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#imaginal discs

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Drosophila -l

Imaginal discs in Drosophila are responsible for:

Within Drosophila larvae, imaginal discs are invaginated epithelial sacs of diploid cells set aside during embryogenesis, quiescent initially then proliferating during larval instars under influence of insulin and ecdysone signaling. Each disc possesses determined fate mapping to specific adult appendage determined by homeotic genes: wing disc forms wing and thorax, leg disc leg, eye-antennal disc eye and antenna. During metamorphosis triggered by ecdysone pulse at pupariation, discs evert, elongate, differentiate adult cuticle structures while larval tissues undergo programmed histolysis. Hence discs are responsible for adult structure formation underlying holometabolous transition.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Imaginal discs adult formation.

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Drosophila -ll

Imaginal discs responsible for:

Imaginal discs are monolayer epithelial sacs invaginated during embryogenesis, proliferating throughout larval instars as diploid precursors held undifferentiated by ecdysone and juvenile hormone balance. At pupariation, ecdysone pulse triggers disc eversion, elongation, and differentiation into adult external structures: wings, legs, eyes, antennae, halters, genitalia. They do not contribute to embryonic segmentation, larval cuticle, or germline, which arises from pole cells. Disc patterning uses conserved morphogens Wingless, Decapentaplegic, and Hedgehog establishing anteroposterior and dorsoventral axes within each disc, analogous to vertebrate limb bud patterning, forming adult body after histolysis of larval tissues during metamorphosis.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Imaginal discs - adult structure precursors patterned by Wg and Dpp.

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Fertilization in mammals-lll

Imaginal discs primarily form:

Drosophila larva contains sacs of diploid epithelial cells called imaginal discs invaginated from larval epidermis during embryogenesis, specified by homeotic gene expression and held quiescent during larval feeding stages. Upon metamorphosis triggered by ecdysone pulse, discs evert, elongate and differentiate into adult structures: wing discs form wings and thorax, leg discs legs, eye-antenna discs eyes and antennae, genital discs external genitalia. Larval organs like salivary glands histolyze. Thus imaginal discs represent primordia for adult body plan, not larval organs, embryonic segments or gametes, enabling complete reorganization during pupariation and demonstrating imaginal disc patterning via morphogens Decapentaplegic and Wingless gradients.

Ref: Cohen, Annu Rev Cell Dev Biol 1993: Imaginal discs specification and patterning for adult Drosophila structures during metamorphosis.

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