Correction to: Gene-environment interaction between lead and Apolipoprotein E4 causes cognitive behavior deficits in mice.

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Lead exposure in late adolescence through adulthood impairs short-term spatial memory and the neuronal differentiation of adult-born cells in C57BL/6 male mice.

Lead is a neurotoxicant of immense public health importance. Epidemiology studies suggest that heavy metal exposure may be associated with an increased risk of cognitive decline, yet few studies to date have assessed the effect of adult lead exposure on cognitive behavior in animal models. Here, we exposed 6-week-old male C57BL/6 mice to 0.2% lead acetate via drinking water for 12 weeks starting at 6 weeks of age and then assessed for deficits in hippocampus-dependent spatial memory and impairment of adult hippocampal neurogenesis. Lead did not cause locomotor deficits or anxiety in the open field test. However, we found that adult, subchronic lead exposure was sufficient to cause deficits in spatial short-term memory and these deficits persisted through at least 2 months post-lead exposure. Furthermore, we observed that lead-treated mice had fewer adult-born, mature neurons in the dentate gyrus of the hippocampus compared to control animals, suggesting that lead exposure during adolescence and adulthood may impair the neuronal differentiation of adult-born cells. These data suggest that adult lead exposure is sufficient to cause persistent deficits in spatial short-term memory and impair key processes in adult hippocampal neurogenesis.

Cadmium impairs the survival and proliferation of cultured adult subventricular neural stem cells through activation of the JNK and p38 MAP kinases.

Cadmium (Cd) is a heavy metal with a long biological half-life in humans and is recognized as a toxic pollutant. Cd is also a potential neurotoxicant and its exposure is associated with olfactory impairment in humans. However, the molecular and cellular mechanisms of Cd neurotoxicity are not well defined. Adult neurogenesis is a process that generates functional neurons from adult neural stem/progenitor cells (aNPCs). It occurs in specific regions of the adult brain including the subventricular zone (SVZ) along the lateral ventricles in mammals, a process that is critical for olfaction. Various external stimuli can modulate adult neurogenesis and the effect of neurotoxicants on adult neurogenesis is just beginning to be elucidated. Since Cd exposure can impair olfaction in humans, the goal of this study is to investigate the effects of Cd on SVZ adult neurogenesis and underlying mechanisms using primary cultured SVZ-aNPCs. In this study, we report that low-level Cd exposure decreases cell number, induces apoptosis, and inhibits cell proliferation in SVZ-aNPCs. Furthermore, Cd exposure significantly increases phosphorylation of c-Jun NH2-terminal kinase (JNK), and p38 MAP kinase in these cells, indicative of JNK and p38 activation. Pharmacological inhibition of JNK or p38 MAPK kinases attenuated Cd-induced cell loss and apoptosis. Cd treatment did not cause cell loss or apoptosis in SVZ-aNPCs prepared from transgenic mice null for the neural-specific JNK3 isoform. These data suggest a critical role for p38 and JNK3 MAP kinases in Cd neurotoxicity. These results are, to our knowledge, the first demonstration that Cd impairs SVZ adult neurogenesis in vitro, which may contribute to its neurotoxicity in olfaction.

Gene-environment interaction between lead and Apolipoprotein E4 causes cognitive behavior deficits in mice.

BACKGROUND: Alzheimer's disease (AD) is characterized by progressive cognitive decline and memory loss. Environmental factors and gene-environment interactions (GXE) may increase AD risk, accelerate cognitive decline, and impair learning and memory. However, there is currently little direct evidence supporting this hypothesis. METHODS: In this study, we assessed for a GXE between lead and ApoE4 on cognitive behavior using transgenic knock-in (KI) mice that express the human Apolipoprotein E4 allele (ApoE4-KI) or Apolipoprotein E3 allele (ApoE3-KI). We exposed 8-week-old male and female ApoE3-KI and ApoE4-KI mice to 0.2% lead acetate via drinking water for 12 weeks and assessed for cognitive behavior deficits during and after the lead exposure. In addition, we exposed a second (cellular) cohort of animals to lead and assessed for changes in adult hippocampal neurogenesis as a potential underlying mechanism for lead-induced learning and memory deficits. RESULTS: In the behavior cohort, we found that lead reduced contextual fear memory in all animals; however, this decrease was greatest and statistically significant only in lead-treated ApoE4-KI females. Similarly, only lead-treated ApoE4-KI females exhibited a significant decrease in spontaneous alternation in the T-maze. Furthermore, all lead-treated animals developed persistent spatial working memory deficits in the novel object location test, and this deficit manifested earlier in ApoE4-KI mice, with female ApoE4-KI mice exhibiting the earliest deficit onset. In the cellular cohort, we observed that the maturation, differentiation, and dendritic development of adult-born neurons in the hippocampus was selectively impaired in lead-treated female ApoE4-KI mice. CONCLUSIONS: These data suggest that GXE between ApoE4 and lead exposure may contribute to cognitive impairment and that impaired adult hippocampal neurogenesis may contribute to these deficits in cognitive behavior. Together, these data suggest a role for GXE and sex differences in AD risk.

Rapid recombination mapping for high-throughput genetic screens in Drosophila.

Mutagenesis screens are a staple of classical genetics. Chemical-induced mutations, however, are often difficult and time-consuming to identify. Here, we report that recombination analysis with pairs of dominant visible markers provides a rapid and reliable strategy to map mutations in Drosophila melanogaster. This method requires only two generations and a total of six crosses in vials to estimate the genetic map position of the responsible lesion with high accuracy. This genetic map position can then be reliably used to identify the mutated gene through complementation testing with an average of nine deficiencies and Sanger sequencing. We have used this approach to successfully map a collection of mutations from an ethyl methanesulfonate-based mutagenesis screen on the third chromosome. We propose that this method also may be used in conjunction with whole-genome sequencing, particularly when multiple independent alleles of the mutated locus are not available. By facilitating the rapid identification of mutated genes, our mapping strategy removes a primary obstacle to the widespread use of powerful chemical mutagenesis screens to understand fundamental biological phenomena.