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Aluminium alloy AA 5083 [Al-4·4Mg-0·7Mn-0·15Cr (wt-%)], powder was ball milled in liquid nitrogen via the cryomilling method to obtain a nanocrystalline (NC) structure. Samples of the powder were hot vacuum degassed to remove interstitial contaminants, then consolidated by hot isostatic pressing (HIPing) at six temperatures (from 0·46Tm to 0·89Tm), before being high strain rate forged (HSRF) to produce plate material. The microstructure was analysed at the different processing stages. The compressive properties of the as HIPed material, plus tensile properties of the final product were studied. Despite grain growth during HIPing, an ultrafine grain (UFG) structure was retained in the consolidated material, which consequently had increased strength over conventionally processed AA 5083. As the HIP temperature was increased, the density increased. Strength changes were minimal in compression and tension with varying HIP temperature, once near full density was attained at 275°C (∼0·64TM). Yield strength data indicate negligible variation in the grain size of the materials. [ABSTRACT FROM AUTHOR]

Four young male patients with keratoconus had traumatic dehiscence of the surgical wound after penetrating keratoplasty. Two were rendered aphakic by the trauma, and in one patient the lens was dislocated posteriorly. In each case the dehiscence was repaired by resuturing the original corneal graft. Despite marked corneal oedema in the immediate postoperative period all four grafts deturgesced and subsequently cleared. The follow-up has been a minimum of 23 months. We recommend therefore primary resuturing of traumatic wound dehiscence after keratoplasty, anterior vitrectomy if the lens dislodged, and prophylactic antibiotics postoperatively. The clearing of the initially oedematous grafts in each case illustrates the resilience of the corneal endothelium. [ABSTRACT FROM PUBLISHER]

The transition of undifferentiated A spermatogonia to differentiated spermatogonia requires the action of retinoic acid (RA). The synthesis of retinoic acid from retinal in the seminiferous epithelium is a result of the action of aldehyde dehydrogenases termed ALDH1A1, ALDH1A2, and ALDH1A3. We used a mouse with a global deletion of the Aldh1a1 gene that is phenotypically normal and the CRE -loxP approach to eliminate Aldh1a2 genes globally and from Sertoli cells and germ cells. The results show that global elimination of Aldh1a1 and Aldh1a2 genes blocks spermatogenesis but does not appear to affect viability. The cell specific elimination of Aldh1a2 gene showed that retinoic acid synthesis by Sertoli cells is required for the initial round of spermatogonial differentiation but that there is no requirement for retinoic acid synthesis by germ cells. In both the global gene deletion and the cell specific gene deletions the maintenance of Aldh1a3 activity could not compensate., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer KR declared a shared affiliation with the authors to the handling editor at the time of review., (Copyright © 2022 Topping and Griswold.)

All-trans-retinoic acid (atRA), the active metabolite of vitamin A, is an essential signaling molecule in all chordates. Global knockouts of the atRA clearing enzymes Cyp26a1 or Cyp26b1 are embryonic lethal. In adult rodents, inhibition of Cyp26a1 and Cyp26b1 increases atRA concentrations and signaling. However, postnatal knockout of Cyp26a1 does not cause a severe phenotype. We hypothesized that Cyp26b1 is the main atRA clearing Cyp in postnatal mammals. This hypothesis was tested by generating tamoxifen-inducible knockout mouse models of Cyp26b1 alone or with Cyp26a1. Both mouse models showed dermatitis, blepharitis, and splenomegaly. Histology showed infiltration of inflammatory cells including neutrophils and T lymphocytes into the skin and hyperkeratosis/hyperplasia of the nonglandular stomach. The mice lacking both Cyp26a1 and Cyp26b1 also had a reduced lifespan, failed to gain weight, and showed fat atrophy. There were significant changes in vitamin A homeostasis. Postnatal knockout of Cyp26b1 resulted in increased atRA concentrations in the skin while the postnatal knockout of both Cyp26a1 and Cyp26b1 resulted in increased atRA concentrations in the liver, serum, skin, spleen, and intestines. This study demonstrates the paramount role of Cyp26b1 in regulating retinoid homeostasis in postnatal life., (© 2020 Federation of American Societies for Experimental Biology.)

