Permeability of polydisperse solid foams

The effect of polydispersity on foam permeability is investigated by numerical simulations. Foam structures are first generated by Laguerre tessellations via the Neper software and relaxed to minimize the surface energy via the Surface Evolver software. The fluid flow and permeability are then calculated by means of pore-network simulations, by considering either fully open-cell foams or foams with randomly selected closed windows. Different configurations of window aperture are used, including identical window aperture size, identical window aperture ratio, or random window aperture ratio. The main results are obtained for the case of foams having identical and uniform window aperture ratios. For such foams and at constant mean pore size, foam permeability is found to strongly increase with the polydispersity degree. The numerical results are employed to discuss the validity of the mean pressure field assumption used to calculate the foam permeability, the effect of small pores, and the definition of an equivalent Kelvin foam size. We show that as long as the fluctuations of the window aperture ratio remain low, foam permeability can be estimated by using the mean pressure field hypothesis. The weak effect of small pores on permeability is related to their small contribution to the overall fluid volume fraction. Finally, various estimations of the equivalent Kelvin foam size based on pore-size distribution are proposed.

Multiscale prediction of acoustic properties for glass wools: Computational study and experimental validation

This work is concerned with the multiscale prediction of the transport and sound absorption properties associated with industrial glass wool samples. In the first step, an experimental characterization is performed on various products using optical granulometry and porosity measurements. A morphological analysis, based on scanning electron imaging, is further conducted to identify the probability density functions associated with the fiber angular orientation. The key morphological characterization parameters of the microstructure, which serve as input parameters of the model, include the porosity, the weighted volume diameter accounting for both lengths and diameters of the analyzed fibers (and therefore the specific surface area of the random fibrous material), and the preferred out-of-plane fiber orientation generated by the manufacturing process. A computational framework is subsequently proposed and allows for the reconstruction of an equivalent fibrous network. A fully stochastic microstructural model, parameterized by the probability laws inferred from the database, is also proposed herein. Multiscale simulations are carried out to estimate transport properties and sound absorption. With no adjustable parameter, the results accounting for ten different samples obtained with various processing parameters are finally compared with the experimental data and used to assess the relevance of the reconstruction procedures and the multiscale computations.

Stochastic hyperelastic constitutive laws and identification procedure for soft biological tissues with intrinsic variability

In this work, we address the constitutive modeling, in a probabilistic framework, of the hyperelastic response of soft biological tissues. The aim is on the one hand to mimic the mean behavior and variability that are typically encountered in the experimental characterization of such materials, and on the other hand to derive mathematical models that are almost surely consistent with the theory of nonlinear elasticity. Towards this goal, we invoke information theory and discuss a stochastic model relying on a low-dimensional parametrization. We subsequently propose a two-step methodology allowing for the calibration of the model using standard data, such as mean and standard deviation values along a given loading path. The framework is finally applied and benchmarked on three experimental databases proposed elsewhere in the literature. It is shown that the stochastic model allows experiments to be accurately reproduced, regardless of the tissue under consideration.

Complementation of Seed Maturation Phenotypes by Ectopic Expression of ABSCISIC ACID INSENSITIVE3, FUSCA3 and LEAFY COTYLEDON2 in Arabidopsis

ABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3) and LEAFY COTYLEDON2 (LEC2), collectively the AFL, are master regulators of seed maturation processes. This study examined the role of AFL in the production of seed reserves in Arabidopsis. Quantification of seed reserves and cytological observations of afl mutant embryos show that protein and lipid but not starch reserves are spatially regulated by AFL. Although AFL contribute to a common regulation of reserves, ABI3 exerts a quantitatively greater control over storage protein content whereas FUS3 controls lipid content to a greater extent. Although ABI3 controls the reserve content throughout the embryo, LEC2 and FUS3 regulate reserves in distinct embryonic territories. By analyzing the ability of an individual ectopically expressed AFL to suppress afl phenotypes genetically, we show that conserved domains common to each component of the AFL are sufficient for the initiation of storage product synthesis and the establishment of embryo morphology. This confirms redundancy among the AFL and indicates a threshold necessary for function within the AFL pool. Since no individual AFL was able to suppress the tolerance to desiccation, mid- and late-maturation programs were uncoupled.

