Molecular basis of differential adventitious rooting competence in poplar genotypes

Recalcitrant adventitious root (AR) development is a major hurdle in propagating commercially important woody plants. Although significant progress has been made to identify genes involved in subsequent steps of AR development, the molecular basis of differences in apparent recalcitrance to form AR between easy-to-root and difficult-to-root genotypes remains unknown. To address this, we generated cambium tissue-specific transcriptomic data from stem cuttings of hybrid aspen, T89 (difficult-to-root) and hybrid poplar OP42 (easy-to-root), and used transgenic approaches to verify the role of several transcription factors in the control of adventitious rooting. Increased peroxidase activity was positively correlated with better rooting. We found differentially expressed genes encoding reactive oxygen species scavenging proteins to be enriched in OP42 compared with T89. A greater number of differentially expressed transcription factors in cambium cells of OP42 compared with T89 was revealed by a more intense transcriptional reprograming in the former. PtMYC2, a potential negative regulator, was less expressed in OP42 compared with T89. Using transgenic approaches, we demonstrated that PttARF17.1 and PttMYC2.1 negatively regulate adventitious rooting. Our results provide insights into the molecular basis of genotypic differences in AR and implicate differential expression of the master regulator MYC2 as a critical player in this process.

Nitric Oxide Synthase activity in major depressive episodes before and after antidepressant treatment: Results of a large case-control treatment study

BACKGROUND

Nitric oxide synthase (NOS) activity, an enzyme potentially involved in the major depressive episodes (MDE), could be indirectly measured by the L-Citrulline/L-Arginine ratio (L-Cit/L-Arg). The aim of this study was: (1) to compare the NOS activity of patients with a MDE to that of healthy controls (HC); (2) to assess its change after antidepressant treatment.

METHODS

A total of 460 patients with a current MDE in a context of major depressive disorder (MDD) were compared to 895 HC for NOS activity (L-Cit/L-Arg plasma ratio). L-Arg and L-Cit plasma levels were measured using a MS-based liquid chromatography method. Depressed patients were assessed at baseline, and after 3 and 6 months of antidepressant treatment for depression severity and clinical response.

RESULTS

Depressed patients had a lower NOS activity than HC at baseline [0.31 ± 0.09 v. 0.38 ± 0.12; 95% confidence interval (CI) -0.084 to -0.062, p < 0.0001]. Lower NOS activity at baseline predicted a higher response rate [odds ratio (OR) = 29.20; 95% CI 1.58-536.37; p = 0.023]. NOS activity in depressed patients increased significantly up to 0.34 ± 0.08 after antidepressant treatment (Est = 0.0034; 95% CI 0.0002-0.0067; p = 0.03).

CONCLUSIONS

Depressed patients have a decreased NOS activity that improves after antidepressant treatment and predicts drug response. NOS activity may be a promising biomarker for MDE in a context of MDD.

A network of stress-related genes regulates hypocotyl elongation downstream of selective auxin perception

The plant hormone auxin, a master coordinator of development, regulates hypocotyl elongation during seedling growth. We previously identified the synthetic molecule RubNeddin 1 (RN1), which induces degradation of the AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) transcriptional repressors INDOLE-3-ACETIC ACID-INDUCIBLE3 (IAA3) and IAA7 in planta and strongly promotes hypocotyl elongation. In the present study, we show that despite the structural similarity of RN1 to the synthetic auxin 2,4-dichlorophenoxyacetic-acid (2,4-D), direct treatments with these compounds in Arabidopsis (Arabidopsis thaliana) result in distinct effects, possibly due to enhanced uptake of RN1 and low-level, chronic release of 2,4-D from RN1 in planta. We confirm RN1-induced hypocotyl elongation occurs via specific TRANSPORT INHIBITOR RESISTANT1 (TIR1)/AUXIN SIGNALING F-BOX (AFB) receptor-mediated auxin signaling involving TIR1, AFB2, and AFB5. Using a transcriptome profiling strategy and candidate gene approach, we identify the genes ZINC FINGER OF ARABIDOPSIS THALIANA10 (ZAT10), ARABIDOPSIS TOXICOS EN LEVADURA31 (ATL31), and WRKY DNA-BINDING PROTEIN33 (WRKY33) as being rapidly upregulated by RN1, despite being downregulated by 2,4-D treatment. RN1-induced expression of these genes also occurs via TIR1/AFB-mediated auxin signaling. Our results suggest both hypocotyl elongation and transcription of these genes are induced by RN1 via the promoted degradation of the AUX/IAA transcriptional repressor IAA7. Moreover, these three genes, which are known to be stress-related, act in an inter-dependent transcriptional regulatory network controlling hypocotyl elongation. Together, our results suggest ZAT10, ATL31, and WRKY33 take part in a common gene network regulating hypocotyl elongation in Arabidopsis downstream of a selective auxin perception module likely involving TIR1, AFB2, and AFB5 and inducing the degradation of IAA7.

The CEP5 Peptide Promotes Abiotic Stress Tolerance, As Revealed by Quantitative Proteomics, and Attenuates the AUX/IAA Equilibrium in Arabidopsis

Peptides derived from non-functional precursors play important roles in various developmental processes, but also in (a)biotic stress signaling. Our (phospho)proteome-wide analyses of C-TERMINALLY ENCODED PEPTIDE 5 (CEP5)-mediated changes revealed an impact on abiotic stress-related processes. Drought has a dramatic impact on plant growth, development and reproduction, and the plant hormone auxin plays a role in drought responses. Our genetic, physiological, biochemical, and pharmacological results demonstrated that CEP5-mediated signaling is relevant for osmotic and drought stress tolerance in Arabidopsis, and that CEP5 specifically counteracts auxin effects. Specifically, we found that CEP5 signaling stabilizes AUX/IAA transcriptional repressors, suggesting the existence of a novel peptide-dependent control mechanism that tunes auxin signaling. These observations align with the recently described role of AUX/IAAs in stress tolerance and provide a novel role for CEP5 in osmotic and drought stress tolerance.

