The role of prohormone convertases in insulin biosynthesis: evidence for inherited defects in their action in man and experimental animals

The hormone insulin remains the cornerstone of diabetic therapy since it is required for almost all cases of Type 1 and many cases of Type 2 diabetes. Since the discovery of insulin in 1921, much has been learned about its chemistry, structure and action as well as its production in the beta cell. Insulin is formed through a series of precursors, beginning with preproinsulin, the protein encoded in the insulin gene. These precursors direct the prohormone into the secretory pathway and ultimately into the secretory granules where it is converted into insulin and C-peptide. These products are stored and secreted together in a highly regulated manner in response to glucose and other stimuli. This review focuses on the recently discovered prohormone convertases, PC2 and PC3 (PC1), the enzymes responsible for the endoproteolytic processing of proinsulin to insulin and C-peptide in the beta cell as well as for the selective processing of proglucagon to glucagon in the alpha cell or GLP1 in intestinal L-cells. PC2 and PC3 are calcium-dependent serine proteases related to the bacterial enzyme subtilisin. They cleave selectively at Lys-Arg or Arg-Arg sites in precursors, generating products with C-terminal basic residues that are then removed by carboxypeptidase E, an exopeptidase. All 3 enzymes are expressed mainly in secretory granules of neuroendocrine cells throughout the body and in the brain. Inherited defects affecting the prohormone-processing enzymes have recently been found in association with unusual syndromes of obesity and other metabolic disorders.

Increased oxidant resistance of alveolar macrophages isolated from rats repeatedly exposed to cadmium aerosols

This study investigated potential mechanisms of oxidant resistance in alveolar macrophages (AM) isolated from Lewis rats exposed repeatedly to cadmium aerosols. Macrophages from Cd-adapted animals significantly greater resistance to oxidant-induced cytotoxicity than control cells when challenged with hydrogen peroxide in vitro. Elevations in glutathione peroxidase and glutathione reductase activities were associated with increased oxidant tolerance but catalase activity was unchanged. Metallothionein (MT) expression (protein and mRNA) was dramatically up-regulated in response to in vivo Cd exposure. A study using immunocytochemistry and in situ hybridization techniques revealed significantly heterogeneity in the expression of metallothionein by AMs. The percentage of AMs positive for MT (protein and mRNA) and the degree of MT expression within individual cells increased in response to additional Cd exposures. A putative state of activation was suggested by differences in size and number of inclusion bodies in macrophages from Cd-adapted animals and by secretion of a cytokine with interleukin-1-like characteristics. In summary, AMs from Cd-adapted animals are distinguished from control cells with respect to: (1) increased oxidant resistance, (2) secretion of cytokines, (3) elevations in enzymes associated with glutathione metabolism, and (4) up-regulation in metallothionein expression.

Expression of extracellular matrix molecules and cell surface molecules in the olfactory nerve pathway during early development

The spatial and temporal expression patterns of several extracellular matrix molecules--laminin and fibronectin and cell surface molecules, neural cell adhesion molecule (NCAM), L1, tenascin, chondroitin sulfate proteoglycan, and peanut agglutinin (PNA) binding sites--were investigated during early olfactory nerve development. NCAM and L1 have similar patterns: They are expressed in the olfactory nerve and on the olfactory receptor neurons (ORNs) commencing with the earliest olfactory axon outgrowth (E12-E15). Their expression patterns suggest that both NCAM and L1 are associated with extension and fasciculation of olfactory axons. A comparison of L1 and olfactory marker protein suggests that L1 is expressed predominantly on immature ORNs. Laminin has an unique punctate staining pattern in the developing olfactory pathway as early as E12. These laminin puncta might play a role in olfactory neurite outgrowth and guidance. At E14, when pioneer olfactory axons enter the brain, the laminin-positive meninges on the surface of the olfactory bulb primordium break down but remain intact in the rest of the telencephalon. This suggests a functional interaction between the olfactory axons and the glial-pial barrier. Fibronectin staining is diffuse throughout the cranial mesenchyme but is absent from the olfactory nerve pathway. No specific patterns of tenascin or chondroitin sulfate, were observed during early olfactory development. PNA binding sites were associated with olfactory axon fasciculation. The expression of several extracellular matrix molecules and cell surface molecules is spatially and temporally regulated in the developing olfactory system. These molecules, thus, may play functional roles in olfactory axon outgrowth, fasciculation, and/or guidance.

