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#cell fate

32 public questions tagged with this topic.

Stem Cell -ll

Which of the following is true about asymmetric stem cell division?

Asymmetric division preserves tissue architecture by simultaneously producing one copy of mother stem cell retaining niche attachment and one daughter committed to differentiation and departure. Niche signals maintain polarity proteins that orient mitotic spindle perpendicular to basement membrane, ensuring one daughter remains niche-attached retaining integrin signaling and high Wnt activity, while other detaches and encounters differentiation cues like high Notch ligand or Wnt attenuation. This outcome maintains stem pool size during homeostasis unlike symmetric divisions that either expand or deplete pool, and it operates in both multipotent and unipotent contexts widely.

Ref: Morrison & Kimble, Nature 2006; Gilbert, Chapter 6: Asymmetric division stem and differentiated daughters maintenance.

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Induction Morphogen -ll

In the 'French flag model' of morphogen action, what determines cell fate?

Lewis Wolpert's French flag model proposed that positional information is encoded by a diffusible morphogen gradient. Cells detect local ligand concentration through surface receptors and intracellular transducers, converting continuous gradient into discrete thresholds. Low, intermediate and high doses activate distinct enhancers and transcription factors, producing three broad fate domains resembling a tricolour flag. Thus fate depends not on receptor number, mitotic rate or linear distance but on quantitative interpretation of morphogen exposure during patterning of limb buds, neural tube and Drosophila imaginal discs and vertebrate axis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: French Flag Model and Morphogen Gradients.

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Induction Morphogen -ll

Which of the following is a feature of permissive interaction?

Permissive inductive interaction occurs when responding tissue is already specified toward a particular fate and inducing tissue merely provides supportive environment, nutrients, extracellular matrix or generic trophic factors enabling self-differentiation rather than conveying new positional information. For instance, many developing epithelia require underlying mesenchyme as permissive scaffold maintaining survival but retain intrinsic program without instruction. Instructive interaction contrasts by directly imposing new fate through specific instructive ligands qualitatively altering transcription including BMP inhibitors inducing neural fate. Permissive responses do not require quantitative dose of signal and show responder autonomy once specification achieved previously.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Permissive vs Instructive Inductive Interactions.

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Specification Determination-l

Which of the following is an example of conditional specification?

Conditional specification enables cells to maintain broader potential, and multipotency exemplifies this property where single progenitor can generate multiple differentiated cell types depending on environmental context. Early blastomeres of mammals, sea urchins and fish exhibit multipotency, giving rise to diverse lineages in response to varying inductive cues like FGF, BMP and Notch. This flexibility reflects absence of locked cytoplasmic determinants and dependence on extrinsic signaling gradients for lineage restriction and differentiation control. Multipotent progenitors serve as paradigm for regulative, conditional development, contrasting determined unipotent precursors following autonomous trajectories toward single fate exclusively.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 5: Multipotency and Conditional Specification Concepts.

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Specification Determination-l

Which statement is true about the role of cytoplasmic determinants?

Cytoplasmic determinants are maternal effect products localized asymmetrically within egg that instruct early lineage decisions before zygotic genome activation dominates. Their precise segregation during cleavage allocates distinct transcription factor activities to daughter cells, initiating fate decisions prior to extensive inductive signaling. Examples include VegT directing endoderm in Xenopus vegetal hemisphere, and PIE-1 repressing transcription in C. elegans germline precursors preserving totipotency. By providing spatially restricted information, determinants establish initial polarity, organize gastrulation movements and activate specific gene regulatory networks critical for axis formation, germ layer allocation and early body plan foundation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Role of Cytoplasmic Determinants in Early Fate Decisions.

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Specification Determination-l

Which of the following describes a labile stage in cell commitment?

Specification represents labile, flexible commitment phase where cells exhibit preferential differentiation in neutral culture but retain ability to reverse fate when exposed to heterologous inductive environments. This reversibility defines its instability, contrasting irreversible determination where fate lockdown via epigenetic mechanisms prevents redirection. Developmental biologists test lability experimentally by heterotopic transplantation: specified tissue may adapt to new location, revealing incomplete commitment. Thus specification is considered unstable intermediate between naive totipotency and final determination, gradually narrowing potency through cumulative inductive interactions over developmental time and progressive chromatin restriction ensuring ordered lineage progression.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 5: Specification as Labile Commitment Phase.

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Specification Determination-l

What is a key feature of syncytial specification in Drosophila?

