KOROPATNICK, T; KIMBELL, J. R.; MCFALL-NGAI, M. J.; University of Hawaii, Honolulu: Bacteria-induced loss of ciliated epithelia: bacterial signal factors, hemocytes, and the light organ of a squid

The loss of a ciliated epithelium is a common event during the metamorphosis of marine invertebrate larvae; however few studies have explored the underlying mechanisms. The squid Euprymna scolopes possesses a light organ which, upon inoculation with the bioluminescent bacterial symbiont Vibrio fischeri, will undergo metamorphosis involving the regression of a pair of elaborate ciliated epithelial fields (CEF). The CEF are involved in gathering the symbionts from the environment through ciliary motion and mucus secretion. The symbionts then migrate into the light organ and colonize epithelium-lined crypts, some distance from the superficial CEF. Previously we showed that light organ morphogenesis involves widespread cell death in the ciliated epithelia, and infiltration of host blood cells (hemocytes). Two bacterial envelope components, lipopolysaccharide and peptidoglycan, induced the complete morphogenic program. The present study used confocal microscopy to explore the cellular interactions leading to CEF regression. An examination of the temporal and spatial pattern of hemocyte migration suggests that hemocytes specifically infiltrate the morphogenic CEF, and the initial signal for migration occurs prior to crypt colonization, while the bacteria are gathering in mucus secreted by the CEF. However, data suggest that hemocyte migration is not sufficient to induce CEF regression, suggesting an additional signal is required for complete regression to occur. This signal involves the down-regulation of nitric oxide synthase in cells of the CEF, and a change in gene expression of the migrant hemocytes. Funded by NSF IBN0211738, NIH AIR0150661, and a Canadian NSERC scholarship to T. Koropatnick.