Coding-Complete Genome Sequences of an Omicron Subvariant (BA.5.2.20) of SARS-CoV-2.

Here, we present the complete coding sequences of two severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strains that were recovered from a nasopharyngeal swab from a female patient and the second viral passage in cell culture. After testing, both strains were identified as BA.5.2.20, a subvariant of Omicron.

Acaricidal efficacy of ultraviolet-C irradiation of Tetranychus urticae adults and eggs using a pulsed krypton fluoride excimer laser.

BACKGROUND: Pulsed ultraviolet (UV)-C light sources, such as excimer lasers, are used in emerging non-thermal food-decontamination methods and also have high potential for use in a wide range of microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using female adults and eggs of a model organism, the two-spotted spider mite Tetranychus urticae. METHODS: UV-C light was generated by a pulsed krypton fluoride excimer laser operating at 248-nm emission wavelength. The pulse energy and pulse repetition rate were 5 mJ and up to 100 Hz, respectively. The distance from the light source to the target was 150 mm; the target surface area was 2.16 cm2. The exposure time for the mites and fresh eggs varied from 1 to 4 min at 5-300 mW, which corresponded to UV doses of 5-80 kJ/m2. Post-irradiation acaricidal effects (mite mortality) were assessed immediately and also measured at 24 h. The effects of UV-C irradiation on the hatchability of eggs were observed daily for up to 12 days post-irradiation. RESULTS: The mortality of mites at 5 and 40 kJ/m2 was 26% and 92%, respectively. Mite mortality reached 98% at 80 kJ/m2. The effect of exposure duration on mortality was minimal. The effect of irradiation on egg hatchability was even more significant than that on adult mite mortality, i.e. about 100% egg mortality at an accumulated dose of as little as 5 kJ/m2 for each exposure time. CONCLUSIONS: A high rate of mite mortality and lethal egg damage were observed after less than 1 min of exposure to 5 mJ UV-C pulsed irradiation at 60 Hz. Pending further developments (such as beam steering, beam shaping and miniaturisation) and feasibility studies (such as testing with mites in real-life situations), the reported results and characteristics of the UV-C generator (modulation of energy output and adaptability to varying spot sizes) open up the use of this technology for a vast field of acaricidal applications that require long-range radiation.

Telecommunication Facilities, Key Support for Data Management and Data Sharing by a Biological Mobile Laboratory Deployed to Counter Emerging Biological Threats and Improve Public Health Crisis Preparedness.

In the case of rapid outbreaks of infectious diseases in remote locations, the lack of real-time information from the field and rapid spread of misinformation can be a major issue. To improve situational awareness and decision-making at all levels of operational deployment, there is an urgent need for accurate, reliable, and timely results from patients from the affected area. This requires a robust and fast channel of communication connecting first responders on-site, crisis managers, decision-makers, and the institutions involved in the survey of the crisis at national, regional, and international levels. This has been the rationale sustaining the development of advanced communication tools in the Biological Light Fieldable Laboratory for Emergencies (B-LiFE). The benefit of terrestrial (TETRA, LTE, 5G, and Wi-Fi-Fi) and SatCom communications is illustrated through a series of missions and exercises conducted in the previous five years. These tools were used by B-LiFE operators to provide accurate, comprehensive, timely, and relevant information and services in real time. The focus of this article is to discuss the development and benefits of the integration of multi-mission, multi-user nomadic, rapidly deployable telecommunication nodes for emergency uses (TEN) in the capacity of B-LiFE. Providing reliable communication channels through TEN enables the development and use of an ICT toolbox called MIML_LIMS (multi-institution, multi-mission, multi-laboratory LIMS), a tool which is mandatory for efficient and secure data management and data sharing by a mobile laboratory.

Diagnostic Value of IgM and IgG Detection in COVID-19 Diagnosis by the Mobile Laboratory B-LiFE: A Massive Testing Strategy in the Piedmont Region.

