br Introduction Arsenic is a well known toxic metalloid and

Introduction Arsenic is a well-known toxic metalloid, and both a naturally occurring and anthropogenic environmental contaminant (Hughes et al., 2011). As such, arsenic levels are regulated in public drinking water supplies in the US and other countries. In accordance with World Health Organization guidelines, the maximum contaminant level (MCL) for arsenic set by the US Environmental Protection Agency (EPA) is 10μg/L. However, in some parts of the world, arsenic contamination of drinking water can reach several thousand micrograms per liter (Nordstrom, 2002). Ingestion of such highly contaminated water by pregnant women, leading to in utero arsenic exposure of the developing fetus, is associated with several adverse birth conditions, including low birth weight (Huyck et al., 2007; Llanos and Ronco, 2009; Rahman et al., 2009; Xu et al., 2011), increased risk of infection (Rahman et al., 2011), and spontaneous abortion and infant mortality (Myers et al., 2010; Sohel et al., 2010), as well as increased risk of certain diseases in later life (reviewed in (Farzan et al., 2013)). Less is understood about lower exposure levels, despite their relevance to millions of people worldwide (Nordstrom, 2002). Additionally, while there is evidence to suggest that the response to in utero arsenic exposure varies by fetal sex (Hamadani et al., 2011; Raqib et al., 2009; Xu et al., 2011), the molecular basis for such differences is unknown. Therefore, there is an urgent need to characterize the effects of in utero arsenic at common exposure levels, in a manner that accounts for fetal sex, in order to prevent and treat adverse health outcomes in at-risk populations. With this TIC10 Supplier aim in mind, the current study was performed on a cohort of pregnant women who were exposed to arsenic in drinking water at levels that span above and below the current US MCL. Embryonic development is a highly regulated process that involves numerous biological mechanisms, many of which are controlled by three major developmental signaling pathways: HEDGEHOG (HH), NOTCH and WNT (Clevers, 2006; Briscoe and Therond, 2013; Hori et al., 2013). Cells receiving these signals undergo proliferation, differentiation, and apoptosis, allowing the formation of sophisticated structures and patterns. Activation of each of these signal transduction cascades leads to the transcriptional regulation of a particular set of target genes. These three signaling pathways are also involved in the self-renewal of tissue-specific stem cells that drive organ development and maintain tissue homeostasis in the adult. These stem cells often exhibit high-level expression of “stemness” genes (Boiani and Scholer, 2005). During development, there are extensive cooperative and antagonistic interactions between these pathways, which ultimately determine cell fate. In keeping with their roles in cellular differentiation and embryogenesis, mutations in components of the HH, NOTCH or WNT pathways lead to human developmental disorders. For example, holoprosencephaly (HPE), a birth defect that affects the formation of midline structures and causes facial defects including cleft lip, often results from loss-of-function mutations in one allele of the HH family member SONIC HEDGEHOG (SHH) (Belloni et al., 1996; Roessler et al., 1996). This example underscores the susceptibility of humans to alterations in the activity of these signaling pathways. Although severe disruptions of these developmental pathways in humans likely lead to spontaneous abortion, stillbirth, or distinct birth defects, more subtle alterations in pathway activity, such as those resulting from environmental exposures, may also perturb fetal development and impact long-term health. In this study of a US pregnancy cohort, we sought to identify pivotal developmental genes whose expression in fetal placenta associated with common levels of arsenic exposure. The placenta is a specialized organ that is critical for normal fetal development and survival. In addition, the fetal portion of the placenta shares its genotype and environment with the fetus proper, and so may be viewed as a sentinel for the fetus that can be analyzed in a non-invasive manner. We also examined the association of our candidate developmental genes with infant birth weight, the outcome of fetal growth, which is one important aspect of fetal development. We report here that the placental expression of several key developmental genes associates with in utero arsenic exposure, and further, that many of these genes associate with arsenic in a fetal sex-specific manner. Moreover, we found that expression of the HH pathway gene GLI3 was negatively associated with arsenic exposure but positively associated with birth weight among females. This observation suggests a model whereby in utero arsenic exposure of the female fetus results in reduced placental and possibly fetal GLI3 expression, which in turn leads to reduced birth weight.