Increased oxidant resistance of alveolar epithelial type II cells. Isolated from rats following repeated exposure to cadmium aerosols

Alveolar epithelial type II cells (AEIIC) were isolated from male Lewis rats following repeated in vivo cadmium aerosol exposure and were subsequently evaluated for their oxidant resistance in vitro. AEIIC from Cd-adapted animals removed a greater proportion of hydrogen peroxide from the extracellular milieu and incurred less oxidant-induced cytotoxicity than AEIIC from air controls. This altered response to oxidants occurred coincident with changes in cellular resistance factors. A two-fold increase in glutathione peroxidase activity and a 1.5-fold increase in the activities of glutathione reductase and catalase were observed in Cd-adapted AEIIC compared to control cells. These cells also exhibited a dramatic induction of metallothionein (MT), a thiol-rich protein known to scavenge free radicals in vitro. MT concentration increased as a function of exposure number. MT was localized within the nucleus and cytoplasm of AEIIC by immunocytochemical techniques. MT positive cells showed a wide variation of MT content, particularly in the nucleus. The biochemical and physiological features of these AEIIC may explain, in part, why animals pretreated with Cd aerosols develop cross-tolerance to hyperoxia.

Proteolytic processing mechanisms in the biosynthesis of neuroendocrine peptides: the subtilisin-like proprotein convertases

The recent discovery of a novel family of precursor processing endoproteases has greatly accelerated progress in understanding the complex mechanisms underlying the maturation of prohormones, neuropeptides, and many other precursor-derived proteins. At least six members of this family have been found thus far in mammalian species, several having alternatively spliced isoforms, and related enzymes have been identified in many invertebrates, including molluscs, insects, nematodes, and coelenterates. The proprotein convertases are all dependent on calcium for activity and all possess highly conserved subtilisin-like domains with the characteristic catalytic triad of this serine protease (ordered Asp, His, and Ser along the polypeptide chain). Two members of this family, PC2 (SPC2) and PC1/PC3 (SPC3), appear to play a preeminent role in neuroendocrine precursor processing. Both convertases are expressed only in the brain and in the extended neuroendocrine system, while another important family member--furin/PACE (SPC1)--is expressed more ubiquitously, in almost all tissues, and at high levels in liver. SPC2 and SPC3 exhibit acidic pH optima and other properties which enhance their activity in the acidic, calcium-enriched environment of the dense-core secretory granules of the regulated pathway in neuroendocrine cells, while furin has a neutral pH optimum and is localized predominantly to the trans Golgi network where it is retained by a C-terminal transmembrane domain. Furin processes a wide variety of precursors in the constitutive pathway, such as those of growth factors, receptors, coagulation factors, and viral glycoproteins. Recent findings on the processing of proopiomelanocortin, proinsulin, proglucagon, and several other neuroendocrine precursors by SPC2 and SPC3 are discussed, along with information on the structure, properties, evolution, developmental expression, and regulation of the convertases. An inherited defect in the fat/fat mouse which affects the processing of proinsulin, and probably also many other prohormones, due to a point mutation in carboxypeptidase E has recently been identified and has begun to provide new insights into the functional integration of the individual processing steps.

Synergistic effects of growth factors on the regulation of smooth muscle cell scavenger receptor activity

Rabbit smooth muscle cells (SMC) express types I and II scavenger receptors (ScR) that are up-regulated by platelet secretion products. In the current studies we investigated the effect of growth factors secreted by platelets on ScR activity in rabbit and human SMC. Platelet-derived growth factor (PDGF BB) and transforming growth factor beta 1 (TGF-beta 1) at 10 ng/ml increased ScR activity in rabbit SMC (by approximately 4- and 2-fold, respectively) but not in human SMC. Epidermal growth factor (EGF) or insulin-like growth factor I (IGF-I) alone had little effect on SMC ScR activity. The growth factors had synergistic effects on ScR activity and on types I and II ScR mRNA expression. In rabbit SMC, PDGF BB, EGF, and TGF-beta 1 together stimulated ScR activity 12-fold. In human SMC, EGF and TGF-beta 1, together with either IGF-I or PDGF BB, stimulated receptor activity approximately 7-fold. Growth factor-mediated induction of ScR activity in rabbit and human SMC was blocked by the tyrosine kinase inhibitor tyrphostin 47, whereas the induction of ScR activity in rabbit but not human SMC was blocked by the protein kinase C inhibitor MDL.29,152. Studies using neutralizing antibodies demonstrated that TGF-beta 1 is the predominant factor in in vitro preparations of platelet secretory products which regulates ScR activity. The growth factors that act synergistically in regulating ScR activity in vitro are all present in atherosclerotic lesions, where they are produced by macrophages, endothelial cells, SMC, and platelets. The data suggest that these growth factors may regulate ScR activity in SMC in vivo and contribute to foam cell formation.