Background: Spermatogenesis in mammals is organized in a manner that maximizes sperm production. The central aspect of this organization is the cycle of the seminiferous epithelium that is characterized by an asynchronous repeating series of germ cell associations. These cell associations are the result of a fixed point of entry into the cycle at regular short time intervals and the longer time required for cells to fully differentiate and exit the cycle., Objective: This review will examine the current information on the action and metabolism of retinoic acid in the testis, the interaction of retinoic acid (RA) with the cycle and the spermatogenic wave, and the mechanisms that can lead to synchronous spermatogenesis. Finally, the unique applications of synchronous spermatogenesis to the study of the cycle and the mass isolation of specific germ cell populations are described., Materials and Methods: Retinoic acid metabolism and spermatogonial differentiation have been examined by gene deletions, immunocytochemistry, chemical inhibitors, and mass spectrometry., Results, Discussion, and Conclusion: Both the Sertoli cells and the germ cells have the capacity to synthesize retinoic acid from retinol and in the mouse the entry into the cycle of the seminiferous epithelium, and the subsequent conversion of undifferentiated spermatogonia into differentiating spermatogonia is governed by a peak of RA synthesis occurring at stages VIII-IX of the cycle. Normal asynchronous spermatogenesis can be modified by altering RA levels, and as a result the entire testis will consist of a few closely related stages of the cycle., (© 2019 The Authors. Andrology published by Wiley Periodicals, Inc. on behalf of American Society of Andrology and European Academy of Andrology.)

The all- trans -retinoic acid ( at RA) hydroxylase Cyp26a1 is essential for embryonic development and may play a key role in regulating at RA clearance also in adults. We hypothesized that loss of Cyp26a1 activity via inducible knockout in juvenile or adult mice would result in decreased at RA clearance and increased tissue at RA concentrations and at RA-related adverse effects. To test these hypotheses, Cyp26a1 was knocked out in juvenile and adult male and female Cyp26a1 floxed mice using standard Cre-Lox technology and tamoxifen injections. Biochemical and histological methods were used to study the effects of global Cyp26a1 knockout. The Cyp26a1 knockout did not result in consistent histopathological changes in any major organs. Cyp26a1 -/- mice gained weight normally and exhibited no adverse phenotypes for up to 1 year after loss of Cyp26a1 expression. Similarly, at RA concentrations were not increased in the liver, testes, spleen, or serum of these mice, and the Cyp26a1 knockout did not cause compensatory induction of lecithin:retinol acetyltransferase ( Lrat ) or retinol dehydrogenase 11 ( Rdh11 ) mRNA or a decrease in aldehyde dehydrogenase 1a1 ( Aldh1a1 ) mRNA in the liver compared with tamoxifen-treated controls. However, the Cyp26a1 -/- mice showed increased bone marrow cellularity and decreased frequency of erythroid progenitor cells in the bone marrow consistent with a retinoid-induced myeloid skewing of hematopoiesis. In addition, the Cyp26a1 knockout decreased clearance of exogenous at RA by 70% and increased at RA half-life 6-fold. These findings demonstrate that despite lacking a major impact on endogenous at RA signaling, Cyp26a1 critically contributes as a barrier for exogenous at RA exposure., (© 2019 Zhong et al.)

Background: Male germ cells are unique because they express a substantial number of variants of the general DNA binding proteins, known as histones, yet the biological significance of these variants is still unknown. In the present study, we aimed to address the expression pattern of the testis-specific histone H2B variant (TH2B) and the testis-specific histone H2A variant (TH2A) within the neonatal mouse testis., Results: We demonstrate that TH2B and TH2A are present in a testis-enriched for undifferentiated spermatogonia. Co-localization studies with an undifferentiated marker, ZBTB16, revealed that TH2B and ZBTB16 co-localize in the neonatal testis. Upon the appearance of the primary spermatocytes, TH2B no longer co-localized with the ZBTB16 positive spermatogonia but were instead detected within the differentiating spermatogonia. This pattern of expression where TH2B and ZBTB16 no longer co-localize was maintained in the adult testis., Conclusion: These findings are in contrast to previous studies, which demonstrated that TH2B and TH2A were found only in adult spermatocytes. Our data are in support of a switch in the expression of these variants following the first round of spermatogonial differentiation. These studies reinforce current understandings that spermatogonia within the neonatal mouse testis are inherently different from those residing within the adult testis., (© 2019 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.)

Despite the essential role of the active metabolite of vitamin A, all-trans retinoic acid (atRA) in spermatogenesis, the enzymes, and cellular populations responsible for its synthesis in the postnatal testis remain largely unknown. The aldehyde dehydrogenase 1A (ALDH1A) family of enzymes residing within Sertoli cells is responsible for the synthesis of atRA, driving the first round of spermatogenesis. Those studies also revealed that the atRA required to drive subsequent rounds of spermatogenesis is possibly derived from the ALDH1A enzymes residing within the meiotic and post-meiotic germ cells. Three ALDH1A isozymes (ALDH1A1, ALDH1A2, and ALDH1A3) are present in the testis. Although, ALDH1A1 is expressed in adult Sertoli cells and is suggested to contribute to the atRA required for the pre-meiotic transitions, ALDH1A2 is proposed to be the essential isomer involved in testicular atRA biosynthesis. In this report, we first examine the requirement for ALDH1A2 via the generation and analysis of a conditional Aldh1a2 germ cell knockout and a tamoxifen-induced Aldh1a2 knockout model. We then utilized the pan-ALDH1A inhibitor (WIN 18446) to test the collective contribution of the ALDH1A enzymes to atRA biosynthesis following the first round of spermatogenesis. Collectively, our data provide the first in vivo evidence demonstrating that animals severely deficient in ALDH1A2 postnatally proceed normally through spermatogenesis. Our studies with a pan-ALDH1A inhibitor (WIN 18446) also suggest that an alternative source of atRA biosynthesis independent of the ALDH1A enzymes becomes available to maintain atRA levels for several spermatogenic cycles following an initial atRA injection., (© The Author(s) 2018. Published by Oxford University Press on behalf of Society for the Study of Reproduction.)

