Developmental capacities of immature eye-antennal imaginal discs ofDrosophila melanogaster.

The location of the immature eye-antennal discs ofDrosophila melanogaster in embryos and young larvae was established by means of transplantation experiments. The developmental capacities of these immature discs was then investigated by implanting them into larvae which were ready to metamorphose, thus bypassing large portions of embryonic and larval development. Imaginal eye-antennal discs of embryos and first instar larvae are unable to synthesize eye pigments or secrete cuticle. The discs acquire the first detectable competence in the middle of the second instar, 32-36 hours after hatching, when the eye region of the disc becomes competent to synthesize ommochrome pigments and the rest of the disc becomes competent to secrete a thin untanned, transparent cuticle. Competence to synthesize pteridine pigments becomes evident later, 36-42 hours after hatching. The competence to produce specific bristle and hair patterns is acquired still later, 42-56 hours after hatching. Different regions of the eye-antennal disc acquire competence at different times and the acquisition of competence seems to occur in a proximo-distal sequence within both eye and antennal regions of the disc. In the eye region of the disc, the competence to produce proximal structures such as facets appears before the competence to produce ocelli. Similarly, in the antennal region of the disc, the competence to produce the first antennal segment appears before the competence to produce the third antennal segment or arista. Also, the acquisition of competence to produce a specific cuticular pattern occurs four to six hours earlier in the eye region of the disc than in the antennal region. It was also found that the temporal sequence in which differentiation events actually occur during adult development is similar to the temporal sequence in which specific competences are acquired by the growing immature eye-antennal discs.