Biocatalytic plastics as active and stable materials for biotransformations

Enzyme-containing polymeric materials have been developed that have high activity and stability in both aqueous and organic media. These biocatalytic plastics, containing alpha-chymotrypsin and subtilisin Carlsberg, can contain up to 50% (w/w) total protein in plastic materials such as poly(methyl methacrylate, styrene, vinyl acetate, and ethyl vinyl ether). The activation achieved in organic solvents by incorporating proteases in plastic matrices allows for the efficient synthesis of peptides, and sugar and nucleoside esters. The marriage of enzyme technology with polymer chemistry opens up an array of unique applications for plastic enzymes, including active and stable biocatalysts in paints, coatings, resins, foams, and beads, as well as membranes, fibers, and tubings.

The surgical management of an advanced pterygium involving the entire cornea

PURPOSE

Conjunctival autografting is a well-established surgical procedure to prevent recurrence after pterygium excision. We described a modified technique of harvesting an annular autograft to cover a large conjunctival defect after excision of an extensive primary pterygium that involved three quadrants of the limbus.

METHODS

A 73-year-old Chinese farmer underwent an excision of an advanced right pterygium involving the entire cornea. A free donor graft was then harvested from the remaining superior bulbar conjunctiva to cover the conjunctival defect, which involved approximately-three quadrants of limbus. The undersized graft was split down the center to create an annular graft to cover the defect.

RESULTS

Postoperatively, there has been no recurrence over a total follow-up period of 11 months. Six months after the initial pterygium surgery, he underwent a successful penetrating keratoplasty for residual deep stromal scarring. Visual acuity 5 months after the penetrating keratoplasty remained stable at 6/18.

CONCLUSIONS

This case report shows that a modified technique of conjunctival autografting can be successful in preventing recurrence in an advanced pterygium after excision. Successful visual rehabilitation with a penetrating keratoplasty also was demonstrated in this patient.

Changing indications for penetrating keratoplasty: a newly developed country's experience

PURPOSE

To study the changing indications for penetrating keratoplasty in Singapore and compare local indications with developed countries with established corneal graft programs.

METHODS

A descriptive study of all penetrating keratoplasty cases performed in the Singapore National Eye Center over a 5 year period, from 1 January 1991 to 31 December 1995 using records of the Singapore Eye Bank registry.

RESULTS

A total of 327 penetrating keratoplasties were performed. Bullous keratopathy was the indication in more than a quarter of all cases (26.3%). Aphakic bullous keratopathy (11.6%) and pseudophakic bullous keratopathy (11.3%) accounted for the majority of the bullous keratopathy cases. The other leading indications were regrafts (11.9%), corneal dystrophies (10.4%), traumatic scarring (10.1%) and keratoconus (9.8%). A higher proportion of aphakic and pseudophakic bullous keratopathy as well as regrafts was noted in this series compared to a previous report on corneal transplantation in the 1980s. A rising indication rate of pseudophakic bullous keratopathy, in conjunction with a declining indication rate of herpetic keratitis was observed over the 5 year study period.

CONCLUSIONS

The indications for penetrating keratoplasty in Singapore appear to follow the trend seen in developed Western countries over the past few decades.

Predictors of quality of life after hospital admission for heart attack or angina

This study tests the hypothesis that it is possible to predict people who will have a low quality of life (QOL) 6 months after hospital admission for acute myocardial infarction (AMI) or angina. Among 424 patients discharged from hospital in the Hunter Region of New South Wales with a diagnosis of AMI or angina, follow-up questionnaires were received from 303 at 6 months. Baseline data collected during hospitalisation included demographic variables and the 'emotional' factor of a disease-specific QOL measure using a modified and validated self-administered questionnaire. The full QOL measure comprises 'emotional', 'physical' and 'social' factors, each factor being assessed at the 6-month follow-up. Only baseline 'emotional' QOL score and sex predicted 6-month QOL scores in patients with AMI. Scores were consistently lower in patients with angina, in whom marital and employment status, having had a previous AMI, current cigarette smoking, the presence of cardiac failure and baseline emotional QOL were all significantly associated with the 6-month QOL scores. The assessment of simple measures during hospitalisation for angina can be helpful in predicting those who will have a low QOL 6 months later. They may represent a high-risk group at whom counselling could be directed.

