Meeting Abstract
Iron presents a conundrum to animals: it is necessary for many physiological processes but free molecules of iron catalyze production of reactive oxygen species (ROS). As a consequence, animals tightly regulate the uptake and transport of iron. In most cases, animals use iron in its molecular form, but some animals create iron-mineralized structures. Chitons (Mollusca; Polyplacophora) feed by scraping algae from rocks with rows of teeth carried on a tongue-like radula. Chitons coat their teeth with iron oxides, most notably magnetite, and they constantly produce new rows of teeth. Crystalline structures such as magnetite require specific physiological conditions to grow. To characterize how local physiological conditions vary across the chiton radula, we measured pH, reactive oxygen species, and iron distribution across the tooth rows in the radula of A. granulata. Using a pH-sensitive dye, we discovered a dramatic change in pH across the radula: in contrast to a typical physiological pH ~7 across other tissues, a narrow band of 6 tooth rows was pH 4. To better understand how chitons regulate pH across the radula, we measured the activity of carbonic anhydrase and found that the region of highest activity matched the region of lowest pH. Using a ROS-sensitive fluorescent dye, we found higher amounts of ROS in the low-pH band of the radula, likely due to the presence of higher amounts of free iron. The localized patterns we observed indicate that tightly regulated physiological conditions contribute to the mineralization of iron in the chiton radula. This work increases our understanding of how chitons mineralize teeth with magnetite in spite of the toxicity of free iron and contributes to an understanding of how animals balance iron’s utility with its potential toxicity.
