A non-LTR retroelement extinction in Spermophilus tridecemlineatus

The typical mammalian genome is dominated by two types of transposable elements (TEs), the autonomous and non-autonomous non-LTR retrotransposons, i.e. LINEs and SINEs, and with few exceptions there is a sole active LINE family (L1). During an ongoing investigation of TEs in rodents we determined that overall transposon activity has been steadily declining in Spermophilus tridecemlineatus. More specifically, the typically ubiquitous L1 activity of mammals has decreased drastically within the last 26MY. Indeed, only three L1 insertions with intact ORF1 sequences were readily identifiable and no intact ORF2 sequences were identified. The last L1 and SINE insertions date to ~5.3MYA and 4MYA, respectively. Based on our inability to computationally identify recently inserted L1 elements we suggest that S. tridecemlineatus is experiencing a quiescence or extinction of non-LTR retrotransposon activity. Such a finding represents only the fourth instance of a loss of non-LTR retrotransposon activity identified in mammals and, as such, represents an important additional data point to guide our understanding of LINE dynamics in eutherians.     

Characterization and evolution of 5' and 3' untranslated regions in eukaryotes

Untranslated regions (UTRs) in eukaryotes play a significant role in the regulation of translation and mRNA half-life, as well as interacting with specific RNA-binding proteins. However, UTRs receive less attention than more crucial elements such as genes, and the basic structural and evolutionary characteristics of UTRs of different species, and the relationship between these UTRs and the genome size and species gene number is not well understood. To address these questions, we performed a comparative analysis of 5' and 3' untranslated regions of different species by analyzing the basic characteristics of 244,976 UTRs from three eukaryote kingdoms (Plantae, Fungi, and Protista). The results showed that the UTR lengths and SSR frequencies in UTRs increased significantly with increasing species gene number while the length and G+C content in 5' UTRs and different types of repetitive sequences in 3' UTRs increased with the increase of genome size. We also found that the sequence length of 5' UTRs was significantly positively correlated with the presence of transposons and SSRs while the sequence length of 3' UTRs was significantly positively correlated with the presence of tandem repeat sequences. These results suggested that evolution of species complexity from lower organisms to higher organisms is accompanied by an increase in the regulatory complexity of UTRs, mediated by increasing UTR length, increasing G+C content of 5' UTRs, and insertion and expansion of repetitive sequences.     

Characterization of a novel nm23 gene and its potential roles in gametogenesis in the prawn Macrobrachium rosenbergii (de Man, 1879) (Crustacea: Decapoda)

Nm23 is a family of genes encoding the nucleoside diphosphate (NDP) kinase, which functions in a wide variety of biological processes, including growth, development, differentiation and tumor metastasis. In this study, a novel nm23 gene, designated as Mrnm23, was identified from the freshwater giant prawn Macrobrachium rosenbergii. The full-length cDNA was 776 bp in length, encoding for a protein of 176 amino acids with one typical NDP kinase domain that harbored all the crucial residues for nucleotide binding and enzymatic activity. Like human novel nm23-H1B, the putative protein contained a unique 21-amino-acid NH₂-terminal extension as compared to human nm23 (nm23-H1) homologs. Further, 3 extra amino acid residues prolonged the COOH-terminus. The Mrnm23 was ubiquitously expressed in all tissues examined, including androgenic gland, gill, heart, liver, muscle, ovary, and testis. In situ hybridization to gonad sections indicated that the Mrnm23 mRNA was localized in the cytoplasm of cup-base of differentiating spermatids, in the spike of the umbrella-shaped spermatozoa and in the cytoplasm of the early previtellogenic oocytes, suggesting that the Mrnm23 has potential roles in spermiogenesis and early differentiation of oocyte.     

Intragenic DNA methylation status down-regulates bovine IGF2 gene expression in different developmental stages

DNA methylation is a key epigenetic modification in mammals and has an essential and important role in muscle development. Insulin-like growth factor 2 (IGF2) is a fetal growth and differentiation factor that plays an important role in muscle growth and in myoblast proliferation and differentiation. The aim of this study was to evaluate the expression of IGF2 and the methylation pattern on the differentially methylated region (DMR) of the last exon of IGF2 in six tissues with two different developmental stages. The DNA methylation pattern was compared using bisulfite sequencing polymerase chain reaction (BSP) and combined bisulfite restriction analysis (COBRA). The quantitative real-time PCR (qPCR) analysis indicated that IGF2 has a broad tissue distribution and the adult bovine group showed significant lower mRNA expression levels than that in the fetal bovine group (P < 0.05 or P < 0.01). Moreover, the DNA methylation level analysis showed that the adult bovine group exhibited a significantly higher DNA methylation levels than that in the fetal bovine group (P < 0.05 or P < 0.01). These results indicate that IGF2 expression levels were negatively associated with the methylation status of the IGF2 DMR during the two developmental stages. Our results suggest that the methylation pattern in this DMR may be a useful parameter to investigate as a marker-assisted selection for muscle developmental in beef cattle breeding program and as a model for studies in other species.