The winged helix transcription factor HFH-4 is expressed during choroid plexus epithelial development in the mouse embryo

Mammalian hepatocyte nuclear factor-3 (HNF-3) and the Drosophila homeotic gene fork head proteins are prototypes of an extensive family of cell-specific transcription factors that share homology in the winged helix DNA-binding domain. One of these mammalian family members, HNF-3/fork head homolog-4 (HFH-4), was isolated by PCR amplification of rodent brain cDNA and exhibits abundant expression in the adult bronchiolar epithelium. In this study, we performed in situ hybridization of stage-specific mouse embryos and report on a novel expression pattern of the HFH-4 gene in both the presumptive and differentiated choroid plexus epithelium, which is responsible for the synthesis and secretion of cerebrospinal fluid (CSF) proteins. We also showed that HFH-4 is a potent transcriptional activator in cotransfection assays and defined several protein sequences important for HFH-4 transcriptional activity. We used in vitro DNA-binding site selection with recombinant HFH-4 protein and determined that the HFH-4 protein recognizes the DNA consensus sequences HWDTGTTTGTTTA or KTTTGTTGTTKTW (where H is not G, W is A or T, D is not C, and K is G or T). We used this HFH-4 consensus to identify potential HFH-4 target genes in the choroid plexus epithelium and demonstrated that these promoter sequences bind to recombinant HFH-4 protein in electrophoretic mobility shift assays. Recombinant HFH-4 formed specific protein-DNA complexes with the promoter regions of the human prothrombin, beta amyloid precursor protein, alpha1-antichymotrypsin, cystic fibrosis transmembrane conductance regulator and rodent alpha2-macroglobulin, growth hormone receptors, and insulin-like growth factor II genes. Furthermore, we identified putative HFH-4 target genes in the bronchiolar epithelium including the clara cell secretory protein gene and the HNF-3alpha gene, a winged helix family member involved in the transcriptional regulation of genes in the bronchiolar epithelium. In support of these binding studies, cotransfection assays show that HFH-4 potentiates expression of the HNF-3alpha and clara cell secretory protein promoter regions.

Accurate intraocular pressure measurement in contact lens wearers with normal pressures

PURPOSE

The purpose of this study was to evaluate a modified technique of Goldmann applanation tonometry without the use of fluorescein or anesthesia in normal eyes with contact lenses and to compare this technique with Tono-Pen tonometry.

METHODS

The intraocular pressure (IOP) of 40 normal eyes from 20 volunteers (mean age 25.6 years, range 22-35 years) was measured with and without-1.0 D disposable soft contact lenses in a prospective, masked, randomized study using Goldmann and Tono-Pen tonometry. Goldmann tonometry was performed without fluorescein or anesthesia with contact lenses on. IOP measurement using conventional Goldmann tonometry with fluorescein and without contact lens wear was employed as the standard for comparison.

RESULTS

Goldmann tonometry without fluorescein underestimated IOP levels in a consistent manner, with a bias of -2.15 mmHg (SD +/- 1.97). Goldmann tonometry without fluorescein, in the presence of a contact lens, consistently underestimated IOP levels by -2.90 mmHg (SD +/- 2.37), suggesting that IOP measurement is largely unaffected by the presence of a -1.00 D soft contact lens on the eye. In contrast, Tono-Pen tonometry consistently overestimated IOP levels by +3.93 mmHg (SD +/- 2.17). Given the limits of agreement, these results were fairly consistent.

CONCLUSIONS

The modified technique of Goldmann tonometry without fluorescein reflects standard Goldmann tonometry with fluorescein after a correction factor of +2 mmHg in normal eyes. IOP measurement by this technique does not appear to be significantly affected by the presence of a -1.0 D soft contact lens on the cornea.

