Holliday junctions in the eukaryotic nucleus: resolution in sight?

The Holliday junction is a key recombination intermediate whose resolution generates crossovers. Interplay between recombination, repair and replication has moved the Holliday junction to the center stage of nuclear DNA metabolism. Holliday junction resolvases in the eukaryotic nucleus have long eluded identification. The endonucleases Mus81/Mms4-Eme1 and XPF-MEI-9/MUS312 are structurally related to the archaeal resolvase Hjc and were found to be involved in crossover formation in budding yeast and flies, respectively. Although these endonucleases might represent one class of eukaryotic resolvases, their substrate preference opens up the possibility that junctions other than classical Holliday junctions might contribute to crossovers. Holliday junction resolution to non-crossover products can also be achieved topologically, for example, by the action of RecQ-like DNA helicases combined with topoisomerase III.     

Auxin and embryo axis formation: the ends in sight?

The major axis of polarity of the plant embryo serves as a reference for the formation of meristems and, thus, for all subsequent development. Mechanisms underlying the establishment of the embryo axis itself have remained elusive. This is now changing with recent reports documenting a role for auxin in embryo axis formation. Auxin accumulates dynamically at specific positions that correlate with developmental decisions in early embryogenesis, and this ties developmental decisions to both transport regulators and components of the response machinery. A major challenge for the future is to determine how auxin-dependent processes interact with other as yet unknown factors to mediate differential gene expression patterns in early embryogenesis.     

RNA surveillance by nuclear scanning?

There are many quality-control mechanisms that ensure high fidelity of gene expression. One of these is the nonsense-mediated decay (NMD) pathway, which destroys aberrant mRNAs that contain premature termination codons generated as a result of biosynthetic errors or random and programmed gene mutations. Two complexes that initially bind to RNA in the nucleus have been suggested to be involved in NMD in the cytoplasm. Here we propose an alternative model that involves nuclear scanning, on the basis of recent evidence for nuclear translation.     

Mitochondrial DNA clonality in the dock: can surveillance swing the case?

Mitochondrial DNA (mtDNA) is a favoured tool of evolutionary biologists because its high mutation rate generates enough signal to make inferences about population history over short time frames. Furthermore, mtDNA inheritance is clonal, being transmitted only through the maternal line. This enables evolutionary histories to be assembled without the complexities introduced by biparental recombination. Recently, a single case of human biparental inheritance has been reported. Given this, and the role supposed clonal inheritance has had in shaping our knowledge of human population history, it is essential to establish a method for identifying any recombinant mtDNA molecules in our population. A reliable surveillance mechanism would either maintain our confidence in clonal inheritance or indicate the inaccuracy of our inferences.     

Plasmodium vivax in Africa: hidden in plain sight?

People who live in tropical Africa, south of the Sahara, are predominantly negative for the Duffy blood-group antigen, which mediates invasion of reticulocytes by Plasmodium vivax. Recent reports of a parasite that was molecularly diagnosed as P. vivax from populations who are suspected, or known, to be Duffy negative confound a large body of evidence that states that invasion of P. vivax requires the Duffy antigen. If confirmed, one of several possible explanations is that P. vivax, which originated in Asia, is now evolving to exploit alternate invasion receptors in Africa.     

Human molecular chronotyping in sight?

Recent research on mouse models has taken us closer to deciphering the molecular clock mechanism that defines an individual's 'body time'. How feasible will it be to create a molecular timetable that allows determination of individual body time from tissue harvested at a single time point?