RLK7, a leucine-rich repeat receptor-like kinase, is required for proper germination speed and tolerance to oxidative stress in Arabidopsis thaliana

The leucine-rich repeat class of receptor-like kinase (LRR-RLKs) encoding genes represents the largest family of putative receptor genes in the Arabidopsis thaliana genome. However, very little is known about the range of biological process that they control. We present in this paper the functional characterization of RLK7 that has all the structural features of a receptor-like kinase of the plant-specific LRR type. To this end, we identified and characterized three independent T-DNA insertion mutants, constructed lines carrying truncated versions of this putative receptor, one lacking the cytoplasmic kinase domain (RLK7Δkin) and the other one lacking 14 LRR repeats (RLK7ΔLRR) and generated RLK7 overexpressing lines. We thus provide evidences that RLK7 is involved in the control of germination speed and the tolerance to oxidant stress. First, consistent with the expression kinetics of the RLK7 gene in the seeds, we found that all three mutants showed a delay in germination, whereas the overexpressors, RLK7Δkin and RLK7ΔLRR lines displayed a phenotype of more precocious germination. Second, a non-hypothesis driven proteomic approach revealed that in the seedlings of the three T-DNA insertion lines, four enzymes directly or indirectly involved in reactive oxygen species detoxification, were significantly less abundant. Consistent with this finding, the three mutants were less tolerant than the wild type to a hydrogen peroxide treatment, whereas the overexpressors, RLK7Δkin and RLK7ΔLRR lines presented the opposite phenotype.

ATR3 encodes a diflavin reductase essential for Arabidopsis embryo development

*The Arabidopsis genome possesses two confirmed Cytochrome P450 Reductase (CPR) genes, ATR1 and ATR2, together with a third putative homologue, ATR3, which annotation is questionable. *Phylogenetic analysis classified ATR3 as a CPR-like protein sharing homologies with the animal cytosolic dual flavin reductases, NR1 and Fre-1, distinct from the microsomal CPRs, ATR1 and ATR2. Like NR1 and Fre-1, ATR3 lacks the N-terminal endoplasmic reticulum (ER) anchor domain of CPRs and is localized in the cytoplasm. Recombinant ATR3 in plant soluble extracts was able to reduce cytochrome c but failed to reduce the human P450 CYP1A2. *Loss of ATR3 function resulted in early embryo lethality indicating that this reductase activity is essential. A yeast 2-hybrid screen identified a unique interaction of ATR3 with the homologue of the human anti-apoptotic CIAPIN1 and the yeast Dre2 protein. *This interaction suggests two possible roles for ATR3 in the control of cell death and in chromosome segregation at mitosis. Consistent with these results, the promoter of ATR3 is activated during cell cycle progression. Together these results demonstrated that ATR3 belongs to the NR1 subfamily of diflavin reductases whose characterized members are involved in essential cellular functions.

Interplay between the NADP-linked thioredoxin and glutathione systems in Arabidopsis auxin signaling

Intracellular redox status is a critical parameter determining plant development in response to biotic and abiotic stress. Thioredoxin (TRX) and glutathione are key regulators of redox homeostasis, and the TRX and glutathione pathways are essential for postembryonic meristematic activities. Here, we show by associating TRX reductases (ntra ntrb) and glutathione biosynthesis (cad2) mutations that these two thiol reduction pathways interfere with developmental processes through modulation of auxin signaling. The triple ntra ntrb cad2 mutant develops normally at the rosette stage, undergoes the floral transition, but produces almost naked stems, reminiscent of the phenotype of several mutants affected in auxin transport or biosynthesis. In addition, the ntra ntrb cad2 mutant shows a loss of apical dominance, vasculature defects, and reduced secondary root production, several phenotypes tightly regulated by auxin. We further show that auxin transport capacities and auxin levels are perturbed in the mutant, suggesting that the NTR-glutathione pathways alter both auxin transport and metabolism. Analysis of ntr and glutathione biosynthesis mutants suggests that glutathione homeostasis plays a major role in auxin transport as both NTR and glutathione pathways are involved in auxin homeostasis.

