Mighty Piwis defend the germline against genome intruders

Piwis are a germline-specific subclass of the Argonaute family of RNA interference (RNAi) effector proteins that are associated with a recently discovered group of small RNAs (piRNAs). Recent studies in Drosophila and zebrafish directly implicate Piwi proteins in piRNA biogenesis to maintain transposon silencing in the germline genome (Brennecke et al., 2007; Gunawardane et al., 2007; Houwing et al., 2007). This function may be conserved in mice as loss of Miwi2, a mouse Piwi homolog, leads to germline stem cell and meiotic defects correlated with increased transposon activity (Carmell et al., 2007).     

Molecular steps of G‐overhang generation at human telomeres and its function in chromosome end protection

Telomeric G‐overhangs are required for the formation of the protective telomere structure and telomerase action. However, the mechanism controlling G‐overhang generation at human telomeres is poorly understood. Here, we show that G‐overhangs can undergo cell cycle‐regulated changes independent of telomerase activity. G‐overhangs at lagging telomeres are lengthened in S phase and then shortened in late S/G2 because of C‐strand fill‐in, whereas the sizes of G‐overhangs at leading telomeres remain stable throughout S phase and are lengthened in G2/M. The final nucleotides at measurable C‐strands are precisely defined throughout the cell cycle, indicating that C‐strand resection is strictly regulated. We demonstrate that C‐strand fill‐in is mediated by DNA polymerase α (polα) and controlled by cyclin‐dependent kinase 1 (CDK1). Inhibition of CDK1 leads to accumulation of lengthened G‐overhangs and induces telomeric DNA damage response. Furthermore, depletion of hStn1 results in elongation of G‐overhangs and an increase in telomeric DNA damage. Our results suggest that G‐overhang generation at human telomeres is regulated by multiple tightly controlled processes and C‐strand fill‐in is under the control of polα and CDK1.     

MONITORING THE TREND OF HARBOR SEALS IN PRINCE WILLIAM SOUND,ALASKA, AFTER THE EXXON VALDEZ OIL SPILL

We used aerial counts to monitor the trend in numbers of harbor seals, Phoca vitulina richardsi, in Prince William Sound, Alaska, following the 1989 Exxon Valdez oil spill. Repetitive counts were made at 25 haul-out sites during the annual molt period each year from 1990 through 1997. A generalized linear model indicated that time of day, date, and time relative to low tide significantly affected seal counts. When Poisson regression was used to adjust counts to a standardized set of survey conditions, results showed a highly significant decline of 4.6% per year. Unadjusted counts indicated a slight, but not statistically significant, decline in the number of seals. The number of harbor seals on the trend-count route in eastern and central PWS has been declining since at least 1984, with an overall population reduction of 63% through 1997. Programs to monitor long-term changes in animal population sizes should account for factors that can cause short-term variations in indices of abundance. The inclusion of such factors as covariates in models can improve the accuracy of monitoring programs.     

Genome-Wide Expression Analysis in Fibroblast Cell Lines from Probands with Pallister Killian Syndrome

Pallister Killian syndrome (OMIM: # 601803) is a rare multisystem disorder typically caused by tissue limited mosaic tetrasomy of chromosome 12p (isochromosome 12p). The clinical manifestations of Pallister Killian syndrome are variable with the most common findings including craniofacial dysmorphia, hypotonia, cognitive impairment, hearing loss, skin pigmentary differences and epilepsy. Isochromosome 12p is identified primarily in skin fibroblast cultures and in chorionic villus and amniotic fluid cell samples and may be identified in blood lymphocytes during the neonatal and early childhood period. We performed genomic expression profiling correlated with interphase fluorescent in situ hybridization and single nucleotide polymorphism array quantification of degree of mosaicism in fibroblasts from 17 Caucasian probands with Pallister Killian syndrome and 9 healthy age, gender and ethnicity matched controls. We identified a characteristic profile of 354 (180 up- and 174 down-regulated) differentially expressed genes in Pallister Killian syndrome probands and supportive evidence for a Pallister Killian syndrome critical region on 12p13.31. The differentially expressed genes were enriched for developmentally important genes such as homeobox genes. Among the differentially expressed genes, we identified several genes whose misexpression may be associated with the clinical phenotype of Pallister Killian syndrome such as downregulation of ZFPM2, GATA6 and SOX9, and overexpression of IGFBP2.     

Infection ofArabidopsis thaliana ecotype columbia by tomato spotted wilt virus

Mechanical inoculation ofArabidopsis thaliana ecotype Columbia with tomato spotted wilt virus led to viral replication and spread as determined by dot blot and ELISA analysis. Severe symptoms were observed three to four weeks post-inoculation. Early symptoms were manifested as chlorotic spots on uninoculated leaves. Later in the infection process, some plants showed complete chlorosis and wilting prior to bolting. Bolts that were developed by infected plants were chlorotic and deformed. These preliminary results suggest thatA. thaliana could become a model system for the genetic analysis of host factors required for the replication of viruses in the family Bunyaviridae, which includes viruses that cause important diseases of both plants and animals.     

