Identification and characterization of a salivary gland enhancer. K.D. Henderson , D.J. Andrew. Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, MD 21205, (410)614-2645.

   Our lab studies the morphogenesis of the embryonic salivary gland as a model for regulation of gene expression by homeotic genes. Salivary glands form early in embryogenesis in parasegment 2 (PS2) from a ventral-lateral plate of cells. The function of the homeotic genes Sex combs reduced ( Scr), extradenticle (exd), and homothorax (hth) are required to activate salivary gland gene expression. However these genes do not activate salivary gland gene expression in the dorsal region of PS2 due to Decapentaplegic (DPP) signaling. Characterizing a salivary gland enhancer will therefore allow us to determine how homeotic gene activity is spatially restricted. We have identified a 12 kb salivary gland enhancer from the dCREB-A gene, that drives expression of a b-galactosidase reporter gene in the salivary gland and amnioserosa. We are currently testing this enhancer genetically to determine if its expression is regulated by Scr, exd, hth, and DPP signaling. We are also testing smaller portions of this enhancer to identify the minimal enhancer required for salivary gland expression. Once this enhancer is identified, we will determine what sites are bound by SCR, EXD and HTH and how DPP signaling blocks transcriptional activation from this enhancer in dorsal regions of PS2.