The alpha-N-acetyl-glucosaminidase gene is transcriptionally activated in male and female gametes prior to fertilization and is essential for seed development in Arabidopsis

Sugar residues in proteoglycan complexes carry important signalling and regulatory functions in biology. In humans, heparan sulphate is an example of such a complex polymer containing glucosamine and N-acetyl-glucosamine residues and is present in the extracellular matrix. Although heparan sulphate has not been found in plants, the At5g13690 gene encoding the alpha-N-acetyl-glucosaminidase (NAGLU), an enzyme involved in its catabolism, is present in the Arabidopsis genome. Among our collection of embryo-defective lines, a plant was identified in which the T-DNA had inserted into the AtNAGLU gene. The phenotype of atnaglu is an early arrest of seed development without apparent male or female gametophytic effects. These data demonstrated the essential function in Arabidopsis consistent with the contribution of NAGLU to the Sanfilippo syndrome in human. Expression of AtNAGLU in plants was shown to be prevalent during reproductive development. The presence of AtNAGLU mRNA was observed during early and late male gametogenesis and in each cell of the embryo sac at the time of fertilization. After fertilization, AtNAGLU was expressed in the embryo, suspensor, and endosperm until the cotyledonary stage embryo. This precise pattern of expression identifies the cells and tissues where a remodelling of the N-acetyl-glucosamine residues of proteoglycan complexes is occurring. This work provides original evidence of the important role of N-acetyl-glucosamines in plant reproductive development.

AtCXXS: atypical members of the Arabidopsis thaliana thioredoxin h family with a remarkably high disulfide isomerase activity

The Arabidopsis thaliana thioredoxin subgroup h III is composed of four members and includes the two monocysteinic (CXXS) thioredoxins encoded by the genome. We show that AtCXXS1 is the ortholog of monocysteinic thioredoxins present in all higher plants. In contrast, unicellular algae and the moss Physcomitrella patens do not encode monocysteinic thioredoxin. AtCXXS2, the second monocysteinic thioredoxin of Arabidopsis has no ortholog in any other higher plants. It probably appeared recently by duplications of a dicysteinic thioredoxin of the same subgroup h III. Both monocysteinic thioredoxins show a low disulfide reductase activity in vitro but are very efficient as disulfide isomerases in RNAse refolding tests. The possible interactions of these proteins with the glutathione glutaredoxin pathway are discussed on the basis of recent papers.

Characterization of leafy cotyledon1-like during embryogenesis in Theobroma cacao L

Theobroma cacao L., an economically important crop for developing countries, can be experimentally propagated by somatic embryogenesis. Because of their potential roles in embryogenesis, a gene candidate strategy was initiated to find gene homologues of the members of the leafy cotyledon family of transcription factors. A homologue of the leafy cotyledon1-like gene, that encodes the HAP 3 subunit of the CCAAT box-binding factor, was found in the cocoa genome (TcL1L). The translated peptide shared a high amino acid sequence identity with the homologous genes of Arabidopsis thaliana, Phaseolus coccineus and Helianthus annuus. TcL1L transcripts mainly accumulated in young and immature zygotic embryos, and, to a lesser extent, in young and immature somatic embryos. In situ hybridization specified the localization of the transcripts as being mainly in embryonic cells of young embryos, the meristematic cells of the shoot and root apex of immature embryos, and in the protoderm and epidermis of young and immature embryos, either zygotic or somatic. Non-embryogenic explants did not show TcL1L expression. Ectopic expression of the TcL1L gene could partially rescue the Arabidopsis lec1 mutant phenotype, suggesting a similarity of function in zygotic embryogenesis.

