Alcohol dependence activates ventral tegmental area projections to central amygdala in male mice and rats

The neural adaptations that occur during the transition to alcohol dependence are not entirely understood but may include a gradual recruitment of brain stress circuitry by mesolimbic reward circuitry that is activated during early stages of alcohol use. Here, we focused on dopaminergic and nondopaminergic projections from the ventral tegmental area (VTA), important for mediating acute alcohol reinforcement, to the central nucleus of the amygdala (CeA), important for alcohol dependence-related negative affect and escalated alcohol drinking. The VTA projects directly to the CeA, but the functional relevance of this circuit is not fully established. Therefore, we combined retrograde and anterograde tracing, anatomical, and electrophysiological experiments in mice and rats to demonstrate that the CeA receives input from both dopaminergic and nondopaminergic projection neurons primarily from the lateral VTA. We then used slice electrophysiology and fos immunohistochemistry to test the effects of alcohol dependence on activity and activation profiles of CeA-projecting neurons in the VTA. Our data indicate that alcohol dependence activates midbrain projections to the central amygdala, suggesting that VTA projections may trigger plasticity in the CeA during the transition to alcohol dependence and that this circuit may be involved in mediating behavioral dysregulation associated with alcohol dependence.

Novel Anti-TM4SF1 Antibody-Drug Conjugates with Activity against Tumor Cells and Tumor Vasculature

Antibody-drug conjugates (ADC) represent a promising therapeutic modality for managing cancer. Here, we report a novel humanized ADC that targets the tetraspanin-like protein TM4SF1. TM4SF1 is highly expressed on the plasma membranes of many human cancer cells and also on the endothelial cells lining tumor blood vessels. TM4SF1 is internalized upon interaction with antibodies. We hypothesized that an ADC against TM4SF1 would inhibit cancer growth directly by killing cancer cells and indirectly by attacking the tumor vasculature. We generated a humanized anti-human TM4SF1 monoclonal antibody, v1.10, and armed it with an auristatin cytotoxic agent LP2 (chemical name mc-3377). v1.10-LP2 selectively killed cultured human tumor cell lines and human endothelial cells that express TM4SF1. Acting as a single agent, v1.10-LP2 induced complete regression of several TM4SF1-expressing tumor xenografts in nude mice, including non-small cell lung cancer and pancreas, prostate, and colon cancers. As v1.10 did not react with mouse TM4SF1, it could not target the mouse tumor vasculature. Therefore, we generated a surrogate anti-mouse TM4SF1 antibody, 2A7A, and conjugated it to LP2. At 3 mpk, 2A7A-LP2 regressed several tumor xenografts without noticeable toxicity. Combination therapy with v1.10-LP2 and 2A7A-LP2 together was more effective than either ADC alone. These data provide proof-of-concept that TM4SF1-targeting ADCs have potential as anticancer agents with dual action against tumor cells and the tumor vasculature. Such agents could offer exceptional therapeutic value and warrant further investigation. Mol Cancer Ther; 14(8); 1868-76. ©2015 AACR.

Secretion from bacterial versus mammalian cells yields a recombinant scFv with variable folding properties

Escherichia coli (E. coli) is the most commonly used organism for expressing antibody fragments such as single chain antibody Fvs (scFvs). Previously, we have utilized E. coli to express well-folded scFvs for characterization and engineering purposes with the goal of using these engineered proteins as building blocks for generating IgG-like bispecific antibodies (BsAbs). In the study, described here, we observed a significant difference in the secondary structure of an scFv produced in E. coli and the same scFv expressed and secreted from chinese hamster ovary (CHO) cells as part of a BsAb. We devised a proteolytic procedure to separate the CHO-derived scFv from its antibody-fusion partner and compared its properties with those of the E. coli-derived scFv. In comparison to the CHO-derived scFv, the E. coli-derived scFv was found trapped in a misfolded, but monomeric state that was stable for months at 4 °C. The misfolded state bound antigen in a heterogeneous fashion that included non-specific binding, which made functional characterization challenging. This odd incidence of obtaining a misfolded scFv from bacteria suggests careful characterization of the folded properties of bacterially expressed scFvs is warranted if anomalous issues with antigen-binding or non-specificity occur during an engineering campaign. Additionally, our proteolytic methodology for obtaining significant levels of intact scFvs from highly expressed IgG-like antibody proteins serves as a robust method for producing scFvs in CHO without the use of designed cleavage motifs.

A stable IgG-like bispecific antibody targeting the epidermal growth factor receptor and the type I insulin-like growth factor receptor demonstrates superior anti-tumor activity

The epidermal growth factor receptor (EGFR) and the type I insulin-like growth factor receptor (IGF-1R) are two cell surface receptor tyrosine kinases known to cooperate to promote tumor progression and drug resistance. Combined blockade of EGFR and IGF-1R has shown improved anti-tumor activity in preclinical models. Here, we report the characterization of a stable IgG-like bispecific antibody (BsAb) dual-targeting EGFR and IGF-1R that was developed for cancer therapy. The BsAb molecule (EI-04), constructed with a stability-engineered single chain variable fragment (scFv) against IGF-1R attached to the carboxyl-terminus of an IgG against EGFR, displays favorable biophysical properties for biopharmaceutical development. Biochemically, EI-04 bound to human EGFR and IGF-1R with sub nanomolar affinity, co-engaged the two receptors simultaneously, and blocked the binding of their respective ligands with similar potency compared to the parental monoclonal antibodies (mAbs). In tumor cells, EI-04 effectively inhibited EGFR and IGF-1R phosphorylation, and concurrently blocked downstream AKT and ERK activation, resulting in greater inhibition of tumor cell growth and cell cycle progression than the single mAbs. EI-04, likely due to its tetravalent bispecific format, exhibited high avidity binding to BxPC3 tumor cells co-expressing EGFR and IGF-1R, and consequently improved potency at inhibiting IGF-driven cell growth over the mAb combination. Importantly, EI-04 demonstrated enhanced in vivo anti-tumor efficacy over the parental mAbs in two xenograft models, and even over the mAb combination in the BxPC3 model. Our data support the clinical investigation of EI-04 as a superior cancer therapeutic in treating EGFR and IGF-1R pathway responsive tumors.

