Block of HAC1 mRNA translation by long-range base pairing is released by cytoplasmic splicing upon induction of the unfolded protein response

Expression of the yeast transcription factor Hac1p, which controls the unfolded protein response, is regulated posttranscriptionally. Hac1p is only produced when an intron at the 3' end of its mRNA is removed by a nonconventional, regulated splicing reaction. We show that a previously unrecognized base-pairing interaction between the intron and the 5' untranslated region is required and sufficient to block mRNA translation. Unspliced HAC1 mRNA is stable, located in the cytosol, and is associated with polyribosomes, yet does not produce protein, indicating that the ribosomes engaged on the mRNA are stalled. We show that the polysomal, cytoplasmic pool of HAC1 mRNA is a substrate for splicing, suggesting that the stalled ribosomes may resume translation after the intron is removed.

Yeast cytoplasmic and mitochondrial methionyl-tRNA synthetases: two structural frameworks for identical functions

The yeast Saccharomyces cerevisiae possesses two methionyl-tRNA synthetases (MetRS), one in the cytoplasm and the other in mitochondria. The cytoplasmic MetRS has a zinc-finger motif of the type Cys-X(2)-Cys-X(9)-Cys-X(2)-Cys in an insertion domain that divides the nucleotide-binding fold into two halves, whereas no such motif is present in the mitochondrial MetRS. Here, we show that tightly bound zinc atom is present in the cytoplasmic MetRS but not in the mitochondrial MetRS. To test whether the presence of a zinc-binding site is required for cytoplasmic functions of MetRS, we constructed a yeast strain in which cytoplasmic MetRS gene was inactivated and the mitochondrial MetRS gene was expressed in the cytoplasm. Provided that methionine-accepting tRNA is overexpressed, this strain was viable, indicating that mitochondrial MetRS was able to aminoacylate tRNA(Met) in the cytoplasm. Site-directed mutagenesis demonstrated that the zinc domain was required for the stability and consequently for the activity of cytoplasmic MetRS. Mitochondrial MetRS, like cytoplasmic MetRS, supported homocysteine editing in vivo in the yeast cytoplasm. Both MetRSs catalyzed homocysteine editing and aminoacylation of coenzyme A in vitro. Thus, identical synthetic and editing functions can be carried out in different structural frameworks of cytoplasmic and mitochondrial MetRSs.

Electrophysiological changes after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in age related macular degeneration

AIM

To evaluate electrophysiological changes after 360 degrees retinotomy and macular translocation for subfoveal choroidal neovascularisation in patients with age related macular degeneration (AMD).

METHODS

A consecutive series of 32 patients suffering from subfoveal choroidal neovascularisation secondary to AMD underwent 360 degrees retinotomy and macular translocation. The ERG served as the main parameter of the study and was recorded 1 day before the translocation surgery and no earlier than 4 weeks after the silicone oil removal.

RESULTS

The scotopic ERG amplitudes were significantly reduced after translocation surgery. Depending on the applied flash luminance the mean b-wave amplitude reduction of the scotopic ERG varied between 67% (0.2 cd.s/m2) and 74% (0.03 cd.s/m2). The a-waves and b-waves of the saturating light response decreased significantly by 46% and 59%, respectively. The photopic a-wave and b-wave amplitudes were significantly lower after the translocation surgery resulting in a mean reduction of 27% and 43%, respectively.

CONCLUSIONS

Although macular translocation may provide the potential of preserving and even restoring vision in patients with subfoveal choroidal neovascular membranes secondary to AMD the present study indicates that a significant electrophysiological decrease is caused by surgical procedures associated with this technique. Further research is necessary to clarify if certain modifications of the surgical procedure are able to substantially reduce the neuroretinal trauma.

Improvement of macular function by membrane differential filtration in diabetic retinopathy

BACKGROUND

Alterations of blood rheology are assumed to substantially contribute to the pathogenesis of diabetic retinopathy. Membrane differential filtration (MDF) is an extracorporeal treatment which is able to optimize rheological parameters by eliminating high molecular weight proteins and lipoproteins from the blood. The present study was designed to investigate the effects of repetitive MDF on visual function in diabetic retinopathy.