Coronavirus disease 2019 (COVID-19) is an acute infectious disease caused by the novel coronavirus (SARS-CoV-2) identified in 2019. The COVID-19 outbreak continues to have devastating consequences for human lives and the global economy. The B-LiFe mobile laboratory in Piedmont, Italy, was deployed for the surveillance of COVID-19 cases by large-scale testing of first responders. The objective was to assess the seroconversion among the regional civil protection (CP), police, health care professionals, and volunteers. The secondary objective was to detect asymptomatic individuals within this cohort in the light of age, sex, and residence. In this paper, we report the results of serological testing performed by the B-LiFe mobile laboratory deployed from 10 June to 23 July 2020. The tests included whole blood finger-prick and serum sampling for detection of SARS-CoV-2 spike receptor-binding domain (S-RBD) antibodies. The prevalence of SARS-CoV-2 antibodies was approximately 5% (294/6013). The results of the finger-prick tests and serum sample analyses showed moderate agreement (kappa = 0.77). Furthermore, the detection rates of serum antibodies to the SARS-CoV-2 nucleocapsid protein (NP) and S-RBD among the seroconverted individuals were positively correlated (kappa = 0.60), at least at the IgG level. Seroprevalence studies based on serological testing for the S-RBD protein or SARS-CoV-2 NP antibodies are not sufficient for diagnosis but might help in screening the population to be vaccinated and in determining the duration of seroconversion.

Adult human liver mesenchymal progenitor cells express phenylalanine hydroxylase.

Phenylketonuria (PKU) is one of the most prevalent inherited metabolic diseases and is accountable for a severe encephalopathy by progressive intoxication of the brain by phenylalanine. This results from an ineffective L-phenylalanine hydroxylase enzyme (PAH) due to a mutated phenylalanine hydroxylase (PAH) gene. Neonatal screening programs allow an early dietetic treatment with restrictive phenylalanine intake. This diet prevents most of the neuropsychological disabilities but remains challenging for lifelong compliance. Adult-derived human liver progenitor cells (ADHLPC) are a pool of precursors that can differentiate into hepatocytes. We aim to study PAH expression and PAH activity in a differenciated ADHLPC. ADHLPC were isolated from human hepatocyte primary culture of two different donors and differenciated under specific culture conditions. We demonstrated the high expression of PAH and a large increase of PAH activity in differenciated LPC. The age of the donor, the cellular viability after liver digestion and cryopreservation affects PAH activity. ADHLPC might therefore be considered as a suitable source for cell therapy in PKU.

Downregulation of Sox9 expression associates with hepatogenic differentiation of human liver mesenchymal stem/progenitor cells.

Understanding the mechanisms triggering hepatogenic differentiation of stem/progenitor cells would be useful for studying postnatal liver regeneration and development of liver cell therapies. Many evidences support the involvement of Sox9 transcription factor in liver development. Here, we investigate the possibility of liver mesenchymal stem/progenitor cells to constitutively express Sox9 by using reverse transcription-quantitative polymerase chain reaction, immunocytochemistry, and western blotting. The involvement of Sox9 in hepatogenic differentiation was assessed by following its expression at different steps of the process, evaluating the impact of its altered expression, and analyzing its expression in human liver disease specimen. Liver mesenchymal stem/progenitor cells constitutively express Sox9 at both the mRNA and protein levels. Upon hepatogenic differentiation, Sox9 expression is downregulated mainly in the maturation step after oncostatin M treatment. Induction of Sox9 expression using transforming growth factor beta is accompanied with a decrease of the quality of hepatogenic differentiation. Blunting Sox9 expression using specific ShRNA clearly alters the levels of several hepatic markers, an effect confirmed in HepG2 cells. In human liver disease specimen, Sox9 expression is enhanced at both the mRNA and protein levels compared with healthy donors. The current data demonstrate that Sox9 may play a pivotal role in hepatocyte lineage development, including adult liver mesenchymal stem/progenitor cells. Further studies on the identification of pathways regulated by or regulating Sox9 will certainly gain insight into the molecular networks controlling hepatogenic differentiation.

Efficient ROSA26-based conditional and/or inducible transgenesis using RMCE-compatible F1 hybrid mouse embryonic stem cells.

The conditional Cre/loxP system and/or the doxycycline (Dox) inducible Tet-on/off system are widely used in mouse transgenesis but often require time consuming, inefficient cloning/screening steps and extensive mouse breeding strategies. We have therefore developed a highly efficient Gateway- and recombinase-mediated cassette exchange (RMCE)-compatible system to target conditional and/or inducible constructs to the ROSA26 locus of F1 hybrid Bl6/129 ESCs, called G4 ROSALUC ESCs. By combining the Cre/loxP system with or without the inducible Tet-on system using Gateway cloning, we can rapidly generate spatial and/or temporal controllable gain-of-function constructs that can be targeted to the RMCE-compatible ROSA26 locus of the G4 ROSALUC ESCs with efficiencies close to 100 %. These novel ESC-based technologies allow for the creation of multiple gain-of-function conditional and/or inducible transgenic ESC clones and mouse lines in a highly efficient and locus specific manner. Importantly, incorporating insulator sequences into the Dox-inducible vector system resulted in robust, stable transgene expression in undifferentiated ESCs but could not fully overcome transgene mosaicism in the differentiated state.

