SUMOylation- and GAR1-Dependent Regulation of Dyskerin Nuclear and Subnuclear Localization.

The nuclear and subnuclear compartmentalization of the telomerase-associated protein and H/ACA ribonucleoprotein component dyskerin is an important although incompletely understood aspect of H/ACA ribonucleoprotein function. Four SUMOylation sites were previously identified in the C-terminal nuclear/nucleolar localization signal (N/NoLS) of dyskerin. We found that a cytoplasmic localized C-terminal truncation variant of dyskerin lacking most of the C-terminal N/NoLS represents an under-SUMOylated variant of dyskerin compared to wild-type dyskerin. We demonstrate that mimicking constitutive SUMOylation of dyskerin using a SUMO3 fusion construct can drive nuclear accumulation of this variant and that the SUMO site K467 in this N/NoLS is particularly important for the subnuclear localization of dyskerin to the nucleolus in a mature H/ACA complex assembly- and SUMO-dependent manner. We also characterize a novel SUMO-interacting motif in the mature H/ACA complex component GAR1 that mediates the interaction between dyskerin and GAR1. Mislocalization of dyskerin, either in the cytoplasm or excluded from the nucleolus, disrupts dyskerin function and leads to reduced interaction of dyskerin with the telomerase RNA. These data indicate a role for dyskerin C-terminal N/NoLS SUMOylation in regulating the nuclear and subnuclear localization of dyskerin, which is essential for dyskerin function as both a telomerase-associated protein and as an H/ACA ribonucleoprotein.

The role of discography in lumbar disc disease: a comparative study of magnetic resonance imaging and discography.

This study reviews prospectively a series of 29 patients who were examined by magnetic resonance imaging (MRI) and discography for degenerative disc disease. All had persistent low-back pain and non-diagnostic initial investigations, including plain films, myelography and/or computed tomography (CT). The imaging characteristics for degenerative disc disease correlated in 65 out of 73 intervertebral levels. All symptomatic discs were degenerate on both MRI and discography. Features of degenerative disc disease on MRI were assessed retrospectively, with a view to identifying the symptomatic level as defined by discography. MRI could not reliably detect this level, particularly in those with multi-level degenerative disc disease. Positive reproduction of symptoms at discography was the criteria used for surgery. All 12 patients in this group had posterior spinal fusion performed. Nine improved and three were unchanged. Of the ancillary features associated with disc degeneration, only a bulging annulus fibrosis proved to be of any value on MRI. Nonetheless, MRI should be used as the primary investigation in this patient group as it can lead to a marked reduction in the number of disc levels requiring injection.