METHODS

11 patients (11 eyes) with nonproliferative or inactive proliferative diabetic retinopathy underwent three treatment cycles during a mean period of 18 weeks. The best corrected visual acuity served as the main parameter of the study. The measurement of visual acuity, visual field, biochemical and rheological parameters was carried out 24 hours pre and post each treatment cycle and at follow up. The mean follow up time was 9 weeks during the post treatment period.

RESULTS

Compared to baseline examination the visual acuity improved stepwise by a mean value of 1.4 lines (p = 0.02) after the last treatment and remained stable at follow up (1.3 lines, p < 0.001). The mean defect of the visual field was reduced by 2.8 dB (p = 0.13) after the treatment period and by 2.5 dB (p = 0.016) at follow up, respectively.

CONCLUSIONS

Repetitive treatment with membrane differential filtration is able to improve visual function in patients with diabetic retinopathy. The present study suggests that repetitive membrane differential filtration treatment could be a useful adjunct along with laser treatment to influence the clinical course of diabetic maculopathy.

Intracellular signaling from the endoplasmic reticulum to the nucleus: the unfolded protein response in yeast and mammals

Cellular survival of endoplasmic reticulum stress requires the unfolded protein response (UPR), a stress response first elucidated genetically in yeast. While we continue to refine our knowledge of the yeast system, especially the breadth and significance of the transcriptional response, conservation of the system's elements has allowed identification of corresponding and additional components of the mammalian UPR. Recent results reveal that the output of the mammalian UPR reaches beyond transcriptional regulation of secretory pathway components to control of general translation, the cell cycle and programmed cell death.

Effects of protein tyrosine kinase inhibitor genistein on retinal function in superfused vertebrate retina

The aim of this study was to evaluate safe concentrations of genistein for a potential intraocular application using the isolated retina technique on bovine retina preparations. Bovine retinas were isolated and perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded as a transretinal potential using silver/silver-chloride electrodes. After recording of stable ERG amplitudes, genistein was added to the solution in different concentrations. The percentage of b-wave reduction under the drug was calculated. We also studied the influence of genistein on the a-wave amplitude. After the addition of aspartate, the b-wave amplitude was reduced continuously until unmasked a-wave amplitudes were reached. Genistein was then added to the aspartate containing perfusate. The percentage of a-wave amplitude reduction under the drug was calculated. Concentrations of 3.3 microMol/l and higher were found to reduce the b-wave amplitude. The a-wave amplitude was not changed by the applied concentrations. The ERG only showed toxic effects from genistein beyond concentrations that were found to inhibit endothelial cell growth in vitro. In previous studies, beneficial effects on trabecular meshwork cells were present for genistein concentrations which are distinctly higher than the maximum nontoxic concentration reported here. It was shown that the photoreceptor layer is not affected at the examined concentration range. Therefore, we attribute the toxic effects to postsynaptic interaction of genistein. Intraocular application of genistein in a sufficient concentration seems possible.

Towards ensuring the safety of vitamins and minerals

Today, there is a clear need for a risk assessment for vitamins and minerals because the total daily intake for nutrients through regular food, fortified products (Functional Food) and supplements may very well reach critical levels for an individual consumer. Several expert panels of the European Union, the UK, Japan and China will publish their reports on this issue in the near future. The Food and Nutrition Board of the Institute of Medicine of the US/Canada has already published a new standard. The board has defined the so-called Tolerable Upper Intake Level (UL) as the highest level of daily intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Their determination involves a multi-step risk assessment procedure on the basis of mainly human data. Several daily UL values that have already been published are of special interest, e.g. 1 mg folic acid, 50 microg vitamin D, 1 g vitamin E, 2 g vitamin C, 2.5 g calcium, 350 mg magnesium.

