Coordinated eye growth in sophisticated arthropod visual systems

University Of Cincinnati Main Campus, Cincinnati OH

Investigators

Abstract

One of the most important features of any image-forming eye is correct focusing, which relies on the precise spacing between the lens and retina. Substantial data show how this coordination is established in vertebrates. However, some of the most basic questions concerning how eye components are coordinated in invertebrates remain unanswered. This project primarily focuses on Sunburst Diving Beetles as a particularly valuable system for analyzing these key factors because they can be manipulated on the molecular level and their larvae have extremely sophisticated eyes, the focus of which can be quantified. To test for the generality of the identified mechanisms, and in specific instances dissect them further, synergistic experiments are performed on the genetically powerful fly model Drosophila melanogaster. The eyes of both animals are evaluated using a micro-ophthalmoscope that has recently been developed in the host laboratory. Preliminary findings suggest that both beetle and fly eyes are able to develop astonishingly precise focus in the absence of visual feedback. If confirmed, invertebrate eyes could become an important general model for precisely tuned organ development that is easily assessable and can be manipulated at the molecular-genetic level. The execution of this project involves training of many undergraduate and graduate students, who will also actively participate in outreach activities. In addition, the project involves the development of synergistic teaching modules. The principal eyes of diving beetle larvae are sophisticated visual organs that rapidly grow to ~130% of their original size at the second to third instar transition. It is likely that such eye elongation involves changes in osmotic pressure. The lens also needs to be reformed, which takes considerably longer (~8 h) and likely involves some of the 10 lens proteins that have been identified through a previous collaboration of the PI and Co-PI. Aim 1 of the project uses a unique live imaging technique (the micro-ophthalmoscope) that allows direct visualization of the retina and measurement of the refractive states (focusing into infinity or being near- or far-sighted) of very small invertebrate eyes, including those of the diving beetle larvae and individual D. melanogaster ommatidia. This technique is used in combination with traditional optical methods and behavioral tests in diving beetles to test if visual input is necessary for proper eye growth in these animals. Aim 2 uses physical manipulations and pharmacology to evaluate the contribution of osmotic pressure to eye-tube growth and aim 3 uses in situ hybridization, immunostaining, and RNAi knockdowns of the identified lens proteins to investigate how the complex Thermonectus lenses change focal lengths. Targeted parallel experiments on D. melanogaster explore the generality of specific findings. It is expected that this integrative approach will provide some of the first data to address the long overdue question of how eye growth is coordinated in arthropods. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.