Glued(1) (Gl(1)) mutants produce a truncated protein that acts as a poison subunit and disables the cytoplasmic retrograde motor dynein. Heterozygous mutants have axonal defects in the adult eye and the nervous system. Here we show that selective expression of the poison subunit in neurons of the giant fiber (GF) system disrupts synaptogenesis between the GF and one of its targets, the tergotrochanteral motorneuron (TTMn). Growth and pathfinding by the GF axon and the TTMn dendrite are normal, but the terminal of the GF axon fails to develop normally and becomes swollen with large vesicles. This is a presynaptic defect because expression of truncated Glued restricted to the GF results in the same defect. When tested electrophysiologically, the flies with abnormal axons show a weakened or absent GF-TTMn connection. In Glued(1) heterozygotes, GF-TTMn synapse formation appears morphologically normal, but adult flies show abnormal responses to repetitive stimuli. This physiological effect is also observed when tetanus toxin is expressed in the GFs. Because the GF-TTMn is thought to be a mixed electrochemical synapse, the results show that Glued has a role in assembling both the chemical and electrical components. We speculate that disrupting transport of a retrograde signal disrupts synapse formation and maturation.

Abstract:Metamorphosis is a crucial life-history event that can change an organism's form, function, behavior, and ecological interactions. In the Mollusca, several neurotransmitters and neuromodulators play inductive or inhibitory roles in the pathways that govern larval metamorphosis. Nitric oxide (NO) has been implicated in developmental processes in vertebrates and arthropods, but not previously in molluscs. We determined that NO donors block pharmacologically induced metamorphosis in the mud snail Ilyanassa obsoleta, whereas injections of inhibitors of nitric oxide synthase (NOS) allow competent larvae to become juveniles. We describe a new developmental role for NO, as an endogenous inhibitor of molluscan metamorphosis.

In order to determine the timing of events during the assembly of a neural circuit in Drosophila we targeted expression of the temperature-sensitive shibire gene to the giant fiber system and then disrupted endocytosis at various times during development. The giant fiber retracted its axon or incipient synapses when endocytosis was blocked at critical times, and we perceived four phases to giant fiber development: an early pathfinding phase, an intermediate phase of synaptogenesis, a late stabilization process and, finally, a mature synapse. By co-expressing shibire ts and semaphorin 1a we provided evidence that Semaphorin 1a was one of the proteins being regulated by endocytosis and its removal was a necessary part of the program for synaptogenesis. Temporal control of targeted expression of the semaphorin 1a gene showed that acute excess Semaphorin 1a had a permanent disruptive effect on synapse formation.

Abstract:Adult Ilyanassa obsoleta recruit from the plankton to surface sediments of intertidal mudflats along the U.S. East Coast as a result of metamorphic induction of planktonic larvae by environmental cues. A previous researcher discovered that seawater extracts of mud from juvenile habitats could induce metamorphosis and provided evidence that the inductive agent was of biological origin. Because juvenile I. obsoleta are herbivorous and grow when fed diets of benthic diatoms, we hypothesized that benthic diatoms or their associated microflora might be responsible for producing a metamorphic stimulus. We tested extracts of a culture of mixed diatoms and extracts of cultures of 6 diatom species isolated from mudflat sediments along the coast of North Carolina in which sexually mature and immature adult (juvenile) I. obsoleta commonly co-occur. We also tested extracts of one diatom culture isolated at the Friday Harbor Laboratories (Friday Harbor, WA). We found differential effects among the diatom species tested. One centric diatom, Coscino-discus sp., induced metamorphosis at levels close to those triggered by a known neuroactive compound, serotonin. Several species of benthic diatoms displayed neutral effects, showing little or no inductive capability. In one experiment, an unidentified pennate diatom species appeared to inhibit spontaneous metamorphosis that occurred in some competent larvae. We hypothesize that Coscinodiscus sp. or its associated microflora, is part of a suite of benthic species that is either indicative of a favorable juvenile environment or is itself part of the postmetamorphic diet. Our results also indicate that larval Ilyanassa demonstrated positive, neutral, and perhaps even negative responses to potential metamorphic cues.

A ABSTRACT (Maximum 200 Words)This paper describes an effective process for development of engineering models and discrete event simulations as part of the system engineering effort supporting Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR) and weapon system development. Application of modeling and simulation techniques throughout the system life cycle has been directed as an element of Defense acquisition reform, and has been demonstrated to be effective in reducing cost, risk, and improving system performance. Development of an executable model of the proposed system, which encompasses the functional architecture, process models, rules, and a data representation, allows the architect to ensure the design concept meets functional requirements. When this is carried a step further by developing a simulation of the architecture, or architectural components, it becomes possible to assess performance capabilities. A virtual model of the system can be executed to predict these characteristics and validate its likely fulfillment of operational requirements. This paper provides a step-by-step discussion of a process for developing system performance models and simulations, concluding with a synopsis of key areas for program manager attention. SUBJECT TERMS System Performance Modeling in C4ISR/Weapon System Design and Development ABSTRACTThis paper describes an effective process for development of engineering models and discrete event simulations as part of the system engineering effort supporting Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR) and weapon system development. Application of modeling and simulation techniques throughout the system life cycle has been directed as an element of Defense acquisition reform, and has been demonstrated to be effective in reducing cost, risk, and improving system performance. Development of an executable model of the proposed system, which encompasses the functional architecture, process models, rules, and a data representation, allows the architect to ensure the design concept meets functional requirements. When this is carried a step further by developing a simulation of the architecture, or architectural components, it becomes possible to assess performance capabilities. A virtual model of the system can be executed to predict these characteristics and validate its likely fulfillment of operational requirements. This paper provides a step-by-step discussion of a process for developing system performance models and simulations, concluding with a synopsis of key areas for program manager attention.