Multifaceted physiological response allows yeast to adapt to the loss of the signal recognition particle-dependent protein-targeting pathway

Translational control has recently been recognized as an important facet of adaptive responses to various stress conditions. We describe the adaptation response of the yeast Saccharomyces cerevisiae to the loss of one of two mechanisms to target proteins to the secretory pathway. Using inducible mutants that block the signal recognition particle (SRP) pathway, we find that cells demonstrate a physiological response to the loss of the SRP pathway that includes specific changes in global gene expression. Upon inducing the loss of the SRP pathway, SRP-dependent protein translocation is initially blocked, and cell growth is considerably slowed. Concomitantly, gene expression changes include the induction of heat shock genes and the repression of protein synthesis genes. Remarkably, within hours, the efficiency of protein sorting improves while cell growth remains slow in agreement with the persistent repression of protein synthesis genes. Our results suggest that heat shock gene induction serves to protect cells from mislocalized precursor proteins in the cytosol, whereas reduced protein synthesis helps to regain efficiency in protein sorting by reducing the load on the protein translocation apparatus. Thus, we suggest that cells trade speed in cell growth for fidelity in protein sorting to adjust to life without SRP.

Basis for regulated RNA cleavage by functional analysis of RNase L and Ire1p

RNase L and Ire1p are members of a superfamily of regulated endoribonucleases that play essential roles in mediating diverse types of cellular stress responses. 2'-5' oligoadenylates, produced in response to interferon treatment and viral double-stranded RNA, are necessary to activate RNase L. In contrast, unfolded proteins in the endoplasmic reticulum activate Ire1p, a transmembrane serine/threonine kinase and endoribonuclease. To probe their similarities and differences, molecular properties of wild-type and mutant forms of human RNase L and yeast Ire1p were compared. Surprisingly, RNase L and Ire1p showed mutually exclusive RNA substrate specificity and partially overlapping but not identical requirements for phylogenetically conserved amino acid residues in their nuclease domains. A functional model for RNase L was generated based on the comparative analysis with Ire1p that assigns novel roles for ankyrin repeats and kinase-like domains.

Primary non familial amyloidosis of the vitreous and subretinal amyloid bodies

We report a case of primary non familial amyloidosis of the vitreous and subretinal amyloid bodies. Pars plana vitrectomy and subretinal numerable clusters of cystic-like glistering material were extracted. The diagnosis was confirmed only by histological findings.

Influence of membrane differential filtration on the natural course of age-related macular degeneration: a randomized trial

PURPOSE

Membrane differential filtration is able to optimize rheologic parameters by eliminating high molecular weight proteins and lipoproteins from the blood. Following the hypothesis that these changes result in an improvement of the microcirculation, the authors tested the efficacy of membrane differential filtration in improving visual function in patients with age-related macular degeneration (ARMD).

METHODS

Forty patients (40 eyes) were randomized into two groups. The treatment group was treated five times over a period of 21 weeks. In both groups, 9/20 of the eyes showed subfoveolar subretinal neovascularization. The main parameter of the study was visual acuity (VA). Electroretinogram (ERG), electrooculogram, and macular visual evoked potentials were also recorded. Plasma and whole blood viscosity and erythrocyte aggregation were measured.

RESULTS

The 20 patients treated repeatedly over a period of 21 weeks showed a mean improvement of 0.63 lines (SD 1.8) of VA on Early Treatment Diabetic Retinopathy Study charts. The control group showed a deterioration of 0.94 lines (SD 1.7) compared to VA at baseline examination. The amplitude of the ERG photopic a-wave and the flicker ERG was significantly increased. The rheologic parameters were lowered in all treated patients.

CONCLUSION

Repetitive treatment with membrane differential filtration is able to improve visual acuity of patients with ARMD and the natural course of this disease. Several questions arise from the results of this study. Further research will show if it is possible to optimize the selection of patients for subgroups with predictive responses through morphologic and functional tests and how to create an optimized and individual treatment strategy determined by the quality, intensity, and frequency of treatment sessions.

Synthesis of analogues of the O-beta-D-ribofuranosyl nucleoside moiety of liposidomycins. Part 2: role of the hydroxyl groups upon the inhibition of MraY

O-beta-D-ribofuranosyl nucleoside I is the minimal structural entity of liposidomycins that maintains enzyme inhibitory activity on MraY. A set of compounds with hydroxyl patterns different from I has been synthesized. The presence of a hydroxyl group in the 3" position is essential for the activity. The 3'-deoxy derivative (IV), however, shows a 5-fold improved potency.

