Developmental control of transduced dopa decarboxylase genes in D. melanogaster

The orphan nuclear receptor DHR38 influences transcription of the DOPA decarboxylase gene in epidermal and neural tissues of Drosophila melanogaster

The DOPA decarboxylase gene (Ddc) belongs to the "early-late" class of ecdysone-inducible genes in Drosophila melanogaster. Its expression is up-regulated in epidermal tissues by the ecdysone receptor acting through a response element, EcRE. In this paper, we show that another member of the nuclear receptor superfamily, DHR38, may act as a repressor of epidermal Ddc while inducing Ddc expression in neuronal cells. DHR38 does not behave as a classical co-repressor of the ecdysone receptor though, since the site through which DHR38 acts is distinct from the EcRE. Ectopic expression of a Dhr38 cDNA from a heat-shock promoter completely repressed transcription from the endogenous Ddc promoter and from an intact reporter construct in the hypoderm and in imaginal discs. Ectopic DHR38 had no effect on the transcription of a reporter driven by a Ddc fragment missing the DHR38 binding site. Neither reporter expression nor endogenous Ddc transcript levels were affected in a Dhr38 mutant background. Because most mutant organisms pupariate apparently normally and many of these survive to eclose, we believe that some functional redundancy exists within the Dhr38 regulatory network operating in epidermal tissues. In contrast to its apparent repressor function in epidermal tissues, DHR38 may act as a positive regulator of neural Ddc expression. Ectopic expression of DHR38 throughout the CNS induced as much as a 20-fold increase in Ddc transcripts in the set of neurons in which DDC normally appears.

Dopa decarboxylase: a model gene-enzyme system for studying development, behavior, and systematics

Throughout its long evolutionary history, the Dopa decarboxylase gene (Ddc) has acquired a variety of functions in insects. The enzyme (DDC) catalyzes the production of the neural transmitters dopamine and serotonin. Not surprisingly, evidence of the enzyme's involvement in the behavior of insects is beginning to accumulate. In addition, DDC plays a role in wound healing, parasite defense, pigmentation, and cuticle hardening. A high degree of sequence conservation has allowed comparisons of the Ddc-coding regions from various insects, facilitating a number of recent studies on insect systematics. This review outlines the diverse functions of Ddc and illustrates how studies of this model system address many questions on insect neurobiology, developmental biology, and systematics.

Drosophila wing melanin patterns form by vein-dependent elaboration of enzymatic prepatterns

BACKGROUND

Animal melanin patterns are involved in diverse aspects of their ecology, from thermoregulation to mimicry. Many theoretical models have simulated pigment patterning, but little is known about the developmental mechanisms of color pattern formation. In Drosophila melanogaster, several genes are known to be necessary for cuticular melanization, but the involvement of these genes in melanin pattern evolution is unknown. We have taken a genetic approach to elucidate the developmental mechanisms underlying melanin pattern formation in various drosophilids.

RESULTS

We show that, in D. melanogaster, tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) are required for melanin synthesis. Ectopic expression of TH, but not DDC, alone was sufficient to cause ectopic melanin patterns in the wing. Thus, changes in the level of expression of a single gene can result in a new level of melanization. The ontogeny of this ectopic melanization resembled that found in Drosophila species bearing wing melanin patterns and in D. melanogaster ebony mutants. Importantly, we discovered that in D. melanogaster and three other Drosophila species these wing melanin patterns are dependent upon and shaped by the circulation patterns of hemolymph in the wing veins.

CONCLUSIONS

Complex wing melanin patterns are determined by two distinct developmental mechanisms. Spatial prepatterns of enzymatic activity are established late in wing development. Then, in newly eclosed adults, melanin precursors gradually diffuse out from wing veins and are oxidized into dark brown or black melanin. Both the prepatterning and hemolymph-supplied components of this system can change during evolution to produce color pattern diversity.

