PET/CT Imaging of c-Myc Transgenic Mice Identifies the Genotoxic N-Nitroso-Diethylamine as Carcinogen in a Short-Term Cancer Bioassay

Background: More than 100,000 chemicals are in use but have not been tested for their safety. To overcome limitations in the cancer bioassay several alternative testing strategies are explored. The inability to monitor non-invasively onset and progression of disease limits, however, the value of current testing strategies. Here, we report the application of in vivo imaging to a c-Myc transgenic mouse model of liver cancer for the development of a short-term cancer bioassay. Methodology/Principal Findings: mCT and 18 F-FDG mPET were used to detect and quantify tumor lesions after treatment with the genotoxic carcinogen NDEA, the tumor promoting agent BHT or the hepatotoxin paracetamol. Tumor growth was investigated between the ages of 4 to 8.5 months and contrast-enhanced mCT imaging detected liver lesions as well as metastatic spread with high sensitivity and accuracy as confirmed by histopathology. Significant differences in the onset of tumor growth, tumor load and glucose metabolism were observed when the NDEA treatment group was compared with any of the other treatment groups. NDEA treatment of c-Myc transgenic mice significantly accelerated tumor growth and caused metastatic spread of HCC in to lung but this treatment also induced primary lung cancer growth. In contrast, BHT and paracetamol did not promote hepatocarcinogenesis. Conclusions/Significance: The present study evidences the accuracy of in vivo imaging in defining tumor growth, tumor load, lesion number and metastatic spread. Consequently, the application of in vivo imaging techniques to transgeni

Sterility and Gene Expression in Hybrid Males of Xenopus laevis and X. muelleri

BACKGROUND: Reproductive isolation is a defining characteristic of populations that represent unique biological species, yet we know very little about the gene expression basis for reproductive isolation. The advent of powerful molecular biology tools provides the ability to identify genes involved in reproductive isolation and focuses attention on the molecular mechanisms that separate biological species. Herein we quantify the sterility pattern of hybrid males in African Clawed Frogs (Xenopus) and apply microarray analysis of the expression pattern found in testes to identify genes that are misexpressed in hybrid males relative to their two parental species (Xenopus laevis and X. muelleri). METHODOLOGY/PRINCIPAL FINDINGS: Phenotypic characteristics of spermatogenesis in sterile male hybrids (X. laevis x X. muelleri) were examined using a novel sperm assay that allowed quantification of live, dead, and undifferentiated sperm cells, the number of motile vs. immotile sperm, and sperm morphology. Hybrids exhibited a dramatically lower abundance of mature sperm relative to the parental species. Hybrid spermatozoa were larger in size and accompanied by numerous undifferentiated sperm cells. Microarray analysis of gene expression in testes was combined with a correction for sequence divergence derived from genomic hybridizations to identify candidate genes involved in the sterility phenotype. Analysis of the transcriptome revealed a striking asymmetric pattern of misexpression. There were only about 140 genes misexpressed in hybrids compared to X. laevis but nearly 4,000 genes misexpressed in hybrids compared to X. muelleri. CONCLUSIONS/SIGNIFICANCE: Our results provide an important correlation between phenotypic characteristics of sperm and gene expression in sterile hybrid males. The broad pattern of gene misexpression suggests intriguing mechanisms creating the dominance pattern of the X. laevis genome in hybrids. These findings significantly contribute to growing evidence for allelic dominance in hybrids and have implications for the mechanism of species differentiation at the transcriptome level