#stem cell division

Stem Cell -ll

Which type of stem cell division results in an increase in stem cell number?

Symmetric self-renewing division produces two daughters both retaining stem character, full self-renewal transcriptional program, and niche responsiveness, thereby increasing absolute stem cell number inside tissue. This mode dominates during development to rapidly expand progenitor pools, during wound healing to repopulate emptied niches, and in culture systems where niche constraints are experimentally relaxed. Mechanistically, mitotic spindle orientation parallel to niche basement membrane places both daughters within Wnt-rich microenvironment, preserving expression of Lgr5 and other stem markers. Conversely asymmetric division maintains constant numbers, while symmetric differentiating divisions generate two committed cells causing contraction.

Ref: Watt & Hogan, Science 2000; Morrison & Kimble, Nature 2006: Symmetric self-renewal expands stem pool.

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Stem Cell -ll

The term 'population asymmetry' in stem cell division means:

Stem cell systems often maintain steady state through population asymmetry rather than invariant asymmetric division of every single cell synchronously. Individual stem cells stochastically adopt variable fates: some undergo symmetric self-renewal generating two stem cells, some undergo symmetric differentiation producing two committed progenitors, while overall population balance remains constant due to neutral competition and niche space limitation. Lineage tracing in mouse intestine, epidermis, and testis supports this probabilistic model. Consequently population-level equilibrium emerges without requiring each division to be strictly asymmetric, and niche signals modulate probabilities rather than dictate identical division rates.

Ref: Klein & Simons, Development 2011; Gilbert, Chapter 6: Population asymmetry stochastic division model tissue homeostasis.

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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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Stem Cell -lll

Which type of stem cell division stabilizes the stem cell population while producing differentiated progeny?

Asymmetric division intrinsically or extrinsically partitions fate determinants, producing one daughter retaining stem cell identity within the protective niche and another exiting to differentiate. Spindle orientation, evolutionarily conserved Par polarity proteins, Numb segregation, and polarized Notch signaling ensure unequal inheritance of transcription factors and organelles. This elegant mechanism preserves constant stem pool size during steady-state homeostasis while continuously supplying progenitors for tissue turnover. In contrast, symmetric self-renewing divisions expand pool during development, while symmetric differentiation depletes it, illustrating dynamic regulation of tissue balance throughout life.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Stem cell self-renewal, asymmetric division and determinant segregation.

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Stem Cell -lll

Which type of stem cell division increases the stem cell pool?

Stem cell pool expansion occurs through symmetric self-renewing division where mother produces two daughters retaining stem identity and potency. This mode dominates during embryonic development, regeneration after injury and early culture expansion driven by high Wnt, EGF and absence of differentiation cues like BMP. Asymmetric division maintains constant pool size generating one stem and one differentiating daughter, symmetric differentiating division depletes pool generating two differentiated cells, and population asymmetry describes stochastic balancing across population. Balanced control between symmetric self-renewal and asymmetric divisions governs tissue growth, aging and homeostasis preventing exhaustion.

Ref: Morrison and Kimble, Nature 2006, Symmetric Self-Renewing Division Expands Stem Pool.

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