Stable IgG-like bispecific antibodies directed toward the type I insulin-like growth factor receptor demonstrate enhanced ligand blockade and anti-tumor activity

Bispecific antibodies (BsAbs) target multiple epitopes on the same molecular target or different targets. Although interest in BsAbs has persisted for decades, production of stable and active BsAbs has hindered their clinical evaluation. Here, we describe the production and characterization of tetravalent IgG-like BsAbs that combine the activities of allosteric and competitive inhibitors of the type-I insulin-like growth factor receptor (IGF-1R). The BsAbs, which were engineered for thermal stability, express well, demonstrate favorable biophysical properties, and recognize both epitopes on IGF-1R. Only one BsAb with a unique geometry, denoted BIIB4-5scFv, was capable of engaging all four of its binding arms simultaneously. All the BsAbs (especially BIIB4-5scFv) demonstrated enhanced ligand blocking over the single monoclonal antibodies (mAbs), particularly at high ligand concentrations. The pharmacokinetic profiles of two IgG-like BsAbs were tested in nude mice and shown to be comparable with that of the parental mAbs. The BsAbs, especially BIIB4-5scFv, demonstrated an improved ability to reduce the growth of multiple tumor cell lines and to inhibit ligand-induced IGF-1R signaling in tumor cells over the parental mAbs. BIIB4-5scFv also led to superior tumor growth inhibition over its parental mAbs in vivo. In summary, BsAbs that bridge multiple inhibitory mechanisms against a single target may generally represent a more effective strategy for intervention in oncology or other indications compared with traditional mAb therapy.

Stability engineering of scFvs for the development of bispecific and multivalent antibodies

Single-chain Fvs (scFvs) are commonly used building blocks for creating engineered diagnostic and therapeutic antibody molecules. Bispecific antibodies (BsAbs) hold particular interest due to their ability to simultaneously bind and engage two distinct targets. We describe a technology for producing stable, scalable IgG-like bispecific and multivalent antibodies based on methods for rapidly engineering thermally stable scFvs. Focused libraries of mutant scFvs were designed using a combination of sequence-based statistical analyses and structure-, and knowledge-based methods. Libraries encoding these designs were expressed in E. coli and culture supernatants-containing soluble scFvs screened in a high-throughput assay incorporating a thermal challenge prior to an antigen-binding assay. Thermally stable scFvs were identified that retain full antigen-binding affinity. Single mutations were found that increased the measured T(m) of either the V(H) or V(L) domain by as much as 14 degrees C relative to the wild-type scFv. Combinations of mutations further increased the T(m) by as much as an additional 12 degrees C. Introduction of a stability-engineered scFv as part of an IgG-like BsAb enabled scalable production and purification of BsAb with favorable biophysical properties.

Anti-tumor activity of stability-engineered IgG-like bispecific antibodies targeting TRAIL-R2 and LTbetaR

Bispecific antibodies (BsAbs) represent an emerging class of biologics that achieve dual targeting with a single agent. Recombinant DNA technologies have facilitated a variety of creative bispecific designs with many promising therapeutic applications; however, practical methods for producing high quality BsAbs that have good product stability, long serum half-life, straightforward purification, and scalable production have largely been limiting. Here we describe a protein-engineering approach for producing stable, scalable tetravalent IgG-like BsAbs. The stability-engineered IgG-like BsAb was envisioned to target and crosslink two TNF family member receptors, TRAIL-R2 (TNF-Related Apoptosis Inducing Ligand Receptor-2) and LTbetaR (Lymphotoxin-beta Receptor), expressed on the surface of epithelial tumor cells with the goal of triggering an enhanced anti-tumor effect. Our IgG-like BsAbs consists of a stability-engineered anti-LTbetaR single chain Fv (scFv) genetically fused to either the N- or C-terminus of the heavy chain of a fulllength anti-TRAIL-R2 IgG1 monoclonal antibody. Both N- or C-terminal BsAbs were active in inhibiting tumor cell growth in vitro, and with some cell lines demonstrated enhanced activity relative to the combination of parental Abs. Pharmacokinetic studies in mice revealed long serum half-lives for the BsAbs. In murine tumor xenograft models, therapeutic treatment with the BsAbs resulted in reduction in tumor volume either comparable to or greater than the combination of parental antibodies, indicating that simultaneously targeting and cross-linking receptor pairs is an effective strategy for treating tumor cells. These studies support that stability-engineering is an enabling step for producing scalable IgG-like BsAbs with properties desirable for biopharmaceutical development.