The first zygotic division in Arabidopsis requires de novo transcription of thymidylate kinase

Re-activation of cell division after fertilization involves the specific regulation of a set of genes. To identify genes involved in the gametophytic to sporophytic transition, we screened Arabidopsis T-DNA insertion lines for early seed abortion at the zygote (zeus) or one-cell embryo stages (cyclops), and characterized a sporophytic zygote-lethal mutation, zeus1. ZEUS1 encodes a thymidylate kinase (AtTMPK) that synthesizes dTDP and is involved in the regulation of DNA replication. Unlike in yeast and animals, the single AtTMPK gene is capable of producing two proteins by alternative splicing; the longer isoform is targeted to the mitochondria, the shorter to the cytosol. Transcription of AtTMPK is activated during the G(1)/S-phase transition of the cell cycle, similarly to yeast and mammalian orthologues. In AtTMPK:GUS plants, the reporter gene was preferentially expressed in cells undergoing division, but was not detected during the male and female gametophytic mitoses. GUS expression was observed in mature embryo sacs prior to fertilization, and this expression may indicate the time of synchronization of the gamete cell-cycle phases. Identification of ZEU1 emphasizes the importance of control of the metabolism of DNA in the regulation of the G(1)/S-phase transition at fertilization.

QQT proteins colocalize with microtubules and are essential for early embryo development in Arabidopsis

During Arabidopsis embryogenesis, the control of division between daughter cells is critical for pattern formation. Two embryo-defective (emb) mutant lines named quatre-quart (qqt) were characterized by forward and reverse genetics. The terminal arrest of qqt1 and qqt2 embryos was at the octant stage, just prior to the round of periclinal divisions that establishes the dermatogen stage . Homozygous embryos of a weaker allele of qqt1 were able to divide further, resulting in aberrant periclinal divisions. These phenotypic analyses support an essential role of the QQT proteins in the correct formation of the tangential divisions. That an important proportion of qqt1 embryos were arrested prior to the octant stage indicated a more general role in cell division. The analysis of QQT1 and QQT2 genes revealed that they belong to a small subgroup of the large family encoding ATP/GTP binding proteins, and are widely conserved among plants, vertebrates and Archaea. We showed that QQT1 and QQT2 proteins interact with each other in a yeast two-hybrid system, and that QQT1 and QQT2 tagged by distinct fluorescent probes colocalize with microtubules during mitosis, in agreement with their potential role in cell division and their mutant phenotype. We propose that QQT1 and QQT2 proteins participate in the organization of microtubules during cell division, and that this function is essential for the correct development of the early embryo.

A bona fide La protein is required for embryogenesis in Arabidopsis thaliana

Searches in the Arabidopsis thaliana genome using the La motif as query revealed the presence of eight La or La-like proteins. Using structural and phylogenetic criteria, we identified two putative genuine La proteins (At32 and At79) and showed that both are expressed throughout plant development but at different levels and under different regulatory conditions. At32, but not At79, restores Saccharomyces cerevisiae La nuclear functions in non-coding RNAs biogenesis and is able to bind to plant 3'-UUU-OH RNAs. We conclude that these La nuclear functions are conserved in Arabidopsis and supported by At32, which we renamed as AtLa1. Consistently, AtLa1 is predominantly localized to the plant nucleoplasm and was also detected in the nucleolar cavity. The inactivation of AtLa1 in Arabidopsis leads to an embryonic-lethal phenotype with deficient embryos arrested at early globular stage of development. In addition, mutant embryonic cells display a nucleolar hypertrophy suggesting that AtLa1 is required for normal ribosome biogenesis. The identification of two distantly related proteins with all structural characteristics of genuine La proteins suggests that these factors evolved to a certain level of specialization in plants. This unprecedented situation provides a unique opportunity to dissect the very different aspects of this crucial cellular activity.

AKRP and EMB506 are two ankyrin repeat proteins essential for plastid differentiation and plant development in Arabidopsis

EMB506 is a chloroplast protein essential for embryo development, the function of which is unknown. A two-hybrid interaction screen was performed to provide insight into the role of EMB506. A single interacting partner, AKRP, was identified among a cDNA library from immature siliques. The AKR gene (Zhang et al., 1992, Plant Cell 4, 1575-1588) encodes a protein containing five ankyrin repeats, very similar to EMB506. Protein truncation series demonstrated that both proteins interact through their ankyrin domains. Using reverse genetics, we showed that loss of akr function resulted in an embryo-defective (emb) phenotype indistinguishable from the emb506 phenotype. Transient expression of the signal peptide of AKRP fused to green fluorescent protein demonstrated the chloroplast localization of AKRP. The ABI3 promoter was used to express AKR in a seed-specific manner in order to analyse the post-embryonic effect of AKR loss of function in akr/akr seedlings. Homozygous fertile and viable akr/akr plants were obtained. These plants exhibited mild to severe defects in chloroplast and leaf cellular organization. We conclude that EMB506 and AKRP are involved in crucial and tightly controlled events in plastid differentiation linked to cell differentiation, morphogenesis and organogenesis during the plant life cycle.

