To provide context for the diversifications of archosaurs, the group that includes crocodilians, dinosaurs and birds, we generated draft genomes of three crocodilians, Alligator mississippiensis (the American alligator), Crocodylus porosus (the saltwater crocodile), and Gavialis gangeticus (the Indian gharial). We observed an exceptionally slow rate of genome evolution within crocodilians at all levels, including nucleotide substitutions, indels, transposable element content and movement, gene family evolution, and chromosomal synteny. When placed within the context of related taxa including birds and turtles, this suggests that the common ancestor of all of these taxa also exhibited slow genome evolution and that the relatively rapid evolution of bird genomes represents an autapomorphy within that clade. The data also provided the opportunity to analyze heterozygosity in crocodilians, which indicates a likely reduction in population size for all three taxa through the Pleistocene. Finally, these new data combined with newly published bird genomes allowed us to reconstruct the partial genome of the common ancestor of archosaurs providing a tool to investigate the genetic starting material of crocodilians, birds, and dinosaurs.

Chicken repeat 1 (CR1) retroposons are long interspersed elements (LINEs) that are ubiquitous within amniote genomes and constitute the most abundant family of transposed elements in birds, crocodilians, turtles, and snakes. They are also present in mammalian genomes, where they reside as numerous relics of ancient retroposition events. Yet, despite their relevance for understanding amniote genome evolution, the diversity and evolution of CR1 elements has never been studied on an amniote-wide level. We reconstruct the temporal and quantitative activity of CR1 subfamilies via presence/absence analyses across crocodilian phylogeny and comparative analyses of 12 crocodilian genomes, revealing relative genomic stasis of retroposition during genome evolution of extant Crocodylia. Our large-scale phylogenetic analysis of amniote CR1 subfamilies suggests the presence of at least seven ancient CR1 lineages in the amniote ancestor; and amniote-wide analyses of CR1 successions and quantities reveal differential retention (presence of ancient relics or recent activity) of these CR1 lineages across amniote genome evolution. Interestingly, birds and lepidosaurs retained the fewest ancient CR1 lineages among amniotes and also exhibit smaller genome sizes. Our study is the first to analyze CR1 evolution in a genome-wide and amniote-wide context and the data strongly suggest that the ancestral amniote genome contained myriad CR1 elements from multiple ancient lineages, and remnants of these are still detectable in the relatively stable genomes of crocodilians and turtles. Early mammalian genome evolution was thus characterized by a drastic shift from CR1 prevalence to dominance and hyperactivity of L2 LINEs in monotremes and L1 LINEs in therians.

The availability of complete mitochondrial genome (mtgenome) data for Diptera, one of the largest metazoan orders, in public databases is limited. The advent of high throughput sequencing technology provides the potential to generate mtgenomes for many species affordably and quickly. However, these technologies need to be validated for dipterans as the members of this clade play important economic and research roles. Illumina and 454 sequencing platforms are widely used in genomic research involving non-model organisms. The Illumina platform has already been utilized for generating mitochondrial genomes without using conventional long range PCR for insects whereas the power of 454 sequencing for generating mitochondrial genome drafts without PCR has not yet been validated for insects. Thus, this study examines the utility of 454 sequencing approach for dipteran mtgenomic research. We generated complete or nearly complete mitochondrial genomes for Cochliomyia hominivorax, Haematobia irritans, Phormia regina and Sarcophaga crassipalpis using a 454 sequencing approach. Comparisons between newly obtained and existing assemblies for C. hominivorax and H. irritans revealed no major discrepancies and verified the utility of 454 sequencing for dipteran mitochondrial genomes. We also report the complete mitochondrial sequences for two forensically important flies, P. regina and S. crassipalpis, which could be used to provide useful information to legal personnel. Comparative analyses revealed that dipterans follow similar codon usage and nucleotide biases that could be due to mutational and selection pressures. This study illustrates the utility of 454 sequencing to obtain complete mitochondrial genomes for dipterans without the aid of conventional molecular techniques such as PCR and cloning and validates this method of mtgenome sequencing in arthropods.

BACKGROUND African-Americans (Afr-Amr) with head and neck squamous cell carcinoma (HNSCC) have a lower survival rate than Caucasians (Cau). This study investigates the functional importance of ancestry-informative SNPs in HNSCC and also examines the effect of functionally important genetic elements on racial disparities in HNSCC survival. METHODS Ancestry-informative SNPs, RNAseq, methylation, and copy number variation data for 316 oral cavity and laryngeal cancer patients were analyzed across 178 DNA repair genes. The results of eQTL analyses were also replicated using a Gene Expression Omnibus (GEO) dataset. The effects of eQTLs on overall survival (OS) and disease-free survival (DFS) were evaluated. RESULTS Five ancestry-related SNPs were identified as cis-eQTLs in the POLB gene (FDR<0.01). The homozygous/ heterozygous genotypes containing the Afr-allele showed higher POLB expression relative to the homozygous Cau-allele genotype (P<0.001). A replication study using a GEO dataset validated all five eQTLs, also showing a statistically significant difference in POLB expression based on genetic ancestry (P=0.002). An association was observed between these eQTLs and OS (P<0.037; FDR<0.0363) as well as DFS of oral cavity and laryngeal cancer patients treated with platinum-based chemotherapy and/or radiotherapy (P=0.018 to 0.0629; FDR<0.079). Genotypes containing the Afr-allele were associated with poor OS/DFS compared to homozygous genotypes harboring the Cau-allele. CONCLUSIONS Our analyses show that ancestry-related alleles could act as eQTLs in HNSCC and support the association of ancestry-related genetic factors with survival disparity in patients diagnosed with oral cavity and laryngeal cancer.