Peroxisome remnants in pex3delta cells and the requirement of Pex3p for interactions between the peroxisomal docking and translocation subcomplexes

During peroxisomal matrix protein import, the peroxisomal targeting signal receptors recognize cargo in the cytosol and interact with docking and translocation subcomplexes on the peroxisomal membrane. Using immunoprecipitations of multiple protein components, we show that in Pichia pastoris the docking subcomplex consists of the unique peroxins Pex13p, Pex14p and Pex17p, whereas the putative translocation subcomplex has all three RING-finger peroxins, Pex2p, Pex10p and Pex12p, as unique constituents. We identify Pex3p as a shared component of both subcomplexes. In pex3delta cells, the unique constituents of the docking subcomplex interact as they do in wild-type cells, but the assembly of the translocation subcomplex is impaired and its components are present at reduced levels. Furthermore, several interactions detected in wild-type cells between translocation and docking subcomplex components are undetectable in pex3delta cells. Contrary to previous reports, pex3delta cells have peroxisome remnants that pellet during high-speed centrifugation, associate with membranes on floatation gradients and can be visualized by deconvolution microscopy using antibodies to several peroxins which were not available earlier. We discuss roles for Pex3p in the assembly of specific peroxisomal membrane protein subcomplexes whose formation is necessary for matrix protein import.

Endosome-associated complex, ESCRT-II, recruits transport machinery for protein sorting at the multivesicular body

Sorting of ubiquitinated endosomal membrane proteins into the MVB pathway is executed by the class E Vps protein complexes ESCRT-I, -II, and -III, and the AAA-type ATPase Vps4. This study characterizes ESCRT-II, a soluble approximately 155 kDa protein complex formed by the class E Vps proteins Vps22, Vps25, and Vps36. This protein complex transiently associates with the endosomal membrane and thereby initiates the formation of ESCRT-III, a membrane-associated protein complex that functions immediately downstream of ESCRT-II during sorting of MVB cargo. ESCRT-II in turn functions downstream of ESCRT-I, a protein complex that binds to ubiquitinated endosomal cargo. We propose that the ESCRT complexes perform a coordinated cascade of events to select and sort MVB cargoes for delivery to the lumen of the vacuole/lysosome.

Pichia pastoris Pex14p, a phosphorylated peroxisomal membrane protein, is part of a PTS-receptor docking complex and interacts with many peroxins

The peroxisomal protein import machinery plays a central role in the assembly of this organelle in all eukaryotes. Genes encoding components of this machinery, termed peroxins or Pex proteins, have been isolated and characterized in several yeast species and in mammals, including humans. Here we report on one of these components, Pex14p, from the methylotrophic yeast Pichia pastoris. Work in other organisms has shown that Pex14p is located on the cytoplasmic surface of the peroxisomal membrane and binds peroxisomal targeting signal (PTS) receptors carrying proteins bound for the peroxisomal matrix, results that have led to the hypothesis that Pex14p is a receptor-docking protein. P. pastoris Pex14p (PpPex14p) behaves like an integral membrane protein, with its C-terminus exposed on the cytosolic side of the peroxisomal membrane. PpPex14p complexes with many peroxins, including Pex3p (Snyder et al., 1999b), Pex5p, Pex7p, Pex13p, Pex17p, itself, and a previously unreported peroxin, Pex8p. A portion of Pex14p is phosphorylated, but both phosphorylated and unphosphorylated forms of Pex14p interact with several peroxins. The interactions between Pex14p and other peroxins provide clues regarding the function of Pex14p in peroxisomal protein import.

Import of peroxisomal matrix and membrane proteins

This review summarizes the progress made in our understanding of peroxisome biogenesis in the last few years, during which the functional roles of many of the 23 peroxins (proteins involved in peroxisomal protein import and peroxisome biogenesis) have become clearer. Previous reviews in the field have focussed on the metabolic functions of peroxisomes, aspects of import/biogenesis the role of peroxins in human disease, and involvement of the endoplasmic reticulum in peroxisome membrane biogenesis as well as the degradation of this organelle. This review refers to some of the earlier work for the sake of introduction and continuity but deals primarily with the more recent progress. The principal areas of progress are the identification of new peroxins, definition of protein-protein interactions among peroxins leading to the recognition of complexes involved in peroxisomal protein import, insight into the biogenesis of peroxisomal membrane proteins, and, of most importance, the elucidation of the role of many conserved peroxins in human disease. Given the rapid progress in the field, this review also highlights some of the unanswered questions that remain to be tackled.

The peroxin Pex19p interacts with multiple, integral membrane proteins at the peroxisomal membrane

Pex19p is a protein required for the early stages of peroxisome biogenesis, but its precise function and site of action are unknown. We tested the interaction between Pex19p and all known Pichia pastoris Pex proteins by the yeast two-hybrid assay. Pex19p interacted with six of seven known integral peroxisomal membrane proteins (iPMPs), and these interactions were confirmed by coimmunoprecipitation. The interactions were not reduced upon inhibition of new protein synthesis, suggesting that they occur with preexisting, and not newly synthesized, pools of iPMPs. By mapping the domains in six iPMPs that interact with Pex19p and the iPMP sequences responsible for targeting to the peroxisome membrane (mPTSs), we found the majority of these sites do not overlap. Coimmunoprecipitation of Pex19p from fractions that contain peroxisomes or cytosol revealed that the interactions between predominantly cytosolic Pex19p and the iPMPs occur in the organelle pellet that contains peroxisomes. These data, taken together, suggest that Pex19p may have a chaperone-like role at the peroxisome membrane and that it is not the receptor for targeting of iPMPs to the peroxisome.

Ulnar neuropathy as a complication of macular hole surgery

OBJECTIVE

To report a series of patients manifesting ulnar neuropathy as an extraocular complication following macular hole surgery and facedown positioning.

METHODS

Retrospective chart review of 7 patients identified by the operating surgeon as developing ulnar neuropathy during the immediate postoperative period after undergoing vitrectomy surgery with fluid-gas exchange for macular hole followed by at least 1 week of strict facedown positioning.

