Stem Cell -l

Stem Cell -l

A key characteristic distinguishing stem cells from progenitor cells is:

The fundamental distinction lies in lifespan and self-renewal capacity. Stem cells maintain indefinite self-renewal through telomerase activity, DNA repair proficiency, and symmetric self-renewing divisions, persisting throughout organismal lifetime. Progenitor or transit-amplifying cells exhibit limited proliferative potential, typically fewer than ten divisions, before senescence or terminal differentiation. Stem cells also retain broader potency and ability to regenerate tissue after injury, while progenitors are more fate-restricted. Both can differentiate, but only stem cells combine lifelong persistence with self-renewal, making them true reservoir for tissue turnover.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Stem vs progenitor self-renewal.

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Stem Cell -l

Which of the following statements about stem cell differentiation is incorrect?

Stem cell differentiation is highly orchestrated, not stochastic uncontrolled process. Lineage commitment involves progressive restriction through transcription factor networks, chromatin remodeling, and repression of alternative fates. Niche signals such as Wnt, BMP, Notch, and FGF provide positional information, while intrinsic epigenetic modifiers like Polycomb and Trithorax establish memory. Under specific experimental conditions, differentiation can be reversed via induced pluripotency or transdifferentiation using defined factors. Random differentiation would disrupt tissue architecture and cause tumorigenesis. Therefore regulated, stepwise commitment with reversible plasticity under defined reprogramming defines contemporary differentiation paradigms.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Regulation of differentiation.

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Stem Cell -l

Which of the following is an example of a stem cell niche?

A functional niche must provide structural support, adhesive contacts, and signaling milieu that maintains stemness. The intestinal crypt exemplifies this model: Paneth cells intercalated with Lgr5-positive stem cells at crypt base secrete Wnt3, EGF, and Notch ligands DLL1 and DLL4, creating high Wnt environment. Stromal telocytes and basement membrane contribute R-spondin and BMP inhibitors. This arrangement promotes proliferation and suppresses differentiation upward along villus. Mature red blood cells, trophoblast, and apoptotic cells lack stem-supporting signaling capacity, thus not considered niches. Crypt architecture demonstrates niche control of division mode and lineage output.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Intestinal crypt as niche example.

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Stem Cell -l

A transit-amplifying cell is:

Stem cell hierarchy includes long-lived quiescent stem cells, short-lived rapidly cycling transit-amplifying cells, and terminally differentiated cells. Transit-amplifying cells are committed progenitors derived from stem cell division, undergoing limited rounds of symmetric divisions to expand progenitor pool before terminal differentiation. Found in intestinal crypts, epidermis, and testes, they increase proliferative output while protecting stem cells from replication stress and mutation accumulation. They express differentiation markers like EGF receptor and have reduced self-renewal. Understanding this intermediate amplification stage explains how small stem pools generate large numbers of differentiated tissue cells efficiently.

Ref: Potten & Loeffler, Development 1990; Gilbert, 12th ed., Chapter 6: Transit-amplifying cells.

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Stem Cell -l

Which experiment first demonstrated the existence of pluripotent stem cells?

Pluripotency concept evolved from teratocarcinoma studies showing embryonal carcinoma cells could contribute to tissues. The definitive demonstration came with isolation of mouse embryonic stem cells in 1981 by Evans and Kaufman and independently by Martin. Cultured inner cell mass cells on feeder layers with LIF remained undifferentiated, expressed alkaline phosphatase, formed teratomas containing three germ layers, and contributed to chimeras including germline. This proved stable pluripotent lines exist in culture. Cloning Dolly and mesenchymal stem cell discovery addressed totipotency reversal and multipotency, not primary pluripotency proof.

Ref: Evans & Kaufman, Nature 1981; Gilbert, 12th ed., Chapter 6: Mouse ES isolation.

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Stem Cell -l

Hematopoietic stem cells (HSCs) can differentiate into:

Hematopoietic stem cells reside in bone marrow endosteal and perivascular niches, characterized by CD34, Sca-1, c-Kit markers in mouse. They are multipotent, giving rise to all blood lineages through stepwise commitment: common myeloid progenitor producing erythrocytes, platelets, granulocytes, monocytes, and common lymphoid progenitor producing B, T, and NK cells. Regulation involves transcription factors GATA1, PU.1, Ikaros, cytokines SCF, IL-3, IL-7. HSCs do not generate neurons, epithelial cells, or muscle fibers under normal physiology, maintaining strict hematopoietic fate through niche-derived Notch and Wnt signals.

Ref: Orkin & Zon, Cell 2008; Gilbert, 12th ed., Chapter 6: Hematopoietic stem cells.

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Stem Cell -l

Which statement about induced pluripotent stem cells (iPSCs) is false?

