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#cell communication

11 public questions tagged with this topic.

Morphogen Induction-l

Which of the following is an example of a juxtacrine signaling pathway?

Juxtacrine signaling requires direct membrane apposition where ligand retained on surface of one cell activates receptor on neighboring cell without secretion. Canonical example is Notch-Delta: Delta family ligand on signaling cell binds Notch receptor, inducing proteolytic cleavages by ADAM and gamma-secretase releasing intracellular domain that activates transcription via CSL. BMP-Wnt interaction represents paracrine crosstalk where secreted morphogens antagonize or synergize via extracellular binding, diffusing at distance, not contact-dependent signal. TGF-beta-Smad and FGF-Erk also represent diffusible paracrine with intracellular cascades. Therefore juxtacrine hallmark is cell-contact dependence without extracellular gradient, typified by Notch-Delta lateral inhibition mechanism controlling fate.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Juxtacrine versus Paracrine Signaling.

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Induction Morphogen -ll

Which of the following is NOT a characteristic of paracrine signaling?

Paracrine signaling is short-range communication where secreted proteins travel tens to hundreds of micrometers through extracellular matrix, binding receptors on nearby cells. It involves ligand-receptor interaction, gradient formation, endocytic clearance and threshold-dependent gene activation, exemplified by FGF, Hedgehog, Wnt and TGF-beta families patterning embryonic fields. Communicating with distant organs requires endocrine signaling via bloodstream, such as insulin, estrogen or growth hormone traveling systemically and acting at low concentration. Paracrine cannot act systemically due to dilution, matrix binding and rapid degradation by proteases. Therefore systemic distant organ communication is not paracrine characteristic, distinguishing it from endocrine mode.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Paracrine vs Endocrine Signaling.

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Induction Morphogen -ll

Which signaling type involves diffusion of molecules to nearby cells?

Paracrine signaling involves secretion of soluble ligands that diffuse locally through extracellular matrix to affect neighboring cells within several cell diameters. Ligands like FGF, Hedgehog, BMP and EGF bind cognate receptor tyrosine kinases or serine-threonine kinases activating MAPK or Smad cascades. Concentration declines with distance, enabling gradient formation and threshold responses. Juxtacrine requires direct membrane contact via Notch-Delta, autocrine targets same producing cell, synaptic is specialized neuronal transmission via neurotransmitters. Paracrine underlies embryonic induction, wound healing, lateral inhibition and is primary mode of morphogen dispersal in developing epithelia and mesenchyme.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Paracrine Signaling Mechanisms.

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Paracrine Factor

Which of the following is NOT a characteristic of paracrine signaling?

Paracrine factors act locally over microns, not systemically via bloodstream like hormones. They rely on diffusion, facilitated transport, cytonemes or exosomes over 10-100 cell diameters, rapidly degraded or sequestered by proteoglycans and antagonists like Noggin, Chordin. Endocrine hormones such as estrogen, thyroxine travel meters via blood, requiring high stability and low clearance. Paracrine mode involves ligand-receptor binding triggering MAPK, Smad cascades guiding organogenesis, wound healing, stem cell niches. Morphogen gradients emerge precisely because signaling range limited, whereas endocrine provides uniform concentration distinguishing local developmental patterning versus organism-wide homeostasis and metabolic control mechanisms.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Paracrine versus endocrine signaling distance comparison.

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Paracrine Factor

Which type of signaling involves the diffusion of molecules over a short distance to regulate neighboring cells?

Paracrine signaling involves localized secretion of ligands acting over few cell diameters, contrasting endocrine long-range circulation and autocrine self signaling. Ligands like FGF, Wnt, Hedgehog, TGF-beta bind receptors on nearby cells triggering intracellular cascades guiding differentiation, proliferation, migration. This mode enables morphogen gradients patterning fields, such as limb progress zone or neural tube where concentration interprets fate via thresholds. Diffusion limited by extracellular matrix heparan sulfates, proteolysis, receptor-mediated endocytosis, antagonists ensures short-range effect allowing precise spatial control during organogenesis without systemic hormonal influence or direct cell contact needed for juxtacrine.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Paracrine signaling definition - short-range communication via morphogen gradients.

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Sea urchin -lll

Micromere signaling induces adjacent cells via:

Adjacent to micromeres, macromeres and large micromeres receive inductive signal mediated by direct cell contact requiring juxtacrine interaction. Micromeres express transmembrane ligand Delta following derepression of HesC by Pmar1. Neighboring cells express Notch receptor; Delta binding triggers gamma-secretase cleavage releasing Notch intracellular domain NICD that translocates to nucleus activating transcription of secondary mesenchyme genes gcm, gataE, foxA for pigment and blastocoelar cells and endoderm. This Delta-Notch induction specifies non-skeletogenic mesoderm. Blocking Notch with DAPT inhibitor eliminates secondary mesenchyme, while Delta misexpression induces ectopic mesoderm, proving essential vegetal patterning mechanism.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 10: Micromere Delta-Notch signaling induces adjacent cells mesoderm.

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Dictyostelium

High extracellular cAMP induces:

High ambient extracellular cAMP acts as positional cue favoring prespore differentiation through sustained protein kinase A activation. At millimolar levels, cAMP saturates desensitization mechanisms, maintaining intracellular messenger elevated, inducing transcription of prespore-specific genes encoding spore coat proteins while repressing prestalk markers. Low-density monolayer experiments show cAMP plus conditioned medium induces prespore markers, whereas DIF-1 alone induces prestalk. High cAMP therefore mirrors posterior slug environment where prespore cells reside. Prestalk formation prefers low cAMP together with DIF-1, vegetative growth requires folate, slug dispersal demands low cAMP oscillations, highlighting dosage-dependent fate specification mechanism.

Ref: Methods in Molecular Biology, Prespore induction by high cAMP - SP70 expression and PKA signaling mechanism.

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Dictyostelium

Chemical attracting aggregation secreted every:

Effective long-range aggregation requires non-continuous pulsatile emission of cAMP rather than steady gradient. Pacemaker cells spontaneously release cAMP every five to ten minutes, generating concentric waves degraded between pulses by extracellular phosphodiesterase PdsA. Intervals shorter than one to two minutes prevent receptor resensitization, while intervals longer than fifteen minutes degrade signal relay. Oscillatory frequency emerges from adaptation loop involving cAR1 phosphorylation, G protein activation, ACA refractory period, and PdsA recovery. Chemotacting amoebae move only during rising phase, pausing during falling phase, producing characteristic streaming pattern that efficiently gathers tens of thousands of cells toward center.

Ref: Cell, Dictyostelium cAMP waves - PdsA degradation and 5-10 minute oscillation dynamics in aggregation.

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Cell Signaling ELR Pathways - I

Notch signaling involves

proteolytic cleavage of receptor, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling Fundamental PrinciplesI

Inputs to cell signaling include

all of these, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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