Diffusion tensor imaging (DTI) is an exciting new MRI modality that can reveal detailed anatomy of the white matter. DTI also allows us to approximate the 3D trajectories of major white matter bundles. By combining the identified tract coordinates with various types of MR parameter maps, such as T 2 and diffusion properties, we can perform tract-specific analysis of these parameters. Unfortunately, 3D tract reconstruction is marred by noise, partial volume effects, and complicated axonal structures. Furthermore, changes in diffusion anisotropy under pathological conditions could alter the results of 3D tract reconstruction. In this study, we created a white matter parcellation atlas based on probabilistic maps of 11 major white matter tracts derived from the DTI data from 28 normal subjects. Using these probabilistic maps, automated tract-specific quantification of fractional anisotropy and mean diffusivity were performed. Excellent correlation was found between the automated and the individual tractography-based results. This tool allows efficient initial screening of the status of multiple white matter tracts.

Targeted delivery of proteins to distinct plasma membrane domains is critical to the development and maintenance of polarity in epithelial cells. We used confocal and time-lapse total internal reflection fluorescence microscopy (TIR-FM) to study changes in localization and exocytic sites of post-Golgi transport intermediates (PGTIs) carrying GFP-tagged apical or basolateral membrane proteins during epithelial polarization. In non-polarized Madin Darby Canine Kidney (MDCK) cells, apical and basolateral PGTIs were present throughout the cytoplasm and were observed to fuse with the basal domain of the plasma membrane. During polarization, apical and basolateral PGTIs were restricted to different regions of the cytoplasm and their fusion with the basal membrane was completely abrogated. Quantitative analysis suggested that basolateral, but not apical, PGTIs fused with the lateral membrane in polarized cells, correlating with the restricted localization of Syntaxins 4 and 3 to lateral and apical membrane domains, respectively. Microtubule disruption induced Syntaxin 3 depolarization and fusion of apical PGTIs with the basal membrane, but affected neither the lateral localization of Syntaxin 4 or Sec6, nor promoted fusion of basolateral PGTIs with the basal membrane.

Maintenance of genomic stability is essential for normal organismal development and is vital to prevent diseases such as cancer. As genetic information is packaged into chromatin, it has become increasingly clear that the chromatin environment plays an important role in DNA damage response. However, how DNA repair is controlled by epigenetic mechanisms is not fully understood. Here we report the identification and characterization of lysine-specific histone demethylase 5B (KDM5B), a member of the JmjC domaincontaining histone demethylases, as an important player in multiple aspects of DNA double-strand break (DSB) response in human cells. We found that KDM5B becomes enriched in DNA-damage sites after ironizing radiation and endonuclease treatment in a poly(ADP ribose) polymerase 1-and histone variant macroH2A1.1-dependent manner. We showed that KDM5B is required for efficient DSB repair and for the recruitment of Ku70 and BRCA1, the essential component of nonhomologous end-joining and homologous recombination, respectively. Significantly, KDM5B deficiency disengages the DNA repair process, promotes spontaneous DNA damage, activates p53 signaling, and sensitizes cells to genotoxic insults. Our results suggest that KDM5B is a bona fide DNA damage response protein and indicate that KDM5B is an important genome caretaker and a critical regulator of genome stability, adding to the understanding of the roles of epigenetics in the maintenance of genetic fidelity.chromatin modification | histone methylation | genome maintenance T he ability of cells to maintain genome integrity is vital for cellular homeostasis. Defects in the maintenance of genome stability underlie a number of developmental disorders and human diseases including cancer (1-3). Compared with other types of DNA lesions, DNA double-strand breaks (DSBs) are particularly dangerous to cells because failure to repair these kinds of damage in an appropriate manner can cause cell death, and aberrant repair can lead to gross chromosomal abnormalities that may eventually lead to tumorigenesis (1, 2, 4).Upon detection of DSBs, cells activate local and global DNA damage response (DDR) events that promote cell-cycle checkpoint activation and DNA repair signaling (5, 6). For example, in response to DSBs, phosphorylation of the histone variant H2AX (γH2AX) by DDR protein kinases such as ataxia telangiectasia mutated (ATM) (7) creates an extensive modified chromatin environment that allows spatiotemporal redistribution and accumulation of checkpoint and repair factors, including DNAdamage check point-1 (MDC1) and breast cancer susceptibility gene 1 (BRCA1), into repair centers, forming microscopically visible nuclear aggregates known as foci (4, 8). The two extensively studied DSB repair pathways are homologous recombination (HR) and nonhomologous end-joining (NHEJ) (2, 9). In NHEJ, the DSB ends are blocked from 5′ end resection and held in a close proximity by DSB end-binding protein complex, the Ku70-Ku80 heterodimer (10). NHEJ promotes direct ligation of the DSB end...