RESULTS

All 7 patients developed symptoms of ulnar neuropathy, including paresthesias, dysesthesias, pain, weakness, and muscle atrophy. Signs included abnormal electromyogram, prolonged nerve conduction velocities, and impaired neurologic clinical test results in patients examined. Symptoms did not resolve with cessation of facedown positioning, and with follow-up ranging from 3 to 24 months all patients had persistent symptoms. All patients had positioned themselves with their arms continuously flexed. Three of 7 patients had placed pressure directly on their bent elbows.

CONCLUSIONS

Ulnar neuropathy is an extraocular complication of macular hole surgery that can be attributed to arm position during postoperative facedown positioning. Surgeons performing macular hole surgery should caution their patients to minimize the amount of time spent with their elbows in a flexed position. Particular effort should be made to minimize pressure on the bent elbow.

Pex17p is required for import of both peroxisome membrane and lumenal proteins and interacts with Pex19p and the peroxisome targeting signal-receptor docking complex in Pichia pastoris

Pichia pastoris PEX17 was cloned by complementation of a peroxisome-deficient strain obtained from a novel screen for mutants disrupted in the localization of a peroxisomal membrane protein (PMP) reporter. PEX17 encodes a 267-amino-acid protein with low identity (18%) to the previously characterized Saccharomyces cerevisiae Pex17p. Like ScPex17p, PpPex17p contains a putative transmembrane domain near the amino terminus and two carboxyl-terminal coiled-coil regions. PpPex17p behaves as an integral PMP with a cytosolic carboxyl-terminal domain. pex17Delta mutants accumulate peroxisomal matrix proteins and certain integral PMPs in the cytosol, suggesting a critical role for Pex17p in their localization. Peroxisome remnants were observed in the pex17Delta mutant by morphological and biochemical means, suggesting that Pex17p is not absolutely required for remnant formation. Yeast two-hybrid analysis demonstrated that the carboxyl terminus of Pex19p was required for interaction with Pex17p lacking the carboxyl-terminal coiled-coil domains. Biochemical evidence confirmed the interaction between Pex19p and Pex17p. Additionally, Pex17p cross-linked to components of the peroxisome targeting signal-receptor docking complex, which unexpectedly contained Pex3p. Our evidence suggests the existence of distinct subcomplexes that contain separable pools of Pex3p, Pex19p, Pex17p, Pex14p, and the peroxisome targeting signal receptors. These distinct pools may serve different purposes for the import of matrix proteins or PMPs.

Pex22p of Pichia pastoris, essential for peroxisomal matrix protein import, anchors the ubiquitin-conjugating enzyme, Pex4p, on the peroxisomal membrane

We isolated a Pichia pastoris mutant that was unable to grow on the peroxisome-requiring media, methanol and oleate. Cloning the gene by complementation revealed that the encoded protein, Pex22p, is a new peroxin. A Deltapex22 strain does not grow on methanol or oleate and is unable to import peroxisomal matrix proteins. However, this strain targets peroxisomal membrane proteins to membranes, most likely peroxisomal remnants, detectable by fluorescence and electron microscopy. Pex22p, composed of 187 amino acids, is an integral peroxisomal membrane protein with its NH2 terminus in the matrix and its COOH terminus in the cytosol. It contains a 25-amino acid peroxisome membrane-targeting signal at its NH2 terminus. Pex22p interacts with the ubiquitin-conjugating enzyme Pex4p, a peripheral peroxisomal membrane protein, in vivo, and in a yeast two-hybrid experiment. Pex22p is required for the peroxisomal localization of Pex4p and in strains lacking Pex22p, the Pex4p is cytosolic and unstable. Therefore, Pex22p anchors Pex4p at the peroxisomal membrane. Strains that do not express Pex4p or Pex22p have similar phenotypes and lack Pex5p, suggesting that Pex4p and Pex22p act at the same step in peroxisome biogenesis. The Saccharomyces cerevisiae hypothetical protein, Yaf5p, is the functional homologue of P. pastoris Pex22p.

Current popularity of pneumatic retinopexy

PURPOSE

To compare the popularity of pneumatic retinopexy (PR) in 1997 with its popularity in 1990 among retinal specialists.

METHODS

In 1997, a survey was mailed to the 1994-1995 members of the Retina or Vitreous Societies who lived in the United States or Canada, asking how they would manage a hypothetical retinal detachment. The choices were limited to PR, segmental scleral buckling, scleral bucking with encircling, primary vitrectomy, and Lincoff balloon. The results of the survey were compared with those previously reported by a similar survey in 1990.

RESULTS

The majority (55%) of respondents selected PR, which is a twofold increase over those who preferred it in 1990 (odds ratio 2.08; 95% confidence interval 1.53, 2.85). The popularity of PR was inversely proportional to the length of time the respondents had been in practice. If the eye with the hypothetical detachment had pseudophakia, only 30% of respondents selected PR. If the eye had additional tears, vitreous hemorrhage, or lattice degeneration, only about one-sixth preferred PR.

CONCLUSION

Pneumatic retinopexy was much more popular in 1997 than it was in 1990. Its popularity continues to be influenced by the age of the surgeon and by the complexity of the detachment.

