Deletion scanning of the regulatory sequences of the Fbp1 gene of Drosophila melanogaster using P transposase-induced deficiencies

Molecular Characteristics of Fat Body Protein 1 in the Oriental Fruit Fly, Bactrocera dorsalis

Simple Summary

Bactrocera dorsalis fat body protein 1 (Bdfbp1) cDNA was cloned. The deduced amino acid sequence contains three motifs: hemocyanin N, high molecular weight glutenin (gultenin hmw), and hemocyanin C from N to C termini. The glutenin hmw allows Bdfbp1 to fold into a compact form for storage. Bdfbp1 was highly expressed in the late third instar larvae and day 0 pupae. This suggests that Bdfbp1 is stored during larval stages as a storage protein for construction of adult tissues during pupal stages, and may be associated with adult eclosion.

Abstract

Bactrocera dorsails fat body protein 1 (Bdfbp1) cDNA was cloned (GenBank accession no. MT514270), and the complete 3,749-bp cDNA encoded a 1,152-amino acid protein. The phylogenetic relationship of dipteran fbp1s was analyzed. The sequence XP_028900815 from the insect genome project for Zeugodacus cucurbitae (LOC105219342) was proposed that two fbp1 genes were present in the sequence. The developmental transcriptional expression profiles were determined. In the larval stages, Bdfbp1 mRNA had significantly higher expression in the late third instar larvae compared with first, second, and early third instar larvae. In the pupal stages, the highest expression of Bdfbp1 mRNA was found in the newly pupated pupae and then decreased with age. In the fat body of female adults, Bdfbp1 was highly expressed in newly emerged samples and decreased rapidly over the following three days. In the fat body of male adults, Bdfbp1 was highly expressed in newly eclosed samples. RNAi treatment decreased the expression level of Bdfbp1 without statistical difference. However, RNAi treatment significantly decreased the rate of eclosion. These results suggest that Bdfbp1 may function as a storage protein and be associated with adult eclosion.

TheDrosophila ACP65A cuticle gene: Deletion scanning analysis ofcis-regulatory sequences and regulation by DHR38

The regulatory sequences of the Drosophila ACP65A cuticle gene were analyzed in vivo in transgenic flies, using both fusion genes constructs and transposase-mediated deletions within a P element containing ACP65A regulatory sequences fused to the lacZ gene (deletion scanning). The sequences located between -594 and +161 are sufficient to confer both temporal and spatial expression specificities, indicating the presence of tissue-specific enhancers and response elements to hormone-induced factors. In addition, timing of expression and tissue-specificity appear to be controlled by distinct cis-regulatory elements, which suggests the existence of independent hormonal and tissue-specific signaling pathways. Gain and loss of function studies also implicate DHR38, the Drosophila homolog of the vertebrate NGFI-B-type nuclear receptors, as an important activator of the ACP65A gene.

Female-specific expression of a hexamerin gene in larvae of an autogenous mosquito

Fourth-instar larvae of the autogenous mosquito, Aedes atropalpus, synthesize three hexamerins or hexameric storage proteins which are distinguished by different methionine and aromatic amino-acid contents. One protein, Hexamerin-1.2 (AatHex-1.2) is only found in female larvae and pupae. In order to investigate the molecular basis for this sex-specific accumulation, we have cloned and sequenced the cDNA encoding AatHex-1.2 and isolated and sequenced over 1 kb of the 5' flanking region of the AatHex-1.2 gene. The AatHex-1.2 transcript encodes a 81.6-kDa hexamerin subunit which contains 19.8% phenylalanine, tyrosine and tryptophan and 8.6% methionine residues. The single-copy AatHex-1.2 gene consists of three exons and two small introns located at its 5' end. A 2.3-kb AatHex-1.2 mRNA accumulates only in female larvae and pupae and is expressed at very low levels in adult female mosquitoes. The temporal expression profile of this transcript is typical of other mosquito hexamerin genes, with rapid disappearance of the mRNA shortly after pupation. Hence this is the first observation of exclusively female-specific gene activity during preadult development of an insect. In the 5' flanking region of the AatHex-1.2 gene, we identified putative binding sites for transcription factors, such as GATA, C/EBP and Doublesex, typically involved in fat body- and female-specific gene activity in Diptera. These findings suggest that mechanisms for sex-specific transcription in the fat body may be well conserved between flies and mosquitoes.

