Genetic and molecular variation in the RpII215 region of Drosophila melanogaster

Scribble and Discs Large mediate tricellular junction formation

Junctional complexes that mediate cell adhesion are key to epithelial integrity, cell division and permeability barrier formation. In Drosophila, the scaffolding proteins Scribble (Scrib) and Discs Large (Dlg) are key regulators of epithelial polarity, proliferation, assembly of junctions and protein trafficking. We found that Scrib and Dlg are necessary for the formation of the tricellular junction (TCJ), a unique junction that forms in epithelia at the point of convergence of three neighboring cells. Scrib and Dlg are in close proximity with the TCJ proteins Gliotactin (Gli) and Bark Beetle (Bark), and both are required for TCJ protein recruitment. Loss of Bark or Gli led to basolateral spread of the TCJ complex at the cell corners. Loss of the septate junction proteins Nrx-IV and the Na⁺/K⁺ ATPase also resulted in basolateral spread of the entire TCJ complex at the cell corners. The Scrib PDZ1-2 domains and the Dlg GUK domain are necessary for Bark and Gli localization to the TCJ. Overall, we propose a model in which Scrib and Dlg are key components of the TCJ, and form a complex with Bark and Gli.

Intron delays and transcriptional timing during development

The time taken to transcribe most metazoan genes is significant because of the substantial length of introns. Developmentally regulated gene networks, where timing and dynamic patterns of expression are critical, may be particularly sensitive to intron delays. We revisit and comment on a perspective last presented by Thummel 16 years ago: transcriptional delays may contribute to timing mechanisms during development. We discuss the presence of intron delays in genetic networks. We consider how delays can impact particular moments during development, which mechanistic attributes of transcription can influence them, how they can be modeled, and how they can be studied using recent technological advances as well as classical genetics.

The novel transcription factor e(y)2 interacts with TAF(II)40 and potentiates transcription activation on chromatin templates

Weak hypomorph mutations in the enhancer of yellow genes, e(y)1 and e(y)2, of Drosophila melanogaster were discovered during the search for genes involved in the organization of interaction between enhancers and promoters. Previously, the e(y)1 gene was cloned and found to encode TAF(II)40 protein. Here we cloned the e(y)2 gene and demonstrated that it encoded a new ubiquitous evolutionarily conserved transcription factor. The e(y)2 gene is located at 10C3 (36.67) region and is expressed at all stages of Drosophila development. It encodes a 101-amino-acid protein, e(y)2. Vertebrates, insects, protozoa, and plants have proteins which demonstrate a high degree of homology to e(y)2. The e(y)2 protein is localized exclusively to the nuclei and is associated with numerous sites along the entire length of the salivary gland polytene chromosomes. Both genetic and biochemical experiments demonstrate an interaction between e(y)2 and TAF(II)40, while immunoprecipitation studies demonstrate that the major complex, including both proteins, appears to be distinct from TFIID. Furthermore, we provide genetic evidence suggesting that the carboxy terminus of dTAF(II)40 is important for mediating this interaction. Finally, using an in vitro transcription system, we demonstrate that recombinant e(y)2 is able to enhance transactivation by GAL4-VP16 on chromatin but not on naked DNA templates, suggesting that this novel protein is involved in the regulation of transcription.

Transcriptional competition and homeosis in Drosophila

Interference between different classes of RNA polymerase II alleles causes a mutant phenotype called the "Ubx effect" that resembles one seen in flies haploinsufficient for the transcription factor, Ultrabithorax (Ubx). Flies carrying the mutation in the largest subunit of Drosophila RNA polymerase II, RpII215(4), display the Ubx effect when heterozygous as in RpII215(4)/+ but not when homozygous mutant or wild type. In this report we demonstrate that the interaction between alleles in different classes of polymerase occurs even in the absence of transcription by the wild-type polymerase. We utilized the resistance to the transcriptional inhibitor alpha-amanitin conferred by RpII215(4) to show that RpII215(4)/+ flies raised on alpha-amanitin-containing food still show the Ubx effect and are indistinguishable from flies raised on normal food. We demonstrate using HPLC that the intracellular concentration of alpha-amanitin in the developing larvae is sufficient to inhibit transcription by alpha-amanitin-sensitive polymerase. Furthermore, fluorescein-labeled alpha-amanitin accumulates in imaginal discs, which are the precursor cells for the tissue showing the homeotic transformation in adults. We conclude that the interaction between different classes of RNA polymerase II alleles resulting in the Ubx effect occurs prior to the block in transcription caused by alpha-amanitin.