Differentiated umbilical cord matrix stem cells as a new in vitro model to study early events during hepatitis B virus infection.

UNLABELLED: The role of cell differentiation state on hepatitis B virus (HBV) replication has been well demonstrated, whereas how it determines cell susceptibility to HBV entry is far less understood. We previously showed that umbilical cord matrix stem cells (UCMSC) can be differentiated towards hepatocyte-like cells in vitro. In this study we infected undifferentiated (UD-) and differentiated (D-) UCMSCs with HBV and studied the infection kinetics, comparing them to primary human hepatocytes (PHHs). UD-UCMSCs, although permissive to viral binding, had a very limited uptake capacity, whereas D-UCMSCs showed binding and uptake capabilities similar to PHHs. Likewise, asialoglycoprotein receptor (ASGPR) was up-regulated in UCMSCs upon differentiation. In D-UCMSCs, a dose-dependent inhibition of HBV binding and uptake was observed when ASGPR was saturated with known specific ligands. Subsequent viral replication was shown in D-UCMSCs but not in UD-UCMSCs. Susceptibility of UCMSCs to viral replication correlated with the degree of differentiation. Replication efficiency was low compared to PHHs, but was confirmed by (1) a dose-dependent inhibition by specific antiviral treatment using tenofovir; (2) the increase of viral RNAs along time; (3) de novo synthesis of viral proteins; and (4) secretion of infectious viral progeny. CONCLUSION: UCMSCs become supportive of the entire HBV life cycle upon in vitro hepatic differentiation. Despite low replication efficiency, D-UCMSCs proved to be fully capable of HBV uptake. Overall, UCMSCs are a unique human, easily available, nontransformed, in vitro model of HBV infection that could prove useful to study early infection events and the role of the cell differentiation state on such events.

Adult human liver mesenchymal stem/progenitor cells participate in mouse liver regeneration after hepatectomy.

The advances in stem cell science have promoted research on their use in liver regenerative medicine. Beyond the demonstration of their ability to display metabolic functions in vitro, candidate cells should demonstrate achievable in situ differentiation and ability to participate to liver repopulation. In this work, we studied the in vivo behavior of adult liver mesenchymal stem/progenitor cells (ADHLSCs) after transplantation into immunodeficient mice. The kinetics of engraftment and in situ hepatogenic differentiation were analyzed. Response of transplanted ADHLSCs to regenerative stimulus was also evaluated. Nondifferentiated ADHLSCs were intrasplenically transplanted into SCID mice. Efficiency of transplantation was evaluated at the level of engraftment and in situ differentiation using immunohistochemistry, in situ hybridization, and RT-PCR. After bromodeoxyuridine (BrdU) implantation, proliferation of transplanted ADHLSCs in response to 20% hepatectomy was assessed using immunohistochemistry. We demonstrated that ADHLSC engraftment in the SCID mouse liver was low but remained stable up to 60 days posttransplantation, when albumin (ALB) immunopositive ADHLSCs were still detected and organized as clusters. Coexpression of ornithine transcarbamylase (OTC) demonstrated ADHLSC in situ differentiation mostly near the hepatic portal vein. After 20% hepatectomy on 1 month transplanted mice, the percentage of BrdU and human ALB immunopositive ADHLSCs increased from 3 to 28 days post-BrdU implantation to reach 31.3 ± 5.4% of the total analyzed human cells. In the current study, we demonstrate that transplanted ADHLSCs are able to differentiate in the non preconditioned SCID mouse liver mainly in the periportal area. In response to partial hepatectomy, integrated ADHLSCs proliferate and participate to recipient mouse liver regeneration.

Opposing roles for Hoxa2 and Hoxb2 in hindbrain oligodendrocyte patterning.

