Analysis of a DNase I-hypersensitive site in transgenic Drosophila reveals a key regulatory element of Sgs3

Drosophila Sgs genes: stage and tissue specificity of hormone responsiveness

The up- and down-regulation of the salivary gland secretion protein (Sgs) genes during the third larval instar of Drosophila melanogaster are controlled by fluctuations of the titre of the steroid hormone 20-hydroxyecdysone (20E). Induction of these genes by a low hormone titre is a secondary response to 20E mediated by products of 20E-induced 'early' genes. Surprisingly, in the case of the Sgs-4 gene this response also requires a direct contribution of the 20E-receptor complex. A model is presented which proposes that the Sgs genes, and other 20E-regulated genes with similar temporal expression profiles, are regulated by complex hormone response units. The hormonal signal is effectively transmitted by these response units only after binding of additional factors, e.g. secretion enhancer binding proteins, which act together in a synergistic manner with the 20E receptor and early gene products to establish a stage- and tissue-specific expression pattern.

GEBF-I in Drosophila species and hybrids: the co-evolution of an enhancer and its cognate factor

The activation of the Drosophila melanogaster salivary gland secretion protein gene Sgs-3 is marked by important changes in chromatin structure in the distal regulatory region at -600 bp from the Sgs-3 start site. A stage- and tissue-specific glue enhancer binding factor, GEBF-I, binds in vitro to sequences from this region. Previous studies have revealed considerable variation in the DNA sequences of comparable regions in the related Drosophila species, D. simulans, D. erecta and D. yakuba. We detected GEBF-I-like proteins in these species, which appear to evolve as rapidly as the corresponding DNA sequences, and studied in detail the binding characteristics of the GEBF-I proteins of the two most closely related species, D. melanogaster and D. simulans. In crosses between these species, certain strains produce hybrid larvae which, unexpectedly, synthesised a single intermediate form of the protein. This suggests that the factor is subject to species-specific post-transcriptional modifications. In these hybrid larvae, which carry one D. melanogaster and one D. simulans Sgs-3 gene, the hybrid GEBF-I protein appears equally effective in the induction of both target genes.

cis-acting sequences required for expression of the divergently transcribed Drosophila melanogaster Sgs-7 and Sgs-8 glue protein genes

The Sgs-7 and Sgs-8 glue genes at 68C are divergently transcribed and are separated by 475 bp. Fusion genes with Adh or lacZ coding sequences were constructed, and the expression of these genes, with different amounts of upstream sequences present, was tested by a transient expression procedure and by germ line transformation. A cis-acting element for both genes is located asymmetrically in the intergenic region between -211 and -43 bp relative to Sgs-7. It is required for correct expression of both genes. This element can confer the stage- and tissue-specific expression pattern of glue genes on a heterologous promoter. An 86-bp portion of the element, from -133 to -48 bp relative to Sgs-7, is shown to be capable of enhancing the expression of a truncated and therefore weakly expressed Sgs-3 fusion gene. Recently described common sequence motifs of glue gene regulatory elements (T. Todo, M. Roark, K. Vijay Raghavan, C. A. Mayeda, and E.M. Meyerowitz, Mol. Cell. Biol. 10:5991-6002, 1990) are located within this 86-bp region.

cis-acting sequences required for expression of the divergently transcribed Drosophila melanogaster Sgs-7 and Sgs-8 glue protein genes

The Sgs-7 and Sgs-8 glue genes at 68C are divergently transcribed and are separated by 475 bp. Fusion genes with Adh or lacZ coding sequences were constructed, and the expression of these genes, with different amounts of upstream sequences present, was tested by a transient expression procedure and by germ line transformation. A cis-acting element for both genes is located asymmetrically in the intergenic region between -211 and -43 bp relative to Sgs-7. It is required for correct expression of both genes. This element can confer the stage- and tissue-specific expression pattern of glue genes on a heterologous promoter. An 86-bp portion of the element, from -133 to -48 bp relative to Sgs-7, is shown to be capable of enhancing the expression of a truncated and therefore weakly expressed Sgs-3 fusion gene. Recently described common sequence motifs of glue gene regulatory elements (T. Todo, M. Roark, K. Vijay Raghavan, C. A. Mayeda, and E.M. Meyerowitz, Mol. Cell. Biol. 10:5991-6002, 1990) are located within this 86-bp region.

