The regulation of two salivary gland genes by the winged-helix protein FORK HEAD. E.W. Abrams , D.J. Andrew. Dept Cell Biol & Anatomy, Johns Hopkins Univ Sch Med, Baltimore, MD.

   The homeodomain protein SEX COMBS REDUCED (SCR) is responsible for the specification of the Drosophila embryonic salivary gland during development. Among the genes regulated by SCR in the salivary gland are those encoding the transcription factors TRACHEALESS (TRH), dCREB-A, and FORK HEAD (FKH). We are interested in dissecting the regulatory pathway involved in the formation of the salivary gland. Upon searching the Berkeley Drosophila Genome Project database, we found ten EST cDNAs that are up-regulated in the Drosophila embryonic salivary gland and have strong homology to genes that code for proteins in the secretory pathways of yeast and/or mammals. This finding is not surprising, because making a secretory organ like the salivary gland should require elevated levels of the secretory pathway components. Furthermore, we found that the salivary gland expression of two of these ESTs, which have strong homology to either the Prolyl-4-hydroxylase alpha subunit (PH(II)a) or Protein Disulfide Isomerase (PDI(II)), is dependant on the transcription factor FKH; although their expression is independent of TRH and dCREB-A. To learn how FKH controls the expression of theses genes, we are fusing upstream genomic fragments to the reporter gene, lac-Z, introducing these constructs into flies, and assaying expression of b-gal. Once minimal FKH-dependent salivary gland enhancers are identified in this way, in vitro binding studies with FKH will be initiated. Sites bound by FKH will be tested for their roles in the in vivo expression of PH(II)a and PDI(II).