Spermatogenesis in mammals is a very complex, highly organized process, regulated in part by testosterone and retinoic acid (RA). Much is known about how RA and testosterone signaling pathways independently regulate this process, but there is almost no information regarding whether these two signaling pathways directly interact and whether RA is crucial for steroidogenic cell function. This study uses a transgenic mouse line that expresses a dominant-negative form of RA receptor α (RAR-DN) and the steroidogenic cell-specific Cre mouse line, Cyp17 iCre, to generate male mice with steroidogenic cells unable to perform RA signaling. Testes of mutant mice displayed increased apoptosis of pachytene spermatocytes, an increased number of macrophages in the interstitium and a loss of advanced germ cells. Additionally, blocking RA signaling in Leydig cells resulted in increased permeability of the blood-testis barrier, decreased levels of the steroidogenic enzyme cytochrome P450 17a1 and decreased testosterone levels. Surprisingly, the epididymides of the mutant mice also displayed an abnormal phenotype. This study demonstrates that RA signaling is required in steroidogenic cells for their normal function and, thus, for male fertility., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

Spermatogenesis in mammals occurs in a very highly organized manner within the seminiferous epithelium regulated by different cell types in the testis. Testosterone produced by Leydig cells regulates blood-testis barrier formation, meiosis, spermiogenesis, and spermiation. However, it is unknown whether Leydig cell function changes with the different stages of the seminiferous epithelium. This study utilized the WIN 18,446 and retinoic acid (RA) treatment regime combined with the RiboTag mouse methodology to synchronize male germ cell development and allow for the in vivo mapping of the Leydig cell translatome across the different stages of one cycle of the seminiferous epithelium. Using microarrays analysis, we identified 11 Leydig cell-enriched genes that were expressed in stage-specific manner such as the glucocorticoid synthesis and transport genes, Cyp21a1 and Serpina6. In addition, there were nine Leydig cell transcripts that change their association with polysomes in correlation with the different stages of the spermatogenic cycle including Egr1. Interestingly, the signal intensity of EGR1 and CYP21 varied among Leydig cells in the adult asynchronous testis. However, testosterone levels across the different stages of germ cell development did not cycle. These data show, for the first time, that Leydig cell gene expression changes in a stage-specific manner during the cycle of the seminiferous epithelium and indicate that a heterogeneous Leydig cell population exists in the adult mouse testis.

The nucleosome core particle (NCP) is the basic structural unit for genome packaging in eukaryotic cells and consists of DNA wound around a core of eight histone proteins. DNA access is modulated through dynamic processes of NCP disassembly. Partly disassembled structures, such as the hexasome (containing six histones) and the tetrasome (four histones), are important for transcription regulation in vivo. However, the pathways for their formation have been difficult to characterize. We combine time-resolved (TR) small-angle X-ray scattering and TR-FRET to correlate changes in the DNA conformations with composition of the histone core during salt-induced disassembly of canonical NCPs. We find that H2A-H2B histone dimers are released sequentially, with the first dimer being released after the DNA has formed an asymmetrically unwrapped, teardrop-shape DNA structure. This finding suggests that the octasome-to-hexasome transition is guided by the asymmetric unwrapping of the DNA. The link between DNA structure and histone composition suggests a potential mechanism for the action of proteins that alter nucleosome configurations such as histone chaperones and chromatin remodeling complexes., Competing Interests: The authors declare no conflict of interest.

The mechanical response of heterophase interfaces has attracted substantial attention in recent years. Here, we utilized an in situ transmission electron microscopy (TEM) technique to isolate an individual nanoscale ceramic/metal interface and characterize its nanomechanical response. The interface, at which there was a Mg-rich segregation nanolayer between the single crystal ceramic (B4C) and the polycrystalline metal (Al alloy, AA5083), was determined to have a bond strength greater than 1.5 GPa. Bimodal failure and metallic grain rotation occurred in the metallic region, allowing the interface to accommodate a deformation strain of 5.4%. The roles of elemental segregation and nanoscale dimensions on interfacial debonding mechanisms are discussed.

