
http://mollusc.med.cornell.edu;
~20%-40% of whole CNS is identified and characterized functionally
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Community
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# of labs
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>50 (US,
Japan, France, Italy, Russia)
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70-80 all working
on nervous system and behavior
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# of investigators
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>500
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200-300
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References
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E.
H. Davidson, R. A. Cameron, A. Ransick (1998). Specification of
cell fate in the sea urchin embryo: summary and some proposed mechanisms.
Development 125, 3269-3290.
C.-H. Yuh,
H. Bolouri, E. H. Davidson (1998). Genomic cis-regulatory logic:
functional analysis and computational model of a sea urchin gene
control system. Science 279, 1896-1902. ed.
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DeZazzo, J.
& Tully, T (1995). Dissection of memory formation. From behavioral
pharmacoloty to molecular genetics. Trends Neurosci. 18:212-218.
Bailey, C.H.,
Bartsch, D. & Kandel, E.R. (1996). Toward a molecular definition
of long-term memory storage. PNAS USA 93: 13445-13425.
Kandel, E.R.
(1979). The Behavioral Biology of Aplysia: A Contribution to the
comparative Study of Opisthobranch Molluscs. San Francisco: Freeman
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Information
Provided By:
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E.
Davidson |
E. Kandel
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