TISSUE-SPECIFIC REGULATION BY ECDYSONE - DISTINCT PATTERNS OF EIP28 29 EXPRESSION ARE CONTROLLED BY DIFFERENT ECDYSONE RESPONSE ELEMENTS/

The Eip28/29 gene of Drosophila is an example of a tissue- and stage-s pecific ecdysone-responsive gene, lis diverse patterns of expression d uring the third larval instar and a synopsis of those patterns in term s of expression groups have been reported previously. Here we have stu died the expression (in transgenic flies) of reporter genes controlled by Eip28/29-derived flanking DNA. During the middle and late third in star, most tissues exhibit normal expression patterns when controlled by one of two classes of regulatory sequences. Class A sequences inclu de only 657 Np of 5' flanking DNA from Eip28/29. Class B sequences inc lude an extended 3' flanking region and a minimal (less than or equal to 93 Np) 5' flanking region. The class B sequences include all those elements known to be important for ecdysone induction in cultured cell s. They are sufficient to direct the normal premetamorphic induction o f Eip28/29 in the lymph glands, hemocytes, proventriculus, and Malpigh ian tubules. This is consistent with our suggestion that Kc cells are derived from embryonic hematopoietic cells. It is remarkable that the epi dermis requires only class A sequences. These are sufficient to vp -regulate expression at mid-instar and to down-regulate expression at metamorphosis. It follows that the epidermis uses EcREs distinct from those that function in Kc cells. ii is possible that the Upstream EcRE , which is nearly silent in Kc cells, is active in the epidermis. (C) 1994 Wiley-Liss, Inc.