The modulation of DNA accessibility by nucleosomes is a fundamental mechanism of gene regulation in eukaryotes. The nucleosome core particle (NCP) consists of 147 bp of DNA wrapped around a symmetric octamer of histone proteins. The dynamics of DNA packaging and unpackaging from the NCP affect all DNA-based chemistries, but depend on many factors, including DNA positioning sequence, histone variants and modifications. Although the structure of the intact NCP has been studied by crystallography at atomic resolution, little is known about the structures of the partially unwrapped, transient intermediates relevant to nucleosome dynamics in processes such as transcription, DNA replication and repair. We apply a new experimental approach combining contrast variation with time-resolved small angle X-ray scattering (TR-SAXS) to determine transient structures of protein and DNA constituents of NCPs during salt-induced disassembly. We measure the structures of unwrapping DNA and monitor protein dissociation from Xenopus laevis histones reconstituted with two model NCP positioning constructs: the Widom 601 sequence and the sea urchin 5S ribosomal gene. Both constructs reveal asymmetric release of DNA from disrupted histone cores, but display different patterns of protein dissociation. These kinetic intermediates may be biologically important substrates for gene regulation., (© The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.)

We have shown here that the cytosolic bacterial chaperone SecB is a structural dimer of dimers that undergoes a dynamic equilibrium between dimer and tetramer in the native state. We demonstrated this equilibrium by mixing two tetrameric species of SecB that can be distinguished by size. We showed that the homotetrameric species exchanged dimers, because when the mixture was analyzed both by size exclusion chromatography and native polyacrylamide gel electrophoresis a third hybrid tetrameric species was detected. Furthermore, treatment of SecB with 5,5'-dithiobis-(2-nitrobenzoic acid), which modifies the sulfhydryl group on cysteines, caused irreversible dissociation to a dimer indicating that cysteine must be involved in the stabilizing interactions at the dimer interface. It is clear that the two dimer-dimer interfaces of the SecB tetramer are differentially stable. Dissociation at one interface allows for a dynamic dimer-tetramer equilibrium. Because only dimers were exchanged it is clear that the other interface between dimers is significantly more stable, otherwise oligomers should have formed with a random distribution of monomers.

Objective: To evaluate the efficacy of ketorolac tromethamine 0.5% ophthalmic solution, prednisolone acetate 1.0% ophthalmic solution, and ketorolac and prednisolone combination therapy in the treatment of acute, visually significant, cystoid macular edema (CME) occurring after cataract extraction surgery., Design: Randomized, double-masked, prospective trial., Participants: Twenty-eight patients who had undergone cataract extraction and in whom clinical CME developed within 21 to 90 days after cataract surgery., Methods: Patients were randomized to topical therapy with ketorolac (group K), prednisolone (group P), or ketorolac and prednisolone combination therapy (group C) four times daily. Treatment was continued until CME resolved or for 3 months, whichever occurred first. Treatment was then tapered over 3 weeks. Examinations were monthly and included Snellen visual acuity, contrast sensitivity, Amsler grid, slit-lamp examination, dilated fundus examination, and fluorescein angiography., Results: Twenty-six of 28 patients completed the study. Patients were enrolled an average of 48 days after surgery. The average improvements in Snellen visual acuity were as follows: 1.6 lines in group K, 1.1 lines in group P, and 3.8 lines in group C. This reached statistical significance for all visits when group C was compared with group P, and for visits 4 and 5 when group C was compared with group K. Group C reached a mean change of two lines or more by visit 2; at no time did either group K or P reach a mean two-line improvement. At no time was a significant difference detected between group K and P with regard to visual acuity or change from baseline. A two-line or more improvement in Snellen acuity was achieved in 16 of 26 patients (61%). Analysis by group revealed four of eight patients (50%) in group P, six of nine patients (67%) in group K, and eight of nine patients (89%) in group C who had achieved a two-line or more improvement. In patients who did improve two lines or more, improvement occurred an average of 2.75 months after initiating therapy in group P, 1.43 months in group K, and 1.33 months in group C. Improvements in contrast sensitivity and leakage on fluorescein angiography tended to mirror improvements in Snellen acuity., Conclusions: Treatment of acute, visually significant pseudophakic CME with ketorolac and prednisolone combination therapy appears to offer benefits over monotherapy with either agent alone. Patients were more likely to experience recovery of two lines or more of visual acuity. Patients treated with combination therapy or ketorolac monotherapy responded more quickly than did patients treated with prednisolone alone.

