@misc{sternberg_gooding_hotchkiss_leblanc_2010, title={Environmental-endocrine control of reproductive maturation in gastropods: implications for the mechanism of tributyltin-induced imposex in prosobranchs}, volume={19}, ISSN={["1573-3017"]}, DOI={10.1007/s10646-009-0397-z}, abstractNote={Prosobranch snails have been afflicted globally by a condition whereby females develop male sex characteristics, most notably a penis. This condition, known as imposex, has been causally associated with the ubiquitous environmental contaminant tributyltin (TBT). Deduction of the mechanism by which TBT causes imposex has been hampered by the lack of understanding of the normal endocrine regulation of reproductive tract recrudescence in these organisms. We have reviewed the relevant literature on the environmental and endocrine factors that regulate reproductive tract recrudescence, sexual differentiation, and reproduction in gastropods. We provide a cohesive model for the environmental-endocrine regulation of reproduction in these organisms, and use this information to deduce a most likely mechanism by which TBT causes imposex. Photoperiod appears to be the predominant environmental cue that regulates reproductive tract recrudescence. Secondary cues include temperature and nutrition which control the timing of breeding and egg laying. Several hormone products of the central and peripheral nervous systems have been identified that contribute to recrudescence, reproductive behaviors, oocyte maturation and egg laying. Retinoic acid signaling via the retinoid X-receptor (RXR) has shown promise to be a major regulator of reproductive tract recrudescence. Furthermore, TBT has been shown to be a high affinity ligand for the RXR and the RXR ligand 9-cis retinoic acid causes imposex. We propose that TBT causes imposex through the inappropriate activation of this signaling pathway. However, uncertainties remain in our understanding of the environmental-endocrine regulation of reproduction in gastropods. Definitive elucidation of the mechanism of action of TBT awaits resolution of these uncertainties.}, number={1}, journal={ECOTOXICOLOGY}, author={Sternberg, Robin M. and Gooding, Meredith P. and Hotchkiss, Andrew K. and LeBlanc, Gerald A.}, year={2010}, month={Jan}, pages={4–23} }
 @article{gooding_leblanc_2004, title={Seasonal variation in the regulation of testosterone levels in the eastern mud snail (Ilyanassa obsoleta)}, volume={123}, DOI={10.1111/j.1744-7410.2004.tb00158.x}, abstractNote={Abstract.  Some gastropods appear to utilize a strategy for regulating testosterone levels that is atypical of such processes thus far identified in other metazoans. While most animals convert testosterone largely to polar derivatives that are readily eliminated from the organism, the mud snail Ilyanassa obsoleta converts testosterone to apolar testosterone‐fatty acid esters that are retained by the organism. In the present study, we tested the hypothesis that fatty acid esteri‐fication serves to store testosterone and that stored testosterone‐fatty acid ester pools vary through the reproductive cycle of the snail. This hypothesis was tested by 1) modulating total testosterone levels in individual snails and measuring the amount of the hormone stored as the fatty acid ester relative to the amount retained as free steroid and 2) measuring changes in esterified testosterone in a field population of snails during their reproductive cycle. Adult snails were experimentally manipulated to contain from ∼36–300% the level of total testosterone measured in unmanipulated individuals. The amount of testosterone‐fatty acid ester present in these organisms increased in direct proportion to the level of total testosterone, while, free testosterone levels remained relatively constant. These observations suggest that free testosterone levels are regulated in the snail by fatty acid esterification/de‐esterification processes. Among field sampled snails, testosterone existed predominantly in the free, non‐esterified form at the onset and end of the egg laying period. At other times, the majority of testosterone was sequestered as fatty acid esters. This study provides compelling evidence that free testosterone levels in the mud snail are regulated through fatty acid esterification/de‐esterification processes and this regulatory function contributes to seasonal fluctuations in free testosterone levels.}, number={3}, journal={Invertebrate Biology}, author={Gooding, M. P. and LeBlanc, Gerald}, year={2004}, pages={237–243} }
 @article{gooding_wilson_folmar_marcovich_leblanc_2003, title={The biocide tributyltin reduces the accumulation of testosterone as fatty acid esters in the mud snail (Ilyanassa obsoleta)}, volume={111}, ISSN={["0091-6765"]}, DOI={10.1289/ehp.5779}, abstractNote={Imposex, the development of male sex characteristics by female gonochoristic snails, has been documented globally and is causally associated with exposure to the ubiquitous environmental contaminant tributyltin (TBT). Elevated testosterone levels in snails also are associated with TBT, and direct exposure to testosterone has been shown to cause imposex. We discovered previously that the mud snail (Ilyanassa obsoleta)biotransforms and retains excess testosterone primarily as fatty acid esters. The purpose of this study was to determine whether TBT interferes with the esterification of testosterone, resulting in the elevated free (unesterified) testosterone