A UAS site substitution approach to the in vivo dissection of promoters: interplay between the GATAb activator and the AEF-1 repressor at aDrosophilaecdysone response unit

An ecdysone response unit (EcRU) directs the expression of the Fat body protein 1 (Fbp1) gene in the third instar larval Drosophila fat body. The tissue-specific activity of this regulatory element necessitates the binding of both the ligand-activated EcR/USP ecdysone receptor and GATAb. To analyze the role played by GATAb in the regulation of the Fbp1 EcRU activity, we have replaced the GATA-binding sites GBS1, GBS2 and GBS3 in the Fbp1 EcRU with UAS sites for the yeast GAL4 activator and tested the activity of the mutagenized Fbp1 EcRUs in transgenic lines, either in the presence or absence of ubiquitously expressed GAL4. Our results reveal that GATAb plays two distinguishable roles at the Fbp1 EcRU that contribute to the tissue-specific activity of this regulatory element. On the one hand, GATAb mediates a fat body-specific transcriptional activation. On the other hand, it antagonizes specifically in the fat body a ubiquitous repressor that maintains the Fbp1 EcRU in an inactive state, refractory to activation by GAL4. We identified this repressor as AEF-1, a factor previously shown to be involved in the regulation of the Drosophila Adh and yp1-yp2 genes. These results show that, for a functional dissection of complex promoter-dependent regulatory pathways, the replacement of specific regulatory target sites by UAS GAL4 binding sites is a powerful alternative to the widely used disruption approach.

Dynamic expression of broad-complex isoforms mediates temporal control of an ecdysteroid target gene at the onset of Drosophila metamorphosis

Metamorphosis in Drosophila melanogaster is orchestrated by the steroid hormone ecdysone, which triggers a cascade of primary-response transcriptional regulators and secondary effector genes during the third larval instar and prepupal periods of development. The early ecdysone-response Broad-Complex (BR-C) gene, a key regulator of this cascade, is defined by three complementing functions (rbp, br, and 2Bc) and encodes several distinct zinc-finger-containing isoforms (Z1 to Z4). Using isoform-specific polyclonal antibodies we observe in the fat body a switch in BR-C isoform expression from the Z2 to the other three isoforms during the third instar. We show that the 2Bc(+) function that corresponds presumably to the Z3 isoform is required for the larval fat body-specific expression of a transgenic construct (AE) in which the lacZ gene is under the control of the ecdysone-regulated enhancer and minimal promoter of the fat body protein 1 (Fbp1) gene. Using hs(BR-C) transgenes, we demonstrate that overexpression of Z1, Z3, or Z4, but not Z2, is able to rescue AE activity with faithful tissue specificity in a BR-C null (npr1) genetic context, demonstrating a partial functional redundancy between Z1, Z3, and Z4 isoforms. We also show that continuous overexpression of Z2 during the third instar represses AE, while conversely, expression of Z3 earlier than its normal onset induces precocious expression of the construct. This finding establishes a tight correlation between the dynamic pattern of expression of the BR-C isoforms and their individual repressive or inductive roles in AE regulation. Altogether our results demonstrate that the balance between BR-C protein isoforms in the fat body mediates, in part, the precise timing of the ecdysone activation of the AE construct but does not modulate its tissue specificity.

Overlapping Lsp-2 gene sequences target expression to both the larval and adult Drosophila fat body

Larval serum protein-2 gene (Lsp-2) of Drosophila melanogaster encodes one of the major hexameric haemolymph proteins of third-instar larvae and a major component of adult serum. Regulated transcription of Lsp-2 results in high-level, ecdysone-stimulated expression throughout the larval fat body and low-level, spatially restricted expression in the adult fat cells. To localize cis-acting regulatory sequences responsible for the stage- and tissue-specific activity at Lsp-2, the expression of Lsp-2-lacZ fusion genes was studied by P element-mediated germline transformation of Drosophila. A 230 base pair larval enhancer, which includes an ecdysone response element (EcRE), specifically targets gene activity to the larval fat body. Although the adult mode of Lsp-2 expression depends on the larval enhancer, additional negative regulatory elements dictate both tissue-specificity and unique spatial restriction within the adult fat body. Implications of these findings for the identification of fat body-specific gene regulatory units in other insects are discussed.

Enhancer-trap targeting at the Broad-Complex locus of Drosophila melanogaster

Here, we describe the exact replacement of a defective unmarked P element by an enhancer-trap transposon marked by the miniwhite gene and carrying lacZ as a reporter gene. The original defective P element was located in an intron of the Broad-Complex (BRC), a key gene involved in metamorphosis. Replacement events resulted from conversions induced by the P-element transposase from a donor enhancer-trap element located on another chromosome. Six independent conversion events were selected. In all converted chromosomes, the enhancer-trap transposon was in the same orientation as the original P element. From the pattern of X-gal staining observed, lacZ expression likely reflects the regulatory influence of BRC enhancers on the convertant transposon. Reversion to wild type was achieved by excision of the enhancer-trap transposon. The six convertants were analyzed in detail at the nucleotide level. The occurrence of a polymorphism at position 33 of the P-element sequences led us to propose a conversion mechanism involving homologous P sequences for repair. This is in contrast to previously analyzed P-element transposase-induced conversion events and proposed models relying on sequence identity between genomic Drosophila sequences. The lack of any homology requirement other than between P element sequences means that our findings can be easily generalized. Targeting a marked P-element derivative at a precise site without loss or addition of genetic information makes it possible to exploit the hundreds of defective P elements scattered throughout the Drosophila genome by replacing them with engineered P elements, already available.