Phosphorylation of elongation factor-2 kinase differentially regulates the enzyme's stability under stress conditions

Chronic infection with hepatitis B virus (HBV) is associated with the majority of cases of hepatocellular carcinoma (HCC) in China. Despite this, there is no effective method for the early detection of HBV-induced liver cancer. Aberrant fucosylation is known to occur during the development of HCC. We, therefore, developed a method of applying matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to analyze the relationship between aberrant fucosylation, tumor genesis and progression of HBV-associated HCC, and to establish proteomic profiling of serum for early diagnosis of HCC. The MALDI-TOF MS was based on Lens culinaris agglutinin (LCA) lectin magnetic beads and their affinity for separation. The method was applied initially to a 'training' cohort of 111 serum samples obtained from subjects in China with no liver disease (n=26), chronic hepatitis B without cirrhosis (n=21), HBV-infected cirrhosis (n=32), or HBV-infected HCC (n=32). In contrast to previous findings, the results of our profiling analysis demonstrated defucosylation on some of the glycoproteins involved in HCC. HCC was then diagnostically classified in a 'blind test' cohort (n=96). In this group we demonstrated that, HCC could be distinguished from all serum samples, HBV-associated chronic liver disease, and HBV-associated cirrhosis with a sensitivity/specificity of 70%/70%, 78%/74%, and 81%/82%, respectively. When combined with serum alpha-fetoprotein detection (AFP>20 ng/mL), the sensitivity/specificity improved to 78%/88%, 85%/88%, and 89%/91%, respectively. In conclusion, serum glycoprotein fucosylation abnormalities have diverse forms in patients with HCC. MALDI-TOF MS profiling of aberrant serum fucosylated glycoproteins distinguished HCC from controls with high accuracy.     

Solution structure of the core SMN-Gemin2 complex

In humans, assembly of spliceosomal snRNPs (small nuclear ribonucleoproteins) begins in the cytoplasm where the multi-protein SMN (survival of motor neuron) complex mediates the formation of a seven-membered ring of Sm proteins on to a conserved site of the snRNA (small nuclear RNA). The SMN complex contains the SMN protein Gemin2 and several additional Gemins that participate in snRNP biosynthesis. SMN was first identified as the product of a gene found to be deleted or mutated in patients with the neurodegenerative disease SMA (spinal muscular atrophy), the leading genetic cause of infant mortality. In the present study, we report the solution structure of Gemin2 bound to the Gemin2-binding domain of SMN determined by NMR spectroscopy. This complex reveals the structure of Gemin2, how Gemin2 binds to SMN and the roles of conserved SMN residues near the binding interface. Surprisingly, several conserved SMN residues, including the sites of two SMA patient mutations, are not required for binding to Gemin2. Instead, they form a conserved SMN/Gemin2 surface that may be functionally important for snRNP assembly. The SMN-Gemin2 structure explains how Gemin2 is stabilized by SMN and establishes a framework for structure-function studies to investigate snRNP biogenesis as well as biological processes involving Gemin2 that do not involve snRNP assembly.     

Environmental,geographical and time-related impacts on avian malaria infections in native and introduced populations of house sparrows (Passer domesticus), a globally invasive species

Aim

The increasing spread of vector-borne diseases has resulted in severe health concerns for humans, domestic animals and wildlife, with changes in land use and the introduction of invasive species being among the main possible causes for this increase. We explored several ecological drivers potentially affecting the local prevalence and richness of avian malaria parasite lineages in native and introduced house sparrows (Passer domesticus) populations.

Location

Global.

Time period

2002–2019.

Major taxa studied

Avian Plasmodium parasites in house sparrows.

Methods

We analysed data from 2,220 samples from 69 localities across all continents, except Antarctica. The influence of environment (urbanization index and human density), geography (altitude, latitude, hemisphere) and time (bird breeding season and years since introduction) were analysed using generalized additive mixed models (GAMMs) and random forests.

Results

Overall, 670 sparrows (30.2%) were infected with 22 Plasmodium lineages. In native populations, parasite prevalence was positively related to urbanization index, with the highest prevalence values in areas with intermediate urbanization levels. Likewise, in introduced populations, prevalence was positively associated with urbanization index; however, higher infection occurred in areas with either extreme high or low levels of urbanization. In introduced populations, the number of parasite lineages increased with altitude and with the years elapsed since the establishment of sparrows in a new locality. Here, after a decline in the number of parasite lineages in the first 30 years, an increase from 40 years onwards was detected.

Main conclusions

Urbanization was related to parasite prevalence in both native and introduced bird populations. In invaded areas, altitude and time since bird introduction were related to the number of Plasmodium lineages found to be infecting sparrows.