levels associated with imposex. Exposure of snails to environmentally relevant concentrations of TBT (> or = 1.0 ng/L as tin) significantly increased the incidence of imposex. Total (free + esterified) testosterone levels in snails were not altered by TBT; however, free testosterone levels increased with increasing exposure concentration of TBT. TBT-exposed snails were given [14C]]testosterone to measure the production of [14C]testosterone-fatty acid esters. The production of testosterone-fatty acid esters decreased with increasing exposure concentration of TBT. These results indicate that TBT elevates free testosterone levels in snails by decreasing the production or retention of testosterone-fatty acid esters. These findings were confirmed among field-sampled snails where individuals collected from a high-tin-affected site exhibited a greater incidence of imposex, higher free testosterone levels, and lower testosterone-fatty acid ester levels when compared with individuals sampled from a low-tin-affected site. Decreased testosterone-fatty acid esterification among TBT-treated snails was not caused by direct inhibition of the acyl coenzyme A:testosterone acyltransferase (ATAT) enzyme responsible for testosterone esterification, nor by suppressed ATAT protein expression. The target of TBT may be a co-contributor to the testosterone fatty esterification process or a factor in the enhanced hydrolysis of the testosterone-fatty acid pool.}, number={4}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Gooding, MP and Wilson, VS and Folmar, LC and Marcovich, DT and LeBlanc, GA}, year={2003}, month={Apr}, pages={426–430} }
 @article{gooding_leblanc_2001, title={Biotransformation and disposition of testosterone in the eastern mud snail Ilyanassa obsoleta}, volume={122}, ISSN={["0016-6480"]}, DOI={10.1006/gcen.2001.7630}, abstractNote={Elevated testosterone levels have been reported to be associated with imposex (pseudohermaphroditism), the superimposition of male characteristics such as a penis and vas deferens on female gonachoristic snails. Tributyltin (TBT), a marine biocide in anti-fouling paints, is a known causal agent of imposex. Evidence suggests that imposex is elicited by TBT-mediated changes in the biotransformation and disposition of testosterone. To identify potential targets of TBT in gastropod species susceptible to imposex, biotransformation and disposition of testosterone in normal individuals must first be characterized. Nonimposex mud snail, Ilyanassa obsoleta, readily extracted [(14)C]testosterone, added to aqueous media, and converted the testosterone to at least five apolar conjugates designated AP1 through AP5. All were retained by the organisms. No significant amount of [(14)C]testosterone was retained or eliminated as polar metabolites. Following enzymatic hydrolysis of the most abundant metabolite (AP1), free fatty acids and [(14)C]testosterone were liberated. Furthermore, AP1 was produced when homogenized snail tissue was incubated with [(14)C]testosterone and oleoyl coenzyme A or palmitoyl coenzyme A. These results indicate that AP1, which represents over 70% of the testosterone biotransformation products, is a fatty acid ester of testosterone. Apolar metabolites AP2-AP5 might represent testosterone derivatives that are multiply conjugated to fatty acid molecules. Fatty acid conjugates of testosterone have not been previously described in the gastropods. The esterification of testosterone to fatty acids might be a mechanism where by steroid titers are regulated and could represent a target of TBT toxicity.}, number={2}, journal={GENERAL AND COMPARATIVE ENDOCRINOLOGY}, author={Gooding, MP and LeBlanc, GA}, year={2001}, month={May}, pages={172–180} }
 @article{gooding_gallardo_leblanc_1999, title={Imposex in three marine gastropod species in Chile and potential impact on muriciculture}, volume={38}, ISSN={["1879-3363"]}, DOI={10.1016/S0025-326X(99)00167-8}, abstractNote={A survey of imposex was conducted between the Bay of San Vicente, Concepción, Chile (36° 50′) and the Bay of Renocavi, Puerto Montt, Chile (41° 35′), to determine if imposex is occurring in an area of collection and cultivation of the gastropod, Chorus giganteus. Imposex was recorded in three chilean muricids C. giganteus, Xanthochorus cassidiformis and Nucella crassilabrum complex. Percentage of imposex in females sampled ranged from 0% to 100%. The degree of expression of imposex was not so severe as to elicit sterility in the individuals surveyed. Incidence of imposex was as high as 47% in areas of harvest of C. giganteus for reproductive and cultivation studies for commercial production of this species. A six percent incidence of imposex was observed in Nucella proximal to the facility for cultivation of C. giganteus. Gastropods of the genus Nucella are used in other countries to monitor incidence of imposex and have demonstrated sensitivity toward tributyltin (TBT), the associated causal agent. Since sex of individuals in muriciculture is determined by the presence or absence of a penis, imposex may lead to erroneous classification of males and females. The incidence and severity of imposex in C. giganteus and related species may have a negative impact on sustainable cultivation and harvest of gastropods in Chile.}, number={12}, journal={MARINE POLLUTION BULLETIN}, author={Gooding, M and Gallardo, C and Leblanc, G}, year={1999}, month={Dec}, pages={1227–1231} }