Genetic control of photoreceptor terminal differentiation in Drosophila melanogaster

Why do photoreceptors differentiate in the eye? Though simple, biologically this is an important question, and it may prove complex to answer. To present a bigger picture: animals have evolved a diversity of highly specialised sensory organs, which they use to obtain information from their environment and thus survive. These organs contain different types of receptor neurons. For example, there are chemoreceptors in the labellum and in the antennae of insects, or mechanoreceptors in the inner ear of vertebrates... and each of these types of receptor neurons specifically possesses the molecular machinery to detect and transduce stimuli from one particular sensory modality. In the case of the eye, it contains photoreceptor neurons, which are specialised in light detection. Neither photoreceptors nor most of the components of the phototransduction cascade appear commonly outside the eye. Therefore, what are mechanisms that ensure that photoreceptors differentiate correctly in the eye, and not in other body parts? To start answering this question, first it might be useful to understand the early-acting process of eye field specification. This depends on a group of transcription factors that are collectively called the ‘retinal determination network’ (RDN), and work in combination with each other to confer eye identity to the developing, multipotent tissue. RDN genes are both necessary and sufficient for eye formation in different animal species, from Drosophila to vertebrates, and they tend to act through an evolutionarily conserved sequence of transcriptional events. First in this sequence, following the Drosophila nomenclature, the transcription factor Eyeless activates the expression of sine oculis and eyes absent. Then, Sine oculis and Eyes absent form a heterodimer and direct eye formation. Despite the importance of the RDN, until recently, little was known about its targets, or about the molecular mechanisms by which it coordinates eye development. In particular, how does it instruct photoreceptor differentiation? Our work suggests that a key step in this process is coordinated by the zinc finger transcription factor glass, which is a direct target of Sine oculis. While previous literature has shown that the Glass protein is primarily expressed in photoreceptors, its role in these cells was not known because it was believed that glass mutant photoreceptor precursors died during metamorphosis. Contrary to former studies, we demonstrate that glass mutant photoreceptor precursors survive and are present in the adult retina, but fail to mature as functional photoreceptors. Importantly, we have found that Glass is required for the expression of virtually all the proteins that are involved in the phototransduction cascade, and thus glass mutant flies are blind. Consistent with this, ectopic expression of Glass is able to induce some phototransduction components in the brain. Another step in the formation of photoreceptors is regulated by the homeodomain transcription factor Hazy, which is a direct target of Glass. While we show that both Glass and Hazy act synergistically to induce the expression of phototransduction proteins, we have also found that Glass can initiate the expression of most of the components of the phototransduction machinery in a Hazy-independent manner, and that hazy mutant flies only fail to detect white light after they are older than five days. Glass seems to be both required and sufficient for the expression of Hazy, and inducing Hazy in the retina partly rescues the glass mutant phenotype. Taken together, our results show a transcriptional link between the RDN and the expression of the proteins that adult Drosophila photoreceptors need to sense light, placing Glass at a key position in this developmental process. Finally, we compare the expression pattern of Glass in Drosophila and in the annelid Platynereis, and discuss the possibility that Glass plays an evolutionarily conserved role across different phyla.Warum bilden sich Fotorezeptoren gerade im Auge aus? Obwohl diese Frage einfach erscheint, ist sie aus biologischer Sicht doch sehr bedeutend und bedarf eventuell einer komplexen