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#experimental technique

2 public questions tagged with this topic.

Stem Cell -lll

Which experimental technique was used to identify iPSCs?

Shinya Yamanaka's landmark screen systematically tested 24 embryonic stem cell-associated transcription factors for ability to reactivate Fbx15 beta-geo and endogenous Oct4 promoter in mouse fibroblasts. Through iterative elimination of dispensable candidates, minimal cocktail Oct4, Sox2, Klf4, and c-Myc, termed OSKM, proved sufficient to induce pluripotent colonies contributing to chimeras and germline transmission. Overexpression via retroviral vectors triggered mesenchymal to epithelial transition, global DNA demethylation, and reactivation of endogenous pluripotency network, revolutionizing regenerative biology and earning Nobel recognition for cellular reprogramming concept.

Ref: Takahashi & Yamanaka, Cell 2006; Gilbert, Chapter 6: OSKM factors induce pluripotency in somatic fibroblasts.

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Properties of Plasma Membrane

Which experimental technique is used to study lipid movement in membranes?

Experimental investigation of lipid dynamics in plasma membranes of living cells requires fluorescence techniques capable of micrometer spatial resolution and millisecond temporal. FRAP fluorescence recovery after photobleaching involves incorporating fluorescent lipid analogs NBD-phosphatidylethanolamine BODIPY-phosphatidylcholine DiI dialkylcarbocyanine into bilayer at low mole fraction, or fluorescent protein fusions GFP-tagged for proteins. Focused laser beam bleaches circular spot one to four micrometer diameter irreversible photodestruction, subsequent recovery of fluorescence intensity monitored at low laser power as unbleached fluorophores diffuse from adjacent regions into bleached zone following Fick laws. Analysis yields diffusion coefficient D and mobile fraction Mf reflecting barriers cytoskeleton fences eighty nanometer corrals and lipid raft domains ordered phases slowing recovery. Complementary methods single particle tracking gold conjugated lipids high speed video, fluorescence correlation spectroscopy FCS confocal fluctuation. Western blotting separates denatured subunits by SDS-PAGE immunodetection does not report movement, X-ray crystallography determines static atomic coordinates crystalline lattice, PCR amplifies DNA. FRAP remains gold standard quantifying lateral movement of lipids and proteins supporting fluidity concept and membrane organization measurement.

Ref: Axelrod et al., Fluorescence Recovery After Photobleaching FRAP Method, Biophys J 1976.

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