A role for the auxin precursor anthranilic acid in root gravitropism via regulation of PIN-FORMED protein polarity and relocalisation in Arabidopsis

distribution of auxin within plant tissues is of great importance for developmental plasticity, including root gravitropic growth. Auxin flow is directed by the subcellular polar distribution and dynamic relocalisation of auxin transporters such as the PIN-FORMED (PIN) efflux carriers, which can be influenced by the main natural plant auxin indole-3-acetic acid (IAA). Anthranilic acid (AA) is an important early precursor of IAA and previously published studies with AA analogues have suggested that AA may also regulate PIN localisation. Using Arabidopsis thaliana as a model species, we studied an AA-deficient mutant displaying agravitropic root growth, treated seedlings with AA and AA analogues and transformed lines to over-produce AA while inhibiting its conversion to downstream IAA precursors. We showed that AA rescues root gravitropic growth in the AA-deficient mutant at concentrations that do not rescue IAA levels. Overproduction of AA affects root gravitropism without affecting IAA levels. Treatments with, or deficiency in, AA result in defects in PIN polarity and gravistimulus-induced PIN relocalisation in root cells. Our results revealed a previously unknown role for AA in the regulation of PIN subcellular localisation and dynamics involved in root gravitropism, which is independent of its better known role in IAA biosynthesis.

[Interest of scopolamine as a treatment of major depressive disorder]

INTRODUCTION

The number of patients with depression in the world is 350 millions according to estimates. The search for new treatments, particularly in forms of resistant depression, is necessary given the growing number of patients experiencing treatment failure and resistance. Scopolamine, an anticholinergic antimuscarinic molecule, is one of the treatments under evaluation. It falls within the assumptions of cholinergic disruption of the pathophysiology of depression, at different levels (genetic, receptorial [muscarinic and glutamate receptors], hormonal, synaptic…). In 2006, a pilot study made to evaluate the role of the cholinergic system in cognitive symptoms of depression found unexpected results regarding the antidepressant effect of scopolamine in depressive patients. Since that time other studies have been conducted to evaluate the benefits of treatment with intravenous injections of scopolamine.

OBJECTIVE

Our main objective was to evaluate the interest of scopolamine as an antidepressant treatment in depressed populations.

METHODS

We conducted a literature review with the aim of assessing the effectiveness of treatment with scopolamine in uni- and bipolar patients with depressive symptoms. The protocol consisted of two injection blocks (each block consisting of three injections spaced fifteen minutes apart within three to five days) of active ingredient or placebo crossover. The selected patients were between 18 and 45years and had the DSM-IV major depressive disorder or bipolar disorder criteria. Regarding the methods of measurement, the primary endpoint was the reduction in scores of the Montgomery Asberg Depression Rating Scale (MADRS) with a total response defined by a decrease of more than 50 % of the score and remission corresponding to a MADRS score<10. Seven sessions of evaluations were performed.

RESULTS

The published results are promising in terms of efficiency with rapid antidepressant effect, a total response rate ranging from 59-64% and a remission rate of between 37 and 55% in uni- and bipolar patients, which persists at least 15days. The treatment was well tolerated by patients with relatively mild and transient side effects the most common being the sensation of sleepiness that was also found in the placebo group. There were no serious side effects such as heart failure or confusion. In terms of mood, there was no becoming manic or hypomanic even for bipolar patients.

CONCLUSION

The results are encouraging, but there is concern for the moment because of the few studies, so to date there is little data on the subject including medium and long term.

Live cell imaging of FM4-64, a tool for tracing the endocytic pathways in Arabidopsis root cells

Confocal live imaging of the amphiphilic styryl dye FM4-64 is a valuable technique to monitor organelle dynamics and in particular endocytic pathways. After application in plants, FM4-64 immediately stains the plasma membrane and is then integrated on vesicles following endomembrane system-dependent internalization processes. Over time, FM4-64 becomes distributed throughout the full vesicular network from the plasma membrane to the vacuole, including the components of the secretory pathways. Here we provide succinct examples of the many important developmental processes in plants that rely on endocytosis and describe two suitable methods to trace the endocytic pathways in Arabidopsis thaliana root cells based on the uptake of FM4-64.

Adventitious root formation in tree species: involvement of transcription factors

Adventitious rooting is an essential step in the vegetative propagation of economically important horticultural and woody species. Populus has emerged as an experimental model for studying processes that are important in tree growth and development. It is highly useful for molecular genetic analysis of adventitious roots in trees. In this short review, we will highlight the recent progress made in the identification of transcription factors involved in the control of adventitious rooting in woody species. Their regulation will be discussed.

Unraveling plant hormone signaling through the use of small molecules

Plants have acquired the capacity to grow continuously and adjust their morphology in response to endogenous and external signals, leading to a high architectural plasticity. The dynamic and differential distribution of phytohormones is an essential factor in these developmental changes. Phytohormone perception is a fast but complex process modulating specific developmental reprogramming. In recent years, chemical genomics or the use of small molecules to modulate target protein function has emerged as a powerful strategy to study complex biological processes in plants such as hormone signaling. Small molecules can be applied in a conditional, dose-dependent and reversible manner, with the advantage of circumventing the limitations of lethality and functional redundancy inherent to traditional mutant screens. High-throughput screening of diverse chemical libraries has led to the identification of bioactive molecules able to induce plant hormone-related phenotypes. Characterization of the cognate targets and pathways of those molecules has allowed the identification of novel regulatory components, providing new insights into the molecular mechanisms of plant hormone signaling. An extensive structure-activity relationship (SAR) analysis of the natural phytohormones, their designed synthetic analogs and newly identified bioactive molecules has led to the determination of the structural requirements essential for their bioactivity. In this review, we will summarize the so far identified small molecules and their structural variants targeting specific phytohormone signaling pathways. We will highlight how the SAR analyses have enabled better interrogation of the molecular mechanisms of phytohormone responses. Finally, we will discuss how labeled/tagged hormone analogs can be exploited, as compelling tools to better understand hormone signaling and transport mechanisms.