During localization to the periplasmic space or to the outer membrane of Escherichia coli some proteins are dependent on binding to the cytosolic chaperone SecB, which in turn is targeted to the membrane by specific interaction with SecA, a peripheral component of the translocase. Five variant forms of SecB, previously demonstrated to be defective in mediating export in vivo (Gannon, P. M., and Kumamoto, C. A. (1993) J. Biol. Chem. 268, 1590-1595; Kimsey, H. K., Dagarag, M. D., and Kumamoto, C. A. (1995) J. Biol. Chem. 270, 22831-22835) were investigated with respect to their ability to bind SecA both in solution and at the membrane translocase. We present evidence that at least two regions of SecA are involved in the formation of active complexes with SecB. The variant forms of SecB were all capable of interacting with SecA in solution to form complexes with stability similar to that of complexes between SecA and wild-type SecB. However, the variant forms were defective in interaction with a separate region of SecA, which was shown to trigger a change that was correlated to activation of the complex. The region of SecA involved in activation of the complexes was defined as the extreme carboxyl-terminal 21 aminoacyl residues.

Variant forms of SecB with substitutions of aminoacyl residues in the region from 74 to 80 were analyzed with respect to their ability to bind a physiological ligand, precursor galactose-binding protein, and to their oligomeric states. SecBL75Q and SecBE77K are tetramers with affinity for ligand indistinguishable from that of the wild-type SecB, and thus the export defect exhibited by strains producing these variants must result from an effect on interactions between SecB and other components. SecBF74I is tetrameric but binds ligand with a lower affinity. Substitutions at positions 76, 78, and 80 cause a shift in the equilibrium so that the SecB tetramer dissociates into dimers. We conclude that the tetramer is a dimer of dimers and that the residues Cys76, Val78, and Gln80 must be involved either directly or indirectly in forming the interface between dimers. These variant species are defective in binding ligand; however, because their oligomeric state is altered no conclusion can be drawn concerning the direct role of these residues in ligand binding.

Objective: To characterize 20 cases of retinal detachment (RD) following surgical repair of macular holes., Methods: Retrospective review of 20 eyes in 16 patients (4 patients [25%] had bilateral macular hole repairs with subsequent RD) who developed RD in the same eye in which surgical repair of a macular hole had been performed., Results: Twenty detachments in 16 patients were reviewed. The average duration between macular hole repair and presentation of RD was 5.5 weeks. The inferior retina was involved more frequently than the superior retina. A total of 76% of all breaks were located inferiorly. Ten of the 20 eyes were asymptomatic at the time the detachment was diagnosed. Of the 20 eyes, 19 underwent surgical repair, all with anatomic reattachment. At final follow-up, the macular hole was closed in all 20 eyes, and 60% of the patients had final visual acuity improved by 2 lines or more over that before their macular hole repair., Conclusion: Retinal detachment is a complication of macular hole surgery. These detachments tend to occur within the first 2 months of follow-up, and have a high success rate of anatomic reattachment with surgery. The occurrence of RD does not preclude improved final visual acuity.

The chaperone protein SecB is dedicated to the facilitation of export of proteins from the cytoplasm to the periplasm and outer membrane of Escherichia coli. It functions to bind and deliver precursors of exported proteins to the membrane-associated translocation apparatus before the precursors fold into their native stable structures. The binding to SecB is characterized by a high selectivity for ligands having nonnative structure but a low specificity for consensus in sequence among the ligands. A model previously presented (Randall LL, Hardy SJS, 1995, Trends Biochem Sci 20:65-69) to rationalize the ability of SecB to distinguish between the native and nonnative states of a polypeptide proposes that the SecB tetramer contains two types of subsites for ligand binding: one kind that would interact with extended flexible stretches of polypeptides and the other with hydrophobic regions. Here we have used titration calorimetry, analytical ultracentrifugation, and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to obtain evidence that such distinguishable subsites exist.

