Browsing by Author "Walter, Peter"

Protein folding in the endoplasmic reticulum is a complex process whose malfunction is implicated in disease and aging. By using the cell's endogenous sensor (the unfolded protein response), we identified several hundred yeast genes with roles in endoplasmic reticulum folding and systematically characterized their functional interdependencies by measuring unfolded protein response levels in double mutants. This strategy revealed multiple conserved factors critical for endoplasmic reticulum folding, including an intimate dependence on the later secretory pathway, a previously uncharacterized six-protein transmembrane complex, and a co-chaperone complex that delivers tail-anchored proteins to their membrane insertion machinery. The use of a quantitative reporter in a comprehensive screen followed by systematic analysis of genetic dependencies should be broadly applicable to functional dissection of complex cellular processes from yeast to human.

The unfolded protein response (UPR) allows cells to adjust secretory pathway capacity according to need. Ire1, the endoplasmic reticulum (ER) stress sensor and central activator of the UPR is conserved from the budding yeast Saccharomyces cerevisiae to humans. Under ER stress conditions, Ire1 clusters into foci that enable optimal UPR activation. To discover factors that affect Ire1 clustering, we performed a high-content screen using a whole-genome yeast mutant library expressing Ire1-mCherry. We imaged the strains following UPR induction and found 154 strains that displayed alterations in Ire1 clustering. The hits were enriched for iron and heme effectors and binding proteins. By performing pharmacological depletion and repletion, we confirmed that iron (Fe3+) affects UPR activation in both yeast and human cells. We suggest that Ire1 clustering propensity depends on membrane composition, which is governed by heme-dependent biosynthesis of sterols. Our findings highlight the diverse cellular functions that feed into the UPR and emphasize the cross-talk between organelles required to concertedly maintain homeostasis.

Background: Rhegmatogenous retinal detachment is the most common retinological emergency threatening vision, with an incidence of 1 in 10 000 persons per year, corresponding to about 8000 new cases in Germany annually. Without treatment, blindness in the affected eye may result. Method: Selective review of the literature. Results: Rhegmatogenous retinal detachment typically presents with the perception of light flashes, floaters, or a "dark curtain." In most cases, the retinal tear is a consequence of degeneration of the vitreous body. Epidemiologic studies have identified myopia and prior cataract surgery as the main risk factors. Persons in the sixth and seventh decades of life are most commonly affected. Rhegmatogenous retinal detachment is an emergency, and all patients should be seen by an ophthalmologist on the same day that symptoms arise. The treatment consists of scleral buckle, removal of the vitreous body (vitrectomy), or a combination of the two. Anatomical success rates are in the range of 85% to 90%. Vitrectomy is followed by lens opacification in more than 70% of cases. The earlier the patient is seen by an ophthalmologist, the greater the chance that the macula is still attached, so that visual acuity can be preserved. Conclusion: Rhegmatogenous retinal detachment is among the main emergency indications in ophthalmology. In all such cases, an ophthalmologist must be consulted at once.

To identify risk factors associated with best-corrected visual acuity (BCVA) 1 year after initial surgery following primary vitrectomy (PV) and scleral buckling surgery (SB) for rhegmatogenous retinal detachment (RRD). Relating the final BCVA at the 1-year follow-up visit to pre- and intraoperative findings in the "randomized, prospective, multicenter clinical trial comparing scleral buckling versus primary vitrectomy for repair of rhegmatogenous retinal detachment" (SPR Study) using multivariate statistical methods. In the phakic subtrial, final BCVA is associated with the number of breaks (p = 0.0259), duration of symptoms (p = 0.0476), baseline BCVA (p = 0.0002), retinal detachment central to major vessels arcades (p = 0.0088), total detachment (p = 0.0027), and chain formation of breaks (p = 0.0129). In the pseudophakic/aphakic subtrial, final BCVA is related to the number of retinal breaks (p = 0.0010), secondary cataract or central capsular fibrosis (p = 0.0141), intraoperative laser photocoagulation (p = 0.0373), and inferior detachment with breaks below the 4 and 8 o'clock positions (p = 0.0173). Final BCVA is the most important outcome for patients undergoing RRD surgery. Our results demonstrate that the final BCVA is related to a higher preoperative number of breaks in both subtrials. Additional risk factors varied between phakic and pseudophakic subgroups.

Purpose: The 'Scleral buckling versus primary vitrectomy in rhegmatogenous retinal detachment study' (SPR study) is a randomized multicentre trial comparing primary vitrectomy (PV) and scleral buckling surgery (SB) for rhegmatogenous retinal detachment (RRD). This subanalysis was conducted to identify risk factors associated with anatomical outcomes. Methods: Relating the anatomical success results at the 1-year follow-up visit to pre- and intraoperative findings using multivariate statistical methods. Results: In the phakic subtrial, anatomical success was negatively associated with the number of breaks (p < 0.0001), break extension > 1 clock hour (p = 0.0005) and intraoperative use of cryotherapy (p = 0.0484). It was positively associated with retinal breaks with irregular edges (p = 0.0353) and subretinal fluid drainage (p = 0.0155). In the pseudophakic/aphakic subtrial, anatomical success was negatively associated with the number of retinal breaks (p = 0.0004) and previous YAG capsulotomy (p = 0.0256), and the combined effect of the surgical procedure and intraoperative use of laser (p = 0.0229). Conclusion: Primary anatomical success is an important result for patients undergoing RRD surgery. Our data demonstrate that the final anatomical outcome is related to a higher preoperative number of breaks and cryotherapy in phakic eyes. Additional risk factors varied between phakic and pseudophakic subgroups. Our findings may be used to facilitate the prognosis of future patients with RRD.

Eisosomes are stable domains at the plasma membrane of the budding yeast Saccharomyces cerevisiae and have been proposed to function in endocytosis. Eisosomes are composed of two main cytoplasmic proteins, Pil1 and Lsp1, that form a scaffold around furrow-like plasma membrane invaginations. We show here that the poorly characterized eisosome protein Seg1/Ymr086w is important for eisosome biogenesis and architecture. Seg1 was required for efficient incorporation of Pil1 into eisosomes and the generation of normal plasma membrane furrows. Seg1 preceded Pil1 during eisosome formation and established a platform for the assembly of other eisosome components. This platform was further shaped and stabilized upon the arrival of Pil1 and Lsp1. Moreover, Seg1 abundance controlled the shape of eisosomes by determining their length. Similarly, the Schizosaccharomyces pombe Seg1-like protein Sle1 was necessary to generate the filamentous eisosomes present in fission yeast. The function of Seg1 in the stepwise biogenesis of eisosomes reveals striking architectural similarities between eisosomes in yeast and caveolae in mammals.