In vivo expression of metallothionein in rat alveolar macrophages and type II epithelial cells following repeated cadmium aerosol exposures

This study examined the ability of alveolar macrophages and alveolar type II epithelial cells to accumulate cadmium (Cd) and to express metallothionein (MT). Lung cells were isolated from Lewis rats repeatedly exposed to a Cd aerosol (1.6 mg Cd/m3). Intracellular Cd concentration rose following Cd exposure and showed an increasing rend as a function of exposure number. Alveolar macrophages accrued approximately four times more Cd than type II epithelial cells similarly exposed. Macrophages and type II cells responded to the presence of intracellular Cd by increasing MT protein levels. MT concentration was highly correlated with intracellular Cd. Immunocytochemical studies revealed that not all macrophages and type II cells from Cd-exposed animals were immunopositive for MT and that the intensity of immunostaining varied within each cell population. Although a greater percentage of macrophages were immunopositive for MT than type II cells, a greater proportion of type II cells showed moderate and dark MT staining patterns. Oligonucleotide probes, shown to distinguish between MT-1 and MT-2 mRNA isoforms, were used to test for cell-specific differences in MT isoform gene expression. The basal level of MT-1 mRNA was greater in macrophages than in type II cells. Following Cd administration, the level of MT-1 mRNA and MT-2 mRNA increased in each cell class but the response to Cd was three times greater in alveolar macrophages. Neither macrophages nor type II cells expressed MT mRNA isoforms in equal proportions. Macrophages expressed more MT-1 mRNA when exposed to air and more MT-2 mRNA in response to Cd exposure. Type II cells, on the other hand, expressed more MT-2 mRNA than MT-1 mRNA regardless of whether the cells were exposed to air or Cd. In conclusion, the present study has demonstrated that (1) alveolar macrophages and type II cells respond to in vivo Cd exposure by increasing MT protein and mRNA levels; (2) MT expression is greater in macrophages than in type II cells and correlates well with intracellular Cd concentration; and (3) the MT-2 mRNA to MT-1 mRNA ratio is cell and treatment specific.

Molecular modeling of the substrate specificity of prohormone convertases SPC2 and SPC3

In this paper we describe the results of molecular modeling of the structures of the active sites of two subtilisin-like prohormone convertases (SPCs), SPC2 (PC2) and SPC3 (PC1/PC3). These enzymes are members of a recently discovered family of cellular proteases involved in the processing of precursor proteins. Although these proteases all possess catalytic domains similar to the bacterial subtilisins no tertiary structural data from x-ray analysis are yet available. We have shown that despite the high structural homology of the subtilisins and the SPCs, the structure of the loop which lies immediately below the active sites differs due to the presence of a cis-peptide bond (Tyr167-Pro168) in this loop in the subtilisins and its absence in the SPCs. Accordingly, we have proposed a new alignment for the amino acid sequences of the SPCs in this region. Both SPC2 and SPC3 participate in the processing of prohormones at dibasic cleavage sites, typically Lys-Arg or Arg-Arg. To investigate the structural basis of the substrate specificity of these SPCs, we have carried out molecular mechanic calculations of the optimal arrangement and interactions of peptide substrates containing several residues of arginine or lysine, i.e. Arg, Ala-Ala-Ala-Arg, Arg-Ala-Ala-Arg, Arg-Ala-Arg-Arg, Arg-Ala-Lys-Arg, in the putative active sites. Such subtilisin-based modeling has allowed us to identify those negatively charged residues, Asp and Glu, in the S1, S2, and S4 subsites, which can directly interact with basic residues in the substrates via formation of salt bridges and thereby contribute to the substrate selectivity of the SPCs.

