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YAP Signaling
/ YAP SIG-nuh-ling / · Acronym from Yes-associated protein, with Yes referring to the Yamaguchi sarcoma viral oncogene homolog.
YAP signaling is a mechanotransduction pathway in which the transcriptional coactivators YAP and TAZ relay mechanical and biochemical signals to the nucleus to regulate cell proliferation, differentiation, and organ size.
YAP signaling integrates inputs including cell density, mechanical tension, extracellular matrix stiffness, and G-protein-coupled receptor activation to control tissue growth. When the upstream Hippo kinase cascade is active, LATS1 and LATS2 kinases phosphorylate YAP at serine 127 and TAZ at serine 89, creating 14-3-3 binding sites that sequester both coactivators in the cytoplasm. Dephosphorylated YAP and TAZ translocate to the nucleus, where they partner with TEAD transcription factors to drive expression of proliferative and anti-apoptotic genes including CTGF, CYR61, and survivin.
Substrate stiffness profoundly influences this localization: cells on rigid 40-kilopascal matrices show predominantly nuclear YAP, while cells on soft 1-kilopascal substrates retain cytoplasmic YAP. Aberrant YAP activation occurs in over 60 percent of human cancers, promoting tumor growth, metastasis, and resistance to targeted therapies.
YAP and TAZ lack both nuclear localization signals and nuclear export signals, entering and exiting the nucleus purely by passive diffusion through nuclear pores. Their subcellular distribution is therefore governed entirely by phosphorylation-dependent cytoplasmic retention versus nuclear TEAD binding, with no active transport machinery involved.
YAP is a transcription factor. YAP cannot bind DNA directly; it is a transcriptional coactivator that must recruit DNA-binding TEAD proteins to regulate target gene expression.
During zebrafish liver regeneration following partial hepatectomy, YAP rapidly dephosphorylates and accumulates in hepatocyte nuclei within 6 hours of surgery. This nuclear accumulation drives a roughly 10-fold increase in hepatocyte proliferation, restoring the liver to its original mass within approximately 7 days.
Yeast Cell Model
/ yeest sel MOD-ul / · Old English: gist (yeast) + cell + model
Yeast cell model is a research system that uses yeast, most commonly baker's yeast, to investigate fundamental eukaryotic cell processes because yeast shares conserved molecular machinery with human cells while remaining far easier to culture and manipulate genetically.
Saccharomyces cerevisiae shares approximately 60 percent of its protein-coding genes with humans and carries homologs of many cell-cycle regulators, including cyclins, cyclin-dependent kinases, and checkpoint kinases. Its doubling time of roughly 90 minutes and tolerance for large-scale genetic manipulation make genome-wide screens practical in days rather than months. The yeast genome was fully sequenced in 1996, making S.
cerevisiae the first eukaryote with a completely known genetic blueprint, and the resulting gene deletion library now covers over 6,000 individual knockouts. Fission yeast (Schizosaccharomyces pombe) complements the baker’s yeast model by offering a distinct lineage useful for studying chromosome segregation and RNA splicing, processes that differ subtly between the two species.
Leland Hartwell, Paul Nurse, and Tim Hunt shared the 2001 Nobel Prize in Physiology or Medicine for discoveries about cell-cycle control made largely in yeast. Hartwell's screen of temperature-sensitive S. cerevisiae mutants in the 1970s identified over 100 CDC genes, most of which have direct human counterparts mutated in cancer.
Cell Cycle →Yeast is too simple to teach us about human cells. Yeast shares the core eukaryotic machinery for DNA replication, protein secretion, and organelle biogenesis with human cells, and discoveries made first in yeast have repeatedly translated directly into human disease biology.
Yeast →Researchers used baker's yeast to identify the RAD52 epistasis group of DNA repair genes, which encode proteins that sense double-strand breaks and coordinate homologous recombination. Human orthologs of these genes, including RAD51 and the BRCA2-interacting domain, were subsequently found to be mutated in hereditary breast and ovarian cancer syndromes.
Yellow Fluorescent Protein
/ YEL-oh floo-REH-sent PROH-teen / · From Latin flavus, yellow, and fluere, to flow, referring to the light emission wavelength.
Yellow Fluorescent Protein is an engineered variant of green fluorescent protein that emits yellow light at approximately 527 nanometers when excited by blue light, used as a genetically encoded marker to track proteins in living cells.
YFP was created by introducing a threonine-to-tyrosine substitution at position 203 of the green fluorescent protein sequence from the jellyfish Aequorea victoria, shifting the emission peak from 509 nanometers to 527 nanometers. This spectral shift made it possible to image two differently tagged proteins simultaneously in the same living cell, a capability that transformed fluorescence microscopy in the late 1990s. Scientists frequently pair YFP with cyan fluorescent protein in Förster resonance energy transfer experiments, where energy transfer between the two fluorophores occurs only when the tagged proteins come within 1 to 10 nanometers of each other, reporting direct protein-protein interactions in real time.
YFP retains fluorescence across a pH range of roughly 6 to 10, keeping it stable under most physiological conditions. Improved variants including Venus and Citrine mature in approximately 40 minutes and show reduced sensitivity to chloride ions, extending YFP’s usefulness in acidic compartments such as endosomes.
YFP can be split into two non-fluorescent halves that reconstitute fluorescence only when the two halves are brought together by interacting protein partners, a technique called bimolecular fluorescence complementation. This split-YFP approach was first demonstrated by Tom Kerppola's laboratory in 2002 and has since been used to map protein interaction networks inside living plant, yeast, and mammalian cells.
Yellow fluorescent protein naturally exists in organisms. YFP is an engineered protein created by site-directed mutagenesis of wild-type GFP; no organism produces it naturally, and its yellow emission spectrum does not occur in Aequorea victoria or any other known bioluminescent animal.
In studies of synaptic vesicle dynamics, researchers fused YFP to the vesicle protein synaptophysin in cultured rat hippocampal neurons and tracked individual vesicle pools over distances of up to 100 micrometers along axons. Time-lapse imaging revealed that a single presynaptic bouton recycles its entire surface pool of synaptophysin-YFP within approximately 10 minutes of sustained stimulation at 10 hertz.