Although all retroviruses recruit host cell RNAs into virions, both the spectrum of RNAs encapsidated and the mechanisms by which they are recruited remain largely unknown. Here, we used high-throughput sequencing to obtain a comprehensive description of the RNAs packaged by a model retrovirus, murine leukemia virus. The major encapsidated host RNAs are noncoding RNAs (ncRNAs) and members of the VL30 class of endogenous retroviruses. Remarkably, although Moloney leukemia virus (MLV) assembles in the cytoplasm, precursors to specific tRNAs, small nuclear RNAs (snRNAs), and small nucleolar RNAs (snoRNAs) are all enriched in virions. Consistent with their cytoplasmic recruitment, packaging of both pre-tRNAs and U6 snRNA requires the nuclear export receptor Exportin-5. Adenylated and uridylated forms of these RNAs accumulate in cells and virions when the cytoplasmic exoribonuclease DIS3L2 and subunits of the RNA exosome are depleted. Together, our data reveal that MLV recruits RNAs from a novel host cell surveillance pathway in which unprocessed and unneeded nuclear ncRNAs are exported to the cytoplasm for degradation.

Purpose: To evaluate techniques for anatomical and physiological imaging of the intracranial optic nerve (ON), optic chiasm (OC), and optic tract (OT) at 3T with the aim of visualizing axonal damage in multiple sclerosis (MS). Materials and Methods:Imaging was performed on a 3T scanner employing a custom-designed head coil that consisted of a coil array with four coils (30 ϫ 30 cm 2 ). Oblique fast spin echo (FSE) images, magnetization transfer (MT)-enhanced 3D gradient-echo (GRE) time-of-flight (TOF) images, and line scan diffusion images (LSDI) were obtained. Full diffusion tensor (DT) analysis was performed, and apparent diffusion coefficient (ADC), fractional anisotropy (FA), and fiber direction maps were obtained.Results: FSE anatomic images were obtained with an inplane resolution of 0.39 ϫ 0.52 mm 2 . The in-plane resolution of the MT and LSDI images was 0.78 ϫ 0.78 mm 2 . The OC, intracranial ON, and OT can be seen on these images. The dominant fiber orientations in the OC, ON, and OT, as derived from the DT images, are displayed. Conclusion:This study shows that by using 3T and a customdesigned, four-channel head coil, it is possible to acquire highresolution anatomical and physiological images of the OC, ON, and OT. The pilot results presented here pave the way for imaging the anterior visual pathway in patients with MS. IMAGING OF THE OPTIC NERVE (ON) and the optic pathway can assist in the assessment of many causes of injury, such as trauma, inflammation, infection, and tumor. Many patients with multiple sclerosis (MS) exhibit optic neuritis as the first symptom of the disease. Previous MS studies conducted at 1.5T (1-4) demonstrated the potential value of MRI of the ON in MS. However, routine imaging remains a difficult task due to the complexity of the ON and surrounding structures. The main difficulties are the small size of the optic tract (OT); nerve movement; signal from surrounding fat, bone, and cerebrospinal fluid (CSF); and susceptibility effects caused by air in nearby structures.Despite these difficulties, clinical MRI of the ON and optic pathway is promising. Several studies have shown the usefulness of both qualitative (1,5-9) and quantitative (2-4,10,11) MR techniques for diagnosing optic neuritis. One of the criteria for the successful application of these techniques is obtaining high-resolution images. Higher fields (i.e., 3T) and dedicated RF coils may provide better high-resolution imaging. With this in mind, we conducted a study of the ON, optic chiasm (OC), and OT at 3T using a custom-designed phasedarray coil. The combination of these two approaches provides an excellent signal-to-noise ratio (SNR) and allows the acquisition of outstanding high-resolution anatomic images. The SNR achieved offers the opportunity to carry out MRI-based physiological measurements on the OC. In this study we employed two methods: magnetization transfer (MT) imaging and diffusion tensor imaging (DTI).MT imaging is a quantitative technique that involves selective presaturation of the broad macromolecu...

No abstract

The Soviet invasion of Afghanistan in 1979 is often cited as one example of this concept.