Development of a completely encapsulated intraocular pressure sensor

A completely encapsulated intraocular pressure (IOP) sensor equipped with telemetric signal and energy transfer is introduced integrated into a silicone disc for implantation into the eye. After implantation into enucleated pig eyes and into rabbit eyes in vivo, the IOP was recorded and compared to established techniques of IOP measurement. Pressure chamber tests showed that the sensor functioned correctly after biocompatible encapsulation in polydimethylsiloxane. In vivo and in vitro tests in rabbit and pig eyes demonstrated that the implanted system worked with the same precision as established techniques for IOP determination. The correlation between the measurements with the implanted device and pneumotonometry in several experiments was between 0.9 and 0.99. This device serves as a functioning model for the realization of a telemetric IOP sensor for integration into an artificial intraocular lens. Such a device will open new perspectives, not only in the management of glaucoma, but also in basic research for mechanisms of glaucoma.

Prm1p, a pheromone-regulated multispanning membrane protein, facilitates plasma membrane fusion during yeast mating

Cell fusion occurs throughout development, from fertilization to organogenesis. The molecular mechanisms driving plasma membrane fusion in these processes remain unknown. While yeast mating offers an excellent model system in which to study cell fusion, all genes previously shown to regulate the process act at or before cell wall breakdown; i.e., well before the two plasma membranes have come in contact. Using a new strategy in which genomic data is used to predict which genes may possess a given function, we identified PRM1, a gene that is selectively expressed during mating and that encodes a multispanning transmembrane protein. Prm1p localizes to sites of cell-cell contact where fusion occurs. In matings between Deltaprm1 mutants, a large fraction of cells initiate zygote formation and degrade the cell wall separating mating partners but then fail to fuse. Electron microscopic analysis reveals that the two plasma membranes in these mating pairs are tightly apposed, remaining separated only by a uniform gap of approximately 8 nm. Thus, the phenotype of Deltaprm1 mutants defines a new step in the mating reaction in which membranes are juxtaposed, possibly through a defined adherence junction, yet remain unfused. This phenotype suggests a role for Prm1p in plasma membrane fusion.

Transplantation of autologous iris pigment epithelium after removal of choroidal neovascular membranes

BACKGROUND

Transplantation of autologous iris pigment epithelium (IPE) into the subretinal space has been suggested as one approach for the treatment of age-related macular degeneration, as well as for other conditions in which loss of retinal pigment epithelium (RPE) occurs. Surgical removal of choroidal neovascular membranes is associated with traumatic loss of the RPE cell layer, disruption of the integrity of the photoreceptor-RPE complex, and limited visual outcome.

OBJECTIVE

To examine whether IPE cells can substitute for RPE cells to be transplanted to the subretinal space of patients with either RPE degenerative disease or traumatic loss of the RPE cell layer after subretinal surgery.

METHODS

Autologous IPE cells were transplanted to the subretinal space in 20 consecutive patients undergoing removal of subretinal fibrovascular membranes using pars plana vitrectomy. Autologous IPE cells were harvested by iridectomy, isolated, and transplanted directly to the subretinal spaces. Transplants were evaluated for 6 to 11 months by funduscopy, fluorescein angiography, and scanning laser ophthalmoscopic (SLO) microperimetry.

RESULTS

For the entire follow-up period, no evidence of any immunologic response was observed. Revisional surgery was necessary in 3 patients because of complications (rhegmatogenous retinal detachment [n = 1]; proliferative vitreoretinopathy [n = 1]; and macular pucker [n = 1]); 1 patient did not receive IPE cells. Five of 19 phakic eyes underwent cataract surgery; in 1 case this was combined with the vitrectomy. Five patients showed improved visual acuity of 3 to 4 lines, 13 patients had stable visual acuity (+/-2 lines), and 2 patients had reduced visual acuity of 6 lines.

