Paternal care enhances male reproductive success in pine engraver beetles

His117 of the D2 protein of photosystem II (PS II) is a conserved residue in the second transmembrane region of the protein and has been suggested to bind chlorophyll. Nine site-directed mutations were introduced at residue 117, using both photosystem I (PS I)-containing and PS I-less background strains of the cyanobacterium Synechocystis sp. PCC 6803. Of these nine, four (H117C, H117M, H117N, and H117T) were photoautotrophic in the PS I-containing background. The other mutants (H117F, H117L, H117P, H117R, and H117Y) did not accumulate appreciable amounts of PS II in their thylakoids. The type of residues that can functionally replace His117 support the notion of His117 serving as a chlorophyll ligand. The properties of the H117N and H117T mutants were characterized in more detail. Whereas the properties of the H117N mutant were close to those of wild type, in the H117T mutant the 77-K fluorescence emission spectrum shows a much smaller amplitude at 695 nm than expected on the basis of the amount of PS II that is present. Moreover, in H117T, the amount of light needed to half-saturate O2-evolution rates was twofold higher than in the control strain, and the variable fluorescence yield was quenched. However, O2 evolution rates at saturating light intensity and electron-transport kinetics were normal in the mutant. Also, the radical accessory chlorophyll (Chlz+) formed by donation of an electron to the PS-II reaction center could be generated normally by illumination at low temperature in the H117T mutant. We conclude that the chlorophyll associated with residue 117 of the D2 protein is important for efficient excitation transfer between the proximal antenna and the PS II reaction center. A possible mechanism involving a chlorophyll cation to explain the quenching in the H117T mutant is discussed.     

Site-directed mutagenesis of basic arginine residues 305 and 342 in the CP 43 protein of photosystem II affects oxygen-evolving activity in Synechocystis 6803

The intrinsic chlorophyll protein CP 43, a component of photosystem II (PS II) in higher plants, green algae, and cyanobacteria, is encoded by the psbC gene. Oligonucleotide-directed mutagenesis was employed to introduce mutations into a segment of psbC that encodes the large extrinsic loop E of CP 43 in the cyanobacterium Synechocystis 6803. Two mutations, R305S and R342S, each produced a strain with impaired photosystem II activity. The R305S mutant strain grew photoautotrophically at rates comparable to the control strain. Immunological analyses of a number of PSII components indicated that this mutant accumulated normal quantities of PSII proteins. However, this mutant evolved oxygen to only 70% of control rates at saturating light intensities. Measurements of total variable fluorescence yield indicated that this mutant assembled approximately 70% of the PSII centers found in the control strain. The R342S mutant failed to grow photoautotrophically and exhibited no capacity for oxygen evolution. However, when grown photoheterotrophically in medium containing both glucose and 3-(3, 4-dichlorophenyl)-1,1-dimethylurea (DCMU), oxygen-evolving activity was observed in the R342S mutant, but at a low level of approximately 10% of the control rate. Immunological analysis of isolated thylakoid membranes from this mutant also indicated that this strain accumulated normal amounts of PSII core proteins. Total variable fluorescence yields for the R342S mutant indicated that it assembled a severely reduced number of fully functional PSII centers. R305S and R342S mutant strains exhibited, respectively, 2.7- and 4-fold increased sensitivity to photoinactivation. The fluorescence rise times for both mutants were comparable to the control when hydroxylamine was used as electron donor. However, both strains exhibited an increase (2.5- and 8-fold, respectively, for R305S and R342S) in fluorescence rise times with water as an electron donor. These results suggest that the mutations R305S and R342S each produce a defect associated with the oxygen-evolving complex of photosystem II. These are the first site-directed mutations in CP 43 to show such an effect.     

A survey on quantitative microdialysis: theoretical models and practical implications