Hepatocyte nuclear factor 3/fork head homolog 11 is expressed in proliferating epithelial and mesenchymal cells of embryonic and adult tissues

The hepatocyte nuclear factor 3alpha (HNF-3alpha) and 3beta proteins have homology in the winged helix/fork head DNA binding domain and regulate cell-specific transcription in hepatocytes and in respiratory and intestinal epithelia. In this study, we describe two novel isoforms of the winged helix transcription factor family, HNF-3/fork head homolog 11A (HFH-11A) and HFH-11B, isolated from the human colon carcinoma HT-29 cell line. We show that these isoforms arise via differential splicing and are expressed in a number of epithelial cell lines derived from tumors (HT-29, Caco-2, HepG2, HeLa, A549, and H441). We demonstrate that differentiation of Caco-2 cells toward the enterocyte lineage results in decreased HFH-11 expression and reciprocal increases in HNF-3alpha and HNF-3beta mRNA levels. In situ hybridization of 16 day postcoitus mouse embryos demonstrates that HFH-11 expression is found in the mesenchymal and epithelial cells of the liver, lung, intestine, renal cortex, and urinary tract. Although HFH-11 exhibits a wide cellular expression pattern in the embryo, its adult expression pattern is restricted to epithelial cells of Lieberkühn's crypts of the intestine, the spermatocytes and spermatids of the testis, and the thymus and colon. HFH-11 expression is absent in adult hepatocytes, but its expression is reactivated in proliferating hepatocytes at 4, 24, and 48 h after partial hepatectomy. Consistent with these findings, we demonstrate that HFH-11 mRNA levels are stimulated by intratracheal administration of keratinocyte growth factor in adult lung and its expression in an adult endothelial cell line is reactivated in response to oxidative stress. These experiments show that the HFH-11 transcription factor is expressed in embryonic mesenchymal and epithelial cells and its expression is reactivated in these adult cell types by proliferative signals or oxidative stress.

Expression of constitutively active alpha-PAK reveals effects of the kinase on actin and focal complexes

The family of p21-activated protein kinases (PAKs) appear to be present in all organisms that have Cdc42-like GTPases. In mammalian cells, PAKs have been implicated in the activation of mitogen-activated protein kinase cascades, but there are no reported effects of these kinases on the cytoskeleton. Recently we have shown that a Drosophila PAK is enriched in the leading edge of embryonic epithelial cells undergoing dorsal closure (N. Harden, J. Lee, H.-Y. Loh, Y.-M. Ong, I. Tan, T. Leung, E. Manser, and L. Lim, Mol. Cell. Biol. 16:1896-1908, 1996), where it colocalizes with structures resembling focal complexes. We show here by transfection that in epithelial HeLa cells alpha-PAK is recruited from the cytoplasm to distinct focal complexes by both Cdc42(G12V) and Rac1(G12V), which themselves colocalize to these sites. By deletion analysis, the N terminus of PAK is shown to contain targeting sequences for focal adhesions which indicate that these complexes are the site of kinase function in vivo. Cdc42 and Rac1 cause alpha-PAK autophosphorylation and kinase activation. Mapping alpha-PAK autophosphorylation sites has allowed generation of a constitutively active kinase mutant. By fusing regions of Cdc42 to the C terminus of PAK, activated chimeras were also obtained. Plasmids encoding these different constitutively active alpha-PAKs caused loss of stress fibers when introduced into both HeLa cells and fibroblasts, which was similar to the effect of introducing Cdc42(G12V) or Rac1(G12V). Significantly dramatic losses of focal adhesions were also observed. These combined effects resulted in retraction of the cell periphery after plasmid microinjection. These data support our previous suggestions of a role for PAK downstream of both Cdc42 and Rac1 and indicate that PAK functions include the dissolution of stress fibers and reorganization of focal complexes.

Rho family GTPases and neuronal growth cone remodelling: relationship between increased complexity induced by Cdc42Hs, Rac1, and acetylcholine and collapse induced by RhoA and lysophosphatidic acid

Rho family GTPases have been assigned important roles in the formation of actin-based morphologies in nonneuronal cells. Here we show that microinjection of Cdc42Hs and Rac1 promoted formation of filopodia and lamellipodia in N1E-115 neuroblastoma growth cones and along neurites. These actin-containing structures were also induced by injection of Clostridium botulinum C3 exoenzyme, which abolishes RhoA-mediated functions such as neurite retraction. The C3 response was inhibited by coinjection with the dominant negative mutant Cdc42Hs(T17N), while the Cdc42Hs response could be competed by coinjection with RhoA. We also demonstrate that the neurotransmitter acetylcholine (ACh) can induce filopodia and lamellipodia on neuroblastoma growth cones via muscarinic ACh receptor activation, but only when applied in a concentration gradient. ACh-induced formation of filopodia and lamellipodia was inhibited by preinjection with the dominant negative mutants Cdc42Hs(T17N) and Rac1(T17N), respectively. Lysophosphatidic acid (LPA)-induced neurite retraction, which is mediated by RhoA, was inhibited by ACh, while C3 exoenzyme-mediated neurite outgrowth was inhibited by injection with Cdc42Hs(T17N) or Rac1(T17N). Together these results suggest that there is competition between the ACh- and LPA-induced morphological pathways mediated by Cdc42Hs and/or Rac1 and by RhoA, leading to either neurite development or collapse.