A network of local and redundant gene regulation governs Arabidopsis seed maturation

In Arabidopsis thaliana, four major regulators (ABSCISIC ACID INSENSITIVE3 [ABI3], FUSCA3 [FUS3], LEAFY COTYLEDON1 [LEC1], and LEC2) control most aspects of seed maturation, such as accumulation of storage compounds, cotyledon identity, acquisition of desiccation tolerance, and dormancy. The molecular basis for complex genetic interactions among these regulators is poorly understood. By analyzing ABI3 and FUS3 expression in various single, double, and triple maturation mutants, we have identified multiple regulatory links among all four genes. We found that one of the major roles of LEC2 was to upregulate FUS3 and ABI3. The lec2 mutation is responsible for a dramatic decrease in ABI3 and FUS3 expression, and most lec2 phenotypes can be rescued by ABI3 or FUS3 constitutive expression. In addition, ABI3 and FUS3 positively regulate themselves and each other, thereby forming feedback loops essential for their sustained and uniform expression in the embryo. Finally, LEC1 also positively regulates ABI3 and FUS3 in the cotyledons. Most of the genetic controls discovered were found to be local and redundant, explaining why they had previously been overlooked. This works establishes a genetic framework for seed maturation, organizing the key regulators of this process into a hierarchical network. In addition, it offers a molecular explanation for the puzzling variable features of lec2 mutant embryos.

Genetic analysis of two Arabidopsis DNA polymerase epsilon subunits during early embryogenesis

Accurate DNA replication is one of the most important events in the life of a cell. To perform this task, the cell utilizes several DNA polymerase complexes. We investigated the role of DNA polymerase epsilon during gametophyte and seed development using forward and reverse genetic approaches. In Arabidopsis, the catalytic subunit of this complex is encoded by two genes, AtPOL2a and AtPOL2b, whereas the second largest regulatory subunit AtDPB2 is present as a unique complete copy. Disruption of AtPOL2a or AtDPB2 resulted in a sporophytic embryo-defective phenotype, whilst mutations in AtPOL2b produced no visible effects. Loss of AtDPB2 function resulted in a severe reduction in nuclear divisions, both in the embryo and in the endosperm. Mutations in AtPOL2a allowed several rounds of mitosis to proceed, often with aberrant planes of division. Moreover, AtDPB2 was not expressed during development of the female gametophyte, which requires three post-meiotic nuclear divisions. Since a consensus binding site for E2F transcription factors was identified in the promoter region of both genes, the promoter-reporter fusion technique was used to show that luciferase activity was increased at specific phases of the cell cycle in synchronized tobacco BY-2 cells. Our results support the idea that fertilization may utilize the mechanisms of cell cycle transcriptional regulation of genes to reactivate the divisions of the oosphere and central cell.

DOMINO1, a member of a small plant-specific gene family, encodes a protein essential for nuclear and nucleolar functions

Arabidopsis embryos carrying the domino1 mutation grow slowly in comparison with wild type embryos and as a consequence reach only the globular stage at desiccation. The primary defect of the mutation at the cellular level is the large size of the nucleolus that can be observed soon after fertilization in the nuclei of both the embryo and the endosperm. The ultrastructure of mutant nucleoli is drastically different from wild type and points to a fault in ribosome biogenesis. DOMINO1 encodes a protein, which belongs to a plant-specific gene family sharing a common motif of unknown function, present in the tomato DEFECTIVE CHLOROPLASTS AND LEAVES (LeDCL) protein. Using a GFP protein fusion, we show that DOMINO1 is targeted to the nucleus. We propose that inactivation of DOMINO1 has a negative effect on ribosome biogenesis and on the rate of cell division.