The relationship between the transthylakoid pH-gradient, delta pH, and the velocity of photophosphorylation, Vp, in thylakoid membranes from spinach was investigated using the local anesthetic amine procaine as inhibitor of delta pH. When delta pH was driven by Photosystem (PS) II+I-dependent electron flow, passing through the cytochrome b6/f complex, inhibition by procaine was accompanied by an increase of ATP formation. It appeared that procaine allowed for values of Vp similar to those in controls (without procaine) at a significantly lower delta pH than in the controls. In contrast, when delta pH was driven by cyclic electron flow around PS I or by PS-II+I-dependent electron flow via a bypass around the cytochrome b6/f complex, or by PS II alone, procaine simultaneously caused an inhibition of delta pH and a decrease of ATP formation. Inhibition of delta pH by procaine did not induce an electrical membrane potential gradient that otherwise may have energetically compensated for the observed decline of delta pH. The electron flow capacity was unaffected by procaine. However, inhibition of delta pH did not significantly relax pH-dependent control of electron flux. Procaine accelerated ATP hydrolysis by pre-activated thylakoid ATPase to rates which were observed in the presence of uncouplers and had no direct effect on the activation state of the ATPase. The shift in the relationship between delta pH and Vp towards lower delta pH persisted in thermodynamic equilibrium between the phosphorylation potential and delta pH. The data indicated that the unconventional effect of procaine on photophosphorylation may be related to effects on proton translocation at the cytochrome b6/f complex and that a localized protonic coupling may occur between cytochrome b6/f and thylakoid-ATP-synthase complexes.     

Cats are protected against feline immunodeficiency virus infection following vaccination with a homologous AP-1 binding site-deleted mutant

Following establishment, via the vaginal route, of infection with an AP-1 binding-site deleted mutant (delta AP-1) of feline immunodeficiency virus (FIV), cats were challenged with a homologous intact strain (TM2) of FIV. The cats were observed for 23 weeks to evaluate the efficacy of the delta AP-1 against the homologous TM2 strain challenge. These two viruses were differentiated by Southern blotting after amplification of proviral DNA by semi-nested polymerase chain reaction in DNAs of peripheral blood mononuclear cells and tissues. A TM2-specific band was detected in one cat exposed to but not infected with delta AP-1, but not in two delta AP-1-infected. These results indicate that delta AP-1 could protect against subsequent challenge with homologous FIV TM2 strain.     

Functional analysis of combinatorial mutants altered in a conserved region in loop E of the CP47 protein in Synechocystis sp. PCC 6803

Regions in the large lumenally exposed region (loop E) of CP47 affect properties of the watersplitting system in photosystem II (PS II). To investigate the role of these regions, we developed a method for functional complementation of obligate photoheterotrophic mutants carrying a deletion in one such region. Using an obligate photoheterotrophic mutant that carries a short deletion (delta (D440-P447) in loop E of CP47, completely degenerate sequences of eight codons in length were introduced at the site of the deletion. Transformants that were complemented to photoautotrophic growth were selected, and 20 such mutants were studied. Sequence analysis revealed that, as expected, in each of them CP47 had been restored to its wild-type length. However, none of the amino acid residues in the deleted region were found to be critical for function. A negatively charged residue at position 440 and a positively charged one at position 444 were favored but not required. Photoautotrophic growth of mutants obtained varied from almost normal to significantly impaired. The mutants contained 20-100% of the amount of PS II present in the wild type, with PS II amounts correlating with the initial rates of oxygen evolution. The mutants had a high rate of photoinactivation, and many mutants showed an up to 1000-fold increase in chloride requirement for photoautotrophic growth. These phenotypic effects were a direct consequence of the CP47 mutations and were not caused by altered binding of one of the extrinsic proteins. No particular amino acid residues in positions 440-447 of CP47 were found to be indispensable for photoautotrophic growth, and many amino acid combinations in this region support PS II function. However, the mutagenized region is shown to interact with the oxygen-evolving site of PS II and appears to have a direct role in chloride binding.     

Hydrogen bonding of redox-active tyrosine Z of photosystem II probed by FTIR difference spectroscopy

