Thirty years ago, Francois Jacob published an essay in which he asserted that evolutionary innovation, i.e., the emergence of novel form and function over time, is the result of 'tinkering', or the creation of novelty from preexisting characters. This concept has been applied to a variety of levels of biological organization, and organs that interact with light, i.e., eyes and photophores, offer a striking example of this phenomenon. Eyes and photophores are very similar anatomically, although the former receives and the latter emits light. Both organs have dioptrics to modify the light with which they interact (e.g., corneas, lenses, irises, reflectors, etc.). The photophore of the Hawaiian bobtail squid Euprymna scolopes is luminous by virtue of its harboring a pure culture of the luminous bacterium Vibrio fischeri. Earlier studies of this system demonstrated that the lenses and reflectors achieve their structural role by using the same biomolecules in both the eyes and photophores. As the two organs have different functions, it was unexpected that the biochemical convergence would go beyond these dioptrics. However, a preliminary examination of the molecular signature of the light organ suggests that the convergence extends more deeply. Specifically, studies of genes expressed in the E. scolopes photophore demonstrate that it expresses many of the very same genes involved in the visual transduction cascade, i.e., genes expressed in the retina to respond to light. These findings may address an age-old question: " How do bioluminescent animals 'see' their own light so that they can modulate its emission, when the photophore is rarely positioned to be perceived by the eye?" The preliminary data would suggest that photophores perceived their own light directly. The goal of the present work is to begin the characterization of the light-sensing of the squid photophore, addressing three specific aims: 1) to define where in the host tissues that these photoreceptive biomolecules occur; 2) to determine whether interactions of the juvenile host squid with the light-emitting bacteria during development of the symbiosis affect the expression of these biomolecules; and, 3) to characterize the dynamics of these genes over the day-night cycle. These aims will be accomplished by relying on methods that have been developed for the study of the squid-vibrio symbiosis over the last 18 years. Specifically, molecular biology, biochemistry, and confocal and electron microscopy, as well as bacterial genetics will be used to manipulate the system experimentally and analyze these manipulations. The study of the similarities and differences in eyes and photophores will provide biologists with a unique window into how animals can 'tinker' with genes, proteins, cells and tissues to recruit an array of components into a new use. The team that will work to address these issues will include graduate, undergraduate and high school students. The PI's laboratory recruits high school students through Madison's Promega High School Internship Program. In addition to the participating undergraduates here at U Wisconsin, the PI recruits undergraduates from minority institutions for a summer program sponsored by the Howard Hughes Medical Institutes. In this program, the students participate in the UW Wisconsin Program for Scientific Teaching. Students from historically minority institutions work with the PIs graduate students and postdocs, an arrangement that provides a high quality educational experience for the trainee, as well as an intensive teaching experience for the members of the PI's laboratory.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Elizabeth Cropper
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University of Wisconsin Madison
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