Pex19p interacts with Pex3p and Pex10p and is essential for peroxisome biogenesis in Pichia pastoris

We report the cloning and characterization of Pichia pastoris PEX19 by complementation of a peroxisome-deficient mutant strain. Import of peroxisomal targeting signal 1- and 2-containing peroxisomal matrix proteins is defective in pex19 mutants. PEX19 encodes a hydrophilic 299-amino acid protein with sequence similarity to Saccharomyces cerevisiae Pex19p and human and Chinese hamster PxF, all farnesylated proteins, as well as hypothetical proteins from Caenorhabditis elegans and Schizosaccharomyces pombe. The farnesylation consensus is conserved in PpPex19p but dispensable for function and appears unmodified under the conditions tested. Pex19p localizes predominantly to the cytosolic fraction. Biochemical and two-hybrid analyses confirmed that Pex19p interacts with Pex3p, as seen in S. cerevisiae, but unexpectedly also with Pex10p. Two-hybrid analysis demonstrated that the amino-terminal 42 amino acids of Pex19p interact with the carboxyl-terminal 335 amino acids of Pex3p. In addition, the extreme carboxyl terminus of Pex19p (67 amino acids) is required for interaction with the amino-terminal 380 amino acids of Pex10p. Biochemical and immunofluorescence microscopy analyses of pex19Delta cells identified the membrane protein Pex3p in peroxisome remnants that were not previously observed in S. cerevisiae. These small vesicular and tubular (early) remnants are morphologically distinct from other Pppex mutant (late) remnants, suggesting that Pex19p functions at an early stage of peroxisome biogenesis.

Overexpression of Pex15p, a phosphorylated peroxisomal integral membrane protein required for peroxisome assembly in S.cerevisiae, causes proliferation of the endoplasmic reticulum membrane

We have cloned PEX15 which is required for peroxisome biogenesis in Saccharomyces cerevisiae. pex15Delta cells are characterized by the cytosolic accumulation of peroxisomal matrix proteins containing a PTS1 or PTS2 import signal, whereas peroxisomal membrane proteins are present in peroxisomal remnants. PEX15 encodes a phosphorylated, integral peroxisomal membrane protein (Pex15p). Using multiple in vivo methods to determine the topology, Pex15p was found to be a tail-anchored type II (Ncyt-Clumen) peroxisomal membrane protein with a single transmembrane domain near its carboxy-terminus. Overexpression of Pex15p resulted in impaired peroxisome assembly, and caused profound proliferation of the endoplasmic reticulum (ER) membrane. The lumenal carboxy-terminal tail of Pex15p protrudes into the lumen of these ER membranes, as demonstrated by its O-glycosylation. Accumulation in the ER was also observed at an endogenous expression level when Pex15p was fused to the N-terminus of mature invertase. This resulted in core N-glycosylation of the hybrid protein. The lumenal C-terminal tail of Pex15p is essential for targeting to the peroxisomal membrane. Furthermore, the peroxisomal membrane targeting signal of Pex15p overlaps with an ER targeting signal on this protein. These results indicate that Pex15p may be targeted to peroxisomes via the ER, or to both organelles.

Characterization of VPS41, a gene required for vacuolar trafficking and high-affinity iron transport in yeast

Mutations in the yeast gene VPS41 give rise to poor growth on low iron medium, severe alterations in vacuolar morphology, and cause the missorting of membranous and soluble vacuolar proteins. Our studies predict that VPS41 encodes a hydrophilic protein of 992 amino acids that contains no obvious signal sequence or hydrophobic domains. The deduced Vps41p sequence contains a domain rich in glutamic and aspartic residues, as well as a domain with resemblance to a region of clathrin heavy chain. We have also identified and sequenced putative VPS41 homologues from Caenorhabditis elegans, plants, and humans. The VPS41 homologues (but not the yeast VPS41 itself) contain a conserved cysteine-rich RING-H2 zinc finger at their COOH termini. Biochemical experiments suggest that VPS41 functions in post-Golgi protein processing: the deletion mutant exhibits defective high affinity transport due to impaired Fet3p activity and also exhibits defects in the processing and sorting of multiple vacuolar hydrolases.

Novel Golgi to vacuole delivery pathway in yeast: identification of a sorting determinant and required transport component

More than 40 vacuolar protein sorting (vps) mutants have been identified which secrete proenzyme forms of soluble vacuolar hydrolases to the cell surface. A subset of these mutants has been found to show selective defects in the sorting of two vacuolar membrane proteins. Under non-permissive conditions, vps45tsf (SEC1 homolog) and pep12/vps6tsf (endosomal t-SNARE) mutants efficiently sort alkaline phosphatase (ALP) to the vacuole while multiple soluble vacuolar proteins and the membrane protein carboxypeptidase yscS (CPS) are no longer delivered to the vacuole. Vacuolar localization of ALP in these mutants does not require transport to the plasma membrane followed by endocytic uptake, as double mutants of pep12tsf and vps45tsf with sec1 and end3 sort and mature ALP at the non-permissive temperature. Given the demonstrated role of t-SNAREs such as Pep12p in transport vesicle recognition, our results indicate that ALP and CPS are packaged into distinct transport intermediates. Consistent with ALP following an alternative route to the vacuole, isolation of a vps41tsf mutant revealed that at non-permissive temperature ALP is mislocalized while vacuolar delivery of CPS and CPY is maintained. A series of domain-swapping experiments was used to define the sorting signal that directs selective packaging and transport of ALP. Our data demonstrate that the amino-terminal 16 amino acid portion of the ALP cytoplasmic tail domain contains a vacuolar sorting signal which is responsible for the active recognition, packaging and transport of ALP from the Golgi to the vacuole via a novel delivery pathway.

Visual field defects after macular hole surgery. A new finding

PURPOSE

The purpose of the study is to report the problem of a temporal visual field defect occurring after macular hole surgery.

METHODS

The authors reviewed the records of 13 patients found to have visual field defects after vitrectomy for macular holes. Fluorescein angiograms (13 patients), optic nerve photographs (13 patients), focal electroretinograms (3 patients), and nerve fiber analyses (8 patients) were performed in patients with visual field defects.