The TyrZ./TyrZ FTIR difference spectrum is reported for the first time in Mn-depleted photosystem II (PS II)-enriched membranes of spinach, in PS II core complexes of Synechocystis sp. PCC 6803 WT, and in the mutant lacking TyrD (D2-Tyr160Phe). In Synechocystis, the v7'a(CO) and delta(COH) infrared modes of TyrZ are proposed to account at 1279 and 1255 cm-1. The frequency of these modes indicate that TyrZ is protonated at pH 6 and involved in a strong hydrogen bond to the side chain of a histidine, probably D1-His190. A positive signal at 1512 cm-1 is assigned to the v(CO) mode of TyrZ. on the basis of the 27 cm-1 downshift observed upon 13C-Tyr labeling at the Tyr ring C4 carbon. A second IR signal, at 1532 cm-1, is tentatively assigned to the v8a(CC) mode of TyrZ.. The frequency of the v(CO) mode of TyrZ. at 1512 cm-1 is comparable to that observed at 1513 cm-1 for the Tyr. obtained by UV photochemistry of tyrosinate in solution, while it is higher than that of TyrD. in WT PS II at 1503 cm-1 and that of non-hydrogen-bonded TyrD. in the D2-His189Gln mutant at 1497 cm-1 [Hienerwadel, R., Boussac, A., Breton, J., Diner, B. A., and Berthomieu, C. (1997) Biochemistry 36, 14712-14723]. This latter work and the present FTIR study suggest that hydrogen bonding induces an upshift of the v(CO) IR mode of tyrosyl radicals and that TyrZ. forms (a) stronger hydrogen bond(s) than TyrD. in WT PS II. Alternatively, the frequency difference between TyrZ. and TyrD. v(CO) modes could be explained by a more localized positive charge near the tyrosyl radical oxygen of TyrD. than TyrZ.. The TyrZ./TyrZ spectrum obtained in Mn-depleted PS II membranes of spinach shows large similarities with the S3'/S2' spectrum characteristic of radical formation in Mn-containing but Ca(2+)-depleted PS II, in support of the assignment using ESEEM of TyrZ. as being responsible for the split EPR signal observed upon illumination in these conditions [Tang, X.-S., Randall, D. W., Force, D. A., Diner, B. A., and Britt, R. D. (1996) J. Am. Chem. Soc. 118, 7638-7639]. The peak at 1514 cm-1 is assigned to the v(CO) mode of TyrZ. in these preparations, which indicates that Mn depletion only very slightly perturbs the immediate environment of TyrZ. phenoxyl.     

Modification of the water oxidizing complex in leaves of the dgd1 mutant of Arabidopsis thaliana deficient in the galactolipid digalactosyldiacylglycerol

The primary biochemical defect in the genetically well characterized dgd1 mutant of Arabidopsis thaliana causes a 90% reduction in the relative amount of the galactolipid digalactosyldiacylglycerol (DGDG). To study the effect of this DGDG deficiency on photosystem II (PS II), time-resolved transients of laser-flash-induced changes of the relative fluorescence quantum yield Fvar,rel(t) were measured in whole leaves from wild-type and the dgd1 mutant. The results obtained reveal (i) in untreated leaves the decay kinetics of Fvar, rel(t) reflecting QA.- reoxidation by endogenous plastoquinone are very similar in wild-type and the dgd1 mutant at room temperature, (ii) the Arrhenius plot of the temperature dependence of electron transfer from QA.- to QB exhibits a break point at about 19 degrees C in wild-type and about 12 degrees C in the dgd1 mutant, (iii) in leaves treated with DCMU the slow reoxidation of QA.- by the PS II donor side is blocked to a much higher extent in the dgd1 mutant (about 50%) compared to wild-type (about 10%), and iv) the normalized amplitude of Fvar,rel(t = 1 micros) reflecting the percentage of fast P680.+ reduction by YZ exhibits a characteristic period four oscillation in wild-type while this feature is strongly damped in the dgd1 mutant. Presumably, the severe DGDG deficiency is causing the thermal down shift of a lipid phase transition that affects the QA.- reoxidation by QB. Most strikingly, the properties of the WOC are modified as a result of reduced DGDG content. Thus, the lipid DGDG appears to be of structural relevance for the WOC.     

Mutational analysis of the genes encoding the photosystem II proteins in Cyanobacterium synechocystis sp. 6803

Chlorophyll--binding protein CP43 and cytochrome b559, encoded by psbC and psbE/F genes, are the components of photosystem II (PS II). Three psbC- and four psbE/F- mutants were isolated from the collection of PS II-deficient mutants of the cyanobacterium Synechocystis sp. 6803. Restoration of photosynthetic activity was achieved by transformation of psbE/F- mutants with cloned psbE/F gene cluster from wild type cells and each of psbC- mutants--with specific part of wild type psbC gene. DNA fragments carrying the mutations were isolated from mutant cells and sequenced. The mutations which affect PS II activity were identified in psbC gene as "frameshift" mutation, stop-codon formation, or as deletion of three nucleotides resulting in loss of one of three Phe residues in position 422-424 of CP43. Sequence of mutant psbE/F genes revealed single mutations resulting in deletion of Phe-36 or substitution of Pro-63 for Leu in alpha-subunit and Val-29 for Phe in beta-subunit of cytochrome b559.     