Antwort. Allgemein lässt sich sagen, dass Tiere eine Vielfalt von hoch spezialisierten Sinnesorganen entwickelt haben, durch die sie Informationen aus ihrer Umwelt aufnehmen und auf diese Weise ihr Überleben sichern. Diese Organe enthalten verschiedene Arten von Rezeptorneuronen. Zum Beispiel gibt es Chemorezeptoren im Labellum und in den Antennen der Insekten, oder Mechanorezeptoren im Innenohr von Wirbeltieren... und jedes dieser Rezeptorneuronen besitzt eine spezifische molekulare Maschinerie, um Reize einer bestimmten Sinnesmodalität wahrzunehmen und umzuwandeln. Beim Auge sind es Fotorezeptorneuronen, die auf die Wahrnehmung von Lichtreizen spezialisiert sind. Weder die Fotorezeptoren noch die meisten der Komponenten der Fototransduktionskaskade kommen außerhalb des Auges vor. Welche Mechanismen sind demzufolge ausschlaggebend, damit sich Fotorezeptoren im Auge und nicht in anderen Körperteilen entwickeln? Um diese Frage zu beantworten, ist es zunächst wichtig die frühen Mechanismen der Augenspezifizierung zu verstehen. Diese erfolgt unter Einfluss einer Gruppe von Transkriptionsfaktoren, die als „Retinales Determinations Netzwerk“ (RDN) bezeichnet werden. Diese Transkriptionsfaktoren interagieren, um aus dem sich entwickelnden multipotenten Gewebe ein Sehorgan zu bilden. RDN-Gene sind für die Augenentwicklung verschiedener Tierarten, von Drosophila bis zu Wirbeltieren, sowohl notwendig als auch ausreichend. Sie agieren durch eine evolutionär konservierte Sequenz transkriptioneller Mechanismen. An erster Stelle dieser Sequenz, nach der Drosophila Nomenklatur, aktiviert der Transkriptionsfaktor Eyeless die Expression von sine oculis und eyes absent. Anschließend bilden Sine Oculis und Eyes absent ein Heterodimer und induzieren die Entwicklung des Auges. Trotz der Bedeutung des RDNs war bis vor Kurzem nur sehr wenig über seinen Zweck oder die molekularen Mechanismen durch die es die Augenentwicklung koordiniert, bekannt. Vor allem stellt sich die Frage, wie es die Differenzierung der Fotorezeptoren reguliert? Unsere Arbeit legt nahe, dass ein wesentlicher Schritt in diesem Prozess durch den Zinkfinger-Transkriptionsfaktor glass koordiniert wird. Dabei handelt es sich um ein direktes Zielgen von Sine oculis. Obwohl in früheren wissenschaftlichen Arbeiten belegt wurde, dass das Glass-Protein in erster Linie in Fotorezeptoren exprimiert wird, war seine Rolle in diesen Zellen nicht bekannt, da angenommen wurde, dass Fotorezeptoren von glass Mutanten während der Metamorphose absterben. Im Gegensatz zu früheren Studien belegen wir das Überleben der Fotorezeptor-Vorläuferzellen von glass Mutanten und ihre Präsenz in der Retina adulter Fliegen, wobei sie jedoch nicht zu funktionsfähigen Fotorezeptoren heranreifen. Insbesondere konnten wir zeigen, dass Glass für die Expression fast aller Proteine, die in der Fototransduktionskaskade involviert sind, erforderlich ist. Daher sind glass Mutanten blind. In Übereinstimmung mit diesen Erkenntnissen bewirkt die ektopische Expression von Glass die Induktion einiger Komponenten der Fototransduktion im Gehirn. Ein weiterer Schritt in der Bildung von Fotorezeptoren wird reguliert durch den Homeodomänen-Transkriptionsfaktor Hazy, der ein direktes Ziel von Glass ist. Wir zeigen zum einen die synergetische Wirkung von Glass und Hazy bei der Expression von Fototransduktionsproteinen, zum anderen belegen wir, dass Glass die meisten Komponenten der Fototransduktionsmaschinerie unabhängig von Hazy induzieren kann, und dass hazy Mutanten ab dem Alter von fünf Tagen weißes Licht nicht mehr wahrnehmen können. Glass scheint notwendig und ausreichend für die Expression von Hazy zu sein und die Induktion von Hazy in der Retina rettet teilweise den Phänotyp von glass Mutanten. Insgesamt beweisen unsere Ergebnisse einen transkriptionellen Zusammenhang zwischen dem RDN und der Expression von Proteinen, die in Fotorezeptoren von adulten Drosophila Fliegen notwendig sind um Licht wahrzunehmen. Bei diesem Entwicklungsprozess hat Glass eine Schlüsselposition. Schließlich vergleichen wir die Expressionsmuster von Glass in Drosophila und im Anneliden Platynereis und diskutieren die Möglichkeit, dass Glass eine evolutionär konservierte Rolle über verschiedene Phyla hinweg spielt

