Week Three (97% in the course

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Louisiana State University
Biological Sciences
BIOL 3156

Week ThreeSeptember 10September 14Cell Sorting and ReaggregationsDissociation of sponges and reaggregationsoSingle spongepeople would take a sponge take it in CaMgfree seawater soak it for 30 minutes and make sure it is cold Then put it in bolting silk All cells flow through solution and mass is still in silkSpin these down and replace it with normal seawater and then cells will come back together and reform a sponge oDiffering sponge species species specificitynot only can you do this with a single species but you can do it with multiple red and green You take these two sponges and go through the same process and mix the cells together in the normal seawaterEventually the red sponge cells get together and the green sponge cells get together They are capable of sorting themselves into correct populations and speciesReaggregations of sea urchin embryosoSpecific cell sortingSea urchins would be collected and fertilized The zygotes would grow to swimming blastula Then the blastula would put into CaMgfree seawater and the blastula cells all fall apartHe can use seawater with different amount of sucrose and then layer these cells on the top The cells will all float down to the different concentrations of sucrose and seawater The cells will sort out to their correct spatial positions gastrulate and form a sea urchin Differential Cell AffinitiesFig 323Townes and HoltfreteroReaggregated cells become spatially separatedoFinal positions reflect embryonic originsHopethreader took amphibian embryos in the gastrulation stages and separated the cells out using Cafree media then put all of the cells back togetherAs he did this he did novel recombinations of the different germ cell layers that he separated he could put ectoderm and mesoderm together endoderm and mesoderm together etc He saw that every time he did this the cells would become spatially separated in their correct positionsOne always tries to be inside the otherSelective AffinityHoltfreter Fig 324shows different combinations of the germ layers and show that they separate totheir correct spatial positionAfter looking at this they tried to develop a model to show how cells aggregate and get to their spatial positions
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