Induced pluripotent stem cells are engineered by ectopic expression of Yamanaka factors Oct4, Sox2, Klf4, c-Myc in somatic fibroblasts or blood cells, resetting epigenome to embryonic-like state. They self-renew indefinitely and differentiate into derivatives of three germ layers, useful for disease modeling and regenerative medicine without embryo destruction. Unlike embryonic stem cells isolated from blastocyst inner cell mass, iPSCs do not exist naturally in embryos; they require artificial reprogramming. They retain epigenetic memory and potential tumorigenicity, highlighting distinction between natural embryonic pluripotency and laboratory-induced pluripotency.

Ref: Takahashi & Yamanaka, Cell 2006; Gilbert, 12th ed., Chapter 6: iPSC reprogramming.

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Stem Cell -l

What is the correct sequence of lineage commitment in hematopoietic differentiation?

Developmental potency narrows progressively as epigenetic restrictions and lineage-specific transcription factors accumulate. The zygote and early morula are totipotent, producing embryo plus placenta. With blastocyst formation, inner cell mass becomes pluripotent, forming all three germ layers ectoderm, mesoderm, endoderm but not trophectoderm. Subsequently, tissue-specific multipotent stem cells such as hematopoietic stem cells arise, limited to lineages within one germ layer. Finally, unipotent progenitors differentiate into single cell types like erythrocytes or spermatids. This totipotent to pluripotent to multipotent to unipotent hierarchy reflects irreversible chromatin condensation and loss of plasticity.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Hierarchy of potency restriction.

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Stem Cell -l

In which organism is each individual cell totipotent?

Totipotency denotes ability to generate complete organism including embryonic and extraembryonic tissues. While mammalian totipotency is limited to zygote and early blastomeres up to eight-cell stage, certain lower metazoans retain organism-wide cellular plasticity. Hydra, a cnidarian, contains interstitial stem cells distributed throughout body that remain totipotent, capable of forming ectoderm, endoderm, nematocytes, neurons, and germ cells. Each fragment containing interstitial cells can regenerate entire animal. Mice, Drosophila, and zebrafish show lineage-restricted somatic cells early, so individual differentiated cells cannot regenerate whole organisms spontaneously.

Ref: Bosch, Stem Cells 2009; Gilbert, 12th ed., Chapter 6: Totipotency in Hydra interstitial cells.

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Stem Cell -l

Which of the following is NOT an essential property of a stem cell?

Essential stem cell properties include prolonged self-renewal, maintenance of an undifferentiated state with open chromatin, and capacity to differentiate into specialized functional cells under niche cues. Self-renewal involves asymmetric or symmetric divisions preserving stem pool while generating progeny. Limited division potential characterizes transit-amplifying progenitors and differentiated somatic cells subject to Hayflick limit and telomere attrition. True stem cells divide extensively throughout life, expressing telomerase and checkpoint evasion mechanisms. Recognizing unlimited self-renewal versus limited progenitor amplification separates stemness from more restricted proliferative populations during tissue homeostasis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Properties of stem versus progenitors.

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Stem Cell -l

Which signaling pathway is not directly involved in stem cell regulation?

Stem cell self-renewal and differentiation are orchestrated by conserved developmental pathways. Wnt maintains intestinal and embryonic stem cells via beta-catenin and TCF targets, Hedgehog regulates neural and hair follicle stem cell proliferation through Gli transcription factors, JAK-STAT mediates response to cytokines such as LIF and interleukins sustaining Drosophila germline and mammalian hematopoietic stem cells. Complement cascade is an innate immunity effector system for pathogen opsonization, lysis, and inflammation via C3a, C5a, membrane attack complex. It does not directly control core stemness transcription networks, though inflammatory milieu may indirectly influence niches.

Ref: Clevers, Nature 2013; Gilbert, 12th ed., Chapter 6: Wnt, Hedgehog, JAK-STAT in stem cells.

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Stem Cell -l

Which of the following can be derived from mesenchymal stem cells?

Mesenchymal stem cells are multipotent stromal cells from bone marrow, adipose, and perichondrium with mesodermal lineage restriction. They differentiate into cartilage, bone, and adipose tissue through master regulators Sox9 for chondrogenesis, Runx2 and Osterix for osteogenesis, and PPAR-gamma for adipogenesis. Cartilage formation involves condensation, Sox9-driven collagen type II and aggrecan expression, and requires TGF-beta signaling. While transdifferentiation to neurons or islet cells has been reported artificially, physiological derivatives remain skeletal tissues. Thus cartilage represents a canonical natural product of mesenchymal stem cell differentiation.

Ref: Caplan, J Orthop Res 1991; Gilbert, 12th ed., Chapter 6: Mesenchymal differentiation.

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