Dosage compensation of the Drosophila pseudoobscura Hsp82 gene and the Drosophila melanogaster Adh gene at ectopic sites in D. melanogaster

Measurements were made of the amounts of larval RNA transcribed from the autosomal Adh gene of Drosophila melanogaster and the X chromosomal Hsp82 gene of Drosophila pseudoobscura carried on the same P-element transposon inserted at various sites in the D. melanogaster genome. Both genes were fully compensated at sites in euchromatic regions of the X chromosome but neither was compensated at a site in the centric beta-heterochromatin of the X chromosome. No compensation of the D. pseudoobscura Hsp82 gene was found at any of 10 autosomal insertion sites tested. The compensation behavior of the transposed genes was, therefore, not determined by closely linked sequences but instead was determined in each case by their new chromosomal environment.

The Adh gene promoters of Drosophila melanogaster and Drosophila orena are functionally conserved and share features of sequence structure and nuclease-protected sites

The sibling species Drosophila melanogaster and D. orena show similar patterns of alcohol dehydrogenase expression, both spatially and temporally. These two species diverged from a common ancestor 6 million to 15 million years ago, and the DNA sequences of the promoter regions of their Adh genes show a mosaic pattern of conservation and change. By interspecific transformation of D. orena sequences into D. melanogaster, we demonstrate a functional equivalence between these sequences. Using both D. melanogaster embryo extracts and purified transcription factor Adf-1, we compare the protection of these promoter sequences from nuclease, demonstrating considerable conservation.

The Adh gene promoters of Drosophila melanogaster and Drosophila orena are functionally conserved and share features of sequence structure and nuclease-protected sites

The sibling species Drosophila melanogaster and D. orena show similar patterns of alcohol dehydrogenase expression, both spatially and temporally. These two species diverged from a common ancestor 6 million to 15 million years ago, and the DNA sequences of the promoter regions of their Adh genes show a mosaic pattern of conservation and change. By interspecific transformation of D. orena sequences into D. melanogaster, we demonstrate a functional equivalence between these sequences. Using both D. melanogaster embryo extracts and purified transcription factor Adf-1, we compare the protection of these promoter sequences from nuclease, demonstrating considerable conservation.

Molecular genetics of dopa decarboxylase and biogenic amines in Drosophila

The gene Ddc encodes two isoforms of the enzyme dopa decarboxylase in Drosophila. These gene products catalyze the final steps in the synthesis of the biogenic amines serotonin and dopamine. This article summarizes recent progress in understanding the tissue- and cell-specific regulation of Ddc, which occurs at both the transcription and alternate splicing levels. In addition, results that are pertinent to understanding the roles of biogenic amines in the neurophysiology of Drosophila are discussed.

Overlapping transcription units in Drosophila: sequence and structure of the Cs gene

The Cs gene lies between the functionally and evolutionarily related dopa decarboxylase (Ddc) and l(2)amd loci of Drosophila. The Cs and Ddc genes overlap at their 3' ends, implying that the transcription termination signals of these genes are polar, since each gene's primary transcript contains the complement of the other gene's transcription termination signals. The mature transcripts of the Cs and Ddc genes are complementary for a short distance and the primary transcripts may be complementary over thousands of base pairs. Despite intensive mutagenesis in this region, no mutations affecting the Cs transcript have been recovered although over 90 alleles of the two flanking genes (Ddc and l(2)amd) have been identified. Unlike the flanking Ddc and l(2)amd genes, the structure of the Cs gene and the temporal and tissue specificity of Cs expression are inconsistent with any structural or functional relatedness to the Ddc gene family. The internal structure of the Cs transcript is unlike that of most protein coding genes; it contains several open reading frames which are not situated favorably for efficient translation of the Cs message. This unusual internal structure may be the basis of the observed mutational silence of the Cs locus.