Regulation of phosphorylation pathways by p21 GTPases. The p21 Ras-related Rho subfamily and its role in phosphorylation signalling pathways

The oncogenic Ras p21 GTPases regulate phosphorylation pathways that underlie a wealth of activities, including growth and differentiation, in organisms ranging from yeast to human. In metazoa, growth factors trigger conversion of Ras from an inactive GDP-bound form to an active GTP-bound form. This activation of Ras leads to activation of Raf. Raf is one of the initial kinases in the cytoplasmic mitogen-activated protein kinase (MAPK) cascade, involving extracellular-signal-regulated kinases (ERK), which culminates in nuclear transcription. The Ras-related subfamily of Rho p21s, including Rho, Rac and Cdc42 are similarly active in their GTP-bound forms. These p21s mediate growth-factor-induced morphological changes involving actin-based cellular structures. For example, in mammalian fibroblasts, Rho mediates the formation of cytoskeletal stress fibres induced by lysophosphatidic acid, while Rac mediates the formation of membrane ruffles induced by platelet-derived growth factor, and Cdc42 mediates the formation of peripheral filopodia by bradykinin. In some cases, factor-induced Rac activation results in Rho activation, and factor-induced Cdc42 activation leads to Rac activation, as determined by specific morphological changes. Although separate Cdc42/Rac and Rac/Rho hierarchies exist, these might not extend into a linear form (i.e. Cdc42-->Rac-->Rho) since Cdc42 and Rho activities may be competitive or even antagonistic. Thus Cdc42-mediated formation of filopodia is accompanied by loss of stress fibres (whose formation is mediated by Rho). Recently, mammalian kinases that bind to the GTP-bound forms of Rho p21s have been isolated. These kinases include the p21-activated serine/threonine kinase (PAK), which is stimulated by binding to Cdc42 and Rac, and the Rho-binding serine/threonine kinase (ROK), which is not as strongly stimulated by binding. These kinases act as effectors for their p21 partners since they can directly affect the reorganization of the relevant actin-containing structures. ROK promotes the formation of Rho-induced actin-containing stress fibres and focal-adhesion complexes, to which the ends of the stress fibres attach. PAK stimulates the disassembly of stress fibres, which has been shown to accompany formation of Cdc42-induced peripheral-actin-containing structures, including filopodia, which with Rac-induced membrane ruffles play a role in cell movement. PAK also fosters loss of focal-adhesion complexes. Thus, there is cooperation between different Rho p21s as well as antagonism, with their associated kinases having a role in the integration of the reorganization of the actin cytoskeleton. The similarity of PAK to the Saccharomyces cerevisiae kinase Ste20p, which initiates the yeast mating/pheromone MAPK cascade, led to experiments showing that Cdc42 regulates Ste20p in this MAPK pathway. This similarity has also led to the demonstration that mammalian Cdc42 and Rac can signal to the nucleus through MAPK pathways. However, c-Jun N-terminal kinase (JNK, stress-activated protein kinase) rather than ERK, is involved. PAK have been implicated in the JNK pathway, but their exact roles are uncertain. Thus members of the Rho subfamily, and kinases that bind to these p21s are intimately involved in immediate morphological processes as well as long-term transcriptional events.

Asthma presentations to emergency departments in western Sydney during the January 1994 Bushfires

BACKGROUND

From 5 to 12 January 1994, the state of New South Wales suffered from the worst bushfires seen this century. High levels of particulate air pollution were recorded in western Sydney from 7 to 14 January 1994, with nephelometry readings reaching 10.24 beta scat (10(-4)/m) and particulate matter < 10 mu readings peaking at 250.00 micrograms/m3. The aim of this study was to determine whether there was an increase in the proportion of asthma presentations to emergency departments (ED) in western Sydney as a result of the bushfire-generated particulate air pollution.

