#cell regulation

Stem Cell -lll

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

Stem maintenance integrates canonical pathways coordinating self-renewal versus fate choice. Wnt beta-catenin drives intestinal crypt and hematopoietic self-renewal via TCF4 target Myc, JAK-STAT activated by LIF maintains mouse embryonic stem pluripotency and Drosophila male germline via Upd ligand and Stat92E, Hedgehog via Gli supports neural and hair follicle proliferation. Complement cascade constitutes innate immune effector activating C3a C5a opsonization, membrane attack complex and inflammation leading to pathogen clearance not intrinsic stem regulation. While inflammation indirectly modulates niche, complement components are not core fate determinants like Wnt, Hedgehog or JAK-STAT pathways.

Ref: Puri and Bhatt, Stem Cell Signaling, Chapter 3: Wnt, JAK-STAT, Hedgehog in Stem Regulation.

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Fertilization in mammals-lll

Counting factor (smlA) regulates:

Dictyostelium aggregation field size is regulated by autocrine factor called counting factor, identified as smlA secreted glycoprotein complex. It functions as quorum sensor: secreted by starving cells, concentration proportional to cell density modulates adhesion and motility via altering gene expression of adhesion molecules and myosin. High counting factor promotes breakup of streams into smaller aggregates; low promotes larger mounds. Mutants lacking smlA form abnormally large aggregates that produce oversized fruiting bodies, while overexpression yields tiny aggregates. Hence smlA regulates aggregate size ensuring optimal spore-stalk ratio and efficient dispersal rather than directly controlling motility or germination per se.

Ref: Jang & Gomer, Microbiology 2011: Counting factor smlA autocrine regulator of aggregate size in Dictyostelium.

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Cell Signaling Dev Bio & Other Pathways

Hedgehog proteins act as

Morphogens, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling Dev Bio & Other Pathways

APC and Axin function as

Scaffold proteins, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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