Sgs-3 chromatin structure and trans-activators: developmental and ecdysone induction of a glue enhancer-binding factor, GEBF-I, in Drosophila larvae

The transcription of the Drosophila melanogaster 68C salivary gland glue gene Sgs-3 involves the interaction of a distal and a proximal regulatory region. These are marked in vivo by a specific chromatin structure which is established sequentially during development, starting early in embryogenesis. The distal region is characterized by a stage- and tissue-specific DNase I hypersensitive site. A stage- and tissue-specific factor, GEBF-I, binds in this region and is missing in 2B5 mutant larvae which lack Sgs-3 transcripts. This binding involves the simultaneous interaction with two distinct DNA sequences which induces conformational changes in the protein. Salivary glands acquire competence to respond to ecdysone in the mid-third larval instar, whereafter the hormone rapidly induces both the GEBF-I protein and Sgs-3 transcription.

Sgs-3 chromatin structure and trans-activators: developmental and ecdysone induction of a glue enhancer-binding factor, GEBF-I, in Drosophila larvae

The transcription of the Drosophila melanogaster 68C salivary gland glue gene Sgs-3 involves the interaction of a distal and a proximal regulatory region. These are marked in vivo by a specific chromatin structure which is established sequentially during development, starting early in embryogenesis. The distal region is characterized by a stage- and tissue-specific DNase I hypersensitive site. A stage- and tissue-specific factor, GEBF-I, binds in this region and is missing in 2B5 mutant larvae which lack Sgs-3 transcripts. This binding involves the simultaneous interaction with two distinct DNA sequences which induces conformational changes in the protein. Salivary glands acquire competence to respond to ecdysone in the mid-third larval instar, whereafter the hormone rapidly induces both the GEBF-I protein and Sgs-3 transcription.

Fine-structure mutational analysis of a stage- and tissue-specific promoter element of the Drosophila glue gene Sgs-3

The Sgs-3 gene of Drosophila melanogaster exhibits a tightly regulated pattern of expression governed by two functionally equivalent elements within 1 kb of the gene, each of which is sufficient to confer third-instar salivary gland-specific transcription. In this report we describe a detailed functional analysis of one of these, the proximal element. To determine the nucleotides responsible for specific expression, we have introduced mutations into the proximal element and then assessed the effects of each alteration on expression in the developing animal. We have identified six particularly important base pairs which are located in two regions separated by nonessential sequences. These base pairs, along with some surrounding sequence, are conserved within the upstream regions of the three glue genes at 68C. Nearly identical groups of base pairs can be found upstream of the other glue genes which have been cloned. This analysis has allowed us to derive a consensus sequence, which we believe contains binding sites for two different factors which interact to direct third-instar salivary gland-specific expression.

Fine-structure mutational analysis of a stage- and tissue-specific promoter element of the Drosophila glue gene Sgs-3

The Sgs-3 gene of Drosophila melanogaster exhibits a tightly regulated pattern of expression governed by two functionally equivalent elements within 1 kb of the gene, each of which is sufficient to confer third-instar salivary gland-specific transcription. In this report we describe a detailed functional analysis of one of these, the proximal element. To determine the nucleotides responsible for specific expression, we have introduced mutations into the proximal element and then assessed the effects of each alteration on expression in the developing animal. We have identified six particularly important base pairs which are located in two regions separated by nonessential sequences. These base pairs, along with some surrounding sequence, are conserved within the upstream regions of the three glue genes at 68C. Nearly identical groups of base pairs can be found upstream of the other glue genes which have been cloned. This analysis has allowed us to derive a consensus sequence, which we believe contains binding sites for two different factors which interact to direct third-instar salivary gland-specific expression.

Drosophila glue protein gene expression. A proposal for its ecdysone-dependent developmental control

The primary targets of steroid hormones are genes. For the ecdysone-controlled genes of Drosophila larval glue proteins proximal and distal control elements were identified by mutagenesis and sequence comparison. Their presence is required for the correct stage- and tissue-specific expression of these genes. The supposed function of these elements is described in a working model.

Regulatory elements and interactions in the Drosophila 68C glue gene cluster

We reviewed studies on the developmental regulation of the 68C glue gene cluster of Drosophila melanogaster. Extensive transformation analyses of Sgs-3 have shown that four regions necessary for normal expression can be distinguished. The first(+10 to -50) contains the transcription start site and TATA motif. This region can be replaced functionally by corresponding sequences from the hsp70 gene, but it is sensitive to point mutations in the TATA sequence. The second region (-50 to -98) contains more than one upstream sequence that, in combination with the other elements, leads to stage and tissue-specific expression. The third region (centered at -600) contains an element that enhances transcript levels some 20-fold. The final region (between -1.65 and -2.35 kb) contains elements having modest (twofold to threefold) effects on expression, one of which is contained in the coding sequences of Sgs-7, a second member of the cluster.