RESULTS

An absolute, temporal, usually inferior field defect was noted in 13 patients. In eight patients, the defect was detected because of specific reports or retrospective field examination results. Five patients examined in a prospective manner were found to have field defects. No history of abnormal intraocular pressure or direct trauma to the optic nerve or retinal vessels was identified. Four patients showed optic nerve pallor and three had an anomalous-appearing disc. Focal electroretinograms were of similar amplitude in the involved retina compared to corresponding areas in the healthy fellow eye. Nerve fiber analysis showed a reduction in nerve fiber layer thickness correlating to the visual field defect in those eight patients in which this test was used.

CONCLUSION

A significant temporal field defect may occur in patients after otherwise uncomplicated surgery for macular holes. The cause is unclear; however, reductions in nerve fiber layer thickness from the superior and nasal peripapillary area suggest that acute surgical release of the posterior hyaloid and the use of long-acting intraocular gas may in certain patients result in visual field defects.

Mutational activation of the Cpx signal transduction pathway of Escherichia coli suppresses the toxicity conferred by certain envelope-associated stresses

The processing-defective outer membrane porin protein LamBA23D (Carlson and Silhavy, 1993) and a tripartite fusion protein, LamB-LacZ-PhoA (Snyder and Silhavy, 1995), are both secreted across the cytoplasmic membrane of Escherichia coli, where they exert an extracytoplasmic toxicity. Suppressors of these toxicities map to a previously characterized gene, cpxA, that encodes the sensor kinase protein of a two-component regulatory system. These activated cpxA alleles, designated as cpxA*, stimulate transcription of the periplasmic protease DegP (Danese et al., 1995), which in turn catalyses degradation of the tripartite fusion protein. In contrast, degradation of precursor LamBA23D is not significantly stimulated in a cpxA* suppressor background. In fact, increased levels of DegP in a wild-type background stabilized this protein. While a functional degP gene is required for full cpxA*-mediated suppression of both toxic envelope proteins, residual suppression is seen in cpxA* degP::Tn10 double mutants. Furthermore, cpxA* mutations suppress the toxicity conferred by the LamB-LacZ hybrid protein, which exerts its effects in the cytoplasm, sequestered from DegP. Together, these observations suggest that the activated Cpx pathway regulates additional downstream targets that contribute to suppression. A subset of these targets may constitute a regulon involved in relieving extracytoplasmic and/or secretion-related stress.

Overproduction of NlpE, a new outer membrane lipoprotein, suppresses the toxicity of periplasmic LacZ by activation of the Cpx signal transduction pathway

The LamB-LacZ-PhoA tripartite fusion protein is secreted to the periplasm, where it exerts a toxicity of unknown origin during high-level synthesis in the presence of the inducer maltose, a phenotype referred to as maltose sensitivity. We selected multicopy suppressors of this toxicity that allow growth of the tripartite fusion strains in the presence of maltose. Mapping and subclone analysis of the suppressor locus identified a previously uncharacterized chromosomal region at 4.7 min that is responsible for suppression. DNA sequence analysis revealed a new gene with the potential to code for a protein of 236 amino acids with a predicted molecular mass of 25,829 Da. The gene product contains an amino-terminal signal sequence to direct the protein for secretion and a consensus lipoprotein modification sequence. As predicted from the sequence, the suppressor protein is labeled with [3H]palmitate and is localized to the outer membrane. Accordingly, the gene has been named nlpE (for new lipoprotein E). Increased expression of NlpE suppresses the maltose sensitivity of tripartite fusion strains and also the extracytoplasmic toxicities conferred by a mutant outer membrane protein, LamBA23D. Suppression occurs by activation of the Cpx two-component signal transduction pathway. This pathway controls the expression of the periplasmic protease DegP and other factors that can combat certain types of extracytoplasmic stress.

The Cpx two-component signal transduction pathway of Escherichia coli regulates transcription of the gene specifying the stress-inducible periplasmic protease, DegP

DegP is a heat-shock inducible periplasmic protease in Escherichia coli. Unlike the cytoplasmic heat shock proteins, DegP is not transcriptionally regulated by the classical heat shock regulon coordinated by sigma 32. Rather, the degP gene is transcriptionally regulated by an alternate heat shock sigma factor, sigma E. Previous studies have demonstrated a signal transduction pathway that monitors the amount of outer-membrane proteins in the bacterial envelope and modulates degP levels in response to this extracytoplasmic parameter. To analyze the transcriptional regulation of degP, we examined mutations that altered transcription of a degP-lacZ operon fusion. Gain-of-function mutations in cpxA, which specifies a two-component sensor protein, stimulate transcription from degP. Defined null mutations in cpxA or the gene encoding its cognate response regulator, cpxR, decrease transcription from degP. These null mutations also prevent transcriptional induction of degP in response to overexpression of a gene specifying an envelope lipoprotein. Cpx-mediated transcription of degP is partially dependent on the activity of E sigma E, suggesting that the Cpx pathway functions in concert with E sigma E and perhaps other RNA polymerases to drive transcription of degP.