Lymphocyte proliferative responses of goats vaccinated with Brucella melitensis 16M or a delta purE201 strain

The response to a Brucella melitensis purEK deletion mutant, delta purE201 (referred to as strain 201), was compared with the response to its parental strain, 16M, in juvenile goats. Proliferative responses to gamma-irradiated bacteria were detected earlier in strain 201-infected goats. Lymphocytes from strain 16M- or 201-infected goats proliferated in response to one-dimensional polyacrylamide gel electrophoresis-separated proteins of similar mass isolated from strain 16M or Brucella abortus RB51. Data from this study suggest that some antigens stimulating cell-mediated responses are conserved among Brucella species, as 201- and 16M-infected goats recognized similar proteins expressed by RB51 and 16M.     

A glutathione reductase mutant of yeast accumulates high levels of oxidized glutathione and requires thioredoxin for growth

A glutathione reductase null mutant of Saccharomyces cerevisiae was isolated in a synthetic lethal genetic screen for mutations which confer a requirement for thioredoxin. Yeast mutants that lack glutathione reductase (glr1 delta) accumulate high levels of oxidized glutathione and have a twofold increase in total glutathione. The disulfide form of glutathione increases 200-fold and represents 63% of the total glutathione in a glr1 delta mutant compared with only 6% in wild type. High levels of oxidized glutathione are also observed in a trx1 delta, trx2 delta double mutant (22% of total), in a glr1 delta, trx1 delta double mutant (71% of total), and in a glr1 delta, trx2 delta double mutant (69% of total). Despite the exceptionally high ratio of oxidized/reduced glutathione, the glr1 delta mutant grows with a normal cell cycle. However, either one of the two thioredoxins is essential for growth. Cells lacking both thioredoxins and glutathione reductase are not viable under aerobic conditions and grow poorly anaerobically. In addition, the glr1 delta mutant shows increased sensitivity to the thiol oxidant diamide. The sensitivity to diamide was suppressed by deletion of the TRX2 gene. The genetic analysis of thioredoxin and glutathione reductase in yeast runs counter to previous studies in Escherichia coli and for the first time links thioredoxin with the redox state of glutathione in vivo.     

Relationships between chronic oral infectious diseases and systemic diseases

Contact-inhibited catalase-deficient fibroblast cell strain has been established from the homozygous hypocatalasemic C3H/Csb mutant mouse. This cell strain has low level of catalase enzyme activity and has normal level of enzyme activities of both glutathione peroxidase and superoxide dismutase. Catalase-deficient C3H/Csb mutant cell strain is markedly more sensitive to the toxicity of hydrogen peroxide compared to wild-type C3H/Csa cell strain. In addition, mutant cell strain is sensitive to X-rays and near-UV compared to wild-type cell strain, but shows the same sensitivities to topoisomerase II inhibitors, adriamycin and 4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA), and the DNA cross-linking agents, cisdiamminedichloroplatinum (II) (cis-Pt) and trans-diamminedichloroplatinum (II) (trans-Pt). These cell strains will be of use in the study of the roles which catalase plays in the intracellular prevention of DNA damage induced by oxidative stress.     

Immunocytochemical localization and biological activity of hydroxysteroid sulfotransferase in the frog brain

Biosynthesis of the neuroactive steroids pregnenolone sulfate (delta5PS) and dehydroepiandrosterone sulfate (DHEAS) is catalyzed by the enzyme hydroxysteroid sulfotransferase (HST), which transfers the sulfonate moiety from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) on the 3-hydroxy site of steroids. Although high concentrations of delta5PS and DHEAS have been detected in the rat brain, the anatomical localization of HST in the CNS has never been determined. Using an antiserum against rat liver HST, we have investigated the distribution of HST-like immunoreactivity in the CNS of the frog Rana ridibunda. Two populations of HST-immunoreactive neurons were observed in the hypothalamus, and several bundles of positive nerve fibers were visualized in the telencephalon and diencephalon. Incubation of frog brain homogenates with [35S]PAPS and [3H]pregnenolone yielded the formation of several 3H,35S-labeled compounds, including delta5PS and testosterone sulfate. When [3H]dehydroepiandrosterone and [35S]PAPS were used as precursors, one of the 3H,35S-labeled metabolites coeluted with DHEAS. Neosynthesis of [3H]delta5PS and [3H]DHEAS was reduced significantly by 2,4-dichloro-6-nitrophenol, a specific inhibitor of sulfotransferases. The present study provides the first immunocytochemical mapping of HST in the brain. Our data also demonstrate for the first time that biosynthesis of the highly potent neuroactive steroids delta5PS and DHEAS occurs in the CNS of nonmammalian vertebrates.     