The AINTEGUMENTA LIKE1 homeotic transcription factor PtAIL1 controls the formation of adventitious root primordia in poplar

Adventitious rooting is an essential but sometimes rate-limiting step in the clonal multiplication of elite tree germplasm, because the ability to form roots declines rapidly with age in mature adult plant tissues. In spite of the importance of adventitious rooting, the mechanism behind this developmental process remains poorly understood. We have described the transcriptional profiles that are associated with the developmental stages of adventitious root formation in the model tree poplar (Populus trichocarpa). Transcriptome analyses indicate a highly specific temporal induction of the AINTEGUMENTA LIKE1 (PtAIL1) transcription factor of the AP2 family during adventitious root formation. Transgenic poplar samples that overexpressed PtAIL1 were able to grow an increased number of adventitious roots, whereas RNA interference mediated the down-expression of PtAIL1 expression, which led to a delay in adventitious root formation. Microarray analysis showed that the expression of 15 genes, including the transcription factors AGAMOUS-Like6 and MYB36, was overexpressed in the stem tissues that generated root primordia in PtAIL1-overexpressing plants, whereas their expression was reduced in the RNA interference lines. These results demonstrate that PtAIL1 is a positive regulator of poplar rooting that acts early in the development of adventitious roots.

Import of colicins across the outer membrane of Escherichia coli involves multiple protein interactions in the periplasm

Several proteins of the Tol/Pal system are required for group A colicin import into Escherichia coli. Colicin A interacts with TolA and TolB via distinct regions of its N-terminal domain. Both interactions are required for colicin translocation. Using in vivo and in vitro approaches, we show in this study that colicin A also interacts with a third component of the Tol/Pal system required for colicin import, TolR. This interaction is specific to colicins dependent on TolR for their translocation, strongly suggesting a direct involvement of the interaction in the colicin translocation step. TolR is anchored to the inner membrane by a single transmembrane segment and protrudes into the periplasm. The interaction involves part of the periplasmic domain of TolR and a small region of the colicin A N-terminal domain. This region and the other regions responsible for the interaction with TolA and TolB have been mapped precisely within the colicin A N-terminal domain and appear to be arranged linearly in the colicin sequence. Multiple contacts with periplasmic-exposed Tol proteins are therefore a general principle required for group A colicin translocation.

[Strict anteroposterior radiography of the shoulder: value of the assessment of rotator cuff tears]

PURPOSE

To compare the contribution of various radiographic projections in the evaluation of impingement syndrome and rotator cuff tears. Materials and method. We realized a prospective study in 53 patients with suspected rotator cuff tear, evaluated by plain radiographs and arthrography (gold standard). 31 patients were men and 22 were women (mean age 51 years). In all patients, anteroposterior radiograph, strict anteroposterior straight-beam decubitus view and anteroposterior radiograph during Leclercq's maneuver of the affected shoulder were obtained. The population was divided into three groups: group 1: normal arthrography (n=19), group 2: isolated supraspinatus tendon tear (n=23), group 3: rupture of the supraspinatus and infraspinatus tendons (n=11). The acromio-humeral space was measured on all these views and differences between the three groups were statistically analyzed.

RESULTS

There is a significant statistical difference between the height of the acromio-humeral space found in patients with isolated tear of the supraspinatus tendon and those with a tear extending to the infraspinatus tendon (p=0.0001). The ROC methodology showed a better accuracy of the strict anteroposterior straight-beam decubitus view in cases of wide ruptures of the rotator cuff, and this for a selected threshold value of 6 mm.

CONCLUSION

Strict anteroposterior straight-beam decubitus view, seems to be easy to realize, cheap, reproducible and very powerful in the preoperative assessment of patients with suspected rotator cuff tendon tear. It allows an excellent visualization of the acromioclavicular joint.

Structure of the Escherichia coli TolB protein determined by MAD methods at 1.95 A resolution

BACKGROUND

The periplasmic protein TolB from Escherichia coli is part of the Tol-PAL (peptidoglycan-associated lipoprotein) multiprotein complex used by group A colicins to penetrate and kill cells. TolB homologues are found in many gram-negative bacteria and the Tol-PAL system is thought to play a role in bacterial envelope integrity. TolB is required for lethal infection by Salmonella typhimurium in mice.

RESULTS

The crystal structure of the selenomethionine-substituted TolB protein from E. coli was solved using multiwavelength anomalous dispersion methods and refined to 1. 95 A. TolB has a two-domain structure. The N-terminal domain consists of two alpha helices, a five-stranded beta-sheet floor and a long loop at the back of this floor. The C-terminal domain is a six-bladed beta propeller. The small, possibly mobile, contact area (430 A(2)) between the two domains involves residues from the two helices and the first and sixth blades of the beta propeller. All available genomic sequences were used to identify new TolB homologues in gram-negative bacteria. The TolB structure was then interpreted using the observed conservation pattern.

CONCLUSIONS

The TolB beta-propeller C-terminal domain exhibits sequence similarities to numerous members of the prolyl oligopeptidase family and, to a lesser extent, to class B metallo-beta-lactamases. The alpha/beta N-terminal domain shares a structural similarity with the C-terminal domain of transfer RNA ligases. We suggest that the TolB protein might be part of a multiprotein complex involved in the recycling of peptidoglycan or in its covalent linking with lipoproteins.

