Complete mitochondrial genome of the Eurasian flying squirrel Pteromys volans (Sciuromorpha, Sciuridae) and revision of rodent phylogeny

Complete mitogenomes of Turkish tree squirrels, Sciurus anomalus and S. vulgaris, (Sciuridae: Rodentia: Mammalia) and their phylogenetic status within the tribe Sciurini

The genus Sciurus, a member of the family Sciuridae, is widely distributed in the Holarctic region. To better understand mitogenomic characteristics and to reveal internal phylogenetic relationships of the genus, 20 complete mitogenomes of Turkish tree squirrels were successfully sequenced for the first time, including 19 for S. anomalus (from 16,505 bp to 16,510 bp) and one for S. vulgaris (16,511 bp). The mitogenomes of two species were AT-biased. All tRNAs for two species displayed a typical clover-leaf structure, except for tRNA^Ser(AGY). The tRNA Serine1 (S1)-GCT structure lacked the dihydrouridine (DHU) loop and stem. Based on mitogenomic dataset for phylogeny of Sciurinae, phylogenetic analyses (Bayesian Inference and Maximum Likelihood) did not support monophyly of Sciurus and proposed that S. anomalus, the most basal taxa in the Sciurini tribe, had at least five mitogenome lineages, which were also supported by network analysis. The dissimilarities among the five linegaes of S. anomalus ranged from 0.0042 (0.42%) to 0.0062 (0.62%) using K2P sequence pairwise distances. In addition to this mitogenomic analysis result, phylogenetic analyses using the CYTB + D-loop dataset proposed the existence of at least nine lineages for S. anomalus, which was different than those of the previous studies. The current study proposed that the use of mitogenomic data for reconstructing the phylogeny of Turkey' Sciurus holds an important value for revealing evolutionary relationships.

Comparative Morphology of the Lingual Papillae and Their Connective Tissue Cores in the Tongue of Pallas's Squirrel (Callosciurus erythraeus thai, Kloss, 1917)

We observed the morphology of the papilla linguae (filiform, fungiform, foliate, and vallate) and underlying connective tissue cores (CTCs) in Pallas's squirrel (Callosciurus erythraeus thai) using light and scanning electron microscopy. The tongue was caudally elongated and lacked the lingual torus. Filiform papillae were densely distributed along the dorsal surface of the apex, and the rostral and caudal parts of the corpus, but were attenuated in the lingual root. Two or three vallate papillae that were rounded or elongated were situated at the boundary between the caudal part of the corpus and lingual root, and foliate papillae and associated cone-like processes were observable in the lateral margin of the caudal end. The epithelial surface of filiform papillae had a main process and a few associated processes that varied between short and elongated, depending on the location. Filiform papillae CTCs appeared to have a few processes that caudally surrounded a concavity and were morphologically variable based on location. Moreover, fungiform papillae CTCs appeared to be columnar cores and had a shallow convex curve at the top. The Pallas's squirrel's tongue exhibited transitional morphological characteristics between Rodentia and other mammalian species, in that they lacked the lingual torus and had CTCs of lingual papillae that were somewhat morphologically similar to those of other non-Glires species, especially treeshrews and tamarins, rather than those of other Rodentia species.

Sequencing, annotation and analysis of the Syrian hamster (Mesocricetus auratus) transcriptome

Background

The Syrian hamster (golden hamster, Mesocricetus auratus) is gaining importance as a new experimental animal model for multiple pathogens, including emerging zoonotic diseases such as Ebola. Nevertheless there are currently no publicly available transcriptome reference sequences or genome for this species.

