Human telomerase hTERC RNA serves as a template for the catalytic hTERT protein to synthesize telomere repeats at chromosome ends. We have recently shown that some patients with bone marrow failure syndromes are heterozygous carriers for hTERC or hTERT mutations. These sequence variations usually lead to a compromised telomerase function by haploinsufficiency. Here, we provide functional characterization of an additional 8 dis- IntroductionTelomerase is a specialized reverse transcriptase (RT) that adds long, repetitive stretches of simple telomeric DNA sequence (ie, TTAGGG in the vertebrates) onto chromosomal termini. 1 This cellular RT protein (TERT) copies a short stretch of nucleotides located within the template region of an integral RNA component (TERC) into telomeric DNA repeats. 1 Vertebrate TERCs are believed to adopt a complex, folded secondary structure 2 as depicted for human TERC (hTERC) in Figure 1A. We have recently conducted extensive site-directed mutagenesis analysis of hTERC to show that much of the structure folded as predicted. 3 As is true of many biologically active RNA molecules, most of the internally base-paired regions of hTERC can be extensively mutated without loss of function, provided that the normal base-pairing pattern is preserved. 3 However, at certain locations, especially of the single-stranded template region that is copied into telomeric DNA, specific RNA base sequences have been shown to be required for biologic activity. 4 Telomerase catalytic proteins (TERTs) from evolutionary distant organisms share a conserved structural organization that can be divided into 3 functional domains ( Figure 1C). 5 The telomerasespecific domains exist at both the N and C termini of TERTs that are not present in any of the viral RTs. 6 The N-terminal region is required to participate in enzymatic function, 7,8 in assembly of the protein with its integral hTERC RNA component,7,9 and in the homodimerization of the protein (ie, hTERT protein-protein interaction), 7,9,10 whereas the C-terminal domain is required for telomerase-specific activity other than its catalytic function 11,12 as well as in the telomeric nucleotide addition processivity process. [13][14][15] The functional RT domain with the universally conserved RT motifs is almost centrally located in the protein primary sequence ( Figure 1C). The fact that mutations of key residues that are known to affect its conventional RT catalytic activity also negatively influence telomerase activity strongly argues that telomerase RT domain is the catalytic domain of the enzyme complex. 13,[15][16][17][18] Inherited mutations in both hTERC RNA and hTERT protein underlie rare bone marrow failure syndromes, autosomal dominant dyskeratosis congenita (DC) and acquired aplastic anemia (AA). [19][20][21] DC is characterized by abnormal skin pigmentation, nail dystrophy, and oral leukoplakia and is often complicated by life-threatening bone marrow failure and immunodeficiency. 22 Lymphocytes from patients show decreased hTERC expression, decreased t...

A total of 420 rodents in China were examined for Francisella tularensis by polymerase chain reaction. The infection rates were 4.76% in total, and 11.65%, 10.00%, 6.56%, 1.77%, and 0% in Jilin, Xinjiang, Heilongjiang, Inner Mongolia, and Zhejiang, respectively. Sequence analysis showed that all the detected agents belonged to F. tularensis subsp. holarctica.

Background: Tularemia was reported in China over 50 years ago, however, many epidemical characteristics remain unclear. In the present study, the prevalence of Francisella tularensis in ticks was investigated during an epidemiological surveillance in China and then we measured their genetic diversity by conducting multiple-locus variable-number tandem repeat analysis (MLVA).

We report for the first time potential pathogenic mutations in a known telomeric DNA binding protein factor (TIN2) in patients with acquired aplastic anemia. We examined samples collected from 142 AA patients and 289 healthy controls and found several natural sequence changes in the TINF2 gene, which encodes for the TIN2 protein. Lymphocytes collected from patients with TINF2 variant alleles appeared to grow slower in culture than cells collected from either healthy individuals or those who carried inconsequential polymorphic TINF2 sequence changes (SNPs), consistent with the fact that telomere lengths in these patients were shorter than those of healthy individuals of similar age. We introduced natural mutations in the TIN2 promoter region into a TIN2-promoter driven luciferase reporter plasmid and examined their effect on driving luciferase reporter expression. Using a similar approach, we defined both the regulatory DNA elements and transcriptional factors that control TINF2 gene expression under normal physiological condition. Results obtained from these studies were validated in gel-shift (EMSA) and chromatin immunoprecipitation (ChIP) assays. In addition to mutations in the promoter region, numerous natural mutations were identified in the coding region of the TINF2 gene in patients with AA or Dyskeratosis Congenita (DC). We used co-immunoprecipitation assays to test the effect of natural mutations in disrupting TIN2’s interaction with its known protein partners TRF1, TRF2 and TPP1 of the shelterin complex that protects chromosome ends. The results obtained from these studies will be discussed. To our knowledge, this is the first comprehensive functional analysis of all known mutations in the TINF2 gene in patients with AA or DC. This study offers an insight into how TINF2 mutations can lead to telomere shortening effect and to limited marrow stem-cell reserve and renewal capacity in patients with various forms of bone-marrow failure syndromes.