Oligodendrocytes are the myelin-forming cells of the vertebrate CNS. Little is known about the molecular control of region-specific oligodendrocyte development. Here, we show that oligodendrogenesis in the mouse rostral hindbrain, which is organized in a metameric series of rhombomere-derived (rd) territories, follows a rhombomere-specific pattern, with extensive production of oligodendrocytes in the pontine territory (r4d) and delayed and reduced oligodendrocyte production in the prepontine region (r2d, r3d). We demonstrate that segmental organization of oligodendrocytes is controlled by Hox genes, namely Hoxa2 and Hoxb2. Specifically, Hoxa2 loss of function induced a dorsoventral enlargement of the Olig2/Nkx2.2-expressing oligodendrocyte progenitor domain, whereas conditional Hoxa2 overexpression in the Olig2(+) domain inhibited oligodendrogenesis throughout the brain. In contrast, Hoxb2 deletion resulted in a reduction of the pontine oligodendrogenic domain. Compound Hoxa2(-/-)/Hoxb2(-/-) mutant mice displayed the phenotype of Hoxb2(-/-) mutants in territories coexpressing Hoxa2 and Hoxb2 (rd3, rd4), indicating that Hoxb2 antagonizes Hoxa2 during rostral hindbrain oligodendrogenesis. This study provides the first in vivo evidence that Hox genes determine oligodendrocyte regional identity in the mammalian brain.

Bivalirudin in combination with heparin to control mesenchymal cell procoagulant activity.

Islet and hepatocyte transplantation are associated with tissue factor-dependent activation of coagulation which elicits instant blood mediated inflammatory reaction, thereby contributing to a low rate of engraftment. The aim of this study was i) to evaluate the procoagulant activity of human adult liver-derived mesenchymal progenitor cells (hALPCs), ii) to compare it to other mesenchymal cells of extra-hepatic (bone marrow mesenchymal stem cells and skin fibroblasts) or liver origin (liver myofibroblasts), and iii) to determine the ways this activity could be modulated. Using a whole blood coagulation test (thromboelastometry), we demonstrated that all analyzed cell types exhibit procoagulant activity. The hALPCs pronounced procoagulant activity was associated with an increased tissue factor and a decreased tissue factor pathway inhibitor expression as compared with hepatocytes. At therapeutic doses, the procoagulant effect of hALPCs was inhibited by neither antithrombin activators nor direct factor Xa inhibitor or direct thrombin inhibitors individually. However, concomitant administration of an antithrombin activator or direct factor Xa inhibitor and direct thrombin inhibitor proved to be a particularly effective combination for controlling the procoagulant effects of hALPCs both in vitro and in vivo. The results suggest that this dual antithrombotic therapy should also improve the efficacy of cell transplantation in humans.

Hepato-biliary profile of potential candidate liver progenitor cells from healthy rat liver.

AIM: To evaluate the presence of progenitor cells in healthy adult rat liver displaying the equivalent advanced hepatogenic profile as that obtained in human. METHODS: Rat fibroblastic-like liver derived cells (rFLDC) were obtained from collagenase-isolated liver cell suspensions and characterized and their phenotype profile determined using flow cytometry, immunocytochemistry, reverse transcription polymerase chain reaction and functional assays. RESULTS: rFLDC exhibit fibroblastoid morphology, express mesenchymal (CD73, CD90, vimentin, α-smooth muscle actin), hepatocyte (UGT1A1, CK8) and biliary (CK19) markers. Moreover, these cells are able to store glycogen, and have glucose 6 phosphatase activity, but not UGT1A1 activity. Under the hepatogenic differentiation protocol, rFLDC display an up-regulation of hepatocyte markers expression (albumin, tryptophan 2,3-dioxygenase, G6Pase) correlated to a down-regulation of the expression of the biliary marker CK19. CONCLUSION: Advanced hepatic features observed in human liver progenitor cells could not be demonstrated in rFLDC. However, we demonstrated the presence of an original rodent hepato-biliary cell type.

In vitro differentiated adult human liver progenitor cells display mature hepatic metabolic functions: a potential tool for in vitro pharmacotoxicological testing.

The potential use of stem/progenitor cells as alternative cell sources to mature hepatocytes remains basically dependent on their ability to exhibit some, if not all, the metabolic liver functions. In the current study, four major liver functions were investigated in adult derived human liver stem/progenitor cell (ADHLSCs) populations submitted to in vitro hepatogenic differentiation: gluconeogenesis, ammonia detoxification, and activity of phase I and phase II drug-metabolizing enzymes. These acquired hepatic activities were compared to those of primary adult human hepatocytes, the standard reference. Amino acid content was also investigated after hepatogenic differentiation. Differentiated ADHLSCs display higher de novo synthesis of glucose correlated to an increased activity of glucose-6 phosphatase and mRNA expression of key related enzymes. Differentiated ADHLSCs are also able to metabolize ammonium chloride and to produce urea. This was correlated to an increase in the mRNA expression of relevant key enzymes such arginase. With respect to drug metabolism, differentiated ADHLSCs express mRNAs of all the major cytochromes investigated, among which the CYP3A4 isoform (the most important drug-metabolizing enzyme). Such increased expression is correlated to an enhanced phase I activity as independently demonstrated using fluorescence-based assays. Phase II enzyme activity and amino acid levels also show a significant enhancement in differentiated ADHLSCs. The current study, according to data independently obtained in different labs, demonstrates that in vitro differentiated ADHLSCs are able to display advanced liver metabolic functions supporting the possibility to develop them as potential alternatives to primary hepatocytes for in vitro settings.