In vitro characterization of peptidoglycan-associated lipoprotein (PAL)-peptidoglycan and PAL-TolB interactions

The Tol-peptidoglycan-associated lipoprotein (PAL) system of Escherichia coli is a multiprotein complex of the envelope involved in maintaining outer membrane integrity. PAL and the periplasmic protein TolB, two components of this complex, are interacting with each other, and they have also been reported to interact with OmpA and the major lipoprotein, two proteins interacting with the peptidoglycan. All these interactions suggest a role of the Tol-PAL system in anchoring the outer membrane to the peptidoglycan. Therefore, we were interested in better understanding the interaction between PAL and the peptidoglycan. We designed an in vitro interaction assay based on the property of purified peptidoglycan to be pelleted by ultracentrifugation. Using this assay, we showed that a purified PAL protein interacted in vitro with pure peptidoglycan. A peptide competition experiment further demonstrated that the region from residues 89 to 130 of PAL was sufficient to bind the peptidoglycan. Moreover, the fact that this same region of PAL was also binding to TolB suggested that these two interactions were exclusive. Indeed, the TolB-PAL complex appeared not to be associated with the peptidoglycan. This led us to the conclusion that PAL may exist in two forms in the cell envelope, one bound to TolB and the other bound to the peptidoglycan.

Role of TolR N-terminal, central, and C-terminal domains in dimerization and interaction with TolA and tolQ

The Tol-PAL system of Escherichia coli is a multiprotein system involved in maintaining the cell envelope integrity and is necessary for the import of some colicins and phage DNA into the bacterium. It is organized into two complexes, one near the outer membrane between TolB and PAL and one in the cytoplasmic membrane between TolA, TolQ, and TolR. In the cytoplasmic membrane, all of the Tol proteins have been shown to interact with each other. Cross-linking experiments have shown that the TolA transmembrane domain interacts with TolQ and TolR. Suppressor mutant analyses have localized the TolQ-TolA interaction to the first transmembrane domain of TolQ and have shown that the third transmembrane domain of TolQ interacts with the transmembrane domain of TolR. To get insights on the composition of the cytoplasmic membrane complex and its possible contacts with the outer membrane complex, we focused our attention on TolR. Cross-linking and immunoprecipitation experiments allowed the identification of Tol proteins interacting with TolR. The interactions of TolR with TolA and TolQ were confirmed, TolR was shown to dimerize, and the resulting dimer was shown to interact with TolQ. Deletion mutants of TolR were constructed, and they allowed us to determine the TolR domains involved in each interaction. The TolR transmembrane domain was shown to be involved in the TolA-TolR and TolQ-TolR interactions, while TolR central and C-terminal domains appeared to be involved in TolR dimerization. The role of the TolR C-terminal domain in the TolA-TolR interaction and its association with the membranes was also demonstrated. Furthermore, phenotypic studies clearly showed that the three TolR domains (N terminal, central, and C terminal) and the level of TolR production are important for colicin A import and for the maintenance of cell envelope integrity.

Distinct regions of the colicin A translocation domain are involved in the interaction with TolA and TolB proteins upon import into Escherichia coli

Group A colicins need proteins of the Escherichia coli envelope Tol complex (TolA, TolB, TolQ and TolR) to reach their cellular target. The N-terminal domain of colicins is involved in the import process. The N-terminal domains of colicins A and E1 have been shown to interact with TolA, and the N-terminal domain of colicin E3 has been shown to interact with TolB. We found that a pentapeptide conserved in the N-terminal domain of all group A colicins, the 'TolA box', was important for colicin A import but was not involved in the colicin A-TolA interaction. It was, however, involved in the colicin A-TolB interaction. The interactions of colicin A N-terminal domain deletion mutants with TolA and TolB were investigated. Random mutagenesis was performed on a construct allowing the colicin A N-terminal domain to be exported in the bacteria periplasm. This enabled us to select mutant protein domains unable to compete with the wild-type domain of the entire colicin A for import into the cells. Our results demonstrate that different regions of the colicin A N-terminal domain interact with TolA and TolB. The colicin A N-terminal domain was also shown to form a trimeric complex with TolA and TolB.

Crystallization and preliminary crystallographic study of a component of the Escherichia coli tol system: TolB

TolB from Escherichia coli is part of the Tol system used by the group A colicins to penetrate and kill cells. A TolB derivative tagged with six histidines was overexpressed, purified by chelation on a nickel affinity column and crystallized using the SAmBA software to define the optimal crystallization protocol. The crystals belong to the monoclinic system, space group P21 with unit-cell parameters a = 64.48, b = 41.06, c = 78.41 A, beta = 110.78 degrees. Frozen crystals diffract to 1.9 A resolution. Screening for heavy-atom derivatives both on the native TolB and various cysteine-substituted mutants is in progress. In addition, a selenomethionine-substituted protein is being produced in order to use the MAD method for structure determination.

The TolB protein interacts with the porins of Escherichia coli

TolB is a periplasmic protein of the cell envelope Tol complex. It is partially membrane associated through an interaction with the outer membrane lipoprotein PAL (peptidoglycan-associated lipoprotein), which also belongs to the Tol system. The interaction of TolB with outer membrane porins of Escherichia coli was investigated with a purified TolB derivative harboring a six-histidine tag. TolB interacted with the trimeric porins OmpF, OmpC, PhoE, and LamB but not with their denatured monomeric forms or OmpA. These interactions took place both in the presence and in the absence of lipopolysaccharide. TolA, an inner membrane component of the Tol system, also interacts with the trimeric porins via its central periplasmic domain (R. Dérouiche, M. Gavioli, H. Bénédetti, A. Prilipov, C. Lazdunski, and R. Lloubès, EMBO J. 15:6408-6415, 1996). In the presence of the purified central domain of TolA (TolAIIHis), the TolB-porin complexes disappeared to form TolAIIHis-porin complexes. These results suggest that the interactions of TolA and TolB with porins might take place in vivo and might be concomitant events participating in porin assembly. They also suggest that the Tol system as a whole may be involved in porin assembly in the outer membrane.