METHOD

We retrospectively analysed the emergency room attendance books for asthma presentations from seven public hospitals serving the Western Sydney and Wentworth Health Areas over two 6-7 week periods, 17 December 1992 to 31 January 1993, and 17 December 1993 to 31 January 1994. Air pollution and meteorological data were obtained from local monitoring stations.

RESULTS

The difference in the proportion of all ED presentations that were due to asthma during the week of the bushfire-generated air pollution, compared with the same week 12 months before, after adjusting for baseline changes over the 12-month period, was 0.0067 (95% CI: -0.0007, 0.0141). The maximum daily nephelometry reading was not a significant predictor of the daily number of asthma presentations to ED in any of the Poisson regression models.

CONCLUSIONS

The bushfire-generated particulate air pollution in January 1994 did not result in an increase in asthma presentations to ED in western Sydney.

Isolation of the gene coding for Caenorhabditis elegans Rac2 homologue, a Ras-related small GTP-binding protein

When screening a Caenorhabditis elegans genomic library using the human Rac1 cDNA as probe, a hybridizing fragment of 2.7 kb was isolated which contained four exons with high sequence similarity to CeRac1, coding for the nematode homologue of the Ras-related small GTP-binding protein Rac1. The putative translational product of 195 amino acids (aa) from the exons displayed 88% identity to the sequence of CeRac1. Interestingly, three alterations were found in the N-terminal "effector domain' (residues 22-45) which hitherto was identical among all known Rac p21s, suggesting that CeRac2 might have different targets/functions for nematode development. Additionally, an insertion of 4 aa was found in the hypervariable region at the C terminus of CeRac2.

The Caenorhabditis elegans p21-activated kinase (CePAK) colocalizes with CeRac1 and CDC42Ce at hypodermal cell boundaries during embryo elongation

The p21-activated kinase (PAK) is a downstream target of Rac and CDC42, members of the Ras-related Rho subfamily, that mediates signaling pathway leading to cytoskeletal reorganization. To investigate its function in Caenorhabditis elegans development, we have isolated the cDNA coding for the p21-activated kinase homologue (CePAK) from a C. elegans embryonic cDNA library. This 2.35-kilobase pair cDNA encodes a polypeptide of 572 amino acid residues, with the highly conserved N-terminal p21-binding and the C-terminal kinase domains. Similar to its mammalian and Drosophila counterparts, the CePAK protein expressed in E. coli exhibits binding activity toward GTP-bound CeRac1 and CDC42Ce. Polyclonal antibodies raised against the recombinant CePAK recognize a specific 70-kDa protein from embryonic extracts that displays CeRac1/CDC42Ce-binding and kinase activities. Immunofluorescence analysis indicates that CePAK is specifically expressed at the hypodermal cell boundaries during embryonic body elongation, which involves dramatic cytoskeletal reorganization. Interestingly, CeRac1 and CDC42Ce are found at the same location, which might point to their common involvement in hypodermal cell fusion, a crucial morphogenetic event for nematode development.

Luxation of the globe and Crouzon's disease--the first reported case in Singapore

A case of spontaneous luxation of the globe and Crouzon's disease is described. The luxation was reduced under general anaesthesia. Bilateral permanent tarsorrhaphies were performed to prevent further luxations and to decrease the lagophthalmos and corneal exposure. There was also mild bilateral optic atrophy and a left superior oblique palsy. The patient exhibited turricephaly, maxillary hypoplasia and shallow orbits with proptosis. Major reconstructive surgery is not indicated as the patient is already 9 years old and has no mental impairment.