Vegf regulates embryonic erythroid development through Gata1 modulation.

To determine the role of vascular endothelial growth factor (Vegf) in embryonic erythroid development we have deleted or overexpressed Vegf specifically in the erythroid lineage using the EpoR-iCre transgenic line in combination with Cre/loxP conditional gain and loss of function Vegf alleles. ROSA26 promoter-based expression of the Vegf(164) isoform in the early erythroid lineage resulted in a differentiation block of primitive erythroid progenitor (EryP) development and a partial block in definitive erythropoiesis between the erythroid burst-forming unit and erythroid colony-forming unit stages. Decreased mRNA expression levels of the key erythroid transcription factor Gata1 were causally linked to this phenotype. Conditional deletion of Vegf within the erythroid lineage was associated with increased Gata1 levels and increased erythroid differentiation. Expression of a ROSA26-based GATA2 transgene rescued Gata1 mRNA levels and target genes and restored erythroid differentiation in our Vegf gain of function model. These results demonstrate that Vegf modulates Gata1 expression levels in vivo and provides new molecular insight into Vegf's ability to modulate erythropoiesis.

Increased skeletal VEGF enhances beta-catenin activity and results in excessively ossified bones.

Vascular endothelial growth factor (VEGF) and beta-catenin both act broadly in embryogenesis and adulthood, including in the skeletal and vascular systems. Increased or deregulated activity of these molecules has been linked to cancer and bone-related pathologies. By using novel mouse models to locally increase VEGF levels in the skeleton, we found that embryonic VEGF over-expression in osteo-chondroprogenitors and their progeny largely pheno-copied constitutive beta-catenin activation. Adult induction of VEGF in these cell populations dramatically increased bone mass, associated with aberrant vascularization, bone marrow fibrosis and haematological anomalies. Genetic and pharmacological interventions showed that VEGF increased bone mass through a VEGF receptor 2- and phosphatidyl inositol 3-kinase-mediated pathway inducing beta-catenin transcriptional activity in endothelial and osteoblastic cells, likely through modulation of glycogen synthase kinase 3-beta phosphorylation. These insights into the actions of VEGF in the bone and marrow environment underscore its power as pleiotropic bone anabolic agent but also warn for caution in its therapeutic use. Moreover, the finding that VEGF can modulate beta-catenin activity may have widespread physiological and clinical ramifications.

Efficient mouse transgenesis using Gateway-compatible ROSA26 locus targeting vectors and F1 hybrid ES cells.

The ability to rapidly and efficiently generate reliable Cre/loxP conditional transgenic mice would greatly complement global high-throughput gene targeting initiatives aimed at identifying gene function in the mouse. We report here the generation of Cre/loxP conditional ROSA26-targeted ES cells within 3-4 weeks by using Gateway cloning to build the target vectors. The cDNA of the gene of interest can be expressed either directly by the ROSA26 promoter providing a moderate level of expression or by a CAGG promoter placed in the ROSA26 locus providing higher transgene expression. Utilization of F1 hybrid ES cells with exceptional developmental potential allows the production of germ line transmitting, fully or highly ES cell-derived mice by aggregation of cells with diploid embryos. The presented streamlined procedures accelerate the examination of phenotypical consequences of transgene expression. It also provides a unique tool for comparing the biological activity of polymorphic or splice variants of a gene, or products of different genes functioning in the same or parallel pathways in an overlapping manner.

ADAM10, the rate-limiting protease of regulated intramembrane proteolysis of Notch and other proteins, is processed by ADAMS-9, ADAMS-15, and the gamma-secretase.