The N-terminal domain of colicin E3 interacts with TolB which is involved in the colicin translocation step

Colicins use two envelope multiprotein systems to reach their cellular target in susceptible cells of Escherichia coli: the Tol system for group A colicins and the TonB system for group B colicins. The N-terminal domain of colicins is involved in the translocation step. To determine whether it interacts in vivo with proteins of the translocation system, constructs were designed to produce and export to the cell periplasm the N-terminal domains of colicin E3 (group A) and colicin B (group B). Producing cells became specifically tolerant to entire extracellular colicins of the same group. The periplasmic N-terminal domains therefore compete with entire colicins for proteins of the translocation system and thus interact in situ with these proteins on the inner side of the outer membrane. In vivo cross-linking and co-immunoprecipitation experiments in cells producing the colicin E3 N-terminal domain demonstrated the existence of a 120 kDa complex containing the colicin domain and TolB. After in vitro cross-linking experiments with these two purified proteins, a 120 kDa complex was also obtained. This suggests that the complex obtained in vivo contains exclusively TolB and the colicin E3 domain. The N-terminal domain of a translocation-defective colicin E3 mutant was found to no longer interact with TolB. Hence, this interaction must play an important role in colicin E3 translocation.

Expression and glycosylation of the filamentous brush border glycocalyx (FBBG) during rabbit enterocyte differentiation along the crypt-villus axis

The filamentous brush border glycocalyx forming the ‘enteric surface coat’ of the intestinal epithelium is composed in rabbits of a 400 kDa mucin-type glycoprotein, which was purified using the 3A4 monoclonal antibody. This monoclonal antibody recognizes a filamentous brush border glycocalyx-specific glycosidic structure containing an O-acetylated sialic acid, which is absent from all the other glycoproteins in the epithelium, with the exception of certain goblet cell mucins. Here we establish that only 50% of the rabbits tested synthesized this glycosidic structure. Upon immunolabeling surface epithelia and sections of jejunum from these rabbits, the carbohydrate epitope recognized by the 3A4 mAb was found to be present on the filamentous brush border glycocalyx of a variable number of enterocytes, which were patchily distributed over all the villi. This heterogeneous expression of 3A4 antigenicity, which was also observed in the crypts, suggests the existence of differences between the patterns of differentiation of enterocytes, which results in the expression of different pools of glycosyltransferases and/or acetyl transferases. In mature enterocytes, the 3A4 determinants were present only on the filamentous brush border glycocalyx, which is anchored solely to the membrane microdomain at the tip of brush border microvilli. However, expression of 3A4 antigenicity begins in the median third of crypts, in enterocytes with a short, thin brush border devoid of apical filamentous brush border glycocalyx. Here the 3A4 epitopes were present over the whole brush border membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptidoglycan-associated lipoprotein-TolB interaction. A possible key to explaining the formation of contact sites between the inner and outer membranes of Escherichia coli

TolA, -B, -Q, and -R proteins are involved in maintaining the cell envelope integrity of Escherichia coli; they have been parasitized by the group A colicins and the single strand DNA of some filamentous bacteriophages to permit them to enter the cells. TolA and TolR are anchored to the inner membrane by a single transmembrane domain, TolQ is an integral membrane protein with three transmembrane segments, and TolB has recently been found to be periplasmic although it is partially membrane-associated. The latter result suggests that TolB might interact with membrane proteins. Other lines of evidence favor the existence of a Tol complex. To further characterize this complex, we investigated which proteins interact with TolB. For this purpose, two different methods were used. First, we took advantage of the existence of a tagged TolB (TolBep) to perform immunoprecipitation under native conditions in order to preserve the putative associations of TolBep with other proteins. Secondly, in vivo cross-linking experiments with formaldehyde were performed. These two approaches led to the same result and demonstrated for the first time that a component of the Tol system, TolB, interacts with a protein located in the outer membrane, the peptidoglycan-associated lipoprotein.

Maturation and localization of the TolB protein required for colicin import

The tolB gene has been shown previously to encode two proteins of 47.5 kDa (TolB) and 43 kDa (TolB*). To explain the presence of these two forms, two hypotheses have been proposed: TolB might be posttranslationally processed to TolB*, or an internal in-frame translation initiation resulting in TolB* may occur (S. K. Levengood and R. E. Webster, J. Bacteriol. 171:6600-6609, 1989). To address this question, TolB was tagged by inserting in its C-terminal region an epitope recognized by monoclonal antibody 1C11 without altering the function of TolB. It was then demonstrated that the functional protein corresponded to TolB*, the mature periplasmic protein, and that TolB was its precursor form, which was observed only when the protein was overexpressed. These two forms were purified by immunoprecipitation, and their N-terminal sequences were determined. An antibody directed against TolB was raised, which confirmed the results obtained with the tagged TolB.

Expression of sucrase-isomaltase and dipeptidylpeptidase IV in human small intestine and colon

One monoclonal antibody (8A9) against the human sucrase-isomaltase complex and one (4H3) against the human dipeptidylpeptidase IV were produced in the rat and used to immunolabel thin frozen sections of human small intestine and colon. Both enzymes were found to be expressed in the poorly differentiated crypt cells of the small intestine as well as in the mature villous cells, and very low levels were found to be expressed in the colon. Homogeneous immunolabeling of the whole colonic epithelium with the monoclonal antibody 4H3 was often observed, whereas labeling with the monoclonal antibody 8A9, if any, was either restricted to a few crypts and plateaus. The two antibodies were used to perform specific immunoprecipitation of the corresponding antigen, the N-terminal sequence of which was determined after sodium dodecyl sulfate-polyacrylamide gel electrophoresis purification and electroblotting, and were compared with those of other species. In secretor blood group A humans, both the sucrase-isomaltase and the dipeptidylpeptidase IV have type 3 blood group A determinants.

Cellular and subcellular localization of annexin IV in rabbit intestinal epithelium, pancreas and liver

The results of immunoblot analysis performed with a specific monoclonal antibody showed that the intestinal mucosa, pancreas and liver are privileged tissues for the expression of annexin IV. Immunofluorescence labelling of thin frozen sections of these tissues showed a strong concentration of annexin IV along the basolateral domain of the plasma membrane of intestinal absorbing cells, hepatocytes and pancreatic acinar cells, whereas in intestinal mucous secreting cells and centro acinar pancreatic cells, annexin IV was found to be present throughout the cytoplasm.

