The spatio-temporal program of genome replication across eukaryotes is thought to be driven both by the uneven loading of pre-replication complexes (pre-RCs) across the genome at the onset of S-phase, and by differences in the timing of activation of these complexes during S phase. To determine the degree to which distribution of pre-RC loading alone could account for chromosomal replication patterns, we mapped the binding sites of the Mcm2-7 helicase complex (MCM) in budding yeast, fission yeast, mouse and humans. We observed similar individual MCM double-hexamer (DH) footprints across the species, but notable differences in their distribution: Footprints in budding yeast were more sharply focused compared to the other three organisms, consistent with the relative sequence specificity of replication origins in S. cerevisiae. Nonetheless, with some clear exceptions, most notably the inactive X-chromosome, much of the fluctuation in replication timing along the chromosomes in all four organisms reflected uneven chromosomal distribution of pre-replication complexes.

Introduction:Evidence strongly suggests that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer's disease (AD). To date, there have been no validated assays specific for detecting and quantifying oAβ in human blood. Methods:We developed an ultrasensitive oAβ immunoassay using a novel capture antibody (71A1) with N-terminal antibody 3D6 for detection that specifically quantifies soluble oAβ in the human brain, cerebrospinal fluid (CSF), and plasma.Results: Two new antibodies (71A1; 1G5) are oAβ-selective, label Aβ plaques in nonfixed AD brain sections, and potently neutralize the synaptotoxicity of AD brainderived oAβ. The 71A1/3D6 assay showed excellent dilution linearity in CSF and plasma without matrix effects, good spike recovery, and specific immunodepletion. Discussion:We have created a sensitive, high throughput, and inexpensive method to quantify synaptotoxic oAβ in human plasma for analyzing large cohorts of aged and AD subjects to assess the dynamics of this key pathogenic species and response to therapy.

The spatio-temporal program of genome replication across eukaryotes is thought to be driven both by the uneven loading of pre-replication complexes (pre-RCs) across the genome at the onset of S-phase, and by differences in the timing of activation of these complexes during Sphase. To determine the degree to which distribution of pre-RC loading alone could account for chromosomal replication patterns, we identified the binding sites of the Mcm2-7 helicase complex, a key component of the pre-RC that is required for initiation of DNA replication, in budding yeast, fission yeast and mouse. In budding yeast, we detected Mcm2 binding in sharply focused peaks, generally with a single double hexamer bound at known origins of replication. In fission yeast, Mcm2 binding, while still concentrated at known origins, was more diffuse, often with 6 to 8 helicase complexes distributed along 0.5-1.5 kb sized origins, and with significantly more binding between origins. Finally, in mouse, we found even more diffuse Mcm2-7 distribution, with the density of Mcm2-7 binding in G1 recapitulating to a remarkable degree the replication program implemented in S-phase. Computer simulations that assign each licensed origin an equal probability of firing show that the observed Mcm2-7 density distribution in G1 across all three species largely recapitulated the DNA replication program. We conclude that the pattern of origin licensing from yeast to mammals is sufficient to explain most differences in replication timing without invoking an overarching temporal program of origin firing. ResultsInitiation of DNA replication requires activation of the MCM2-7 helicase complex (Mcm2-7) at sites at which this complex was loaded during the preceding G2/M and G1 phases [1][2][3][4].However, the order in which different regions of the genome complete replication is widely assumed to reflect not only the locations of Mcm2-7 loading but also a program of control above the level of loading, in which certain complexes are activated before others [5,6]. The distribution of Mcm2-7 is therefore expected to constrain but not fully determine the program of genome replication. Mcm2-7 encircles approximately 60 base pairs (bp) of DNA as a double hexamer whose monomer components are juxtaposed head-to-head at their N-termini with C-