GRKs in Hedgehog Signaling pp. 135-41
The involvement of G-protein-coupled receptor kinases (GRKs) in Hedgehog (Hh) signaling, a pathway that is essential for tissue patterning and maintenance, has recently attracted much attention. GRKs regulate G-protein-coupled receptor (GPCR) signaling and have an evolutionarily conserved function in promoting high-threshold Hh target gene expression through regulation of Smoothened (Smo), a GPCR family member that activates intracellular Hh signaling. Maier et al. now review the role of GRKs, which act to limit signaling through the Hh pathway while also promoting Smo activity.
Tubulogenesis in the Salivary Gland pp. 142-6
The embryonic salivary gland of Drosophila is a powerful system to analyze the cellular and molecular mechanisms of tubulogenesis in vivo. A number of genes are known to regulate salivary gland migration and/or lumen size. In order to understand how salivary gland migration and lumen size are coordinated, Xu and Myat review their recent studies of the role of the single Drosophila Rho GTPase, Rho1, in salivary gland tubulogenesis. In addition to the requirement of Rho1 in salivary gland invagination and migration, Rho1 was recently shown to control salivary gland lumen width and length during the migration process.
Trait Variability in Drosophila pp. 147-52
Variation within species and populations arises through environmental and genetic factors and ensures that no two individuals are identical. Not all traits show the same degree of intraspecific variation, some traits being much more variable than others. Recently, variability has been proposed to be an evolvable trait itself, subject to natural selection. The difficulty remains in describing what this trait is, specifically. Here, Shingleton and Tang describe their recent study identifying a developmental mechanism that regulates trait variability in response to any source (environmental or genetic) of variation.
Drosophila Central Neurons: Model for Human Diseases pp. 153-7
Synaptic homeostasis is a form of neuronal plasticity that stabilizes activity of neural networks. Both presynaptic and postsynaptic effects are well documented in response to activity changes. Ping and Tsunoda now discuss their recent study showing both synaptic and intrinsic changes in Drosophila central neurons in response to prolonged inactivity. Although mediated by different receptors, synaptic homeostasis in the central nervous system is conserved across species. The authors also demonstrated that nAChRs mediate synaptic homeostasis and are upregulated immediately, subsequently triggering a rapid increase in Shal K+ channels. This is a novel mechanism that regulates synaptic homeostasis to stabilize synaptic potentials. Drosophila central neurons are therefore a good model for the study of cholinergic synaptic homeostasis, regulation and role in disease.
On the Evolution of Gene Organization pp. 158-61
Despite the high levels of genome rearrangement, unusually large regions that remain unaffected have also been uncovered. What mechanism of chromosome evolution has given raise to the conservation of gene order among distantly related species? Díaz-Castillo and Ranz have used chromosome engineering coupled with genome wide expression profiling and phenotypic assays to evaluate the presence and nature of putative constraints acting on one of the largest chromosomal regions conserved across nine species of Drosophila. The authors discuss their recent results and propose that regulatory-based constraints might not suffice to explain the maintenance of gene organization of some chromosome domains over evolutionary time.
More on Polycomb Repression pp. 162-8
Polycomb group (PcG) proteins control a variety of developmental processes in animals and plants. They exist in multiprotein complexes that comprise specific chromatin-modifying enzymatic activities. These complexes co-localize at a large set of genes encoding developmental regulators. Recent analyses in Drosophila suggest that monoubiquitination of histone H2A by the PcG protein Sce is only essential for repression of a subset of PcG target genes but is not required for the PcG-mediated repression of other targets. Now, Scheuermann et al. review the role of H2A monoubiquitination and deubiquitination in Polycomb repression in Drosophila.
Innate Immune Response and Neurodegeneration pp. 169-72
Petersen and Wassarman discuss a new role for Drosophila innate immune response. Recent research suggests that, in addition to combating infection, the innate immune response promotes neurodegeneration. The authors review a recently exposed correlative relationship between the innate immune response and neurodegeneration in a model of human Ataxia-telangiectasia (A-T). Glial cells are responsible for the innate immune response in the A-T model and have also been implicated in neurodegeneration. Additionally, the innate immune response shows a causative role in models of human retinal degenerative disorders and Alzheimer disease. All these observations suggest that activation of the innate immune response is a shared cause of neurodegeneration in different human diseases.
The Drosophila l(2)dtl/cdt2 Gene pp. 173-83
Drosophila l(2)dtl (also called cdt2), a gene essential for embryogenesis, encodes a subunit of a Cullin 4-based E3 ubiquitin ligase complex that targets a number of key cell cycle regulatory proteins, including p21, Cdt1, E2F1 and Set8, to prevent replication defects and maintain cell cycle control. Sloan et al. now investigated the role of l(2)dtl/cdt2 during development and showed that L(2)dtl/Cdt2 is maternally deposited, remains nuclear throughout the cell cycle and has a previously unreported elevated expression in the developing gonads. The authors demonstrate that l(2)dtl/cdt2 is an essential gene for Drosophila development.
Optimizing Scanning Electron Microscopy pp. 184-92
In this issue of Fly, Tardi et al. describe a simple, rapid, optimized approach to low-vacuum scanning electron microscopy that involves minimal preparation of samples. The protocol uses previously frozen adult flies that are mounted on aluminum stubs with carbon cement and directly imaged, with no chemical treatment or sputter coating, and is well suited to large-scale ultrastructural phenotypic analysis in insects, such as taxonomic studies, quantitative genetics and mutant screens. Diverse optimal conditions are described for different organs of the fly.
Keeping Fly Stock Infections in Check pp. 193-204
Infections may endanger fly stocks if left unchecked for. One such infection is caused by an obligate fungal intracellular parasite, Tubulinosema ratisbonensis, which can be found in laboratory stocks. Niehus et al. identified and partially characterized a T. ratisbonensis strain that was infesting their own Drosophila cultures and report on measures to contain and eradicate the infection. The authors have developed a high-throughput qPCR assay that allows the efficient parallel screening of a large number of potentially infested stocks and describe several treatments they investigated to prevent further contamination of stocks.
Need for Speed pp. 205-10
Quantification of the speed of movement in response to environmental and experimental factors is highly useful for behavioral and neurological studies of Drosophila melanogaster. Chan et al. now present a novel signal processing method for quantifying the speed of multiple flies using a system with automatic behavior detection and analysis previously developed to quantify general activity. The authors confirmed the feasibility of using this metric to estimate the speed of movement in a population of flies by evaluating recordings taken from populations maintained at two different temperatures.