Joseph P. Gyekis

Dose-dependent incidence of hepatic tumors in adult mice following perinatal exposure to bisphenol A.

Background: Bisphenol A (BPA) is a high production volume chemical with hormone-like properties that has been implicated as a potential carcinogen. Early-life exposure has been linked to increased risk for precancerous lesions in mammary and prostate glands and the uterus, but no prior study has shown a significant association between BPA exposure and cancer development. Objective: We explored the effects of BPA exposure during gestation and lactation on adult incidence of hepatic tumors in mice. Methods: Isogenic mice were perinatally exposed to BPA through maternal diets containing one of four environmentally relevant doses of BPA (0, 50 ng, 50 μg, or 50 mg per kilogram of diet), and we followed approximately one male and one female per litter until they were 10 months of age. Animals were tested for known risk factors for hepatocellular carcinoma, including bacterial and viral infections. Results: We found dose-dependent incidence of hepatic tumors in 10-month-old BPA-exposed mice. Of the offspring examined, 23% presented with hepatic tumors or preneoplastic lesions. We observed a statistically significant dose–response relationship, with an odds ratio for neoplastic and preneoplastic lesions of 7.23 (95% CI: 3.23, 16.17) for mice exposed to 50 mg BPA/kg diet compared with unexposed controls. Observed early disease onset, absence of bacterial or viral infection, and lack of characteristic sexual dimorphism in tumor incidence support a nonclassical etiology. Conclusions: To our knowledge, this is the first report of a statistically significant association between BPA exposure and frank tumors in any organ. Our results link early-life exposure to BPA with the development of hepatic tumors in rodents, and have potential implications for human health and disease. Citation: Weinhouse C, Anderson OS, Bergin IL, Vandenbergh DJ, Gyekis JP, Dingman MA, Yang J, Dolinoy DC. 2014. Dose-dependent incidence of hepatic tumors in adult mice following perinatal exposure to bisphenol A. Environ Health Perspect 122:485–491; http://dx.doi.org/10.1289/ehp.1307449

No association of genetic variants in BDNF with major depression: A meta- and gene-based analysis†‡

Major depressive disorder (MDD) is a complex psychiatric condition with strong genetic predisposition. The association of MDD with genetic polymorphisms, such as Val66Met (rs6265), in the brain derived neurotrophic factor (BDNF), have been reported in many studies and the results were conflicting. In this study, we performed a systematic literature search and conducted random‐effects meta‐analysis to evaluate genetic variants in BDNF with MDD. A gene‐based analysis was also conducted to investigate the cumulative effects of genetic polymorphisms in BDNF. A total of 28 studies from 26 published articles were included in our analysis. Meta‐analysis yielded an estimated odds ratio (OR) of 0.96 (95% CI: 0.89–1.05; P = 0.402) for Val66Met (rs6265), 0.83 (95% CI: 0.67–1.04; P = 0.103) for 11757C/G, 1.16 (95% CI: 0.74–1.82; P = 0.527) for 270T/C, 1.03 (95% CI: 0.18–5.75; P = 0.974) for 712A/G and 0.98 (95% CI: 0.85–1.14; P = 0.831) for rs988748. The gene‐based analysis indicated that BDNF is not associated with MDD (P > 0.21). Our updated meta‐ and novel gene‐based analyses provide no evidence of the association of BDNF with major depression.

Activity-related behaviors in the hole-board predict nicotine consumption in C57B6 mice perinatally exposed to nicotine

Hole-board behaviors of adolescent C57B/6 mice that had been exposed to nicotine during gestation and suckling were evaluated on postnatal days 34-36. Rearing on all three trials significantly predicted higher nicotine intake on a two-bottle choice test administered from days 37-42. For head pokes, there was a weak trend for lower head poking in the first trial to be predictive of higher nicotine intake. Locomotor activity only predicted higher nicotine consumption on the third trial. These results show that hole-board behaviors predict subsequent nicotine intake in mice exposed to nicotine perinatally, especially after habituation to the apparatus.

