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We wish to understand the mechanisms by which genes control development. We are
studying two sorts of genetic regulatory hierarchies controlling development in Drosophila
melanogaster. One of these specifies the segmentation pattern of the body plan along its
anterior-posterior axis. Within this hierarchy we are mostly concerned with the "homeotic"
genes which act as general transducers of positional information to specify the segmental
identities-i.e., the characteristics that distinguish one metamere from another.

The second kind of hierarchy serves to coordinate temporally the developmental pathways
of different tissues at various stages of development. The coordination signal for these
hierarchies consists of pulses of the steroid hormone ecdysone. Within this hierarchy,
we are mostly concerned with the gene encoding the receptor protein for ecdysone and
the "early" genes which are induced by the ecdysone-receptor complex to yield regulatory
proteins that govern the tissue-specific responses to the ecdysone pulse.

Current work is focused on the most dramatic example of these responses where the
pulse of ecdysone at the end of larval life induces metamorphosis to the adult fly, with
imaginal tissues forming adult structures like eyes, wings, and legs, while strictly larval
tissues are induced to follow a downward path toward histolysis.