Beta-galactosidase is inactivated by intermolecular disulfide bonds and is toxic when secreted to the periplasm of Escherichia coli

The wild-type LamB-LacZ hybrid protein inhibits the export machinery upon induction when assayed by biochemical and genetic techniques, a phenotype referred to as hybrid protein jamming. This hybrid protein also renders cells sensitive to growth in the presence of the inducer maltose, presumably because of the jamming. We constructed a new version of this fusion by adding alkaline phosphatase, encoded by phoA, to the C terminus of the LamB-LacZ hybrid protein. This tripartite protein, LamB-LacZ-PhoA, is as toxic to cells as the hybrid LamB-LacZ; however, it does not jam at temperatures greater than 33 degrees C. Extreme C-terminal sequences of LacZ function as a critical folding domain and are therefore responsible for stabilizing the LacZ structure. To determine if this region of LacZ is important for jamming, we recombined a late nonsense mutation (X90) onto the hybrid construct. We found the toxicity of this new hybrid, LamB-LacZX90, to be nearly identical to that of the full-length protein, but it also does not jam the secretion machinery. This suggests that jamming is caused by LacZ folding. We found no inhibition of secretion in the tripartite and X90 fusion strains at 37 degrees C, suggesting that the toxicity of the new fusions is novel. Under these conditions, the tripartite and X90 fusion proteins form disulfide-bonded aggregates with high molecular weights in the periplasm. Accordingly, we believe that LacZ disrupts some essential function(s) in the periplasm.

Cloning and characterization of the psaE gene of the cyanobacterium Synechococcus sp. PCC 7002: characterization of a psaE mutant and overproduction of the protein in Escherichia coli

The psaE gene, encoding a 7.5 kDa peripheral protein of the photosystem I complex, has been cloned and characterized from the cyanobacterium Synechococcus sp. PCC 7002. The gene is transcribed as an abundant monocistronic transcript of approximately 325 nt. The PsaE protein has been overproduced in Escherichia coli, purified to homogeneity, and used to raise polyclonal antibodies. Mutant strains, in which the psaE gene was insertionally inactivated by interposon mutagenesis, were constructed and characterized. Although the PS I complexes of these strains were similar to those of the wild type, the strains grew more slowly under conditions which favour cyclic electron transport and could not grow at all under photoheterotrophic conditions. The results suggest that PsaE plays a role in cyclic electron transport in cyanobacteria.

Limiting applications of cryotherapy for severe retinopathy of prematurity

In an effort to minimize surgical and visual morbidity of cryotherapy for retinopathy of prematurity (ROP), 18 eyes of 13 patients with 3 to 7 clock hours of stage 3 ROP with "plus" disease were treated by cryotherapy applications limited to the avascular retina adjacent to the areas of stage 3 disease. In 17 of 18 eyes, this limited use of cryotherapy was sufficient to cause regression of ROP without further treatments. After at least 3 months follow-up, ROP outcome showed a normal macular appearance in 16 eyes; two eyes developed macular dragging; no retinal detachments occurred.

Enhanced export of beta-galactosidase fusion proteins in prlF mutants is Lon dependent

We have used fusions of the outer membrane protein LamB to beta-galactosidase (encoded by lacZ) to study the protein export process. This LamB-LacZ hybrid protein blocks export when synthesized at high levels, as evidenced by inducer (maltose) sensitivity, a phenomenon termed LacZ hybrid jamming. The prlF1 mutation relieves LacZ hybrid jamming and allows localization of the fusion protein to a noncytoplasmic compartment. prlF1 and similar alleles are gain-of-function mutations. Null mutations in this gene confer no obvious phenotypes. Extragenic suppressors of a gain-of-function prlF allele have been isolated in order to understand how this gene product affects the export process. The suppressors are all lon null mutations, and they are epistatic to all prlF phenotypes tested. Lon protease activity has been measured in prlF1 cells and shown to be increased. However, the synthesis of Lon is not increased in a prlF1 background, suggesting a previously unidentified mechanism of Lon activation. Further analysis reveals that prlF1 activates degradation of cytoplasmically localized precursors in a Lon protease-dependent manner. It is proposed that accumulation of precursors during conditions of hybrid protein jamming titrates an essential export component(s), possibly a chaperone. Increased Lon-dependent precursor degradation would free this component, thus allowing increased protein export under jamming conditions.

Vitrectomy in eyes at risk for macular hole formation

Fifteen eyes believed to be at increased risk for macular hole formation underwent vitrectomy in an attempt to prevent macular hole formation. Full-thickness macular holes have not developed in 10 of 11 eyes with stage 1 macular holes. Four eyes were noted to have small full-thickness foveal defects (stage 2 macular holes) at the time of vitrectomy. Two of the four eyes have not progressed to macular hole formation and have 20/25 visual acuity. All patients have been followed for a minimum of 13 months (median, 18 months). The 12 eyes that have not experienced macular hole formation have had a significant (P less than 0.001) improvement in vision with seven (58%) attaining visual acuity of 20/25 or better. The postoperative foveal electroretinogram (ERG) amplitude was higher than the preoperative amplitude in five of the six eyes tested.

Temporary keratoprosthesis for combined penetrating keratoplasty, pars plana vitrectomy, and repair of retinal detachment

The Landers-Foulks temporary keratoprosthesis was used to combine penetrating keratoplasty, pars plana vitrectomy, and scleral buckling in the management of 13 eyes with opaque cornea and posterior segment abnormalities. In seven cases, trauma precipitated the ocular disease. Complications of cataract surgery resulted in anterior and posterior segment pathology in six cases. The corneal graft was initially clear in all cases. However, corneal edema complicated phthisis bulbi in four cases and followed homograft reaction in two cases. Eight eyes with retinal detachment (RD) preoperatively were successfully reattached. In five eyes, the retina redetached as these eyes became phthisical. Visual function improved in six cases. In general, eyes with a history of trauma had a much poorer outcome than did eyes with anterior and posterior segment problems related to previous cataract surgery.

An inexpensive fiberoptic light pipe to aid in placement of episcleral radioactive plaques

Episcleral plaque placement requires accurate localization of choroidal melanomas. Available fiberoptic light pipes can be fashioned to become scleral markers and transilluminators. The equipment is available wherever posterior segment surgery is performed. Surgical technique and equipment modifications are described.