Discovery and refinement of muscle weight QTLs in B6 × D2 advanced intercross mice

The genes underlying variation in skeletal muscle mass are poorly understood. Although many quantitative trait loci (QTLs) have been mapped in crosses of mouse strains, the limited resolution inherent in these conventional studies has made it difficult to reliably pinpoint the causal genetic variants. The accumulated recombination events in an advanced intercross line (AIL), in which mice from two inbred strains are mated at random for several generations, can improve mapping resolution. We demonstrate these advancements in mapping QTLs for hindlimb muscle weights in an AIL (n = 832) of the C57BL/6J (B6) and DBA/2J (D2) strains, generations F8-F13. We mapped muscle weight QTLs using the high-density MegaMUGA SNP panel. The QTLs highlight the shared genetic architecture of four hindlimb muscles and suggest that the genetic contributions to muscle variation are substantially different in males and females, at least in the B6D2 lineage. Out of the 15 muscle weight QTLs identified in the AIL, nine overlapped the genomic regions discovered in an earlier B6D2 F2 intercross. Mapping resolution, however, was substantially improved in our study to a median QTL interval of 12.5 Mb. Subsequent sequence analysis of the QTL regions revealed 20 genes with nonsense or potentially damaging missense mutations. Further refinement of the muscle weight QTLs using additional functional information, such as gene expression differences between alleles, will be important for discerning the causal genes.

Genetic and Maternal Effects on Offspring Mortality in Mice

Trade-offs occur when two traits have opposing fitness effects such that positive selection on one trait is constrained by the negative fitness consequences of the other trait. To understand why trade-off may arise we need to study the genetic and non-genetic factors that influence associated traits because these may respond differently to selective pressure. Research into trade-offs has largely focused on the genetic basis of associated traits, yet both maternal effects and epigenetic effects have recently been shown to affect life history traits that play a role in trade-offs. In this study, we analyze genetic, epigenetic and life-history predictors of one of the most important trade-offs, that between offspring number and offspring mortality. Using a large-scale 3-generational intercross between two divergent mouse lines C57BL/6J and DBA/2J, we show that litter size differences between these lines, although significant, are surprisingly not the most important predictors of mortality. Offspring genotype, maternal effects and their interactions are the most influential factors determining mortality. We found significant paternal effects suggesting an important influence of paternal care or potentially the role of imprinted genes. Perhaps contrary to expectations our results further show that the trade-off between offspring number and mortality is not just a simple function of the two factors yielding, on average, an ‘optimal’ litter size at weaning. Indeed if one focused on litter size and mortality alone, the slope of relationship is the same for the two lines, yet they differ in the number of young at weaning. Our study reveals that a perceived trade-off between two traits is governed by a more complex set of interactions between genetic and non-genetic effects.

Genetic architecture for hole‐board behaviors across substantial time intervals in young, middle‐aged and old mice

A quantitative trait locus (QTL) analysis of behaviors across the life span was conducted in F2 mice from a C57BL/6J × DBA/2J cross and 22 BXD recombinant inbred (RI) strains. Mice of three age groups were tested in a hole‐board apparatus for 3 min on three occasions ∼1 month apart (average age at test 150, 450 and 750 days, ∼400 mice per group, divided equally by sex). Quantitative trait loci with small effect size were found on 11 chromosomes for hole‐board activity (Hbact) and hole‐board rearing (Hbrear). Analysis of 22 RI strains tested at 150 and 450 days of age found only suggestive linkage, with four QTL for Hbact overlapping with those from the F2 analysis. There was a significant phenotypic correlation between Hbact and Hbrear (∼0.55–0.69) and substantial commonality among QTL for the two behaviors. QTL analyses of head‐pokes (HP) and fecal boli (FB) only identified QTL at the suggestive level of significance. Age accounted for ∼15% of the phenotypic variance (sex ∼3%), and there were genotype by age interactions at ∼25% of the Hbact and Hbrear QTL. Quantitative trait loci for Hbrear were relatively stable across the three measurement occasions (those for Hbact somewhat less so), although mean levels of each index declined markedly comparing the first to subsequent trials. Considered as a whole, the polygenic system influencing exploratory behaviors accounts for approximately the same amount of phenotypic variance as age (within the range studied), is stable across substantial periods of time, and acts, for the most part, independently of age and sex.