Thyroid transcription factor-1, hepatocyte nuclear factor-3beta, surfactant protein B, C, and Clara cell secretory protein in developing mouse lung

We used immunohistochemical analysis to localize thyroid transcription factor-1 (TTF-1), hepatocyte nuclear factor-3beta (HNF-3beta), prosurfactant proteins B and C (pro-SP-B, pro-SP-C), surfactant protein B (SP-B), and Clara cell secretory protein (CCSP) in developing mouse lung. TTF-1 and HNF-3beta were expressed at the onset of lung morphogenesis (gestational Day 10) and throughout fetal lung development, being detected in the nuclei of airway epithelial cells. TTF-1 was most prominent in distal airway epithelial cells in embryonic lung and HNF-3beta in proximal bronchial and bronchiolar epithelial cells. Pro-SP-B and pro-SP-C were first detected on gestational Day 11, being localized to the cytoplasm of airway epithelial cells. Expression of both pro-proteins was confined to distal airway epithelial cells from gestational Day 12 to Day 16. From gestational Day 17 and thereafter, pro- SP-B was detectable in Type II cells and bronchiolar epithelial cells, whereas pro-SP-C was restricted to Type II cells. SP-B peptide was first detected on gestational Day 17 in the cytoplasm of Type II cells and within the lumen of distal airways. SP-B peptide was detectable only in the cytoplasm of Type II cells in adult lung. CCSP was first detected on gestational Day 17, being localized to the cytoplasm of columnar epithelial cells lining the conducting airways. Pro-SP-B, SF-B, pro-SP-C, and CCSP staining increased before birth. The early expression of TTF-1 and HNF-3beta, preceding and overlapping that of pro-SP-B, mature SP-B, pro-SP-C, and CCSP, supports a regulatory role for TTF-1 and HNF-3beta in lung-specific gene expression.

The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton

The GTPase RhoA has been implicated in various cellular activities, including the formation of stress fibers, motility, and cytokinesis. We recently reported on a p150 serine/threonine kinase (termed ROK alpha) binding RhoA only in its active GTP-bound state and on its cDNA; introduction of RhoA into HeLa cells resulted in translocation of the cytoplasmic kinase to plasma membranes, consistent with ROK alpha being a target for RhoA (T. Leung, E. Manser, L. Tan, and L. Lim, J. Biol. Chem. 256:29051-29054, 1995). Reanalysis of the cDNA revealed that ROK alpha contains an additional N-terminal region. We also isolated another cDNA which encoded a protein (ROK beta) with 90% identity to ROK alpha in the kinase domain. Both ROK alpha and ROK beta, which had a molecular mass of 160 kDa, contained a highly conserved cysteine/histidine-rich domain located within a putative pleckstrin homology domain. The kinases bound RhoA, RhoB, and RhoC but not Rac1 and Cdc42. The Rho-binding domain comprises about 30 amino acids. Mutations within this domain caused partial or complete loss of Rho binding. The morphological effects of ROK alpha were investigated by microinjecting HeLa cells with DNA constructs encoding various forms of ROK alpha. Full-length ROK alpha promoted formation of stress fibers and focal adhesion complexes, consistent with its being an effector of RhoA. ROK alpha truncated at the C terminus promoted this formation and also extensive condensation of actin microfilaments and nuclear disruption. The proteins exhibited protein kinase activity which was required for stress fiber formation; the kinase-dead ROK alpha K112A and N-terminally truncated mutants showed no such promotion. The latter mutant instead induced disassembly of stress fibers and focal adhesion complexes, accompanied by cell spreading. These effects were mediated by the C-terminal region containing Rho-binding, cysteine/histidine-rich, and pleckstrin homology domains. Thus, the multidomained ROK alpha appears to be involved in reorganization of the cytoskeleton, with the N and C termini acting as positive and negative regulators, respectively, of the kinase domain whose activity is crucial for formation of stress fibers and focal adhesion complexes.

The human neuronal alpha 1-chimaerin gene contains a position-dependent negative regulatory element in the first exon

alpha 1-Chimaerin mRNA, which encodes a neuron-specific GTPase-activating protein for the signal transduction molecule p21 Rac, is highly expressed in certain brain regions and neuronal cell lines. The promoter region of human alpha 1-chimaerin transcriptional unit contains no TATA box, Sp1-binding site or initiator motif. However, a CCAAT box located in the proximal promoter region is essential for promoter activity. We now describe a negative regulatory element in the 5' untranslated region of exon 1 of the human alpha 1-chimaerin gene. Deletion of this 70-bp region from the alpha 1-chimaerin minimal promoter increased the promoter activity 5- to 6-fold. The negative element can suppress heterologous thymidine kinase promoter activity in an orientation-independent manner when placed in its native position. However, its function is position-dependent. The presence of a putative factor in rat liver, HepG2 and SK-N-SH cell nuclear extracts but not in rat brain nuclear extract which interacts with this element suggests a possible role of the negative element in controlling the neuron-specific expression of alpha 1-chimaerin in vivo.