Characterization of the neutral aminopeptidase activity associated to the mouse thymocyte-activating molecule

We previously characterized a dimeric, Mr = 115,000, developmentally regulated mouse T cell-activating molecule (THAM). We show in this report that the THAM-specific mAb H194-112 exhibits strong reactivity with several nonlymphoid tissues including polarized enterocytes from small intestine, kidney cortical tubuli, and liver bile ductuli, as well as kidney glomeruli and lung alveoloar pneumocytes. Both the tissue distribution and the structural features of THAM made it likely that this molecule belongs to the ectoenzyme family. This was confirmed by the following experimental evidence: 1) the H194-112+ molecules from enterocyte brush borders (BB) or M14.T thymoma cells were recognized by several antisera specific for intestinal aminopeptidase N (AP-N); 2) mAb H194-112 was found to immunodeplete the AP-N activity from both thymic or enterocyte BB detergent extracts; 3) the hydrophilic, Mr = 115,000 form obtained by papain treatment of thymoma or enterocyte BB could be immunopurified on H194-112 column and exhibited, after hypotonic elution, strong enzymatic activity on the AP-N substrates (i.e., leucyl or alanyl beta-derivatives); 4) mAb H194-112 was found to inhibit the AP-N activity when assayed on alanyl but not leucyl beta-naphthylamide substrate; and 5) preincubation of AP-N with mAb H194-112 prevented the inhibiting effects of bestatin and D,L-methionyl hydroxamate on AP-N activity. These data add a new member to the list of functional ectoenzymatic markers of lymphoid cells (i.e., CD10, CD13, CD26, CD55, and CD73). In view of the known immunomodulating properties of bestatin, one may speculate that the T cell-activating effects of mAb H194-112 is related to an impairment of a surface enzymatic function regulating lymphoid cell activation.

Characterization of the neutral aminopeptidase activity associated to the mouse thymocyte-activating molecule

We previously characterized a dimeric, Mr = 115,000, developmentally regulated mouse T cell-activating molecule (THAM). We show in this report that the THAM-specific mAb H194-112 exhibits strong reactivity with several nonlymphoid tissues including polarized enterocytes from small intestine, kidney cortical tubuli, and liver bile ductuli, as well as kidney glomeruli and lung alveoloar pneumocytes. Both the tissue distribution and the structural features of THAM made it likely that this molecule belongs to the ectoenzyme family. This was confirmed by the following experimental evidence: 1) the H194-112+ molecules from enterocyte brush borders (BB) or M14.T thymoma cells were recognized by several antisera specific for intestinal aminopeptidase N (AP-N); 2) mAb H194-112 was found to immunodeplete the AP-N activity from both thymic or enterocyte BB detergent extracts; 3) the hydrophilic, Mr = 115,000 form obtained by papain treatment of thymoma or enterocyte BB could be immunopurified on H194-112 column and exhibited, after hypotonic elution, strong enzymatic activity on the AP-N substrates (i.e., leucyl or alanyl beta-derivatives); 4) mAb H194-112 was found to inhibit the AP-N activity when assayed on alanyl but not leucyl beta-naphthylamide substrate; and 5) preincubation of AP-N with mAb H194-112 prevented the inhibiting effects of bestatin and D,L-methionyl hydroxamate on AP-N activity. These data add a new member to the list of functional ectoenzymatic markers of lymphoid cells (i.e., CD10, CD13, CD26, CD55, and CD73). In view of the known immunomodulating properties of bestatin, one may speculate that the T cell-activating effects of mAb H194-112 is related to an impairment of a surface enzymatic function regulating lymphoid cell activation.

Confocal microscopy as a tool to reveal the tridimensional organization of intracellular lumens and intercellular cysts in a human colon adenocarcinoma cell line

Adenocarcinoma cells often form intracellular lumens and intercellular cysts. In order to study the structural relationships between these lumens and the apical domain of normal enterocytes, we have applied electron microscopy and confocal microscopy to a cloned cell line derived from the human colon adenocarcinoma cell line LoVo which express a high number of intracellular lumens and intercellular cysts. Microvilli reminiscent of those detected in the brush border of small intestinal cells are formed in the two types of compartments. By immunofluorescence, we found that a 135 kDa membrane glycoprotein characterized by a monoclonal Ab and normally associated with the brush-border of enterocytes is expressed at the surface of the intracellular lumens and intercellular cysts present in the adenocarcinoma cells. Comparison of fluorescence and reflection contrast micrographs obtained by confocal microscopy demonstrate the presence of spherical intracellular lumens in the juxtanuclear region of single cells, and of more complex shaped intercellular cysts located within clusters of cells. The later cells form junctional complexes limiting an apical plasma membrane domain in contact with the intercellular cyst. It is suggested that the intracellular lumens may represent the abortive form of an apical plasma membrane due to the lack of components required to establish epithelial cell contacts. As opposed to conventional fluorescence microscopy, confocal microscopy allows rapid inspection of the tridimensional organization of intracellular lumens and intercellular cysts even when they are located in cell multilayers.

Conformational change of rabbit aminopeptidase N into enterocyte plasma membrane domains analyzed by flow cytometry fluorescence energy transfer

Membrane vesicle preparations are very appropriate material for studying the topology of glycoproteins integrated into specialized plasma membrane domains of polarized cells. Here we show that the flow cytometric measurement of fluorescence energy transfer used previously to study the relationship between surface components of isolated cells can be applied to membrane vesicles. The fluorescein and rhodamine derivatives of a monoclonal antibody (4H7.1) that recognized one common epitope of the rabbit and pig aminopeptidase N were used for probing the oligomerization and conformational states of the enzyme integrated into the brush border and basolateral membrane vesicles prepared from rabbit and pig enterocytes. The high fluorescent energy transfer observed in the case of pig enzyme integrated into both types of vesicles and in the case of the rabbit enzyme integrated into basolateral membrane vesicles agreed very well with the existence of a dimeric organization, which was directly demonstrated by cross-linking experiments. Although with the latter technique we observed that the rabbit aminopeptidase was also dimerized in the brush border membrane, no energy transfer was detected with the corresponding vesicles. This indicates that the relative positions of two associated monomers differ depending on whether the rabbit aminopeptidase is transiently integrated into the basolateral membrane or permanently integrated into the brush border membrane. Cross-linking of aminopeptidases solubilized by detergent and of their ectodomains liberated by trypsin showed that only interactions between anchor domains maintained the dimeric structure of rabbit enzyme whereas interactions between ectodomains also exist in the pig enzyme. This might explain why the noticeable change in the organization of the two ectodomains observed in the case of rabbit aminopeptidase N does not occur in the case of pig enzyme.