Chromatin structure of a P-element-transduced hsp-28 gene in Drosophila melanogaster

The Drosophila hsp-28 gene was heat inducible when transduced to novel chromosomal sites even when no direct selection for transduced gene expression was imposed. The pattern of DNase I-hypersensitive sites 5' to the wild type and transduced copy of hsp-28 was similar. In addition, DNase I-hypersensitive sites occurred within the P-element sequences flanking transduced loci.

Delimiting regulatory sequences of the Drosophila melanogaster Ddc gene

We delimited sequences necessary for in vivo expression of the Drosophila melanogaster dopa decarboxylase gene Ddc. The expression of in vitro-altered genes was assayed following germ line integration via P-element vectors. Sequences between -209 and -24 were necessary for normally regulated expression, although genes lacking these sequences could be expressed at 10 to 50% of wild-type levels at specific developmental times. These genes showed components of normal developmental expression, which suggests that they retain some regulatory elements. All Ddc genes lacking the normal immediate 5'-flanking sequences were grossly deficient in larval central nervous system expression. Thus, this upstream region must contain at least one element necessary for this expression. A mutated Ddc gene without a normal TATA boxlike sequence used the normal RNA start points, indicating that this sequences is not required for start point specificity.

Gene dosage compensation in Drosophila melanogaster

The comparative lack of sexual dimorphism of apricot and other [sex-linked] genes studied is due to "sex-limitation", i.e., to a compensatory influence of the dosage difference between the sexes in respect to other genes in the X-chromosome. The facts are of particular interest from an evolutionary standpoint.

Delimiting regulatory sequences of the Drosophila melanogaster Ddc gene

We delimited sequences necessary for in vivo expression of the Drosophila melanogaster dopa decarboxylase gene Ddc. The expression of in vitro-altered genes was assayed following germ line integration via P-element vectors. Sequences between -209 and -24 were necessary for normally regulated expression, although genes lacking these sequences could be expressed at 10 to 50% of wild-type levels at specific developmental times. These genes showed components of normal developmental expression, which suggests that they retain some regulatory elements. All Ddc genes lacking the normal immediate 5'-flanking sequences were grossly deficient in larval central nervous system expression. Thus, this upstream region must contain at least one element necessary for this expression. A mutated Ddc gene without a normal TATA boxlike sequence used the normal RNA start points, indicating that this sequences is not required for start point specificity.

CNS and hypoderm regulatory elements of the Drosophila melanogaster dopa decarboxylase gene

Expression of the dopa decarboxylase gene (Ddc) is regulated in a tissue- and developmental stage-specific manner throughout the life cycle of the fruit fly, Drosophila melanogaster. Essential Ddc regulatory elements lie within 208 base pairs upstream from the RNA start point. Functional elements within this 5' flanking region were mapped by deletion analysis, which assayed expression in vivo after germline integration via P element vectors. One of the elements is essential for expression in both the larval and adult central nervous system, and at least two other elements are necessary for quantitatively normal expression in the hypoderm. Within each of the intervals that have regulatory effects are found sequence elements conserved between the Ddc genes of two distantly related species of flies. On the basis of this correlation, regulatory functions for these sequence elements can be postulated.

Sequence and expression of the Cc gene, a member of the dopa decarboxylase gene cluster of Drosophila: possible translational regulation

A transcript has been localized proximal to the dopa decarboxylase (Ddc) gene within a cluster of genes involved in cuticle formation and catecholamine metabolism in Drosophila. This gene, which has been identified as I(2)37Cc, maps 2.0kb from the 5' end of the Ddc gene and is transcribed in the same direction as Ddc. We describe a new deficiency which in conjunction with previous deficiencies localizes the I(2)37Cb and I(2)37Cc loci to the cytogenetic interval 5' to Ddc. We present the sequence of the Cc gene and corresponding cDNA. The Cc message contains several open reading frames 5' to the large open reading frame responsible for the lethal complementation group, suggesting that expression of Cc function may be regulated translationally. The Cc transcript is expressed in early embryos, late embryos, late third instar larvae and adults. We discuss the implications of these findings with respect to the gene organization in the region.