Interaction of retinoblastoma gene product with transcription factors ATFa and ATF2

Two highly related transcription factors, activating transcription factors a and 2 (ATFa and ATF2) are able to activate expression in CHO cells of a reporter gene driven by the human transforming growth factor beta 2 gene promoter. This action is dependent on the intact motif CGTCA which is found as part of the cAMP responsive element in a number of promoters and to which both factors can bind in vitro. The retinoblastoma gene product also weakly stimulates expression of this reporter gene but, in combination with the factors, it exhibits a differential action: additive or greater stimulatory effects with ATF2 but strong inhibition of the actions of ATFa. Thus, although both of these two related factors are able to exert the same apparent effect on this promoter, coexpression of the retinoblastoma gene product reveals at least one significant difference in their actions.

Evidence that pioneer olfactory axons regulate telencephalon cell cycle kinetics to induce the formation of the olfactory bulb

Early olfactory axons follow a specific pathway to reach the developing telencephalon. We observed that a subpopulation of these axons, the pioneer olfactory axons, penetrate into the ventricular zone of a highly restricted region of the telencephalon at E13 and E14. At E15, this same telencephalic region evaginates to form the olfactory bulb. To investigate the possibility that the pioneer olfactory axons induce the olfactory bulb by influencing precursor cell populations, we compared cell cycle kinetics and differentiation in the olfactory bulb primordium and the adjacent neocortex using cumulative bromdeoxyuridine labeling. The results showed that, 24 hr after the arrival of the first pioneer axons, the duration of the cell cycle is prolonged significantly in the olfactory bulb primordium. In addition, twice as many cells have exited the mitotic cycle in the olfactory bulb primordium versus the adjacent cortex. These findings suggest that pioneer olfactory axons play a role in the induction of the olfactory bulb by selectively modulating cell cycle kinetics in the olfactory bulb primordium. Afferent axons may influence target morphogenesis by modulating target precursor cell proliferation in other developing neural structures.

Localization and regulation of low affinity nerve growth factor receptor expression in the rat olfactory system during development and regeneration

Nerve growth factor (NGF), a classic neurotrophic factor, promotes neuronal survival, maintenance, regeneration and differentiation in the peripheral nervous system and parts of the central nervous system. NGF activity is mediated by cell surface bound receptors including the low affinity NGF receptor (LNGFr) which is expressed by some peripheral and central neurons and is present on peripheral nerve Schwann cells during development and regeneration. The olfactory system is a useful model for the study of the role of LNGFr in neuronal development and regeneration. The growth of olfactory axons into the brain begins in the embryo and continues through the first few postnatal weeks. In mature animals there is persistent turnover and generation of olfactory receptor neurons (ORNs) and continuous growth of new axons into the olfactory bulb. These new axons grow along the preexisting olfactory pathway. In the mature olfactory system, LNGFr has been observed in the glomerular layer of the olfactory bulb, the target of ORNs. However, neither the cellular localization nor the developmental expression of LNGFr has been characterized. Here, we tested the hypothesis that LNGFr expression is developmentally regulated in the olfactory nerve and is reinduced following injury to the mature olfactory nerve. LNGFr-immunoreactivity (IR) was first observed in the olfactory mucosa at embryonic day (E)13 and in the olfactory nerve at E14. LNGFr-IR increased in the nerve during embryonic development, began to decrease at around postnatal day (P)5 and was scarcely detectable in normal adults. The staining pattern suggests that LNGFr is located on the olfactory nerve Schwann cells. Streaks of LNGFr-IR were present in the adult olfactory nerve. We reasoned that these streaks might represent transient reexpression of LNGFr associated with normal olfactory neuron turnover and replacement. Consistent with this hypothesis, LNGFr was robustly reexpressed in the adult olfactory nerve following lesion of the olfactory epithelium. Starting late in development (E21) and in the adult, LNGFr-IR was also observed on fibers in deep layers of the olfactory bulb. LNGFr-IR was also observed in neurons of the nucleus of the diagonal band (NDB) in the basal forebrain. NDB is the sole source of cholinergic afferents of the olfactory bulb. Thus, we tested the hypothesis that LNGFr in the deep layers of the olfactory bulb is located on NDB axons by making lesions of NDB. Following the lesion, LNGFr-IR disappeared in the deep layers of the olfactory bulb but remained in the glomerular layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Single- and double-label immunocytochemical study of the ovine suprachiasmatic nucleus (SCN): GABAergic and peptidergic relationships

