The light organ symbiosis between the squid Euprymna scolopes and the luminous bacterium Vibrio fischeri represents the most common type of animal-bacterial interaction; i.e., an association of extracellular bacteria with polarized epithelial cells that begins anew each generation. In this two-partner model both the host and symbiont can be raised in the laboratory, and genetic approaches in V. fischeri have been developed to study not only bacterial differentiation, but also how the normal program of host gene expression is affected by genetically altered symbionts. Many of the developmental effects of symbiosis on the host and symbiont, as well as the reciprocal signals that trigger development of the partners, have already been defined. We propose to characterize the individual stages of the signaling process, and to begin to generate ways to model the process of bacteria-induced host development as a whole.
The proposal will address the following specific objectives and questions: I. Describe the signals, signaling targets and pathways that control the bacteria-induced development of two tissues critical in the specific initiation of symbiosis - What is the role of nitric oxide in the specificity and development of the light organ? - Is the NF-kB/Rel family involved in symbiont-induced signaling and, if so, how? II. Determine the role of stage-specific bacterial structures and activities in development - Are activities of the symbiont's flagellar apparatus essential for host signaling? - What changes in symbiont gene expression are a response to interaction with the host? III. Understand why bacterial bioluminescence is essential to host tissue development - Is a host cryptochrome the photoreceptor in luminescence-induced crypt-cell swelling?
To understand the dynamics of animal-bacterial associations, experimental approaches must be interwoven and coordinated. The two research groups collaborating in this proposal strive to achieve this integration. Execution of most of the experiments outlined in the proposal will rely on microscopic, molecular genetic, and biochemical techniques that have been developed for the study of this system. The proposal builds on past results within productive areas, such as studies of the role of nitric oxide in symbiotic development. In addition, questions of a more exploratory nature will be asked with the aim of opening new experimental paradigms, such as how host NF-kB functions in both tissue development and response to bacterial colonization.