Objective: This study aimed to report anatomic and visual acuity outcomes and complications after 1000-centistoke silicone oil was used as a retinal tamponade for the treatment of complex retinal detachments., Design: Prospective observational multicenter study conducted at community and university-based ophthalmology clinics., Participants: The study cohort consisted of 2439 patients (2573 eyes) treated for complex retinal detachments associated with cytomegalovirus (CMV) necrotizing retinitis or a non-CMV etiology, including proliferative diabetic retinopathy, giant retinal tears, proliferative vitreoretinopathy, or ocular trauma., Intervention: Vitrectomy surgery was performed for complex retinal detachment with 1000-centistoke silicone oil as the retinal tamponade., Main Outcome Measures: Anatomic outcomes were complete retinal attachment and macular attachment. Visual acuity outcomes were ambulatory vision (> or = 4/200) and preservation of preoperative visual acuity. Complications were rates of secondary intraocular pressure elevation (> or = 30 mmHg), hypotony (< or = 5 mmHg), corneal opacification (including band keratopathy, corneal edema, and corneal abrasions), oil emulsification, and cataract. Outcomes were assessed 6, 12, and 24 months after surgery., Results: At the 6-month examination, the retina was completely attached in 178 (78%) of 228 CMV eyes and in 855 (70%) of 1219 non-CMV eyes. The macula was attached in 216 (95%) of 228 and 1062 (89%) of 1189 CMV and non-CMV eyes, respectively. Ambulatory vision was noted in 151 (65%) of 234 CMV eyes and in 480 (38%) of 1251 non-CMV eyes. Visual acuity was preserved in 106 (46%) of 230 and 1035 (84%) of 1229 CMV and non-CMV eyes, respectively. The corresponding rates of complications for CMV and non-CMV eyes were: elevated intraocular pressure, 0 (0%) of 196 and 35 (3%) of 1196; hypotony, 11 (6%) of 196 and 228 (19%) of 1196; corneal opacity, 13 (6%) of 229 and 326 (26%) of 1248; emulsification, 3 (1%) of 211 and 29 (3%) of 959; and cataract in phakic eyes, 118 (64%) of 185 and 50 (63%) of 80., Conclusions: Retinal reattachment was achieved in the majority of eyes using vitrectomy and silicone oil retinal tamponade. Complication rates generally were less frequent in CMV eyes, but follow-up was shorter in this group of patients, largely because of reduced life expectancy. Cataract frequently developed in phakic eyes of study patients. Use of 1000-centistoke silicone oil can be considered in the management of complex retinal detachments associated with multiple etiologies.

SecB is a chaperone in Escherichia coli dedicated to export of proteins from the cytoplasm to the periplasm and outer membrane. It functions to bind and deliver precursors of exported proteins to the translocation apparatus before they fold into their native structures, thus maintaining them in a competent state for translocation across the membrane. The natural ligands of SecB are precursor proteins containing leader sequences. There are numerous reports in the literature indicating that SecB does not specifically recognize the leader peptides. However, two published investigations have concluded that the leader peptide is the recognition element (Watanabe M, Blobel G. 1989. Cell 58:685-705; Watanabe M, Blobel G. 1995. Proc Natl Acad Sci USA 92:10133-10136). In this work we use titration calorimetry to show that SecB binds two physiological ligands, which contain leader sequences, with no higher affinity than the same molecules lacking their leader sequences. Indeed, for one ligand the presence of the leader sequence reduces the affinity. Therefore, it can be concluded that the leader sequence provides no positive contribution to the binding energy.

We have shown that the complexes between SecB, a chaperone from Escherichia coli, and two physiological ligands, galactose-binding protein and maltose-binding protein, are in rapid, dynamic equilibrium between the bound and free states. Binding to SecB is readily reversible, and each time the ligand is released it undergoes a kinetic partitioning between folding to its native state and re-binding to SecB. Binding requires that the polypeptide be devoid of tertiary structure; once the protein has folded, it is no longer a ligand. Conditions were established in which folding of the polypeptides was sufficiently slow so that at each cycle of dissociation rebinding was favored over folding and a kinetically stable complex between SecB and each polypeptide ligand was observed. Evidence that the ligand is continually released to the bulk solution and rebound was obtained by altering the conditions to increase the rate of folding of each ligand so that folding of the ligand was faster than reassociation with SecB thereby allowing the system to partition to free SecB and folded polypeptide ligand. We conclude that complexes between the chaperone SecB and ligands are in dynamic, rapid equilibrium with the free states. This mode of binding is simpler than that documented for chaperones that function to facilitate folding such as the Hsp70s and Hsp60s, where hydrolysis of ATP is coupled to the binding and release of ligands. This difference may reflect the fact that SecB does not mediate folding but is specialized to facilitate protein export. Without a requirement for exogenous energy it efficiently performs its sole duty: to keep proteins in a nonnative conformation and thus competent for export.

Purpose: The differentiating characteristics in blebitis and early and late endophthalmitis after glaucoma filtration surgery are reviewed., Methods: All admission records and operative reports, as well as available office notes, on patients with blebitis or bleb-associated endophthalmitis admitted to a large referral eye center from 1985 to 1995 were reviewed retrospectively., Results: Ten cases of blebitis and 33 cases of bleb-associated endophthalmitis were identified. One patient with blebitis progressed to culture-positive endophthalmitis. Of the 33 cases of bleb-associated endophthalmitis, there were 6 cases of early endophthalmitis (before postoperative week 6) and 27 cases of late endophthalmitis. In early endophthalmitis, Staphylococcus epidermidis was isolated on vitreous culture in 4 (67%) of 6 cases, whereas in late endophthalmitis, this organism was isolated in only 1 (4%) of 27 cases. In the 27 late cases, Streptococcus species and gram-negative organisms comprised 48% of isolates; of 33 cases of endophthalmitis, 15 (45%) demonstrated no growth on vitreous culture. Patients with endophthalmitis fared more poorly than those with blebitis in terms of visual outcome., Conclusions: Because blebitis may be prodromal to endophthalmitis, aggressive antimicrobial therapy, perhaps with oral quinolones, is warranted. In addition, patients with blebitis should be observed closely to identify extension into the vitreous cavity so that intravitreous antibiotics can be administered in a timely fashion. Finally, clinicians should not extrapolate the results of the Endophthalmitis Vitrectomy Study to the postfiltration surgery endophthalmitis given the differing pathogenesis and unique spectrum of organisms.

