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#MCQ biology

7 public questions tagged with this topic.

Stem Cell -lll

Which of the following is NOT a function of stem cells?

Physiological stem roles encompass tissue regeneration after injury via symmetric expansion and mobilization, differentiation into specialized cells replenishing turnover, secretion of trophic factors modulating inflammation, angiogenesis and niche, and maintaining homeostatic equilibrium between loss and production. Apoptosis constitutes programmed death mediated by caspase cascade eliminating damaged or unwanted cells, opposite of stem survival function. Stem cells evade apoptosis through Bcl2 and niche PI3K-Akt signals; apoptosis eliminates not generates derivatives. Therefore apoptosis is

Ref: Lanza et al., Essentials of Stem Cell Biology, 3rd ed., Chapter 5: Functions of Stem Cells.

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Stem Cell -lll

Hematopoietic stem cells (HSCs) are classified as:

Hematopoietic stem cells isolated from bone marrow as lineage negative Sca1 positive cKit positive population sustain all blood lineages including myeloid granulocytes, monocytes, erythroid cells and lymphoid B and T cells but not extraembryonic or non-hematopoietic tissues, defining multipotency within hematopoietic system. They self-renew long-term repopulating irradiated recipients and serial transplantation, generate committed progenitors common myeloid progenitor and common lymphoid progenitor via transcription factors GATA1, PU.1, Ikaros. Totipotent generates entire organism including pl

Ref: Orkin and Zon, Hematopoiesis, Chapter 2: Multipotent Hematopoietic Stem Cells Classification.

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Stem Cell -lll

Which stem cell niche is responsible for regulating intestinal stem cells?

Intestinal epithelium renews every 4-5 days from Lgr5 positive crypt base columnar stem cells residing at crypt base intermingled with Paneth cells providing niche signals. Niche constitutes Paneth cells supplying Wnt3, EGF and Notch ligand Dll4, mesenchymal telocytes and Foxl1 fibroblasts producing R-spondins, Gremlin antagonists and BMP inhibitors generating Wnt-high BMP-low environment maintaining self-renewal and repressing differentiation. EphB-Ephrin gradients position cells along crypt-villus axis regulating sorting. Upon Wnt inhibition stem cells differentiate into goblet, enteroendocr

Ref: Barker et al., Nature 2007, Lgr5 Intestinal Crypt Stem Cell Niche and Wnt Signals.

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Stem Cell -lll

Induced pluripotent stem cells (iPSCs) are created by introducing:

Yamanaka reprogramming showed somatic fibroblasts can be reset to pluripotency by ectopic expression of core pluripotency transcription network via retroviral vectors. Oct4 and Sox2 form heterodimer activating Nanog enhancer and auto-regulatory loop, Klf4 co-activates and suppresses p53 apoptosis, c-Myc enhances proliferation and chromatin remodeling facilitating demethylation of Oct4 promoter and reactivation of endogenous pluripotency circuitry. These four factors induce embryonic stem cell-like state expressing alkaline phosphatase, SSEA4, Tra-1-60, able to form teratoma containing three ge

Ref: Takahashi and Yamanaka, Cell 2006, Induction of Pluripotent Stem Cells by OSKM Factors.

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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

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

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Stem Cell -lll

Which of the following cells is totipotent in mammals?

Mammalian zygote formed by fertilization of oocyte and sperm possesses full epigenetic reprogramming capacity to produce complete organism including embryonic and extraembryonic lineages. Fertilization triggers cytoplasmic remodeling resetting parental genomes, protamine-histone exchange and activation of zygotic genome at 2-cell stage in mouse and 4-8 cell in human via maternal factors. Zygote divides into blastomeres each initially totipotent retaining ability to generate both inner cell mass and trophectoderm. Inner cell mass becomes pluripotent losing extraembryonic potency, hematopoietic

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Zygote Totipotency and Blastomere Potential.

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