Molecular analysis of the Methoprene-tolerant gene region of Drosophila melanogaster

Adult functions of juvenile hormone (JH) have been described for Drosophila melanogaster and other dipteran insects, but preadult function for this hormone remains largely unknown in this order of insects. We have identified a mutation of Drosophila, Methoprene-tolerant (Met), which appears to alter JH reception during late larval development. The molecular cloning of Met will be a step toward understanding this gene and possibly identifying a preadult role(s) for JH. Molecular cloning was initiated using the technique of transposon-tagging with a transposable P element. P-element insertional alleles of Met were generated, and genomic libraries were constructed from two of these alleles. From these libraries P-element-bearing clones were isolated that in situ hybridized to the cytogenetic region where Met had been previously localized by genetic methods. Two of the alleles were shown to have complete P-elements inserted in similar, but not identical, locations in the predicted cytogenetic region where Met is located. A late-larval cDNA library was screened to identify transcriptional units in this region, and clones were recovered with homology to a DNA fragment abutting the P-element insertion site. These clones may represent Met cDNA molecules.

DPhK-gamma, a putative Drosophila kinase with homology to vertebrate phosphorylase kinase gamma subunits: molecular characterisation of the gene and phenotypic analysis of loss of function mutants

Partial and total loss of function mutant alleles of a putative Drosophila homologue (DPhK-gamma) of the vertebrate phosphorylase kinase gamma-subunit gene have been isolated. DPhK-gamma is required in early embryonic processes, such as gastrulation and mesoderm formation; however, defects in these processes are seen only when both the maternal and zygotic components of DPhK-gamma expression are eliminated. Loss of zygotic expression alone does not appear to affect normal embryonic and larval development; some pupal lethality is observed but the majority of mutant animals eclose as adults. Many of these adults show defects in their leg musculature (e.g. missing and degenerating muscles), in addition to exhibiting melanised "tumours" on their leg joints. Loss of only the maternal component has no obvious phenotypic consequences. The DPhK-gamma gene has been cloned and sequenced. It has an open reading frame (ORF) of 1680 bp encoding a 560 amino acid protein. The predicted amino acid sequence of DPhK-gamma has two conserved domains, the catalytic kinase and calmodulin-binding domains, separated by a linker sequence. The amino acid sequence of DPhK-gamma is homologous to that of mammalian PhK-gamma proteins but differs in the length and amino acid composition of its linker sequence. The expression of DPhK-gamma mRNA is developmentally regulated. We discuss the implications of these observations.

dishevelled is required during wingless signaling to establish both cell polarity and cell identity

The dishevelled gene of Drosophila is required to establish coherent arrays of polarized cells and is also required to establish segments in the embryo. Here, we show that loss of dishevelled function in clones, in double heterozygotes with wingless mutants and in flies bearing a weak dishevelled transgene leads to patterning defects which phenocopy defects observed in wingless mutants alone. Further, polarized cells in all body segments require dishevelled function to establish planar cell polarity, and some wingless alleles and dishevelled; wingless double heterozygotes exhibit bristle polarity defects identical to those seen in dishevelled alone. The requirement for dishevelled in establishing polarity in cell autonomous. The dishevelled gene encodes a novel intracellular protein that shares an amino acid motif with several other proteins that are found associated with cell junctions. Clonal analysis of dishevelled in leg discs provides a unique opportunity to test the hypothesis that the wingless dishevelled interaction species at least one of the circumferential positional values predicted by the polar coordinate model. We propose that dishevelled encodes an intracellular protein required to respond to a wingless signal and that this interaction is essential for establishing both cell polarity and cell identity.

A kinesin-like protein required for distributive chromosome segregation in Drosophila

The nod gene is required for the distributive segregation of nonexchange chromosomes during meiosis in D. melanogaster. Loss-of-function nod mutations cause nondisjunction and loss of nonrecombinant chromosomes both at meiosis I and during subsequent mitotic divisions. We have cloned the nod locus, examined its expression patterns, and determined its coding sequence. In adults the nod transcript is only present in females, consistent with the observation that males do not use the distributive segregation system. However, the nod locus is also transcribed in the embryonic, larval, and pupal stages of development, and possibly in all dividing cells. Finally, the N-terminal domain of the predicted nod protein has amino acid similarity to the mechanochemical domain of kinesin heavy chain; however, the C-terminal domain is unlike that of kinesin heavy chain or of any previously reported protein. Thus, the nod protein is a member of the kinesin superfamily and may be a microtubule motor.