We report three cases of uveal lymphoid neoplasia that were diagnosed early in their course. One case exhibited a posterior form, presenting with progressive hyperopia from a serous-macular detachment and choroidal involvement along with retrobulbar involvement. This patient was treated with proton beam irradiation. Two cases displayed an anterior form, with fixed fleshy epibulbar masses resembling salmon patches, and choroidal involvement. The histologic findings from biopsy of these anterior masses are presented. One of these patients was treated with complete excision of the mass and double freeze-thaw cryotherapy of the scleral bed, and the other patient was treated with conventional photon beam irradiation. The clinical features of uveal lymphoid neoplasia in its early form are discussed. Evaluation and treatment strategies for these early forms of uveal lymphoid neoplasia are reviewed.

The interaction of the chaperone SecB with ribosome-bound polypeptides that are in the process of elongation has been studied using an in vitro protein synthesis system. The binding is characterized by the same properties as those demonstrated for the binding of SecB to full-length proteins that are in nonnative conformation: it is readily reversible and has no specificity for the leader peptide. In addition, it is shown that the growing polypeptide chains must achieve a critical length to bind tightly enough to allow their isolation in complex with SecB. This explains the longstanding observation that, even when export is cotranslational, it begins late in synthesis. Furthermore, the required length is approximately the same as the length that defines the binding frame within denatured, full-length proteins bound to SecB.

Purpose: The purpose of this study is to assess the rate of posterior segment complications after vitreous surgery for macular holes and to evaluate the effect of such complications on final visual outcome., Methods: The authors reviewed retrospectively all cases of vitreous surgery for macular holes performed between June 1990 and October 1993. Among 98 patients with a followup of 3 months or more, all patients with posterior segment complications during the postoperative course were identified. The rate of complications was compared with that seen after vitreous surgery for macular pucker performed by the same surgeons., Results: Posterior segment complications were noted in 23 (23%) of 98 patients. These included peripheral retinal breaks (3%), rhegmatogenous retinal detachment from a peripheral retinal break (14%), enlargement of the hole (2%), late reopening of the hole (2%), retinal pigment epithelium loss under the hole (1%), photic toxicity (1%), and endophthalmitis (1%). In 40% of these eyes, the final visual acuity was two lines or more below preoperative visual acuity. When compared with the macular pucker group, the rate of posterior segment complications, in particular the rate of peripheral retinal tears and detachments, was significantly higher (P < or = 0.05)., Conclusions: The authors conclude that visually significant posterior segment complications may occur after vitrectomy for macular hole, and the rate of these complications appears to be higher than expected.

The hallmark of the class of proteins called chaperones is the amazing ability to bind tightly to a wide array of polypeptide ligands that have no consensus in sequence; chaperones recognize non-native structure. As a step in the elucidation of the molecular mechanism of such remarkable binding, we have characterized complexes between the bacterial chaperone SecB and a series of ligands related to maltose-binding protein. SecB interacts at multiple sites on its polypeptide ligand. The entire binding region covers approximately half of the primary sequence of maltose-binding protein and comprises contiguous sites positioned around the center of the sequence.

Purpose: This study, comprising 60 patients with coagulase-negative staphylococcal endophthalmitis which occurred after cataract surgery, was designed to define the variation in disease presentation and visual outcome and to evaluate statistically the role of the primary surgery and its management., Methods: An intensive evaluation of microbiological, inpatient, outpatient, and cataract surgery charts was made retrospectively using a standardized protocol. The predictive value of surgical, iatrogenic, and clinical factors was analyzed for their influence on defined aspects of the disease pattern and of the visual results using multiple regression models, via a stepwise technique., Results: There was commonly a significant asymptomatic latent period after cataract surgery. The median diagnostic delay was 7 days; 22% of patients presented after 2 weeks and 12% after 1 month. Symptoms progressed longer than 3 days in 25% of patients. Ten percent had no pain. Clinical variation proved largely unrelated to cataract surgery events and postoperative management; bacterial factors were implicated. Good visual outcome was associated statistically with intensive topical corticosteroid in the symptomatic period, but was negatively associated with operative subconjunctival corticosteroid., Conclusions: The clinical variation in cases of postoperative coagulase-negative staphylococcal endophthalmitis poses particular problems for diagnosis in the outpatient setting. Surgical and perioperative events (except corticosteroid use) probably can be disregarded in studies of endophthalmitis management.