Construction and characterization of avian Escherichia coli cya crp mutants

We constructed delta cya delta crp mutants of two avian septicemic Escherichia coli strains and evaluated their attenuation in virulence. The P1 phage was used to transfer cya::Tn10 from an E. coli K-12 strain into virulent avian O78 and O2 E. coli isolates. Tetracycline-resistant transductants were plated on Bochner-Maloy Medium, and tetracycline-sensitive colonies were selected, then tested by polymerase chain reaction to confirm that they had deletions of the cya gene. Deletions of crp were created by the same technique in isolates with deletions in cya. The delta cya and delta cya delta crp derivatives had slower growth rates, smaller colonies, and impaired fermentation of carbohydrates compared with their wild parents, and they did not revert. Attenuation of the mutant strains was evaluated by subcutaneous (s.c.) inoculation of day-old chicks and by intratracheal (i.t.) inoculation of 9-day-old chicks previously inoculated intranasally with infectious bronchitis virus. For the wild O78 strain and its delta cya and delta cya delta crp derivatives, the percentages of chicks that died within 6 days of s.c. injection of approximately 5 x 10(7) organisms were 100, 60, and 0, respectively. The corresponding percentages for wild-type O2 and its delta cya and delta cya delta crp mutants were 100, 70, and 20 at a dose of approximately 2 x 10(5) organisms. Following i.t. inoculation, group scores based on pathologic and bacteriologic findings were 51%, 15%, and 9% for wild, delta cya, and delta crp O78 strains (inoculum approximately 2 x 10(7) organisms) and 98%, 31%, and 11%, respectively, for the corresponding O2 strains (inoculum approximately 4 x 10(6) organisms). This study demonstrated reduced virulence and stability of the double mutant, which may useful as a live attenuated vaccine against poultry colibacillosis.     

AutoCyte Interactive Screening System. Experience at a university hospital cytology laboratory

The F1-ATPase is a multimeric enzyme (alpha3 beta3 gamma delta epsilon) primarily responsible for the synthesis of ATP under aerobic conditions. The entire coding region of each of the genes was deleted separately in yeast, providing five null mutant strains. Strains with a deletion in the genes encoding alpha-, beta-, gamma- or delta-subunits were unable to grow, while the strain with a null mutation in epsilon was able to grow slowly on medium containing glycerol as the carbon source. In addition, strains with a null mutation in gamma or delta became 100% rho0/rho- and the strain with the null mutation in gamma grew much more slowly on medium containing glucose. These additional phenotypes were not observed in strains with the double mutations: Delta alpha Delta gamma, Delta beta Delta gamma, Deltaatp11 Delta gamma, Delta alpha Delta delta, Delta beta Delta delta or Deltaatp11 Delta delta. These results indicate that epsilon is not an essential component of the ATP synthase and that mutations in the genes encoding the alpha- and beta-subunits and in ATP11 are epistatic to null mutations in the genes encoding the gamma- and delta-subunits. These data suggest that the propensity to form rho0/rho- mutations in the gamma and delta null deletion mutant stains and the slow growing phenotypes of the null gamma mutant strain are due to the assembly of F1 deficient in the corresponding subunit. These results have profound implications for the physiology of normal cells.     

Photosynthetic electron transport involved in PxcA-dependent proton extrusion in Synechocystis sp. Strain PCC6803: effect of pxcA inactivation on CO2, HCO3-, and NO3- uptake

The product of pxcA (formerly known as cotA) is involved in light-induced Na+-dependent proton extrusion. In the presence of 2, 5-dimethyl-p-benzoquinone, net proton extrusion by Synechocystis sp. strain PCC6803 ceased after 1 min of illumination and a postillumination influx of protons was observed, suggesting that the PxcA-dependent, light-dependent proton extrusion equilibrates with a light-independent influx of protons. A photosystem I (PS I) deletion mutant extruded a large number of protons in the light. Thus, PS II-dependent electron transfer and proton translocation are major factors in light-driven proton extrusion, presumably mediated by ATP synthesis. Inhibition of CO2 fixation by glyceraldehyde in a cytochrome c oxidase (COX) deletion mutant strongly inhibited the proton extrusion. Leakage of PS II-generated electrons to oxygen via COX appears to be required for proton extrusion when CO2 fixation is inhibited. At pH 8.0, NO3- uptake activity was very low in the pxcA mutant at low [Na+] (approximately 100 microM). At pH 6.5, the pxcA strain did not take up CO2 or NO3- at low [Na+] and showed very low CO2 uptake activity even at 15 mM Na+. A possible role of PxcA-dependent proton exchange in charge and pH homeostasis during uptake of CO2, HCO3-, and NO3- is discussed.     

