#Hydra

Regeneration -lll

Ectopic tentacle formation in Hydra would result from:

Ectopic tentacle formation in Hydra results from localized hyperactivation of canonical Wnt-beta-catenin pathway lowering organizer threshold. Overexpression of beta-catenin or inhibition of GSK3beta stabilizes beta-catenin throughout body column, leading to formation of supernumerary organizing centers that induce secondary heads with tentacles. Wnt3 overexpression expands tentacle zone, increasing tentacle number per head and inducing ectopic tentacles on body column. Conversely Wnt inhibition blocks tentacle emergence. This demonstrates beta-catenin dosage controls tentacle patterning, with high levels promoting ectopic induction, revealing conserved Wnt organizer function in cnidarian morphallaxis and axial patterning maintenance.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Beta-catenin overexpression causing ectopic tentacles in Hydra.

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Regeneration -lll

Overexpression of β-catenin in Hydra will cause:

Hydra homeostasis and budding regulated by canonical Wnt-beta-catenin pathway concentrated at oral organizer. Overexpression of stable beta-catenin via transgenesis or inhibition of GSK3beta disrupts degradation complex, increasing nuclear beta-catenin throughout body column. This lowers threshold for organizer formation leading to ectopic activation of Wnt3, formation of multiple organizing centers generating supernumerary buds along body column with ectopic tentacles and heads. Enhanced budding rate reflects increased organizer potential, mirroring beta-catenin overexpression in vertebrate axes causing secondary embryonic axes, establishing conserved role of beta-catenin in axial induction.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Beta-catenin overexpression and ectopic budding in Hydra.

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Regeneration -lll

Hydra head formation involves activation of:

Hydra head regeneration depends on establishment of head organizer at oral end. Wnt3 secreted from hypostome stabilizes beta-catenin by inhibiting destruction complex involving GSK3beta, Axin, APC, allowing nuclear translocation and TCF-mediated transcription of organizer genes. Transplantation of Wnt3-expressing tissue induces secondary axis. Pharmacological inhibition of Wnt with iCRT blocks head regeneration, while GSK3 inhibition hyperactivates producing ectopic heads. This conserved canonical Wnt-beta-catenin pathway parallels amphibian Spemann organizer, emphasizing ancient role of beta-catenin in axial organizer formation during morphallactic regeneration and maintaining continuous patterning in adult hydra polyp.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Hydra head formation via Wnt/beta-catenin organizer pathway.

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Sensory Organs - Eye - Structure and Physiology of Vision

Which type of neural system is found in lower invertebrates like Hydra?

Hydra has a simple network of neurons called a nerve net, which lacks a central control system.

Ref: NCERT Class 11 Biology Chapter 18: Neural Control and Coordination Sensory Organs - Eye - Structure and Physiology of Vision

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