P-element-mediated enhancer detection: an efficient method for isolating and characterizing developmentally regulated genes in Drosophila

We describe a new approach for identifying and studying genes involved in Drosophila development. Single copies of an enhancer detector transposon, P[1ArB], have been introduced into flies at many different genomic locations. The beta-galactosidase reporter gene in this construct is influenced by a wide range of genomic transcriptional regulatory elements in its vicinity. Our results suggest that a significant proportion of these regulatory sequences are control elements of nearby Drosophila genes. These genes need not be disrupted for their regulatory elements to be identified by P[1ArB]. The P[1ArB] transposon has been designed to facilitate both rapid cloning and deletion analysis of genomic sequences into which it inserts. Therefore, the enhancer detection system is an efficient method of screening for genes primarily on the basis of their expression pattern and then rapidly analyzing those of particular interest at the molecular and genetic levels.

Molecular cloning of the lethal(1)discs large-1 oncogene of Drosophila

We present a genetic, developmental and molecular analysis of lethal(1)discs large-1[l(1)d.lg-1; Stewart et al., 1972], an oncogene of Drosophila. Mutations in this gene cause the imaginal discs to grow by cell proliferation beyond their normal final size, transform into solid tumors, fuse with one another and the brain, and lose their ability to differentiate. The oncogene represents the only known complementation group between two deficiency breakpoints, and 15 recessive lethal alleles are available. Cloning of the DNA between the two deficiency breakpoints defines a region of 45 +/- 2 kb. The l(1)d.lg-1 transcription unit is identified by both qualitative and quantitative effects of several l(1)d.lg-1 mutations on the RNA transcripts and by the presence of a DNA insert in one of the l(1)d.lg-1 alleles. It gives rise to at least five different transcripts ranging in size from 1.9 to 6.0 kb. Three other transcription units are present within this region, two 5' to the l(1)d.lg-1 gene and one at the 3' end. A near full-length cDNA from one of the larger transcripts of l(1)d.lg-1 has homology to genomic DNA spanning over 20 kb. A developmental profile of l(1)d.lg-1 transcription is presented. We discuss how mutations in this gene could disrupt epithelial structure and how this might be related to the excessive cell proliferation and interdisc fusion that is observed. We also compare this gene with another recessive oncogene of Drosophila, lethal(2)giant larvae, that has been cloned and characterized.

Analysis of the gene encoding the largest subunit of RNA polymerase II in Drosophila

We have characterized RpII215, the gene encoding the largest subunit of RNA polymerase II in Drosophila melanogaster. DNA sequencing and nuclease S1 analyses provided the primary structure of this gene, its 7 kb RNA and 215 kDa protein products. The amino-terminal 80% of the subunit harbors regions with strong homology to the beta' subunit of Escherichia coli RNA polymerase and to the largest subunits of other eukaryotic RNA polymerases. The carboxyl-terminal 20% of the subunit is composed of multiple repeats of a seven amino acid consensus sequence, Tyr-Ser-Pro-Thr-Ser-Pro-Ser. The homology domains, as well as the unique carboxyl-terminal structure, are considered in the light of current knowledge of RNA polymerase II and the properties of its largest subunit. Additionally, germline transformation demonstrated that a 9.4 kb genomic DNA segment containing the alpha-amanitin-resistant allele, RpII215C4, includes all sequences required to produce amanitin-resistant transformants.

Molecular analysis of chemically-induced mutations at the RpII215 locus of Drosophila melanogaster

A substantial fraction, perhaps 50% or more, of spontaneous mutations in Drosophila melanogaster have been shown by molecular analyses to be associated with the presence of a transposable element (TE) inserted into the affected gene. We are interested in the molecular structure of induced mutations in Drosophila, in particular whether TEs are also responsible for a significant proportion of chemically-induced mutations. We report here the molecular analysis of 58 mutations at the RpII215 locus induced with EMS or ENU. While we find evidence for moderately sized deletions at this locus (in 3/58, or 5% of the examined mutants), we failed to detect any mutations which were associated with an insertion event. It may be the case that induced mutations are qualitatively different from spontaneous mutations.