Deletion of the Candida glabrata ERG3 and ERG11 genes: effect on cell viability, cell growth, sterol composition, and antifungal susceptibility

We have cloned and sequenced the structural genes encoding the delta 5,6 sterol desaturase (ERG3 gene) and the 14 alpha-methyl sterol demethylase (ERG11 gene) from Candida glabrata L5 (leu2). Single and double mutants of these genes were created by gene deletion. The phenotypes of these mutants, including sterol profiles, aerobic viabilities, antifungal susceptibilities, and generation times, were studied. Strain L5D (erg3 delta::LEU2) accumulated mainly ergosta-7,22-dien-3 beta-ol, was aerobically viable, and remained susceptible to antifungal agents but had a slower generation time than its parent strain. L5LUD (LEU2 erg11 delta::URA3) strains required medium supplemented with ergosterol and an anaerobic environment for growth. A spontaneous aerobically viable mutant, L5LUD40R (LEU erg11 delta::URA3), obtained from L5LUD (LEU2 erg11 delta::URA3), was found to accumulate lanosterol and obtusifoliol, was resistant to azole antifungal agents, demonstrated some increase in resistance to amphotericin B, and exhibited a 1.86-fold increase in generation time in comparison with L5 (leu2). The double-deletion mutant L5DUD61 (erg3 delta::LEU2 erg11 delta::URA3) was aerobically viable, produced mainly 14 alpha-methyl fecosterol, and had the same antifungal susceptibility pattern as L5LUD40R (LEU2 erg11 delta::URA3), and its generation time was threefold greater than that of L5 (leu2). Northern (RNA) analysis revealed that the single-deletion mutants had a marked increase in message for the undeleted ERG3 and ERG11 genes. These results indicate that differences in antifungal susceptibilities and the restoration of aerobic viability exist between the C. glabrata ergosterol mutants created in this study and those sterol mutants with similar genetic lesions previously reported for Saccharomyces cerevisiae.     

The zntA gene of Escherichia coli encodes a Zn(II)-translocating P-type ATPase

The first Zn(II)-translocating P-type ATPase has been identified as the product of o732, a potential gene identified in the sequencing of the Escherichia coli genome. This gene, termed zntA, was disrupted by insertion of a kanamycin gene through homologous recombination. The mutant strain exhibited hypersensitivity to zinc and cadmium salts but not salts of other metals, suggesting a role in zinc homeostasis in E. coli. Everted membrane vesicles from a wild-type strain accumulated 65Zn(II) and 109Cd(II) by using ATP as an energy source. Transport was sensitive to vanadate, an inhibitor of P-type ATPases. Membrane vesicles from the zntA::kan strain did not accumulate those metal ions. Both the sensitive phenotype and transport defect of the mutant were complemented by expression of zntA on a plasmid.     

The presenilin 1 mutation (M146V) linked to familial Alzheimer's disease attenuates the neuronal differentiation of NTera 2 cells

Mutations in presenilin 1 (PS1) gene are the major cause of early-onset familial Alzheimer's disease. The biological functions of PS1 remain elusive, although accumulating evidence suggests that PS1 may play an important role in development and differentiation. To learn about the significance of PS1 in the differentiation of neuronal cells, we established NTera 2 (NT2) cell lines stably expressing wild-type (wt) or M146V mutant human PS1, and compared the differentiation of both types of cell lines into postmitotic neurons upon retinoic acid (RA) treatment. After 25 days of RA treatment, a significant proportion of cells differentiated into neurons in NT2 cells expressing wt PS1 (27.7% of total cells), which was comparable to that in untransfected cells, whereas very few cells differentiated into neurons in NT2 cells expressing M146V mutant PS1 (2.6% of total cells). These results suggest that mutant PS1 attenuates the potentials of NT2 cells to differentiate into neurons.