Evidence for a selective sweep in the wapl region of Drosophila melanogaster

A scan of the X chromosome of a European Drosophila melanogaster population revealed evidence for the recent action of positive directional selection at individual loci. In this study we analyze one such region that showed no polymorphism in the genome scan (located in cytological division 2C10-2E1). We detect a 60.5-kb stretch of DNA encompassing the genes ph-d, ph-p, CG3835, bcn92, Pgd, wapl, and Cyp4d1, which almost completely lacks variation in the European sample. Loci flanking this region show a skewed frequency spectrum at segregating sites, strong haplotype structure, and high levels of linkage disequilibrium. Neutrality tests reveal that these data are unlikely under both the neutral equilibrium model and the simple bottleneck scenarios. In contrast, newly developed maximum-likelihood ratio tests suggest that strong selection has acted recently on the region under investigation, causing a selective sweep. Evidence that this sweep may have originated in an ancestral population in Africa is presented.     

Pairing between gypsy insulators facilitates the enhancer action in trans throughout the Drosophila genome

The Suppressor of the Hairy wing [Su(Hw)] binding region within the gypsy retrotransposon is the best known chromatin insulator in Drosophila melanogaster. According to previous data, two copies of the gypsy insulator inserted between an enhancer and a promoter neutralize each other's actions, which is indicative of an interaction between the protein complexes bound to the insulators. We have investigated the role of pairing between the gypsy insulators located on homologous chromosomes in trans interaction between yellow enhancers and a promoter. It has been shown that trans activation of the yellow promoter strongly depends on the site of the transposon insertion, which is evidence for a role of surrounding chromatin in homologous pairing. The presence of the gypsy insulators in both homologous chromosomes even at a distance of 9 kb downstream from the promoter dramatically improves the trans activation of yellow. Moreover, the gypsy insulators have proved to stabilize trans activation between distantly located enhancers and a promoter. These data suggest that gypsy insulator pairing is involved in communication between loci in the Drosophila genome.     

Ecdysone-stimulated RNA synthesis in imaginal discs of Drosophila melanogaster

Cytoplasmic RNA from imaginal discs of Drosophila melanogaster, labeled by uridine incorporation in organ culture, has been assayed by hybridization to cytological preparations of polytene chromosomes. RNA labeled during the early stages (first four hours) of ecdysone stimulation was compared to RNA labeled in the absence of the hormone. For the poly(A)-containing fraction (oligo-dT bound), several loci hybridize only RNA labeled in the presence of ecdysone; one locus hybridizes only control RNA. The majority of hybridizing loci are unaffected by the hormone. Of the loci hybridizing RNA not bound to oligo-dT, several appear specific for the ecdysone-treated sample, though most are labeled more heavily with this RNA than with the control. None of the ecdysone-sensitive loci visualized by in situ hybridization are the sites of salivary gland puffs induced by ecdysone on the same time scale.     

Rates of RNA synthesis during early embryogenesis in Drosophila melanogaster

We determined the absolute rates of RNA synthesis during embryogenesis in Drosophila melanogaster by measuring the incorporation of ³H-5-orotic acid into RNA, and the specific activity of the UTP pool. Initially (preblastoderm) the rate of RNA synthesis is relatively high, but declines to a lower level by gastrulation. The data suggest that RNA synthesis is initiated during very early embryogenesis.     

Evidence for a juvenile hormone receptor involved in protein synthesis in Drosophila melanogaster

The larval fat body of newly eclosed adults of Drosophila melanogaster was found to contain a single major binding protein specific for juvenile hormone (JH). Binding to this protein was saturable, of high affinity, and specific for JH III. The protein has a subunit molecular weight (Mr) of 85,000, as determined by photoaffinity labeling. The same or similar JH-binding protein was found in larval fat body and cuticle of third instar larvae and in male accessory glands and heads of newly eclosed adults. It was not found in several other tissues in adults. Male accessory gland cytosol from wild-type flies was found to contain a single binder with a dissociation constant (KD) of 6.7 nM for JH III; a binder in similar preparations from the methoprene-tolerant (Met) mutant had a KD value 6-fold higher. JH III stimulated protein synthesis in glands cultured in vitro, but this effect was reduced in Met flies as compared to wild-type flies, establishing a correlation between JH binding and biological activity of the hormone. In addition, glandular protein accumulation during the first 2 days of adult development was less in Met flies than in wild-type flies. These results strongly suggest that the binding protein we have identified mediates this JH effect in male accessory glands and thus is acting as a JH receptor.     

Evidence for subdomain flexibility in Drosophila melanogaster acetylcholinesterase

The catalytic domain of the acetylcholinesterases is composed of a single polypeptide chain, the folding of which determines two subdomains. We have linked these two subdomains by mutating two residues, I327 and D375, to cysteines, to form a disulfide bridge. As a consequence, the hydrodynamic radius of the protein was reduced, suggesting that there is some flexibility in the subdomain connection. In addition to the smaller size, the mutated protein is more stable than the wild-type protein. Therefore, the flexibility between the two domains is a weak point in terms of protein stability. As expected from the location of the disulfide bond at the rim of the active site, the kinetic studies show that it affects interactions with peripheral ligands and the entrance of some of the bulkier substrates, like o-nitrophenyl acetate. In addition, the mutations affect the catalytic step for o-nitrophenyl acetate and phosphorylation by organophosphates, suggesting that this movement between the two subdomains is connected with the cooperativity between the peripheral and catalytic sites.     

The enhancer of split locus and neurogenesis in Drosophila melanogaster

Enhancer of split (E(spl)) is one of a group of so-called neurogenic genes of Drosophila. We describe two different types of E(spl) alleles, dominant and recessive, which exert opposite effects on both central and peripheral nervous system development. The only extant dominant allele determines a reduction in the number of central neurons and peripheral sensilla; this phenotype is not reduced by a normal complement of wild-type alleles. Since animals carrying a triploidy for the wild-type locus develop similar defects, the dominant allele is probably the result of a gain-of-function mutation. Several recessive alleles, obtained as revertants of the dominant allele, are loss-of-function mutations and determine considerable neural hyperplasia. The present evidence suggests that neural defects of E(spl) mutants are due to defective segregation of neural and epidermal lineages, leading to neural commitment of less or of more cells than in the wild type, depending upon whether the animals carry the dominant or any of the recessive alleles, respectively. Therefore, E(spl) formally behaves as a gene switching between neural and epidermal pathways.