The symbiosis that develops between the sepiolid squid, Euprymna scolopes, and the marine luminous bacterium, Vibrio fischeri, has proven to be an effective model system with which to examine the development of an animal/bacterial mutualism. The initiation and maintenance of a bacterial infection in the juveniile squid that subsequently results in the complex light-emitting organ of the mature squid provides a rare opportunity to discover the significance of interspecies interactions in the control of organ morphogenesis, immunological response, bacterial/host recognition, and the consequences of other developmentally regulated signal processes. It exhibits strain level specificity, presents the accessibility of molecular genetics, includes a raped and complex program of developmental events in the host and symbiont, and allows comparisons between axenic and symbiotic juvenile tissue differentiation. This proposal will focus specifically upon: 1) the temporal characteristics of symbiosis induced morphogenesis; 2) the cellular basis for morphological change of the light organ; 3) the expression and symbiotic roles of indicator proteins; 4) the identification of specificity determinants and colonziation factors; 5) bacterial stress response as signal for symbiotic differentiation; and 6) the temporal and spatial patterns of symbiont gene expression within the developing light organ.
