Meeting Abstract
The number of human-made chemicals present in the environment has increased dramatically in the past century, and while we are only beginning to appreciate how these compounds affect developing organisms, the reality is that vertebrate eggs have always developed in environments that contained natural chemicals. If any of these chemicals were to disrupt embryonic development, this should select for a mechanism to prevent embryonic exposure. Fortunately, most vertebrates possess a suite of enzymes that confer some ability to metabolize environmental chemicals, whether natural or human-made. Here we present evidence that red-eared slider turtle eggs possess enzymes that are capable of metabolizing a common human-made chemical, bisphenol-A (BPA), as it passes from the external environment through the eggshell. Importantly, metabolism does not take place if BPA is injected directly into the yolk, indicating that these enzymes are located in or near outer membranes, and as metabolism is taking place immediately after oviposition, it suggests these enzymes are of maternal origin. Given the recent origin of BPA, these enzymes likely represent a general mechanism for modulating embryonic exposure to a variety of environmental chemicals, and not BPA specifically. These results have important implications for studies of environmental chemicals, as the ability of embryos to respond to exposure to chemicals from outside the egg may be vastly different than exposure to maternally derived chemicals transferred via the yolk. Additionally, variation in maternal enzyme levels, and any contributions to offspring, may provide an opportunity for populations to rapidly respond to exposure to a novel endocrine disruptor.