Cardiovascular Reactivity and Recovery

Acute mental stress leads to transient blood pressure (BP) and heart rate elevations, and these are risk factors for the development of hypertension and heart disease. A corollary is that individuals particularly prone to strong cardiovascular reactivity (CVR) in the lab may experience these responses frequently enough in daily life for these elevations in BP to directly contribute to tissue damage and the occurrence of cardiovascular disease events. In this article, we provide a guide to the methodology of CVR studies. Following a brief review of the empirical literature, we discuss issues regarding the design, implementation, and analysis of reactivity studies.

Replication and discovery of musculoskeletal QTLs in LG/J and SM/J advanced intercross lines

The genetics underlying variation in health‐related musculoskeletal phenotypes can be investigated in a mouse model. Quantitative trait loci (QTLs) affecting musculoskeletal traits in the LG/J and SM/J strain lineage remain to be refined and corroborated. The aim of this study was to map muscle and bone traits in males (n = 506) of the 50th filial generation of advanced intercross lines (LG/SM AIL) derived from the two strains. Genetic contribution to variation in all musculoskeletal traits was confirmed; the SNP heritability of muscle mass ranged between 0.46 and 0.56; and the SNP heritability of tibia length was 0.40. We used two analytical software, GEMMA and QTLRel, to map the underlying QTLs. GEMMA required substantially less computation and recovered all the QTLs identified by QTLRel. Seven significant QTLs were identified for muscle weight (Chr 1, 7, 11, 12, 13, 15, and 16), and two for tibia length, (Chr 1 and 13). Each QTL explained 4–5% of phenotypic variation. One muscle and both bone loci replicated previous findings; the remaining six were novel. Positional candidates for the replicated QTLs were prioritized based on in silico analyses and gene expression in muscle tissue. In summary, we replicated existing QTLs and identified novel QTLs affecting muscle weight, and replicated bone length QTLs in LG/SM AIL males. Heritability estimates substantially exceed the cumulative effect of the QTLs, hence a richer genetic architecture contributing to muscle and bone variability could be uncovered with a larger sample size.

Wetland-Riparian Birds of the Mid-Atlantic Region

Wetland-riparian birds are conspicuous in the Mid-Atlantic Region (MAR), but sometimes use aquatic habitats beyond what is typical for waterfowl, waterbirds, and shorebirds. Over the past two decades, Riparia conducted studies to determine the importance of wetlands and riparian corridors as habitats for birds covering the range from obligate to facultative users. We sampled wetlands used by wood ducks and other waterfowl species common to the Appalachians. We surveyed lakes and their associated fringing wetlands and riparian edges in the glaciated Pocono region. Songbirds were sampled along human disturbance gradients from wetlands into adjacent uplands. In addition, our work developed and tested an innovative way to consider biodiversity through the component life history traits of species in communities—a guild-based approach. The quantification of differences in the life history composition of different communities led to the development of a class of ecological indicators called the Bird Community Index (BCI). In this chapter, we trace the development and application of the BCI and its derivatives, including a multi-metric Regional Index of Biological Integrity for forest riparian ecosystems (RIBI). The chapter progresses through studies of birds using wetland habitats, beginning with obligate species and progressing through facultative users. We conclude with a summary of projects and monitoring protocols that use the BCI for ecological assessment, and a description of emerging issues that make such assessments a conservation imperative for the MAR.