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BIO241 Lecture 23

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Jennifer Harris

Tuesday March 31 2009 Today were going to be starting 2 lectures discussing the development of multicellular organisms MorphogenesisCell differentiationMorphogenesis is the creation of shape so it is the generation of tissue shapesthese tissue shapes form organsthe whole body structureToday well talk about morphogenesis next day well talk about signals controlling cell differentiation But in the body the cell differentiation would happen first The cell would be told what to dothen it changes its cell numbers it changes its cell shape it changes its cellcell interactions to then generate specific tissue shapes that would createorganswhole bodiesSo that is illustrated here st So this step here would be the 1 thing that would happen the cell specialization the cell differentiationthis cell here is told to be something different than its neighboursof course we have many different cell types in our body so therell be many different cell types that would be differentiated from one anotherAnd once this cell has differentiated it will then go down a certain developmental program thats distinct from other cell types Theyll have unique types of cell proliferation some may proliferate to a large degree others may notTheyll change the way they interact with other cells change theiradhesive properties signalingso on change in how they interact with their neighboursThey may also move in different ways change the shape of the cell move to other parts of the bodySo this specialization tells the cell what theyre going to bethen the cell proliferation the changes in cellcell interactionthe changes in cell movement that result then create the tissue structures that make up our bodiesSo these are the main experimental systems that are used to study multicellular developmentSo here we see the nematode C elegans the mouse the frog the fruit fly Arabidopsis is a model for plant development So all of these models here are chosen for certain experimental advantages that they have but they also have different disadvantages as wellSo one example in fruit fly you can learn a lot of things very quickly but are all the systems present in mammalian cells present in the fly No so you can learn a lot quickly then apply that to whats being learned in the mouse which then can be applied to whats happening during humandevelopment or human diseaseSo its important to be studying all of thesethen to have info running bw these different labs so that you can get an overall view of the developmental processAnother key thing about these organisms is that theyre all quite evolutionary distinct So if you find a mechanism thats present in say in all of these then youre really studying a core mechanism of developmentyou can study that very important mechanism that would be important for all multicellular organisms or you could distinguish whats important for animals versus plants whats important for vertebrates versus invertebrates And so through these kinds of combos you can see what are the core mechanismswhat makes different types of organisms uniquegives them their unique developmental programsSo developmental process will create the whole organism but we should also consider developmental processes that generate the organs that make up the bodySo the development of brain which well talk about more in the lecture development of organs like the lungs or the heart Each of these has their unique developmental processesthese organs can develop in a semiautonomous way within our body So theyll each have their developmental programs to create the brain lungs hearts liverso on Importantly multicellular development is not only an embryonic process so its not only during embryogenesis its also happening in adults all the time its happening in us continuallyOne good example of that is the skinHere were looking at a crosssection through the skin here Were looking at skin epithelial cells this is a stratified epithelial layer so its stratified in that theres multiple layers all on top of one other Here at this base of the epithelium we can see the basal laminathen the connective tissue underneath Here we see the epitheliumthe extracellular matrix below Now the developmental process here is happening as we rise up through these layers of cells At the surface of our skin the skin cells on the surface of the skin are constantly flaking off So these cells at the top here as shown in the slide are all dead cells in this upper layer so the surface of our skin are dead cellstheyre constantly being lostSo they need to be replenished continually by cell division thats occurring in this basal layer at the bottom here So here we have this basal cell thats dividing so this would be considered a stem cell so an adult stem cell that is supplying all the cells that are needed to resupply what are lost from the top of this tissue So the stem cell will divide here you can see this basal cell then moving up into another layeryou can see as they go into the upper layers these cells begin to change their properties they change their shapes so at each level theyre differentiatingchanging their shapes to adopt the cell type that are needed at each level until the final stage when they actually become a dead keratinized cell at the top of the skin
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