Therapeutic potential of valproic acid for retinitis pigmentosa.

BACKGROUND/AIM: To examine the efficacy and safety of valproic acid (VPA) in patients with retinitis pigmentosa (RP). METHODS: Thirteen eyes were examined before and after brief treatment (average 4 months) with VPA. Visual fields (VF) for each eye were defined using digitised Goldmann Kinetic Perimetry tracings. VF areas were log-transformed and VF loss/gain relative to baseline was calculated. Visual acuity was measured using a Snellen chart at a distance of 20 feet (6.1 m). Values were converted to the logarithm of the minimum angle of resolution (logMAR) score. RESULTS: Nine eyes had improved VF with treatment, two eyes had decreased VF and two eyes experienced no change, with an overall average increase of 11%. Assuming typical loss in VF area without treatment, this increase in VF was statistically significant (p<0.02). An average decrease (0.172) in the logMAR scores was seen in these 13 eyes, which translates to a positive change in Snellen score of approximately 20/47 to 20/32, which was significant (p<0.02) assuming no loss in acuity without treatment. Side effects were mild and well tolerated. CONCLUSION: Treatment with VPA is suggestive of a therapeutic benefit to patients with RP. A placebo-controlled clinical trial will be necessary to assess the efficacy and safety of VPA for RP rigorously.

Stabilization and localization of Xist RNA are controlled by separate mechanisms and are not sufficient for X inactivation.

These studies address whether XIST RNA is properly localized to the X chromosome in somatic cells where human XIST expression is reactivated, but fails to result in X inactivation (Tinker, A.V., and C.J. Brown. 1998. Nucl. Acids Res. 26:2935-2940). Despite a nuclear RNA accumulation of normal abundance and stability, XIST RNA does not localize in reactivants or in naturally inactive human X chromosomes in mouse/ human hybrid cells. The XIST transcripts are fully stabilized despite their inability to localize, and hence XIST RNA localization can be uncoupled from stabilization, indicating that these are separate steps controlled by distinct mechanisms. Mouse Xist RNA tightly localized to an active X chromosome, demonstrating for the first time that the active X chromosome in somatic cells is competent to associate with Xist RNA. These results imply that species-specific factors, present even in mature, somatic cells that do not normally express Xist, are necessary for localization. When Xist RNA is properly localized to an active mouse X chromosome, X inactivation does not result. Therefore, there is not a strict correlation between Xist localization and chromatin inactivation. Moreover, expression, stabilization, and localization of Xist RNA are not sufficient for X inactivation. We hypothesize that chromosomal association of XIST RNA may initiate subsequent developmental events required to enact transcriptional silencing.

X inactivation analysis and DNA methylation studies of the ubiquitin activating enzyme E1 and PCTAIRE-1 genes in human and mouse.

Previously reported data on the X inactivation status of the ubiquitin activating enzyme E1 (UBE1) gene have been contradictory, and the issue has remained unsettled. Here we present three lines of evidence that UBE1 is expressed from the inactive X chromosome and therefore escapes X inactivation. First, by RNA in situ hybridization, UBE1 RNA is detected from both the active and inactive X chromosomes in human female fibroblasts. Second, UBE1 is expressed in a large panel of somatic cell hybrids retaining inactive human X chromosomes, including two independent hybrids that did not require UBE1 expression for survival. And third, sites at the 5' end of UBE1 are unmethylated on both active and inactive X chromosomes, consistent with the gene escaping inactivation. In order to address whether other genes that escape inactivation map to the same region of the X chromosome, we have also examined the expression of genes mapping adjacent to UBE1. The gene for PCTAIRE-1 (PCTK1) maps within 5 kb of UBE1 and similarly escapes X inactivation by the somatic cell hybrid assay, whereas six other genes that are within 1 Mb of UBE1 in Xp11.23 are silenced on the inactive X chromosome. Comparative mapping studies of the homologous loci in mouse establish that Ube1-x and Pctk1 are also within close physical proximity on the murine X chromosome, and expression studies of the Pctk1 gene determine that, similar to Ube1-x, it is subject to X inactivation in mouse. Methylation of CpG residues at restriction sites at the 5' end of both genes on the murine inactive X chromosome is consistent with both genes being subject to X inactivation in mouse, in contrast to their expression status in humans.

XIST RNA paints the inactive X chromosome at interphase: evidence for a novel RNA involved in nuclear/chromosome structure.

The XIST gene is implicated in X chromosome inactivation, yet the RNA contains no apparent open reading frame. An accumulation of XIST RNA is observed near its site of transcription, the inactive X chromosome (Xi). A series of molecular cytogenetic studies comparing properties of XIST RNA to other protein coding RNAs, support a critical distinction for XIST RNA; XIST does not concentrate at Xi simply because it is transcribed and processed there. Most notably, morphometric and 3-D analysis reveals that XIST RNA and Xi are coincident in 2- and 3-D space; hence, the XIST RNA essentially paints Xi. Several results indicate that the XIST RNA accumulation has two components, a minor one associated with transcription and processing, and a spliced major component, which stably associates with Xi. Upon transcriptional inhibition the major spliced component remains in the nucleus and often encircles the extra-prominent heterochromatic Barr body. The continually transcribed XIST gene and its polyadenylated RNA consistently localize to a nuclear region devoid of splicing factor/poly A RNA rich domains. XIST RNA remains with the nuclear matrix fraction after removal of chromosomal DNA. XIST RNA is released from its association with Xi during mitosis, but shows a unique highly particulate distribution. Collective results indicate that XIST RNA may be an architectural element of the interphase chromosome territory, possibly a component of nonchromatin nuclear structure that specifically associates with Xi. XIST RNA is a novel nuclear RNA which potentially provides a specific precedent for RNA involvement in nuclear structure and cis-limited gene regulation via higher-order chromatin packaging.