27 public questions tagged with this topic.
Transcription factors **regulate gene expression** by helping RNA polymerase bind to DNA and initiating transcription. This follows from NCERT principle where relation explains outcome clearly for students.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Biology - Botany portion covering relevant concept, Topic: Plant structure, physiology and applications.
Original Yamanaka cocktail clearly demonstrated four transcription factors sufficient to convert mouse and human fibroblasts to embryonic stem-like state functionally and transcriptionally. Oct4 is pituitary octamer transcription factor essential for inner cell mass identity and epiblast maintenance, Sox2 partners directly with Oct4 on composite motifs, Klf4 Krüppel-like factor regulates proliferation while suppressing somatic gene expression, c-Myc oncogene enhances chromatin accessibility, glycolytic metabolism, and proliferation kinetics. Later refinements replaced c-Myc with L-Myc or omitt
Ref: Takahashi & Yamanaka, Cell 2006; Yu et al., Science 2007: OSKM combination iPSC generation standard.
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 reprogr
Ref: Chambers & Tomlinson, Cell Stem Cell 2009; Gilbert, Chapter 6: Oct4 Sox2 Nanog core versus p53.
Pluripotency is sustained by a core transcriptional circuitry centered on Oct4, Sox2, and Nanog, which co-occupy enhancers of self-renewal genes and actively repress lineage inducers. Oct4 and Sox2 heterodimerize to activate Fgf4, Utf1, and chromatin remodelers essential for open euchromatin. p53, a tumor suppressor activated by DNA damage, antagonizes reprogramming by inducing p21, apoptosis, and differentiation genes. While Nanog stabilizes network robustness, genetic ablation shows embryonic stem cells can transiently self-renew without it, making p53 functionally outside pluripotency maint
Ref: Yamanaka & Takahashi, Cell 2006; Gilbert, Chapter 6: Pluripotency core Oct4 Sox2 Nanog versus p53 tumor suppressor.
Gli family members Gli1, Gli2, Gli3 are zinc finger transcription factors homologous to Drosophila Cubitus interruptus mediating Hedgehog transcriptional response. In resting state, Suppressor of Fused Sufu sequesters Gli in cytoplasm, promoting sequential phosphorylation by PKA, GSK3, CK1 creating beta-TrCP degron generating repressor Gli3R that blocks targets like Patched1. Upon Hedgehog activation, Smoothened inhibits Sufu and PKA processing, allowing full-length Gli activators Gli1, Gli2A to enter nucleus, inducing Patched1, Gli1 itself, cyclins, Myc, Bcl2. TCF is Wnt effector, STAT cytoki
Ref: Briscoe & Thérond, Nature Reviews Mol Cell Biol 2013: Gli/Ci transcription factors mediate Hedgehog target gene activation.
Neural retina formation from inner layer of optic cup requires sustained Pax6 expression cooperating with Rx, Chx10, and Sox2 transcription factors. Pax6 maintains retinal progenitor multipotency, activates proneural genes Atoh7 and Neurod1 for ganglion and amacrine differentiation, and represses retinal pigmented epithelium fate via Mitf suppression. Sox2 also expressed but alone insufficient, Otx2 specifies RPE, L-Maf drives lens crystallins. Pax6 conditional deletion in optic cup converts presumptive neural retina into pigmented epithelium and abolishes retinogenesis, demonstrating essentia
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Neural retina formation – Pax6 requirement and Mitf repression.
L-Maf, a large Maf bZIP transcription factor expressed in lens placode downstream of Pax6, Sox2, and FGF-BMP signaling, directly regulates crystallin genes essential for transparency. L-Maf binds Maf recognition elements in delta-crystallin enhancer in chick and alphaA-crystallin promoter in mammals, activating high-level expression during fiber cell elongation and organelle loss. It does not induce optic vesicle formation, inhibit Sox2, or prevent corneal differentiation. L-Maf knockout lenses show severe deficiency in crystallin accumulation and fiber elongation arrest, confirming its centra
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: L-Maf regulation of delta-crystallin and lens fiber genes.
Hindlimb bud initiation integrates multiple transcription factors forming coherent feed-forward network upstream of outgrowth. Islet1, a LIM-homeodomain protein expressed early in posterior lateral plate, maintains Pitx1 and Tbx4 expression, Pitx1 directly drives Tbx4 and hindlimb enhancer of FGF10, Tbx4 directly activates FGF10. Knockouts of any single factor reduce hindlimb formation substantially, combined loss abolishes budding and produces amelia with absent hindlimbs. Islet1 also maintains FGF10 independently via Ldb1 cofactor recruitment. Thus early hindlimb initiation relies cooperativ
Ref: Kawakami et al., PNAS 2011, Gilbert Chapter 20: Islet1-Pitx1-Tbx4 network in hindlimb.
REVOLUTA belongs to HD-ZIP III transcription factor family conferring shoot adaxial fate and meristematic activity, while PLT2 belongs to AP2 family specifying root stem cell identity and promoting root genes. In embryonic axis they occupy mutually exclusive domains at shoot-root boundary near hypocotyl junction with sharp border. Genetic analyses and inducible misexpression reveal double-negative regulatory loop: ectopic REV suppresses PLT2 and root programs while inducing STM and WUS, whereas elevated PLT2 suppresses REV. Mutual repression ensures stable partitioning of axis into distinct sh
Ref: Barton et al., Annu Rev Plant Biol; Smith & Long, Plant Physiol: REV and PLT mutual repression defines shoot-root boundary.
Enhancers are DNA sequences that increase the rate of transcription by interacting with transcription factors.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Human Genome Project and DNA Fingerprinting
Enhancers are regulatory sequences that bind transcription factors to increase gene expression.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Prokaryotes have a single RNA polymerase, unlike eukaryotes which have multiple types of RNA polymerases.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Transcription - Mechanism and RNA Polymerase