The transcription factor Glass links eye field specification with photoreceptor differentiation in Drosophila

Eye development requires an evolutionarily conserved group of transcription factors, termed the retinal determination network (RDN). However, little is known about the molecular mechanism by which the RDN instructs cells to differentiate into photoreceptors. We show that photoreceptor cell identity in Drosophila is critically regulated by the transcription factor Glass, which is primarily expressed in photoreceptors and whose role in this process was previously unknown. Glass is both required and sufficient for the expression of phototransduction proteins. Our results demonstrate that the RDN member Sine oculis directly activates glass expression, and that Glass activates the expression of the transcription factors Hazy and Otd. We identified hazy as a direct target of Glass. Induced expression of Hazy in the retina partially rescues the glass mutant phenotype. Together, our results provide a transcriptional link between eye field specification and photoreceptor differentiation in Drosophila, placing Glass at a central position in this developmental process

Mushroom body-specific profiling of gene expression identifies regulators of long-term memory in Drosophila

Memory formation is achieved by genetically tightly controlled molecular pathways that result in a change of synaptic strength and synapse organization. While for short- term memory traces rapidly acting biochemical pathways are in place, the formation of long-lasting memories requires changes in the transcriptional program of a cell. Although many genes involved in learning and memory formation have been identified, little is known about the genetic mechanisms required for changing the transcriptional program during different phases of long-term memory formation. With Drosophila melanogaster as a model system we profiled transcriptomic changes in the mushroom body, a memory center in the fly brain, at distinct time intervals during long- term memory formation using the targeted DamID technique. We describe the gene expression profiles during these phases and tested 33 selected candidate genes for deficits in long-term memory formation using RNAi knockdown. We identified 10 genes that enhance or decrease memory when knocked-down in the mushroom body. For vajk-1 and hacd1, the two strongest hits, we gained further support for their crucial role in learning and forgetting. These findings show that profiling gene expression changes in specific cell-types harboring memory traces provides a powerful entry point to identify new genes involved in learning and memory. The presented transcriptomic data may further be used as resource to study genes acting at different memory phases

Successive requirement of Glass and Hazy for photoreceptor specification and maintenance in Drosophila

Development of the insect compound eye requires a highly controlled interplay between transcription factors. However, the genetic mechanisms that link early eye field specification to photoreceptor terminal differentiation and fate maintenance remain largely unknown. Here, we decipher the function of 2 transcription factors, Glass and Hazy, which play a central role during photoreceptor development. The regulatory interactions between Glass and Hazy suggest that they function together in a coherent feed-forward loop in all types of Drosophila photoreceptors. While the glass mutant eye lacks the expression of virtually all photoreceptor genes, young hazy mutants correctly express most phototransduction genes. Interestingly, the expression of these genes is drastically reduced in old hazy mutants. This age-dependent loss of the phototransduction cascade correlates with a loss of phototaxis in old hazy mutant flies. We conclude that Glass can either directly or indirectly initiate the expression of most phototransduction proteins in a Hazy-independent manner, and that Hazy is mainly required for the maintenance of functional photoreceptors in adult flies

Efficacy of different antifouling treatments for seawater cooling systems

In an industrial seawater cooling system, the effects of three different antifouling treatments, viz. sodium hypochlorite (NaClO), aliphatic amines (Mexel1432) and UV radiation, on the characteristics of the fouling formed were evaluated. For this study a portable pilot plant, as a side-stream monitoring system and seawater cooling system, was employed. The pilot plant simulated a power plant steam condenser, having four titanium tubes under different treatment patterns, where fouling progression could be monitored. The nature of the fouling obtained was chiefly inorganic, showing a clear dependence on the antifouling treatment employed. After 72 days the tubes under treatment showed a reduction in the heat transfer resistance (R) of around 70% for NaClO, 48% for aliphatic amines and 55% for UV, with respect to the untreated tube. The use of a logistic model was very useful for predicting the fouling progression and the maximum asymptotic value of the increment in the heat transfer resistance (DRmax). The apparent thermal conductivity (l) of the fouling layer showed a direct relationship with the percentage of organic matter in the collected fouling. The characteristics and mode of action of the different treatments used led to fouling with diverse physicochemical properties

The molecular genetic analysis of the expanding pachyonychia congenita case collection

BACKGROUND: Pachyonychia congenita (PC) is a rare autosomal dominant keratinizing disorder characterized by severe, painful, palmoplantar keratoderma and nail dystrophy, often accompanied by oral leucokeratosis, cysts and follicular keratosis. It is caused by mutations in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16 or KRT17. OBJECTIVES: To identify mutations in 84 new families with a clinical diagnosis of PC, recruited by the International Pachyonychia Congenita Research Registry during the last few years. METHODS: Genomic DNA isolated from saliva or peripheral blood leucocytes was amplified using primers specific for the PC-associated keratin genes and polymerase chain reaction products were directly sequenced. RESULTS: Mutations were identified in 84 families in the PC-associated keratin genes, comprising 46 distinct keratin mutations. Fourteen were previously unreported mutations, bringing the total number of different keratin mutations associated with PC to 105. CONCLUSIONS: By identifying mutations in KRT6A, KRT6B, KRT6C, KRT16 or KRT17, this study has confirmed, at the molecular level, the clinical diagnosis of PC in these families

Memory phase-specific genes in the Mushroom Bodies identified using CrebB-target DamID.