Results

A cDNA library derived from mRNA and snRNA isolated and pooled from the brains, lungs, spleens, kidneys, livers, and hearts of three adult female Syrian hamsters was sequenced. Sequence reads were assembled into 62,482 contigs and 111,796 reads remained unassembled (singletons). This combined contig/singleton dataset, designated as the Syrian hamster transcriptome, represents a total of 60,117,204 nucleotides. Our Mesocricetus auratus Syrian hamster transcriptome mapped to 11,648 mouse transcripts representing 9,562 distinct genes, and mapped to a similar number of transcripts and genes in the rat. We identified 214 quasi-complete transcripts based on mouse annotations. Canonical pathways involved in a broad spectrum of fundamental biological processes were significantly represented in the library. The Syrian hamster transcriptome was aligned to the current release of the Chinese hamster ovary (CHO) cell transcriptome and genome to improve the genomic annotation of this species. Finally, our Syrian hamster transcriptome was aligned against 14 other rodents, primate and laurasiatheria species to gain insights about the genetic relatedness and placement of this species.

Conclusions

This Syrian hamster transcriptome dataset significantly improves our knowledge of the Syrian hamster's transcriptome, especially towards its future use in infectious disease research. Moreover, this library is an important resource for the wider scientific community to help improve genome annotation of the Syrian hamster and other closely related species. Furthermore, these data provide the basis for development of expression microarrays that can be used in functional genomics studies.

Jumping and gliding rodents: mitogenomic affinities of Pedetidae and Anomaluridae deduced from an RNA-Seq approach

An RNA-Seq strategy was used to obtain the complete set of protein-coding mitochondrial genes from two rodent taxa. Thanks to the next generation sequencing (NGS) 454 approach, we determined the complete mitochondrial DNA genome from Graphiurus kelleni (Mammalia: Rodentia: Gliridae) and partial mitogenome from Pedetes capensis (Pedetidae), and compared them with published rodent and outgroup mitogenomes. We finished the mitogenome sequencing by a series of amplicons using conserved PCR primers to fill the gaps corresponding to tRNA, rRNA and control regions. Phylogenetic analyses of the mitogenomes suggest a well-supported rodent phylogeny in agreement with nuclear gene trees. Pedetes groups with Anomalurus into the clade Anomaluromorpha, while Graphiurus branches within the squirrel-related clade. Moreover, Pedetes+Anomalurus branch with Castor into the mouse-related clade. Our study demonstrates the utility of NGS for obtaining new mitochondrial genomes as well as the importance of choosing adequate models of sequence evolution to infer the phylogeny of rodents.

High throughput transcriptome analysis of lipid metabolism in Syrian hamster liver in absence of an annotated genome

Background

Whole transcriptome analyses are an essential tool for understanding disease mechanisms. Approaches based on next-generation sequencing provide fast and affordable data but rely on the availability of annotated genomes. However, there are many areas in biomedical research that require non-standard animal models for which genome information is not available. This includes the Syrian hamster Mesocricetus auratus as an important model for dyslipidaemia because it mirrors many aspects of human disease and pharmacological responses. We show that complementary use of two independent next generation sequencing technologies combined with mapping to multiple genome databases allows unambiguous transcript annotation and quantitative transcript imaging. We refer to this approach as “triple match sequencing” (TMS).

Results

Contigs assembled from a normalized Roche 454 hamster liver library comprising 1.2 million long reads were used to identify 10’800 unique transcripts based on homology to RefSeq database entries from human, mouse, and rat. For mRNA quantification we mapped 82 million SAGE tags (SOLiD) from the same RNA source to the annotated hamster liver transcriptome contigs. We compared the liver transcriptome of hamster with equivalent data from human, rat, minipig, and cynomolgus monkeys to highlight differential gene expression with focus on lipid metabolism. We identify a cluster of five genes functionally related to HDL metabolism that is expressed in human, cynomolgus, minipig, and hamster but lacking in rat as a non-responder species for lipid lowering drugs.

Conclusions

The TMS approach is suited for fast and inexpensive transcript profiling in cells or tissues of species where a fully annotated genome is not available. The continuously growing number of well annotated reference genomes will further empower reliable transcript identification and thereby raise the utility of the method for any species of interest.