Drosophila embryogenesis begins as syncytium facilitating rapid pattern formation. Nuclei divide thirteen times without cytokinesis, sharing common cytoplasm where Bicoid and Nanos gradients diffuse unimpeded, establishing positional information before membranes form. Gap genes respond to gradient thresholds, initiating segmentation cascade of pair-rule and segment polarity genes through cooperative DNA binding. Only after cellularization at cycle fourteen do cells become individualized, retaining pre-programmed identities through sustained transcription factor networks. Key innovation lies in fate pre-patterning within communal cytoplasmic space, accelerating development and minimizing need for extensive early cell-cell signaling during axis establishment phase.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Syncytial Specification Before Cellularization in Drosophila.

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Specification Determination-l

Which of the following is NOT an example of regulative development?

Regulative development examples include mammalian identical twins arising after splitting of inner cell mass into two embryonic axes, isolated sea urchin blastomeres forming complete larvae, and amphibian transplantation where presumptive epidermis grafted into neural plate adopts neural fate due to BMP inhibition. In all cases, remaining cells compensate for loss or altered position through inductive reprogramming and community effects. C. elegans development is opposite; lineage is essentially invariant, determinants partitioned rigidly, ablation permanently removes tissue. Such mosaic behavior lacks compensation and potency equals fate, illustrating autonomous rather than conditional regulation and not regulative development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 3: Regulative vs Mosaic Examples.

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Specification Determination-l

In conditional specification, what determines cell fate?

Conditional specification asserts that cell fate emerges primarily from extrinsic cues provided by neighboring cells rather than inherited determinants. Surrounding tissues secrete morphogens, contact-dependent ligands like Delta and extracellular matrix components that activate specific signal transduction pathways including Smad, MAPK, Wnt and Notch in responsive cells, reprogramming transcriptional networks. Examples include vertebrate mesoderm induction where vegetal Nodal instructs marginal ectoderm, and neural crest lineage diversification shaped by BMP and Wnt encountered during migration. Because environment instructs identity, cells maintain flexibility, can be redirected by transplantation, and collectively regulate missing parts ensuring robust patterning.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 3: Conditional Specification and Neighbor Interactions.

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Specification Determination-l

Which experiment demonstrated regulative development in sea urchins?

Hans Driesch in 1891 performed landmark sea urchin blastomere isolation demonstrating regulative potential. By mechanically shaking apart two- or four-cell embryos, he found each isolated blastomere developed into complete, proportionate pluteus larva smaller than normal but correctly patterned. This unexpected outcome directly contradicted Roux mosaic results, proving fate not irrevocably allocated through cytoplasmic division. Remaining cells compensated via intercellular signaling respecification, establishing paradigm of conditional development and potency exceeding fate. Driesch experiment shifted embryology from deterministic preformationist determinant views toward modern concept of embryos as self-organizing morphogenetic fields governed by inductive interactions and positional information.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 3: Driesch Experiment and Regulative Development.

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Specification Determination-l

Which of the following statements about cytoplasmic determinants is true?

Cytoplasmic determinants are not uniformly distributed; they are anchored asymmetrically within oocyte via microtubules, actin networks and cortical anchors before fertilization. These localized mRNAs encoding transcription factors, signaling ligands and translational regulators orchestrate early patterning events including axis establishment, germ layer allocation and germ cell specification before major zygotic inductive interactions. Examples include beta-catenin stabilization vegetally in sea urchins driving micromere formation, VegT directing endoderm in Xenopus vegetal hemisphere, and bicoid patterning anterior in flies. Asymmetric inheritance drives differential gene expression crucial for initiating body plan formation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Cytoplasmic Determinants in Patterning.

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Specification Determination-l

In which type of specification does the cell fate depend on cytoplasmic determinants inherited during cleavage?

Autonomous specification depends primarily on inheritance of localized cytoplasmic determinants partitioned unequally during cleavage, rather than ongoing communication between cells. Maternal mRNAs, proteins and organelles concentrated at particular cortical regions of the egg are asymmetrically segregated to specific blastomeres, preconfiguring transcriptional activity and signaling potential. Classic illustrations include macho-1 mRNA directing muscle fate in tunicates, P granules establishing germline identity in C. elegans P lineage, and vegetal determinants activating endoderm in ascidians. Isolated blastomeres thus produce only their intrinsic descendants, revealing programming independent of neighbors.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 3: Autonomous Specification and Cytoplasmic Determinants.

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