The authors conducted a retrospective review of 32 patients with posterior retinal folds following retinal reattachment surgery. Twenty-eight of these patients underwent combined pars plana vitrectomy, fluid-air exchange with either internal drainage through a preexisting retinal break or external drainage of subretinal fluid, and scleral buckle. We believe these drainage techniques resulted in incomplete elimination of subretinal fluid, with resultant sequestration of fluid at the dependent border between attached and detached retina. Metamorphopsia and decreased visual acuity were noted in patients with folds involving the macula. The likelihood of fold formation may be greatly reduced by internal drainage through a posterior retinotomy combined with more complete removal of slowly gravitating fluid as it flows dependently to the drainage site.

Purpose: The coagulase-negative staphylococci are the most common causes of postoperative endophthalmitis. This study investigates the variability in the disease spectrum and visual outcome of coagulase-negative staphylococcal endophthalmitis in a large, single-center series., Methods: Ninety consecutive cases of coagulase-negative staphylococcal endophthalmitis were investigated retrospectively from two time periods, 1978 to 1982 and 1985 to 1987, separated by a transitional period in cataract surgery technique. Using a detailed protocol, inpatient, outpatient, and microbiologic records were analyzed. Six-month visual acuity results were obtained., Results: Diagnosis frequently was delayed, often suspected only after hypopyon development. Thirty-seven percent of patients presented more than 1 week after the inoculating event, and 13% presented after more than 1 month. Variable asymptomatic intervals and gradually worsening inflammatory prodromes are noted. Painless endophthalmitis occurred in 16%. Non-epidermidis infections comprised 28%. With vitrectomy/intraocular antibiotic management, 38% and 68% achieved visual acuities of 20/50 and 20/400, respectively. Overall, 10% of patients developed late retinal detachments. This occurred in only 4% of patients, with endophthalmitis occurring after cataract surgery., Conclusion: Ophthalmologists should become familiar with the emerging concepts of delayed-onset, chronic, and often painless endophthalmitis in which the coagulase-negative staphylococci play a prominent role.

The clinical source of 62 eyes that had been coded for macular degeneration and fibrovascular retinal pigment epithelial (RPE) detachment on fluorescein angiography was reviewed; 17 eyes had signs of a choroidal neovascular membrane (CNVM) at initial examination, and 30 eyes developed a definite CNVM during follow-up examination. Thus, 47 of the 62 eyes (76%) developed a CNVM in association with fibrovascular RPE detachments. Features of fibrovascular RPE detachments include: 1) focal, tiny hyperfluorescent spots at the level of the RPE arising in the mid and late frames of the angiogram, which do not correspond to drusen or foci of depigmentation (stippled hyperfluorescence); 2) intensification of these spots in the later stages of the angiogram; 3) slight enlargement of the spots in the late frames of the angiogram; 4) occasional presence of scant overlying subretinal fluid; and 5) minimal elevation of the RPE. Fibrovascular RPE detachments appear to be a distinct form of an RPE detachment. It is concluded that this sign is associated with a high risk of developing a frank CNVM and is thus a reliable indicator of occult neovascularization.

Two previously healthy patients, a 66-year-old man with blunt trauma to the right eye, and a 28-year-old man with head trauma from a motorcycle accident, were observed to have parafoveal retinal pigment epithelial tears after injury. In both patients, fluorescein angiography demonstrated mottled window defects in the areas of the tears, and blocked fluorescence in the areas of the rolled-up pigment epithelium. Neither eye had evidence of pigment epithelial detachments. We hypothesize that this unusual phenomenon is caused by an acute tractional force oriented tangentially to the macular plane, the result of a rapid spherically expansile deformation of the globe during trauma.

Fifty-one eyes of 48 patients with perforating (through-and-through) injuries of the globe were treated with vitrectomy during a 12-year period. Functional success was obtained in 32 eyes (63%), anatomic success was obtained in nine eyes (17%), and treatment failed in 10 eyes (20%). In 16 eyes (32%), 20/20 to 20/100 visual acuity was obtained; in 17 eyes (33%), 20/200 to 5/200 visual acuity was obtained; and in 18 eyes (35%), less than 5/200 visual acuity was obtained. The mechanism of injury was an important prognostic indicator of final visual outcome. Eight (62%) of 13 eyes that sustained knife or nail injuries achieved a final visual acuity of 20/50 or better, while only six (16%) of 38 eyes [corrected] with missile injuries achieved a similar level of acuity. Final visual outcome correlated well with the state of the macula and was not predicted by preoperative visual acuity. Despite improvement in surgical techniques and instrumentation, no trend toward improved visual outcomes was identified during the 12-year period.