The GTPase-activating protein n-chimaerin cooperates with Rac1 and Cdc42Hs to induce the formation of lamellipodia and filopodia

n-Chimaerin is a GTPase-activating protein (GAP) mainly for Rac1 and less so for Cdc42Hs in vitro. The GAP activity of n-chimaerin is regulated by phospholipids and phorbol esters. Microinjection of Rac1 and Cdc42Hs into mammalian cells induces formation of the actin-based structures lamellipodia and filopodia, respectively, with the former being prevented by coinjection of the chimaerin GAP domain. Strikingly, microinjection of the full-length n-chimaerin into fibroblasts and neuroblastoma cells induces the simultaneous formation of lamellipodia and filopodia. These structures undergo cycles of dissolution and formation, resembling natural morphological events occurring at the leading edge of fibroblasts and neuronal growth cones. The effects of n-chimaerin on formation of lamellipodia and filopodia were inhibited by dominant negative Rac1(T17N) and Cdc42Hs(T17N), respectively. n-Chimaerin's effects were also inhibited by coinjection with Rho GDP dissociation inhibitor or by treatment with phorbol ester. A mutant n-chimaerin with no GAP activity and impaired p21 binding was ineffective in inducing morphological changes, while a mutant lacking GAP activity alone was effective. Microinjected n-chimaerin colocalized in situ with F-actin. Taken together, these results suggest that n-chimaerin acts synergistically with Rac1 and Cdc42Hs to induce actin-based morphological changes and that this action involves Rac1 and Cdc42Hs binding but not GAP activity. Thus, GAPs may have morphological functions in addition to downregulation of GTPases.

Alzheimer's disease and apolipoprotein E genotype in Western Australia: an autopsy-verified series

OBJECTIVE

To determine the relationship between the apolipoprotein E epsilon 4 allele and autopsy-verified Alzheimer's disease (AD) in an Australian population.

DESIGN

Retrospective case-control study.

SETTING

Royal Perth Hospital, Perth, Western Australia (a tertiary referral hospital).

SUBJECTS

50 subjects with "definite" AD (according to the histological and clinical criteria of the Consortium to Establish a Registry for Alzheimer's Disease [CERAD]) and 30 control subjects who had died from a non-neurological disease were randomly selected from the hospital's neuropathology register.

OUTCOME MEASURES

Histological grading of brain sections stained with the modified Bielschowsky stain according to the criteria of CERAD; number (burden) of neuritic plaques; apolipoprotein E genotype (APOE).

RESULTS

Frequency of the epsilon 4 allele was significantly higher in the AD group (37%) than in the control group (2%) (chi 2 = 25.8; P < 0.00001). In the AD group, 50% of subjects were heterozygous for the epsilon 4 allele and 12% were homozygous, while in the control group one subject was heterozygous for the allele and none were homozygous. No association was seen between the epsilon 4 allele and neuritic plaque burden in the hippocampus, entorhinal cortex, middle frontal gyrus or inferior parietal lobule in subjects with AD.

CONCLUSIONS

Our findings confirm an association between the epsilon 4 allele and autopsy-verified AD. The epsilon 4 allele may be an important risk factor for susceptibility to AD in the general Australian population.

A Drosophila homolog of the Rac- and Cdc42-activated serine/threonine kinase PAK is a potential focal adhesion and focal complex protein that colocalizes with dynamic actin structures

Changes in cell morphology are essential in the development of a multicellular organism. The regulation of the cytoskeleton by the Rho subfamily of small GTP-binding proteins is an important determinant of cell shape. The Rho subfamily has been shown to participate in a variety of morphogenetic processes during Drosophila melanogaster development. We describe here a Drosophila homolog, DPAK, of the serine/threonine kinase PAK, a protein which is a target of the Rho subfamily proteins Rac and Cdc42. Rac, Cdc42, and PAK have previously been implicated in signaling by c-Jun amino-terminal kinases. DPAK bound to activated (GTP-bound) Drosophila Rac (DRacA) and Drosophila Cdc42. Similarities in the distributions of DPAK, integrin, and phosphotyrosine suggested an association of DPAK with focal adhesions and Cdc42- and Rac-induced focal adhesion-like focal complexes. DPAK was elevated in the leading edge of epidermal cells, whose morphological changes drive dorsal closure of the embryo. We have previously shown that the accumulation of cytoskeletal elements initiating cell shape changes in these cells could be inhibited by expression of a dominant-negative DRacA transgene. We show that leading-edge epidermal cells flanking segment borders, which express particularly large amounts of DPAK, undergo transient losses of cytoskeletal structures during dorsal closure. We propose that DPAK may be regulating the cytoskeleton through its association with focal adhesions and focal complexes and may be participating with DRacA in a c-Jun amino-terminal kinase signaling pathway recently demonstrated to be required for dorsal closure.

