Karteikarten
Development 4
Karten in diesem Stapel (21)
- 1How many cells and different cell types compose an adult human?Adult human composed of trillions of cells comprising ~250 different major cell-types
- 2How does SKM differentiate?SKM made by myotome region of each somite, induced by signals from adjacent tissues, including Wnt from NT. Induced muscle precursors (myoblasts) kept in mitotic state by FGF. Muscle specific TFs, (MyoD1) inhibit proliferation, promote cell fusion, & activate transcription of genes required 4 SKM differentiation.
- 3What r functional characteristics of SKM?SKM: large multinucleate cells (myofibres), contractile apparatus: sarcomeres (cross-striations), dark band (A): myosin, light band (I): actin, myosin & actin slide // during contraction, muscle specific proteins: a-actin, myosin II, tropomyosin, titin, nebulin, AChR, Creatine PhosphoK
- 4How many genes does human genome contain? Do all cells express them?~20,000 protein coding genes, only 6-7% transcribed by all cells (housekeeping genes required 2 maintain basic cellular functions e.g. metabolism, RNA&protein
synthesis, cell cycle control), vast majority tissue selective genes transcribed by only few cell-types (in some cases only 1) - 5What is differential gene expression?Every cell nucleus contains complete genome established in fertilised egg.
Genes not transcribed in differentiated cells not destroyed or mutated. Only a small % of genome expressed in each cell - 6How is tissue-specific gene transcription controlled?Tissue specific transcription controlled by distal control elements (enhancers) bound by TFs (activators). Enhancers may be 1M bp away from promoter and r brought 2 promoter by DNA bending
proteins. Tissue specific TFs now interact
w/ general TFs & mediator proteins & whole complex regulates RNA synthesis by RNA polymerase II - 7How do epigenetic mechanisms regulate gene transcription?Gene transcription regulated through epigenetic mechanisms that affect chromatin structure, including
modifications of DNA and associated core histones. Methylation of
C in gene promoters associated w/gene silencing, while methylation of core histones associated w/ gene activation & silencing. Acetylation of core histones associated w/gene activation. - 8How is chromatin modified in differentiated cells?Transcribed genes: Histone modifications (H3K4m3, H3K9ac) create loose chromatin, accessible 2 TFs. Non transcribed genes: highly methylated DNA (5mC) & alternative Histone modifications (H3K9m3) create compact chromatin, inaccessible 2 TFs
- 9How are the different tissues organized in Drosophila larva?Cells that form adult cuticle found as undifferentiated discs (imaginal discs) in larva, w/ discs 4 mouth parts, eye antenna, wing, haltere, legs & genitalia. Abdominal segments found as cell nests (histoblasts). Cells differentiate in pupal development.
- 10How stable is determination? How do we know this?Determination is very stable: removing imaginal discs from larvae, cutting them in 2 & transplanting 1/2 2 other larva+1/2 2 adult female several times: most cases disc continues differentiate same tissues but rarely formed different part of cuticle-transdetermination (Ernst Hadorn)
- 11Do non-transcribed genes of differentiated cells retain potential 4 transcription? Can genome be reprogrammed? (SCNT)Nuclear Transfer Xenopus laevis: destroy egg nucleus (UV), inject nucleus isolated from differentiated cell, small % embryos =>tadpoles+adults, most partial, nuclei from these transferred 2 enucleated eggs can form tadpoles+ adults, cells partial embryos grafted host embryo differentiate multiple cell types (ct), 30% intestinal nuclei can form functional non intestinal ct=>genome differentiated cells can b reprogrammed (Sir John Gurdon)
- 12How does % SCNT Xenopus laevis embryos develop normally vary w/ stage at which nucleus taken? What can you conclude?Success rate dropped as progressively later stages used as donors, but even nuclei from tadpoles support normal develop, Gurdon (1962) concluded genome of differentiated cells can be reprogrammed 2 support differentiation of other cell types
- 13What r Campbell & Wilmut famous 4?SCNT in mammals: Campbell & Wilmut (1997) fused enucleated egg w/ cultured mammary gland cell, ~12% reached blastocyst stage, transferred 2 surrogate female, only 1 (0.3%) born alive (Dolly)
- 14Can the genome be reprogrammed?Nuclei can b reprogrammed if placed in
suitable cytoplasmic environment but
frequency very low - 15What r heterokaryons? Give an example. What does this imply?Multinucleate cells w/ genetically different nuclei, e.g. mouse myoblast fused w/ human hepatocyte=>human muscle-specific proteins on heterokaryon PM=> muscle-specific genes transcribed in differentiated liver cells=>mouse myoblast factors activate human muscle genes
- 16What was the muscle determinant that induced muscle-specific gene expression in mouse-myoblast/human hepatocyte heterokaryons?MyoD1: TF in developing SKM cells, from Myogenic Regulatory Factors family (includes Myf5, Myf6, Myogenin), all 4 required 4 muscle develop in vertebrates & transform fibroblasts in2 myoblasts if constitutively expressed
- 17Why are enhancers important in develop?Enhancers act as genetic switches that regulate tissue-specific expression
- 18Can differentiated cells be reprogrammed?Master regulator TF can cause transdifferentiation
- 19Can master regulators restore pluripotency to differentiated cells?Takahashi & Yamanaka (2006) introduced Oct4, Sox2, Myc & Klf4 in2 fibroblasts, <1% somatic cells transformed in2 pluripotent cells resembling ESC, form range different cell-types=>mammalian genome reprogrammable
- 20Which genes confer pluripotency?Oct4, Sox2, Nanog specifically expressed in ICM&required 2 keep pluripotency. 3 genes all encode TF (regulate gene expression in ICM). Downregulated in ICM as cells become committed 2 different germ layers
- 21—
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- Beschreibung
- Cells and development Karteikarten am Development 4, erstellt von Francisco Sacadura am 10/03/2017.
- Erstellt von
- Francisco Sacadura · Mär 2017
- Aktualisiert
- 24 Mär 2017
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