ADAM10 is involved in the proteolytic processing and shedding of proteins such as the amyloid precursor protein (APP), cadherins, and the Notch receptors, thereby initiating the regulated intramembrane proteolysis (RIP) of these proteins. Here, we demonstrate that the sheddase ADAM10 is also subject to RIP. We identify ADAM9 and -15 as the proteases responsible for releasing the ADAM10 ectodomain, and Presenilin/gamma-Secretase as the protease responsible for the release of the ADAM10 intracellular domain (ICD). This domain then translocates to the nucleus and localizes to nuclear speckles, thought to be involved in gene regulation. Thus, ADAM10 performs a dual role in cells, as a metalloprotease when it is membrane-bound, and as a potential signaling protein once cleaved by ADAM9/15 and the gamma-Secretase.

Presenilin clinical mutations can affect gamma-secretase activity by different mechanisms.

Mutations in human presenilin (PS) genes cause aggressive forms of familial Alzheimer's disease. Presenilins are polytopic proteins that harbour the catalytic site of the gamma-secretase complex and cleave many type I transmembrane proteins including beta-amyloid precursor protein (APP), Notch and syndecan 3. Contradictory results have been published concerning whether PS mutations cause 'abnormal' gain or (partial) loss of function of gamma-secretase. To avoid the possibility that wild-type PS confounds the interpretation of the results, we used presenilin-deficient cells to analyse the effects of different clinical mutations on APP, Notch, syndecan 3 and N-cadherin substrate processing, and on gamma-secretase complex formation. A loss in APP and Notch substrate processing at epsilon and S3 cleavage sites was observed with all presenilin mutants, whereas APP processing at the gamma site was affected in variable ways. PS1-Delta9 and PS1-L166P mutations caused a reduction in beta-amyloid peptide Abeta40 production whereas PS1-G384A mutant significantly increased Abeta42. Interestingly PS2, a close homologue of PS1, appeared to be a less efficient producer of Abeta than PS1. Finally, subtle differences in gamma-secretase complex assembly were observed. Overall, our results indicate that the different mutations in PS affect gamma-secretase structure or function in multiple ways.

Conserved residues within the putative active site of gamma-secretase differentially influence enzyme activity and inhibitor binding.

Gamma-secretase performs the final processing step in the generation of amyloid-beta (Abeta) peptides, which are believed to be causative for Alzheimer's disease. Presenilins (PS) are required for gamma-secretase activity and the presence of two essential intramembranous aspartates (D257 and D385) has implicated this region as the putative catalytic centre of an aspartyl protease. The presence of several key hydrogen-bonding residues around the active site of classical aspartyl proteases led us to investigate the role of both the critical aspartates and two nearby conserved hydrogen bond donors in PS1. Generation of cell lines stably overexpressing the D257E, D385E, Y256F and Y389F engineered mutations has enabled us to determine their role in enzyme catalysis and binding of a transition state analogue gamma-secretase inhibitor. Here we report that replacement of either tyrosine residue alters gamma-secretase cleavage specificity, resulting in an increase in the production of the more pathogenic Abeta42 peptide in both cells and membranous enzyme preparations, without affecting inhibitor binding. In contrast, replacement of either of the aspartate residues precludes inhibitor binding in addition to inactivation of the enzyme. Together, these data further incriminate the region around the intramembranous aspartates as the active site of the enzyme, targeted by transition state analogue inhibitors, and highlight the roles of individual residues.

Presenilins mutated at Asp-257 or Asp-385 restore Pen-2 expression and Nicastrin glycosylation but remain catalytically inactive in the absence of wild type Presenilin.

The Presenilins are part of the gamma-secretase complex that is involved in the regulated intramembrane proteolysis of amyloid precursor protein and other type I integral membrane proteins. Nicastrin, Pen-2, and Aph1 are the other proteins of this complex. The Presenilins probably contribute the catalytic activity to the protease complex. However, several investigators reported normal Abeta-peptide generation in cells expressing Presenilins mutated at the putative catalytic site residue Asp-257, contradicting this hypothesis. Because endogenously expressed wild type Presenilin could contribute to residual gamma-secretase activity in these experiments, we have reinvestigated the problem by expressing mutated Presenilins in a Presenilin-negative cell line. We confirm that Presenilins with mutated Asp residues are catalytically inactive. Unexpectedly, these mutated Presenilins are still partially processed into amino- and carboxyl-terminal fragments by a "Presenilinase"-like activity. They are also able to rescue Pen-2 expression and Nicastrin glycosylation in Presenilin-negative cells and become incorporated into large approximately 440-kDa complexes as assessed by blue native gel electrophoresis. Our study demonstrates that the catalytic activity of Presenilin and its other functions in the generation, stabilization, and transport of the gamma-secretase complex can be separated and extends the concept that Presenilins are multifunctional proteins.