This study evaluated the neuropeptide and neurotransmitter content of the ovine suprachiasmatic nucleus (SCN) using both single- and double-label immunocytochemical methods. Single-label immunocytochemistry identified a few lightly labeled gamma aminobutyric acid (GABA) cells within the SCN as well as a dense plexus of fibers staining positive for the GABA biosynthetic enzyme, glutamic acid decarboxylase (GAD). Vasoactive intestinal polypeptide (VIP) fibers exhibited a similar distribution to GAD fibers; VIP cells were found throughout the SCN, as well as in the paraventricular (PVN) and supraoptic nuclei. Both GAD and VIP fibers exited dorsally from the SCN towards the PVN. Neurophysin (NP) and neuropeptide-Y (NPY) fibers were sparsely distributed throughout the SCN. Double-label immunocytochemistry revealed that GAD varicosities were often in close apposition to VIP cells. These results confirm the presence of GABAergic elements within the sheep SCN. Furthermore, they raise the possibility of a GABAergic modulation of VIP neuronal activity within the ovine SCN.

[Effect of arginine on lymphocyte responses to ConA in burned mice]

It is well accepted that nutritional support improves the immunologic functions in burned patients. Arginine has been demonstrated to have tissue-specific properties which induce beneficial effects upon the immune system. A series of experiments are carried out, in order to evaluate the immune effect of arginine on burned mice. 1. Lymphocytes from both burned and unburned mice are harvested and incubated in various concentrations of arginine solution for 72 hours, and ConA-stimulating lymphocyte transformation is determined after incubation. 2. Burned animals are divided into four groups. Standard diets for nutritional support are formulated. These formulas contain an identical carbohydrate and lipid (61% and 15% of total energy respectively) intake with varied proportions of protein for each group (24%, 23%, 22%, and 20% of total energy, respectively), in addition. 0%, 1%, 2% and 4% of protein energy is supplied by arginine for different groups. Lymphocyte proliferations in responses to ConA stimulation are determined on the 7th postburn day. The data shows that, in vitro study, increasing arginine concentrations enhanced lymphocyte responses to ConA. The arginine needed level for optimal lymphocyte responses is 1.8 mmol/L in burned mice and 0.9 mmol/L in unburned controls. This difference indicates that in burned mice, a higher arginine concentration is required for better lymphocyte responses. On the contrary, further increase of arginine concentration do not give better response. When varied amounts of arginine are given in the diet to the burned mice, the degree of lymphocyte response to ConA is different. The amount of arginine which supplies 2% of total energy is found to be optimal.

Mitogen-activated Ca++ channels in human B lymphocytes

Two complementary experimental methods have been used to examine mitogen-induced transmembrane conductances in human B cells using the Daudi cell line as a model for human B cell activation. Spectrofluorometry was used to investigate mitogen-induced changes in [Ca++]i and transmembrane potential. Activation of human B cells with anti-mu antibodies resulted in a biphasic rise in [Ca++]i, the second phase being mediated by the influx of extracellular Ca++. Ca++ influx was inhibited by high [K+]e, suggesting that this influx was transmembrane potential sensitive. Membrane currents of Daudi cells were investigated using voltage clamp techniques. Before mitogenic stimulation, the cells were electrically quiet. Within several minutes of the addition of anti-mu antibodies to the bath solution, inward currents were observed at negative voltages. Whole-cell currents changed instantly with voltage steps and were transmembrane potential sensitive in that at potentials more positive than -40 mV no currents were detectable. A similar conductance was also activated by the introduction of IP3 into the intracellular solution, suggesting that IP3 generation after surface IgM crosslinking is involved in the activation of this conductance. Both anti-mu and IP3 induced currents were blocked by 1 mM La , which is known to block Ca++ channels. These results strongly support the presence of membrane Ca++ channels in human B cells that function in the early stages of activation. Changes in transmembrane potential appear to be important in regulating Ca++ influx. These mechanisms work in concert to regulate the level of [Ca++]i during the early phases of human B cell activation.