Evidence for the transit of aminopeptidase N through the basolateral membrane before it reaches the brush border of enterocytes

In vivo pulse-chase labeling of rabbit jejunum loops was used in conjunction with subcellular fractionation and quantitative immunoprecipitation to determine whether or not the newly synthesized aminopeptidase N transits through the basolateral membrane before it reaches the apical brush border, its final localization. The kinetics of the arrival of the newly synthesized enzyme in the Golgi complex, basolateral and brush border membrane fractions strongly suggest that on leaving the Golgi aminopeptidase N is transiently integrated into the basolateral domain before reaching the brush border.

Further characterization of an early expressed glycoprotein of the rabbit small intestinal brush border. Its interaction with some hydrolases

Mouse 23 B 921 monoclonal antibody recognized a rabbit brush-border antigen with an apparent molecular mass 140 kDa (140-kDa Ag) which, unlike most hydrolases, is expressed in the poorly differentiated crypt cells of the small intestine. Immunoelectron microscopy of brush-border vesicles showed that the 23 B 921 bound to an epitope localized on the outside of the membrane. As is the case with hydrolases the external domain of the 140-kDa Ag constitutes the main part of the molecule, which can be released by papain treatment of brush-border vesicles. The presence of a small hydrophobic domain, anchoring the molecule into the membrane and responsible for its amphipatic character, was shown by its affinity for Triton-X114 micelles. The topological organization in the membrane of 140-kDa Ag seemed to be identical to that of hydrolases. Unlike hydrolases, however, the native structure of the antigen was found from its sensitivity to proteolysis to be very dependent on its integration into the lipid bilayer. Nevertheless, detergent-extracted 140-kDa Ag can be purified by immunoaffinity chromatography although it cannot be stocked for more than 48 h even in the presence of protease inhibitors. The carbohydrate moiety of 140-kDa Ag, bearing the human blood group A determinant, amounts to 20% of the total molecular mass. The existence of some privileged relationship was established between 140-kDa Ag and hydrolases: in the membrane, hydrolases protect the 140-kDa Ag from papain action; after detergent extraction, 140-kDa Ag is strongly associated with several hydrolases particularly disaccharidases.

Subcellular fractionation and subcellular localization of aminopeptidase N in the rabbit enterocytes

A fast and easy procedure is proposed for preparing concomitantly from the same sample of intestinal mucosa of A+ rabbits, four fractions high enriched in the brush-border and basolateral plasma membrane domains, rough endoplasmic reticulum, and smooth endoplasmic reticulum plus Golgi apparatus membranes, respectively. This is the first time the technique of flow fluorometry has been applied to characterize the brush-border and basolateral membrane fractions using polyclonal or monoclonal antibodies against antigens common to or specific for these two plasma membrane domains. This technique definitely proves the presence of aminopeptidase in at least 60% of the basolateral membrane vesicles, where its level is about 4.5% of that in the brush-border membrane vesicles. The endoglycosidase H-sensitive intermediate of glycosylation of aminopeptidase N in the steady state is accumulated in both the rough and smooth endoplasmic reticulum membranes. Although the rough membrane is more extensive it contains only about 40% of this transient form.

Evidence for selective transport of two brush-border glycoproteins from endoplasmic reticulum to Golgi complex in rabbit enterocytes

In vivo pulse-chase labeling of rabbit jejunum loops was used in conjunction with subcellular fractionation and quantitative immunoprecipitation to compare the intracellular transport kinetics of aminopeptidase with that of a 140 kDa brush-border antigen not belonging to the hydrolase class. As judged by the maturation kinetics of Asn-linked glycans, these glycoproteins were found to be transported from the endoplasmic reticulum into the Golgi apparatus at different rates (t1/2 = 25-50 min). The transport from the Golgi complex to the brush-border was rapid and seemed to occur at the same rate for both glycoproteins. In keeping with these kinetic data, the steady-state levels of aminopeptidase and the 140 kDa antigen in the Golgi complex were low, although that of aminopeptidase was significantly higher.

Identification of an early expressed marker of the luminal membrane of rabbit small intestinal columnar cells. Presence of a homologous antigen in kidney proximal tubules and glomeruli

Four monoclonal antibodies have been produced that specifically react with a rabbit intestinal brush-border glycoprotein which migrates in SDS-polyacrylamide gel electrophoresis as a protein of molecular weight 140,000. Contrarily to brush-border hydrolases, it is expressed in poorly differentiated crypt cells of the small intestine. Absent from colon columnar cells, it can be considered to be an early marker of differentiation of absorbing cells of the small intestine. Immunofluorescence technique showed the presence of a homologous antigen in kidney proximal tubule brush-border and podocytes of kidney glomeruli.

Biosynthesis and intracellular pool of aminopeptidase N in rabbit enterocytes

A papain treatment at 15 degrees C and pH 7.3 of a microsomal fraction from rabbit enterocytes quantitatively releases the aminopeptidase N integrated in the plasma membranes without solubilizing the enzyme integrated in the intracellular membranes. Working on A+ rabbits, characterized by the presence on the brush-border hydrolases of glycans corresponding to the human blood group A-determinant structure, it was possible to separate the intracellular aminopeptidase into two major molecular forms with or without these determinants. The molecular form devoid of human blood group A antigenicity corresponds to the only stable intermediate of glycosylation, bearing N-linked high mannose oligosaccharides. This endoglycosidase H-sensitive form is fully active and represents in the steady state about 1% of the total cellular aminopeptidase. It contains a cytoplasmic sequence of about 3000 daltons that has not yet been detected in the mature form. The A antigenicity is acquired simultaneously with processing of high mannose glycans to complex glycans. Pulse chase labeling of jejunum loops with [35S]-methionine showed that the complete processing of the transient form synthesized during 10 min takes 1 hr. During the last 30 min of processing, all the newly transformed molecules are transported to the plasma membrane.