Ultrasonographic features of choroidal malignant melanomas

In a 12-month period 26 eyes were enucleated after an ultrasonographic diagnosis was made of malignant melanoma of the choroid. Histologic features of the tumors were reviewed. The ultrasonographic diagnosis was correct in 100% (26/26) of enucleated eyes. Spontaneous vascular movement (SVM) was identified by standardized A-scan echography in 69% (18/26) of the tumors. Contact B-scan ultrasonography demonstrated choroidal excavation in 65% (17/26) of the melanomas. During the 12-month study period, choroidal excavation was also demonstrated in cases of metastatic choroidal tumors, hemangiomas of the choroid, and long-standing choroidal nevi. The standardized A-scan finding of SVM is a compelling sign in the diagnosis of choroidal malignant melanoma. In contrast, the B-scan finding of choroidal excavation is a less useful sign since it may also be seen in various other ocular lesions.

Retinal detachment and pseudophakia

A consecutive series of pseudophakic retinal detachments was statistically compared with a matched group of aphakic retinal detachments. Distribution of breaks, anatomic results, and final visual acuities were tabulated. Success in reattachment was equal in the two groups, but final visual acuities were better in the aphakic group. Emphasis was placed on the intraoperative ophthalmoscopic examination of pseudophakic eyes with compromised peripheral fundus visibility.

Focal parafoveal retinal telangiectasis

We describe four patients, two of whom are sisters, with an unusual form of retinal telangiectasis. The vascular abnormality is localized to the temporal parafoveal retina and is virtually identical in appearance in every patient. Other characteristics include: both men and women are involved, both eyes are generally affected, and symptoms develop in middle life. Laser photocoagulation succeeds in improving the visual acuity in the treated eyes. The consistency of the appearance and location, and the familial tendency indicates these cases probably form a subgroup of retinal telangiectasis.

Management of surgically dislocated intravitreal lens fragments by pars plana vitrectomy

We examined 26 eyes (19 of them following phacoemulsification) with surgically dislocated intravitreal lens fragments; 24 eyes were subsequently operated on using pars plana vitrectomy for removal of lens fragments. From this select group of patients we found moderate to severe uveitis, glaucoma, and vitreous opacification present in virtually all cases. Less common complications were retinal detachments (six cases) and bullous keratopathy; the latter problem was found most commonly in eyes subjected to anterior segment maneuvers such as the use of lens loops or vitreous irrigation for removal of the lens material. Pars plana vitrectomy proved an excellent method for removal of lens fragments. A simultaneous two-instrument technique using the Wilson foreign-body forceps and the vitrectomy machine facilitated removal of the denser sclerotic lens fragments. This procedure resulted in resolution of the uveitis and glaucoma with improvement in visual acuity in 20 of the 24 eyes. However, only 10 of the 24 patients operated on obtained 20/40 or better visual acuity. A relatively prompt pars plana vitrectomy in eyes subjected to a minimum of surgical trauma yielded the best visual results.

Vitrectomy in the treatment of ocular perforating injuries

Using pars plana (closed) vitrectomy with related procedures we achieved improved vision in certain catagories of perforating ocular injuries. These procedures were particularly useful in removing retained nonmagnetic foreign bodies and correcting retinal detachments associated with traction bands and opaque vitreous. Limited success was obtained with longstanding injuries, double perforations from shotgun injuries, and large corneoscleral lacerations. Early vitreous surgery produced the best results.

Pars plana vitrectomy for removal of intravitreous Cysticercus

Pars plana was used for the removal of an intravitreous cysticercus, with minimal postoperative inflammation and an excellent visual result. This approach avoids lens removal and the visualization provided by the operating microscope allows removal of all vitreous humor particles and debris. The aspirated specimens allowed identification of the Taenia solium cysticercus.

Surgical removal of nonmagnetic foreign bodies

A microsurgical technique for the removal of nonmagnetic foreign bodies in eyes with opaque media incorporated the simultaneous use of the foreign body forcepts with a vitrectomy machine equipped with fiberoptics. The superb viewing system provided by the operating microscope combined with the excellent illumination from intraocular fiberoptics offered precise surgical control. Nonencapsulated nonmagnetic foreign bodies in eyes with clear vitreous cavities were removed by using the operating microscope, corneal contact lens, and foreign body forceps introduced through a pars plana location. Vitrectomy was not performed. The surgical techniques allowed early removal of the foreign body and, in a preliminary series of cases, improved visual results in what is usually a devastating ocular injury.

Retinal hemorrhage associated with thrombasthenia

A healthy 20-year-old man presented with a spontaneous unilateral retinal hemorrhage. Because of a history of easy bruisability, we obtained hematologic studies and diagnosed thrombasthenia, a hereditary hemorrhagic disorder. The association of retinal hemorrhage and thrombasthenia is rare. Thrombasthenia and other platelet functional disorders are becoming better defined as tests for these abnormalities become more reliable and available. Patients with apparent spontaneous retinal hemorrhages of unknown origin should be questioned about hemorrhagic tendencies, and the various tests for hemorrhagic disorders should be obtained. The hematologic survey should include the more sophisticated tests of platelet function. Patients with thrombasthenia should avoid aspirin intake.

A coaxial electrode for intraocular diathermy

A bipolar electrode was used in intraocular coagulation of vessels. This device was a useful adjunct for the coagulation of vessels in diabetic eyes undergoing vitrectomy. No surgical complications due to the diathermy occurred in the first six patients on whom the device was used.