Characterization of the cathepsin B gene and multiple mRNAs in human tissues: evidence for alternative splicing of cathepsin B pre-mRNA

We have cloned and characterized multiple messages for cathepsin B that differ in their 5' and 3' untranslated regions (UTRs) from human kidney and the hepatoma cell line HepG2. A comparison of these messages with the cloned human cathepsin B gene reveals that they arise by alternative splicing of a single gene. Processing at a cryptic intron donor site in exon 11 and splicing to exon 12 produces a 4.0-kb message with an alternate 3' UTR in addition to the 2.3-kb message described previously by Chan et al. (1986). Variable removal of exon 2 produces cathepsin B mRNAs which differ by 88 nucleotides in their 5'-UTRs. The ratio of the 2.3-kb to 4.0-kb transcript is about 2:1 in most of the tissues examined, but the ratio of mRNAs with variant 5' UTRs differs widely. Cathepsin B mRNAs lacking exon 2 are predominant in human tumors. In addition, human breast and colon carcinomas and a human melanoma contain a cathepsin B transcript that is also missing exon 3 encoding the signal peptide and 7 residues of the activation propeptide. An in vitro transcription/translation assay was used to demonstrate that this message could be translated from an internal methionine codon (residue 52), producing a 32-kD product lacking the signal peptide and more than half the propeptide. The transcription/translation assay also demonstrated that the variant messages differ in their rates of translation. The relative rates are about 8:2:1 for mRNA lacking exons 2 and 3 compared to mRNA lacking exon 2 and mRNA containing the full-length 5' end, respectively. These results suggest that the expression of cathepsin B in human tissues may be regulated in part at the level of mRNA processing.

Enhancer-dependent transcription of the epsilon-globin promoter requires promoter-bound GATA-1 and enhancer-bound AP-1/NF-E2

We analyzed epsilon-globin transcription in erythroid cells and in erythroid extracts to determine the requirements for enhancer-dependent expression of this gene. Mutations that abolished GATA-1 binding at a single position in the promoter prevented interaction with enhancers, whereas elimination of a second more distal promoter GATA-1 site had no effect. Deletion or mutation of the GATA-1 sites in either the human beta-globin locus control region DNase-hypersensitive site II enhancer or the chicken beta A/epsilon-globin enhancer did not diminish the ability of the enhancers to interact with the promoter. In contrast, mutation of the AP-1/NF-E2 sites in these enhancers resulted in elimination of enhancement. In vitro transcription of these constructs was promoter dependent and was not sensitive to abolition of GATA-1 binding in the promoter, consistent with the role of GATA-1 solely as a mediator of the enhancer effect. Thus, GATA-1 regulates the response of the epsilon-globin gene to enhancers through a specific site in the promoter and requires enhancer AP-1/NF-E2 binding to transduce the enhancer effect on transcription.

Polarization properties of planar dielectric waveguide gratings

An experimental and theoretical study of polarization properties of planar dielectric waveguide gratings operating at general (oblique) inicidence is reported. The radiation modes coupled out by a surface-relief waveguide grating, when the incident light is not normal to the grating rulings, are linearly polarized for TE excitation and are elliptically polarized for TM excitation. The polarization states of the radiation modes are determined primarily by the polarization state of the principal guided wave in the grating region and by the propagation directions of the radiation modes with respect to the plane of the principal guided wave. Experimental data and numerical results based on three physical models are presented.

[Change of T lymphocyte subsets in peripherial blood of children with malnutrition and zinc deficiency]

Sixty children with malnutrition were investigated in this study. The results showed a reduction of serum zinc in moderate and severe cases compared with the mild and normal groups. OKT3+, OKT4+ and OKT8+ cells in peripheral blood of mild malnutrition were significantly decreased in contrast to normal control. The reductive degree of OKT8+ and OKT4+ cells correlated with the severity of malnutrition. OKT8+, OKT4+ and OKT4+/OKT8+ ratio of moderate and severe malnutrition with infection were much lower than those without infection. Our findings suggested that main effective and regulative cells of cell-mediated immunity were impaired. OKT3+ and OKT4+ cells might be used as a sensitive index for early assessment of the immune function in malnutrition children.

Efficient grating coupling to poly-4BCMU optical waveguides

We report measurements of the refractive indices of poly-4BCMU films and the fabrication of an efficient integrated optical distributed coupler. The refractive index measurements were performed in the visible and near IR using blazed-grating couplers. The analysis led to the optimization of an input coupler with a coupling efficiency larger than 45% at 1.064 microm.

White-light image processing using oriented speckle-screen encoding

We present a new technique of spatially oriented speckle-screen encoding to improve on the grating encoding technique for white-light image processing.