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WVSOM - Molecular-4

Differentiation

QuestionAnswer
Differentiation The process of transformation into a different cell type
Commitment When the developmental fate of a cell becomes restricted, so that it will differentiate in a specific manner
Specification 1st phase of commitment, fate still reversible; ex: ectodermal cell in medial region of trilaminar germ disc specified to develop into neural cell; if micromanipulator used to transfer it to lateral region of disc, it will differentiate into dermal cell
Determination Final phase, when commitment becomes irreversible; commitment may occur before onset of differentiation; some cells are committed early in development, before there are any detectable changes in cell morphology or biochemistry
Autonomous specification Intracellular signals (within cell) controlling cellular differentiation
Intercellular induction Signals between cells controlling cellular differentiation
Hormones Non-nutrient chemicals secreted by one cell to induce a response in another cell
Growth factors Hormones that control cell cycle progression, cellular differentiation or morphogenesis during development
Differentiated cell types Specialized cells within limited or no ability to transform into other cell types
Undifferentiated cell types Cells that have not transformed into a specialized cell type
Specialized cell types Cells with distinctive morphological characteristics and/or molecular processes
Generalized cell types Cells lacking specialized characteristics
Totipotency To have the potential to differentiate into any cell type and produce an entire organism (germ line, gametes, zygotes, and early blastomeres)
Pluripotency, multipotency To have the potential to differentiate into multiple cell types (i.e. hemopoietic cells, fibroblasts)
Stem cells Cells that differentiate into other cell types (i.e. spermatogonia, mesenchymal stem cells); either divide into more stem cells to propagate their own population or they differentiate when they divide
Progenitor (precursor) cells Cells that must differentiate into other cell types and so cannot propagate their own poplation
Blastomere Cells from cleavage stage embryos or blastocyts
Blast cell Stem cells from any embryonic stage; usually named after cell types they produce; i.e. neuroblast (differentiates into neurons)
Mesenchyme Loosely organized blast cells; usually thought of as mesodermal, but they may be derived from the other layers (e.g. ectodermal neural crest cells)
Metaplasia Transformation of one differentiated cell type to another (i.e. smoking can induce pseudostratified epithelium of bronchi to become stratified squamous)
Dedifferentiation To reverse the process of differentiation; for a specialized cell to transform into less specialized cell type
Anaplasia Dedifferentiation to an embryonic cell type
Neoplasia Abnormal, new growth (e.g. tumor formation); most neoplasias are anaplasias
Characteristics of differentiated cells 1. specialized cellular structures and/or functions, 2. slow or arrested cell cycle progression, 3. impaired ability to transform into other cell types
Levels of differentiation Differentiation is not an all-or-none process; some cells more differentiated than others; i.e. zygote = completely undifferentiated (will produce all cell types), hemopoietic cell = more differentiated (can only transform into blood cells)
Development and differentiation process of development = progressive proliferation & differentiation of cells from zygote to adult; # of differentiated cells & degree of differentiation = increases throughout development; totipotent cells become pluripotent, end as differentiated cells
Regeneration and differentiation differentiated cells lose ability to divide and proliferate; cannot proliferate = cannot replenish themselves after damage; highly differentiated cells (muscle, nerve) have little to no regenerative ability
Myogenesis Muscle development; three classes of muslce (smooth, cardiac, skeletal)
Myoblasts Muscle stem cells; myoblast formation is an example of determination; myoblasts will only form muscle
Muscle fibers Muscle cells, often referred to as myocytes or myotubes; multiple myoblasts fuse together to form one large, syncytial skeletal muscle fiber; this is the completion of muscle differentiation
Earliest activators of myogenesis Wnt (went) and Shh (sonic hedge hog); intecellular signaling molecules; secreted by neural cells in embryo
Pax-3 Helix-turn-helix transcription factor that function as upstream activator of MyoD
Helix-loop-helix factors that induce skeletal myogenesis Myf-5, Myf-6, Myo-D, myogenin; factors bind to each other's enhancers (activate each other's transcription)
Myf-6 HLH; upstream activator of Myf-5
Myf-5 and Myo-D HLH; Both contribute to differentiation of somites into myoblasts, although only one is required
Myogenin HLH; Not required for myoblast formation, but is required for final differentiation into skeletal muscle fibers
Positive HLH's Myf-5, Myf-6, MyoD, myogenin
Negative HLH's Id
Ubiquitous HLH's E2A
___ ___ compete with ___ ___ for association with ___ ___ Positive MyoD; negative Id; ubiquitous E2A
Why is Id negative? Lacks DNA binding domain; prevents E2A from activating transcription
MyoD/E2A complex Binds DNA sequence (E box - CannTG) found in promoters & enhancers of many genes required for myogenesis (ex: actins, myosins, troponin, creatine kinase, other HLH genes)
MEF-2 Belong to MADS-box family of transcription factors; expression activated by MyoD and Myf-5; expression = binds HLH heterodimer to form trimeric complex
MEF-2 recognition sequence CTAWWWWTAG (W = A or T); found adjacent to E boxes of many muscle specific promoters/enhancers; MEF-2 cooperates w/ HLH factors to activate muscle specific transcription
Created by: JaneO on 2011-10-02



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