HMB321H1 Lecture Notes - Lecture 18: Adult Stem Cell, Planarian, Symmetry In Biology
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23 MAR 2011
HMB321 L18: Bret Pearson, Planarians a new model to disease and regeneration
-How to establish new human disease models?
-Prebilateria (not bilaterally symmetric, e.g. Sponge and jellyﬁsh)
-Branches into ecdysozoa and deuterostomes (invertebrates; vertebrates)
-As well as lophotrochozoa (diverse species, e.g. Annelids, snails, molluscs)
How to bring new system into the lab?
-Organism should have “special advantages”
-Study adult stem cells
-Develop tools and culture conditions
Planarians and Adult Stem Cells
-Adult stem cell
-Large uncondensed nucleus is a key characteristic (how it was found)
-Non-stem cells are differentiated and have condensed, small nuclei
-Important for tissue homeostasis, injury regeneration => longevity?
-E.g. C. Elegans have 0 divisions and live only 4 days, whereas mice have more divisions
and live up to 3 years, whereas humans have more divisions than mice and live 80 years
or so, BUT…
-Planarians seem to be immortal, i.e. Their division rate seems inﬁnite = immortal?
-Stem cell is only as good as the lineage that it outputs
-Maintenance of correct lineage is unknown process, especially in vertebrates
-This maintenance goes awry in our 20s-30s => organismal senescence vs. Cancer (in
developed countries, in about 1 in 3 humans; hyper-proliferative)
-How stem cells accomplish their lineages?
-Hierarchal => start with Non-stem cell (somatic cell) provides info for adult stem cell (ASC)
-Cell-cell signalling occurs between Niche & ASC
-Stem cells are deﬁned by unique biology of self-renewal (multipotency)
-Progenitor Cells => changes in gene expression for particular line starting
-Post-mitotic progeny => differentiated cells (humans replace 10^10 cells per day;
maintenance of homeostasis)
-Last process = proliferation control?
-Tumour suppressors => can you ﬁgure this out from stem cells to work around
cancer? To ﬁgure out how things go awry?
Challenges in studying adult stem cells
-Unknown cellular lineages
-Cells don’t divide well in culture
-Manipulation of adults is difﬁcult/time consuming (i.e. Decade-long streams in adult cells)
-Accessibility in adults is almost impossible (i.e. Can’t watch the stem cells do anything)
What are planarians?
-Planarians are the garbage can of evolution?
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