3D isotropic high-resolution diffusion-weighted MRI of the whole brain with a motion-corrected steady-state free precession sequence.

The main obstacle to high-resolution (<1.5 mm isotropic) 3D diffusion-weighted MRI is the differential motion-induced phase error from shot-to-shot. In this work, the phase error is addressed with a hybrid 3D navigator approach that corrects motion-induced phase in two ways. In the first, rigid-body motion is corrected for every shot. In the second, repeatable nonrigid-body pulsation is corrected for each portion of the cardiac cycle. These phase error corrections were implemented with a 3D diffusion-weighted steady- state free precession pulse sequence and were shown to mitigate signal dropouts caused by shot-to-shot phase inconsistencies compared to a standard gridding reconstruction in healthy volunteers. The proposed approach resulted in diffusion contrast more similar to the contrast observed in the reference echo-planer imaging scans than reconstruction of the same data without correction. Fractional anisotropy and Color fractional anisotropy maps generated with phase-corrected data were also shown to be more similar to echo-planer imaging reference scans than those generated without phase correction.

Structure and innervation of the labia minora: more than minor skin folds.

OBJECTIVE: : The objective of this study was to examine the histologic features of the labia minora, within the context of the female sexual response. METHODS: : Eight cadaver vulvectomy specimens were used for this study. All specimens were embedded in paraffin and were serially sectioned. Selected sections were stained with hematoxylin and eosin, elastic Masson trichrome, and S-100 antibody stains. RESULTS: : The labia minora are thinly keratinized structures. The primary supporting tissue is collagen, with many vascular and neural elements structures throughout its core and elastin interspersed throughout. CONCLUSIONS: : The labia minora are specialized, highly vascular folds of tissue with an abundance of neural elements. These features corroborate previous functional and observational data that the labia minora engorge with arousal and have a role in the female sexual response.

EM measurements define the dimensions of the "30-nm" chromatin fiber: evidence for a compact, interdigitated structure.

Chromatin structure plays a fundamental role in the regulation of nuclear processes such as DNA transcription, replication, recombination, and repair. Despite considerable efforts during three decades, the structure of the 30-nm chromatin fiber remains controversial. To define fiber dimensions accurately, we have produced very long and regularly folded 30-nm fibers from in vitro reconstituted nucleosome arrays containing the linker histone and with increasing nucleosome repeat lengths (10 to 70 bp of linker DNA). EM measurements show that the dimensions of these fully folded fibers do not increase linearly with increasing linker length, a finding that is inconsistent with two-start helix models. Instead, we find that there are two distinct classes of fiber structure, both with unexpectedly high nucleosome density: arrays with 10 to 40 bp of linker DNA all produce fibers with a diameter of 33 nm and 11 nucleosomes per 11 nm, whereas arrays with 50 to 70 bp of linker DNA all produce 44-nm-wide fibers with 15 nucleosomes per 11 nm. Using the physical constraints imposed by these measurements, we have built a model in which tight nucleosome packing is achieved through the interdigitation of nucleosomes from adjacent helical gyres. Importantly, the model closely matches raw image projections of folded chromatin arrays recorded in the solution state by using electron cryo-microscopy.

A method for the in vitro reconstitution of a defined "30 nm" chromatin fibre containing stoichiometric amounts of the linker histone.

An understanding of the role of higher-order chromatin structure in the regulation of cellular processes such as transcription will require knowledge of the structure of the "30 nm" chromatin fibre and its folding and unfolding pathways. We report an in vitro chromatin reconstitution system, which uses arrays of 12 and 19 copies of a 200 bp repeat of the Widom 601 DNA sequence. Since this DNA sequence binds the histone octamer with much higher affinity than mixed sequence DNA, we have used competitor DNA in the reconstitutions to control the loading of both the histone octamer and linker histone onto the 601 DNA arrays. Using this method we have obtained nucleosome arrays that have one histone octamer and one H5 bound per 200 bp repeat, and hence have the stoichiometric composition of native chromatin. To obtain highly compact 30 nm chromatin fibres, we have investigated a number of folding buffer conditions including varying NaCl or MgCl(2) concentrations. Sedimentation velocity analysis shows that the reconstituted nucleosome arrays have the same folding properties as native chromatin and form highly compact structures in high NaCl concentrations or 1mM MgCl(2). Negative stain and electron cryo-microscopy of the folded arrays show a homogeneous population of folded particles with a uniform diameter of 34 nm. The data presented provide good evidence that the reconstitution method we have developed produces, for the first time, a defined population of folded 30 nm fibres suitable for detailed structural investigation.