Aminopeptidase N- and human blood group A-antigenicity along the digestive tract and associated glands in the rabbit

The cellular localization of an aminopeptidase N homologous to the brush-border intestinal enzyme and that of human blood group A-substances were investigated using the immunofluorescence technique on thin frozen sections (200 nm) of the digestive tract and associated glands of A+ and A- rabbits. Aminopeptidase N was found to be a common specific marker of both the apical region of plasma membrane of acinar cells in submaxillary and parotid glands and pancreas and the brush border of jejunum and colon absorbing cells. In hepatocytes, the enzyme was localized in the sinusoidal domains. Soluble A-substances were present in mucus secretory granules of intestinal goblet cells and those of stomach and gall bladder mucous cells. In contrast, the mucous acini of sublingual and submaxillary glands were devoid of A-antigenicity. The columnar cells of striated ducts of these glands exhibited A-antigenicity. Soluble A-substances were also found in zymogen granules of parotid and pancreas acinar cells and those of stomach chief cells. Moreover, in all cells secreting A-substances, and in the non-secreting absorbing intestinal cells, the glycoproteins of the plasma membrane bore A-determinants. Aminopeptidase N was one of the membrane-bound glycoproteins that bore A-determinants in cells that expressed A-antigenicity.

Technique of end-to-side portacaval shunt in fish (scyliorhinus canicula: small dogfish)

The authors describe a technique of portacaval shunt in a fish (small dogfish) using microsurgery. The techniques of anaesthesia and surgery are described and the results of eight operations are given, which show the problems of this kind of surgery, particularly with healing.

Analysis of two chloride requirements for sodium-dependent amino acid and glucose transport by intestinal brush-border membrane vesicles of fish

Intestinal brush border vesicles of a Mediterranean sea fish (Dicentrarchus labrax) were prepared using the Ca2+-sedimentation method. The transport of glucose, glycine and 2-aminoisobutyric acid is energized by an Na+ gradient (out greater than in). In addition, amino acid uptake requires Cl- in the extravesicular medium (2-aminoisobutyric acid more than glycine). This Na+- and Cl--dependent uptake is electrogenic, since it can be stimulated by negative charges inside the vesicles. The specific Cl- requirement of glycine and 2-aminoisobutyric acid transport is markedly influenced by pH, a change from 6.5 to 8.4 reducing the role played by Cl-. In the presence of Cl-, the Km of 2-aminoisobutyric acid uptake is reduced and its Vmax is enhanced. Cl- affects also a non-saturable Na+-dependent component of this amino acid uptake. Amino acid transport is also increased by intravesicular Cl- (2-aminoisobutyric acid less than glycine). This effect is more concerned with glucose uptake, which can be then multiplied by 2.3. A concentration gradient (in greater than out) as well as the presence of Na+ in the incubation medium seems to enter into this requirement. This intravesicular Cl- effect is not influenced by pH between 6.5 and 8.4.

Further studies on intestinal accumulation of glycine during fasting in rainbow trout (Salmo gairdneri Richardson)

Using the sliced intestine method, we studied in vitro the effects of long-term fasting (4 and 8 weeks) on the accumulation of 0.5 and 10 mM glycine in the mid- and hindgut of the trout. Increased glycine accumulation during fasting was noted when accumulation was calculated per gram of intestinal dry weight, per milliliter of cellular water, but especially per gram of mucosal tissue. The glycine tissue to medium ratios are also higher in fasted intestines, revealing an enhancement of the active pathways of the amino acid transport. After 4 weeks of fasting, the increased glycine accumulation is greater in hindgut, especially for the lowest glycine concentration (0.5 mM). With the highest concentration (10 mM), the effects of fasting similarly decrease in intensity and affect in the midgut and hindgut. After 8 weeks of fasting, the differences between fed and fasted intestines tend to be fewer, probably because of a progressive attenuation of the effect of fasting on the active pathways of glycine accumulation.

A chloride requirement for Na+-dependent amino-acid transport by brush border membrane vesicles isolated from the intestine of a Mediterranean teleost (Boops salpa)

The uptake of D-glucose, 2-aminoisobutyric acid and glycine was studied with intestinal brush border membrane vesicles of a marine herbivorous fish: Boops salpa. The uptake of these three substances is stimulated by an Na+ electrochemical gradient (Cout greater than Cin). For glucose, an increase of the electrical membrane potential generated by a concentration gradient of the liposoluble anion, SCN-, increases the Na+-dependent transport. This responsiveness to the membrane potential was confirmed by valinomycin. Differently from glucose, uptake of glycine and 2-aminoisobutyric acid requires, besides the Na+ gradient, the presence of Cl- on the external side of the vesicles. In the absence of Cl-, amino acid uptake is not stimulated by the Na+ gradient and is not influenced by an electrical membrane potential generated by SCN- gradient (Cout greater than Cin) or by a K+ diffusion potential (Cin greater than Cout). This Cl- requirement differs from the Na+ requirement, since a Cl- gradient (Cout greater than Cin) does not result in an accumulation of glycine or 2-aminoisobutyric acid similar to that produced by an Na+ gradient.

Isolation of brush border membranes in vesicular form from the intestinal spiral valve of the small dogfish (Scyliorhinus canicula)

A simple, rapid method for the preparation of purified brush border membranes in vesicular form from rabbit kidney proximal tubules has been applied with closely similar results to the intestinal spiral valve of the small dogfish (Scyliorhinus conicula). Since the dogfish belongs to one of the most ancient species of fish, it may be suggested that the method is generally applicable to all species later evolved which possess a brush border membrane at the mucosal surface of the cells of the intestine or kidney.