#pluripotency

Stem Cell -l

Which factor is required for maintaining the pluripotency of embryonic stem cells?

Pluripotency in embryonic stem cells depends on a core transcriptional circuit centered on Oct4, Sox2, and Nanog. Oct4, a POU domain transcription factor, activates self-renewal genes and represses differentiation drivers such as Cdx2 and Gata6. Its dosage is critical; too low triggers trophectoderm differentiation, too high pushes toward primitive endoderm and mesoderm. Oct4 collaborates with LIF-STAT3 and FGF signaling to sustain open chromatin and prevent lineage commitment. Loss of Oct4 leads to rapid differentiation, making it indispensable for maintaining the undifferentiated, unlimited proliferative state of embryonic stem cells.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Core pluripotency factors Oct4, Sox2, Nanog.

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Stem Cell -ll

Which statement is false regarding embryonic stem cells?

Embryonic stem cells originate from careful isolation and sustained culture of inner cell mass of preimplantation blastocyst, typically embryonic day 3.5 to 4.5 in mice, dependent on leukemia inhibitory factor and dual inhibition 2i blocking MAPK and GSK3 to prevent differentiation. Trophoblast comprises outer epithelium forming future placenta, expressing Cdx2 and Eomes, separated by first fate decision driven by Hippo signaling. Deriving ESCs from trophoblast contradicts established lineage; embryonic cells are not trophectoderm derivatives and cannot contribute efficiently to placenta inside chimeras.

Ref: Rossant, Stem Cells 2008; Gilbert, Chapter 5: ICM versus trophoblast lineage ESC origin not trophoblast.

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Stem Cell -ll

Which transcription factor is NOT involved in maintaining embryonic stem cell pluripotency?

Embryonic stem cell pluripotency depends critically on autoregulatory loop of Oct4, Sox2, and Nanog binding their own and each other's promoters and enhancers of downstream Esrrb, Klf4, Utf1 and chromatin modifiers. These factors recruit Mediator complex and p300 acetyltransferase to maintain open accessible euchromatin at pluripotency loci. p53, a prominent DNA damage sensor, induces cell cycle arrest, apoptosis, and differentiation by activating p21, Bax, and repressing Nanog transcription. Pharmacological inhibition or temporary genetic deletion of p53 dramatically increases somatic reprogramming efficiency, confirming its role as tumor suppressor antagonizing self-renewal rather than supporting network.

Ref: Chambers & Tomlinson, Cell Stem Cell 2009; Gilbert, Chapter 6: Oct4 Sox2 Nanog core versus p53.

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Fertilization in mammals-ll

Oct4, Sox2, Nanog maintain pluripotency in:

Pluripotency of inner cell mass and derived embryonic stem cells depends on core transcription factor circuit Oct4 Sox2 Nanog forming feed-forward autoregulatory loop. These factors co-bind promoters of self-renewal genes while repressing differentiation drivers like Cdx2 and Gata6 via chromatin remodeling. Active Hippo pathway retaining YAP cytoplasmically permits sustained expression. Withdrawal of any component collapses pluripotency causing precocious trophectoderm or primitive endoderm differentiation. Triad therefore maintains naive state ensuring capability to generate all embryonic lineages upon gastrulation signals, implantation cues, developmental progression and differentiation stimuli in embryogenesis.

Ref: Young, Molecular Biology of Stem Cells: Oct4, Sox2, Nanog core pluripotency circuit in ICM and ES cells.

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Fertilization in mammals-iv

Pluripotency maintained by:

Pluripotency of inner cell mass and embryonic stem cells is maintained by core transcriptional network centered on Oct4, Sox2 and Nanog. These factors co-occupy enhancers of self-renewal genes while repressing lineage-specific differentiation genes via chromatin remodeling. Oct4 and Sox2 form heterodimer activating Nanog promoter, and all three autoregulate and cross-regulate each other creating robust circuit. Stat3 downstream of LIF supports mouse pluripotency but alone insufficient. Nanog alone cannot sustain, nor can FoxA2/Gata6 which actually promote primitive endoderm differentiation, opposing pluripotent state and triggering exit toward differentiated lineages.

Ref: Yamanaka et al., Nature 2006; Gilbert Ch 6: Core pluripotency network Oct4 Sox2 Nanog maintaining embryonic stem cells.

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Animal Tissue Culture 1

Leukemia inhibitory factor (LIF) is used to:

Embryonic stem cells derived from pre-implantation blastocyst inner cell mass ICM three point five days mouse development maintain naive pluripotency defined by capacity to contribute to all three germ layers ectoderm mesoderm endoderm forming teratoma containing differentiated tissues and chimeric mice after blastocyst injection including germ line transmission indicating functional pluripotency plus transcriptome expressing OCT4 SOX2 NANOG core triad forming feedforward loop activating pluripotency enhancers while repressing differentiation genes via recruiting Polycomb repressive complex 2 depositing H3K27me3 at lineage promoters. Maintenance in vitro requires external cytokine signal leukemia inhibitory factor LIF belonging to interleukin-6 family four helix bundle cytokine binding heterodimer gp130 signal transducer and LIF receptor beta LIFRβ activating associated Janus kinases JAK1 JAK2 cross phosphorylating receptor cytoplasmic tyrosine creating docking sites for SH2 domain containing STAT3 signal transducer and activator transcription three that is phosphorylated on tyrosine seven hundred five. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.

Ref: Smith & Hooper Dev Biol 1987 LIF JAK-STAT3 KLF4 pluripotency; Ying Nature 2008 ground state 2i mouse ES naive.

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