Comparison of argon laser iridotomy and sequential argon laser and Nd:YAG laser iridotomy in dark irides

BACKGROUND AND OBJECTIVE

A prospective study was performed to compare argon laser iridotomy and sequential argon laser and Nd:YAG laser iridotomy in dark irides.

PATIENTS AND METHODS

Twenty-four eyes of 17 patients underwent laser iridotomies; 13 underwent argon laser iridotomies and 11 underwent sequential argon laser and Nd:YAG laser iridotomies. The argon laser settings were standardized at 1.2 W, 50-mum spot size, and 0.1-second duration. The Nd:YAG laser was set at 2.5 mJ and single-pulse shots were used.

RESULTS

All of the iridotomies were patent at the end of one treatment session. The mean total energy used for argon laser iridotomy was 8.28 J. For sequential iridotomy, 3.12 J was used for the argon laser stage and 7.5 mJ for the Nd:YAG laser stage.

CONCLUSION

The total argon laser energy used can be reduced by 2.65 times by using the sequential laser iridotomy technique.

Selective up-regulation of alpha 1-chimaerin mRNA in SK-N-SH neuroblastoma cells by K+/-induced depolarisation

The expression of alpha 1-chimaerin, which encodes a neuron-specific GTPase-activating protein for p21rac, is spatially and temporally regulated in vivo. In vitro, expression of the mRNA of both alpha 1-chimaerin and its alternative spliced form, alpha 2-chimaerin, was up-regulated when human neuroblastoma SK-N-SH cells underwent neuronal-type differentiation in a serum-free medium. KCl-induced membrane depolarisation also specifically up-regulated alpha 1-chimaerin mRNA expression in SK-N-SH cells at the transcriptional level. The up-regulation of alpha 1-chimaerin expression by membrane depolarisation is not an immediate early event, and occurs 3 h after KCl treatment. It does not require de novo protein synthesis. The increase in calcium influx via the L-type voltage-sensitive calcium channel as the result of depolarisation is a key event leading to the up-regulation of alpha 1-chimaerin mRNA. alpha 1-Chimaerin expression was also found to respond positively to the hypertonic osmolarity changes. These results suggest that in vivo expression of alpha 1-chimaerin, a potential signal transduction molecule, may be regulated by neuronal/synaptic activity.

The Ras-related GTPase Rac1 binds tubulin

The Ras-related Rho family are involved in controlling actin-based changes in cell morphology. Microinjection of Rac1, RhoA, and Cdc42Hs into Swiss 3T3 cells induces pinocytosis and membrane ruffling, stress fiber formation, and filopodia formation, respectively. To identify target proteins involved in these signaling pathways cell extracts immobilized on nitrocellulose have been probed with [gamma-32P]GTP-labeled Rac1, RhoA, and Cdc42Hs. We have identified two 55-kDa brain proteins which bind Rac1 but not RhoA or Cdc42Hs. These 55-kDa proteins were abundant, had pI values of around 5.5, and could be purified by Q-Sepharose chromatography. The characteristics on two-dimensional gel analysis suggested the proteins comprised alpha- and beta-tubulin. Indeed, beta-tubulin specific antibodies detected one of the purified 55-kDa proteins. Rac1 bound pure tubulin (purified by cycles of polymerization and depolymerization) only in the GTP-bound state. The GTPase negative Rac1 point mutants, G12V and Q61L, did not significantly affect the ability of Rac1 to interact with tubulin while the "effector-site" mutant D38A prevented interaction. These results suggest that the Rac1-tubulin interaction may play a role in Rac1 function.