Margaret J. McFall-Ngai

Our research program has two major focuses: 1) host-bacterial symbiosis; and 2) the 'design' of tissues that interact with light. The experimental strategy for both areas of research relies on methods that have been developed for the study of the squid-vibrio association over the past 30+ years. The projects on symbiosis have centered on the development of the squid-vibrio association as a model for the establishment and maintenance of the chronic colonization of animal epithelia by Gram-negative bacteria. This type of association is perhaps the most common in the animal kingdom. Using this model, we explore critical questions about the phenomenon of beneficial animal-microbe associations, including: 1) With each generation, how does the animal harvest the often-rare symbiont from the environment upon birth or hatching? 2) How do the host and symbiont recognize one another to establish a specific association? 3) How does the bacterial partner influence the developmental program of the host? 4) How is stability achieved and maintained in the mature association? 5) What are the principal differences between how an animal interacts with pathogenic bacterial species and beneficial ones?

Figure illustrates V. fischeri (green) in host tissues (red – cytoskeleton; blue – nuclei)

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Figure illustrates V. fischeri (green) in host tissues (red – cytoskeleton; blue – nuclei)

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In our second research focus, the lab studies the 'design' of tissues that interact with light. The squid-vibrio symbiosis is an association in which luminous bacteria live in the animal host tissues. In such systems, evolutionary tinkering has led to the formation of an organ that bears remarkable similarity to the eye, with cornea, lens, choroid, iris, and tapetum analogues. We have studied this convergence at the biochemical and molecular levels. The light organ expresses genes associated with eye specification during development, and the organ produces the principal proteins of the visual transduction cascade. Recently we showed that the colonization of the light organ not only affects gene expression of the light-organ tissues, but also influences gene expression in the eye, a behavior that is abrogated by colonization of the organ with mutants of the symbiont defective in light production. As part of this effort, our laboratory discovered the first protein-based animal reflector, which forms a tapetum-like structure in the light organ. This protein, which we called reflectin, is now studied by several labs for its properties as a strong proton conductor and an unusual stability biomolecule, features being exploited for applications in industry and biomedicine. Currently, the lab is collaborating with engineers and imagers to define the cell biology of reflector-platelet synthesis and the influence of symbiosis on this process.

Reflectin proteins in platelets of the light organ reflector. Image M. Ladinsky

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Reflectin proteins in platelets of the light organ reflector. Image M. Ladinsky

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