Immunostaining of Whole-Mount Imaginal Discs

The imaginal discs of Drosophila melanogaster are saclike clusters of cells that generate the epidermal structures of the adult head, thorax, and external genitalia during metamorphosis. Imaginal disc precursor cells are segregated from larval cells during embryogenesis and follow an autonomous developmental program within the larva (1 –4 ). They divide extensively while undergoing pattern formation and cell determination but retain their sac-like shape through the third instar (5 ,6 ). The approximate location of the 19 imaginal discs in the third instar larva are shown in Fig. 1 A . A schematic cross section of a typical disc with squamous epithelial cells on one side and columnar epithelial cells on the other is shown in Fig. 1 B . During metamorphosis in the pupa, the sac everts and the columnar epithelial cells form the eyes, antennae, wings, halteres, and other adult epidermal structures (6 ). For excellent reviews of work on imaginal discs prior to 1993, see ref. 8 , and for more recent work, see a new book (9 ) with emphasis on pattern formation.

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