The formation of long-term memories requires changes in the transcriptional program and de novo protein synthesis. One of the critical regulators for long-term memory (LTM) formation and maintenance is the transcription factor CREB. Genetic studies have dissected the requirement of CREB activity within memory circuits, however less is known about the genetic mechanisms acting downstream of CREB and how they may contribute defining LTM phases. To better understand the downstream mechanisms, we here used a targeted DamID approach (TaDa). We generated a CREB-Dam fusion protein using the fruit fly Drosophila melanogaster as model. Expressing CREB-Dam in the mushroom bodies (MBs), a brain center implicated in olfactory memory formation, we identified genes that are differentially expressed between paired and unpaired appetitive training paradigm. Of those genes we selected candidates for an RNAi screen in which we identified genes causing increased or decreased LTM

Resource dedication problem in a multi-project environment

There can be different approaches to the management of resources within the context of multi-project scheduling problems. In general, approaches to multiproject scheduling problems consider the resources as a pool shared by all projects. On the other hand, when projects are distributed geographically or sharing resources between projects is not preferred, then this resource sharing policy may not be feasible. In such cases, the resources must be dedicated to individual projects throughout the project durations. This multi-project problem environment is defined here as the resource dedication problem (RDP). RDP is defined as the optimal dedication of resource capacities to different projects within the overall limits of the resources and with the objective of minimizing a predetermined objective function. The projects involved are multi-mode resource constrained project scheduling problems with finish to start zero time lag and non-preemptive activities and limited renewable and nonrenewable resources. Here, the characterization of RDP, its mathematical formulation and two different solution methodologies are presented. The first solution approach is a genetic algorithm employing a new improvement move called combinatorial auction for RDP, which is based on preferences of projects for resources. Two different methods for calculating the projects’ preferences based on linear and Lagrangian relaxation are proposed. The second solution approach is a Lagrangian relaxation based heuristic employing subgradient optimization. Numerical studies demonstrate that the proposed approaches are powerful methods for solving this problem

The Ursinus Weekly, April 19, 1965

1965 Campus Chest drive opens: From Georgia; From Paoli: From Vietnam • New approach to traditional charity drive announced • Rehearsal underway for play • Dr. Zucker guest on Seminar 610 • U.C. buys land • Dr. Pei to speak • Dental education • Editorial: From Dr. Helfferich; Snubbed? • Britain versus the west coast • Transfer fallacy • ACLU objectives • Unusual honeymoon: Ursinus grad tours Russia • UC celebrities return • Track team loses: F&M snaps 20 meet streak • Tennis team crushed by Swarthmore • Baseball team drops two: LaSalle, Delaware defeat Bears • Ursinus leads lacrosse playday • UC lacrosse team clobbers Penn • Freshman featured as vibes player • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1246/thumbnail.jp

Regulators of Long-Term Memory Revealed by Mushroom Body-Specific Gene Expression Profiling in Drosophila melanogaster

Memory formation is achieved by genetically tightly controlled molecular pathways that result in a change of synaptic strength and synapse organization. While for short- term memory traces, rapidly acting biochemical pathways are in place, the formation of long-lasting memories requires changes in the transcriptional program of a cell. Although many genes involved in learning and memory formation have been identified, little is known about the genetic mechanisms required for changing the transcriptional program during different phases of long-term memory (LTM) formation. With Drosophila melanogaster as a model system, we profiled transcriptomic changes in the mushroom body—a memory center in the fly brain—at distinct time intervals during appetitive olfactory LTM formation using the targeted DamID technique. We describe the gene expression profiles during these phases and tested 33 selected candidate genes for deficits in LTM formation using RNAi knockdown. We identified 10 genes that enhance or decrease memory when knocked-down in the mushroom body. For vajk-1 and hacd1—the two strongest hits—we gained further support for their crucial role in appetitive learning and forgetting. These findings show that profiling gene expression changes in specific cell-types harboring memory traces provides a powerful entry point to identify new genes involved in learning and memory. The presented transcriptomic data may further be used as resource to study genes acting at different memory phases