CONCLUSIONS

In this pilot study, the transplantation of autologous IPE cells was done as an addition to conventional surgical excision of choroidal neovascular membranes. Transplanted cells were well tolerated in the subretinal space and did not adversely affect the function of the photoreceptors, since improvement or stable visual acuity was observed in 18 patients after IPE transplantation. These results suggest that autologous IPE cells may be used as a substitute for autologous RPE cells to transplant to the subretinal space to treat age-related macular degeneration.

Unusual visual evoked potentials in patients with age-related macular degeneration

Among a series of patients with age-related macular degeneration (ARMD), a few individuals could be identified showing larger amplitudes of pattern reversal visual evoked potentials (prVEP) after stimulation of a central 3 degrees field compared to stimulation of a 13 degrees field although in the majority of ARMD patients and in normals, VEP amplitudes increased with increasing field size. An analysis of prVEPs recorded after stimulation of different macular zones showed that the 3 degrees central area and the perifoveal zone contributed differently to the 13 degrees response or macular response. Perifoveal activity in this subgroup of ARMD patients seemed to mask the foveal contribution to the macular prVEP. The cortical magnification factor in ARMD may be higher than in normal controls. Small-field stimulation techniques are therefore also recommended in patients with central retinal pathology.

Mandibular pseudocarcinomatous hyperplasia

AIMS

Three unusual cases of pseudocarcinomatous (pseudoepitheliomatous) hyperplasia (PH) affecting chronic osteomyelitic mandibular sequestra are reported to highlight the differences with the various squamous neoplasms which occur in that site.

METHODS AND RESULTS

In two patients carrying a mandibular graft following the excision of an ameloblastoma, mucosal ulcers resulted in chronic osteomyelitis. In a third patient, an apical dental infection was associated with fistulated osteomyelitis. Histology of the three sequestra showed an intraosseous squamous proliferation. It was characterized by a peripheral involvement of medullary spaces, the more mature epithelial layer covering the bone trabeculae without intervening stroma, and the basal type epithelial layer surrounding a central fibrovascular core. There were no histological or cytological signs of malignancy.

CONCLUSION

PH shows an inverted pattern when compared with the centro-medullary tumoural islands seen in the various oral or odontogenic squamous neoplasms which occur in the jaws. The lack of signs of malignancy distinguish PH from common squamous cell carcinomas. A short clinical course is an important feature in the distinction of PH from the well differentiated squamous cell carcinomas which may develop in fistulated chronic osteomyelitis.

The unfolded protein response regulates multiple aspects of secretory and membrane protein biogenesis and endoplasmic reticulum quality control

The unfolded protein response (UPR) is an intracellular signaling pathway that relays signals from the lumen of the ER to activate target genes in the nucleus. We devised a genetic screen in the yeast Saccharomyces cerevisiae to isolate mutants that are dependent on activation of the pathway for viability. Using this strategy, we isolated mutants affecting various aspects of ER function, including protein translocation, folding, glycosylation, glycosylphosphatidylinositol modification, and ER-associated protein degradation (ERAD). Extending results gleaned from the genetic studies, we demonstrate that the UPR regulates trafficking of proteins at the translocon to balance the needs of biosynthesis and ERAD. The approach also revealed connections of the UPR to other regulatory pathways. In particular, we identified SON1/RPN4, a recently described transcriptional regulator for genes encoding subunits of the proteasome. Our genetic strategy, therefore, offers a powerful means to provide insight into the physiology of the UPR and to identify novel genes with roles in many aspects of secretory and membrane protein biogenesis.

Role of 4.5S RNA in assembly of the bacterial signal recognition particle with its receptor

The mechanism by which a signal recognition particle (SRP) and its receptor mediate protein targeting to the endoplasmic reticulum or to the bacterial plasma membrane is evolutionarily conserved. In Escherichia coli, this reaction is mediated by the Ffh/4.5S RNA ribonucleoprotein complex (Ffh/4.5S RNP; the SRP) and the FtsY protein (the SRP receptor). We have quantified the effects of 4.5S RNA on Ffh-FtsY complex formation by monitoring changes in tryptophan fluorescence. Surprisingly, 4.5S RNA facilitates both assembly and disassembly of the Ffh-FtsY complex to a similar extent. These results provide an example of an RNA molecule facilitating protein-protein interactions in a catalytic fashion.