DOMINO1, a member of a small plant-specific gene family, encodes a protein essential for nuclear and nucleolar functions

Arabidopsis embryos carrying the domino1 mutation grow slowly in comparison with wild type embryos and as a consequence reach only the globular stage at desiccation. The primary defect of the mutation at the cellular level is the large size of the nucleolus that can be observed soon after fertilization in the nuclei of both the embryo and the endosperm. The ultrastructure of mutant nucleoli is drastically different from wild type and points to a fault in ribosome biogenesis. DOMINO1 encodes a protein, which belongs to a plant-specific gene family sharing a common motif of unknown function, present in the tomato DEFECTIVE CHLOROPLASTS AND LEAVES (LeDCL) protein. Using a GFP protein fusion, we show that DOMINO1 is targeted to the nucleus. We propose that inactivation of DOMINO1 has a negative effect on ribosome biogenesis and on the rate of cell division.

Three SAC1-like genes show overlapping patterns of expression in Arabidopsis but are remarkably silent during embryo development

In Saccharomyces cerevisiae, the SAC1 gene encodes a polyphosphoinositide phosphatase (PPIPase) that modulates the levels of phosphoinositides, which are key regulators of a number of signal transduction processes. SAC1p has been implicated in multiple cellular functions: actin cytoskeleton organization, secretory functions, inositol metabolism, ATP transport, and multiple-drug sensitivity. Here, we describe the characterization of three genes in Arabidopsis thaliana, AtSAC1a, AtSAC1b, and AtSAC1c, encoding proteins similar to those of yeast SAC1p. We demonstrated that the three AtSAC1 proteins are functional homologs of the yeast SAC1p because they can rescue the cold-sensitive and inositol auxotroph yeast sac1-null mutant strain. The fact that Arabidopsis and yeast SAC1 genes derived from a common ancestor suggests that this plant multigenic family is involved in the phosphoinositide pathway and in a range of cellular functions similar to those in yeast. Using GFP fusion experiments, we demonstrate that the three AtSAC1 proteins are targeted to the endoplasmic reticulum. Their expression patterns are overlapping, with at least two members expressed in each organ. Remarkably, AtSAC1 genes are not expressed during seed development, and therefore additional phosphatases are required to control phosphoinositide levels in seeds.

Differential expression of the Arabidopsis genes coding for Em-like proteins

Late embryogenesis abundant (lea) genes are a large and diverse group of genes highly expressed during late stages of seed development. Five major groups of LEA proteins have been described. Two Em genes (group I lea genes) are present in the genome of Arabidopsis thaliana L., AtEm1 and AtEm6. Both genes encode for very similar proteins which differ basically in the number of repetitions of a highly hydrophilic amino acid motif. The spatial patterns of expression of the two Arabidopsis Em genes have been studied using in situ hybridization and transgenic plants transformed with the promoters of the genes fused to the beta-glucuronidase reporter gene (uidA). In the embryo, AtEm1 is preferentially expressed in the pro-vascular tissues and in meristems. In contrast, AtEm6 is expressed throughout the embryo. The activity of both promoters disappears rapidly after germination, but is ABA-inducible in roots of young seedlings, although in different cells: the AtEm1 promoter is active in the internal tissues (vasculature and pericycle) whereas the AtEm6 promoter is active in the external tissues (cortex, epidermis and root hairs). The AtEm1 promoter, but not AtEm6, is also active in mature pollen grains and collapsed nectaries of young siliques. These data indicate that the two Em proteins could carry out at least slightly different functions and that the expression of AtEm1 and AtEm6 is controlled at, at least, three different levels: temporal, spatial and hormonal (ABA).

The BANYULS gene encodes a DFR-like protein and is a marker of early seed coat development

Mutations in the BANYULS (BAN) gene lead to precocious accumulation of anthocyanins in immature seed coat in Arabidopsis. The ban -1 allele has been isolated from a collection of T-DNA transformants and found to be tagged by the integrative molecule. The sequencing of wild-type and two independent mutant alleles confirmed the identity of the gene. Analysis of the full-length cDNA sequence revealed an open reading frame encoding a 342 amino acid protein which shared strong similarities with DFR and other enzymes of the phenylpropanoid biosynthesis pathway. BAN expression was restricted to the endothelium of immature seeds at the pre-globular to early globular stages of development as predicted from the maternal inheritance of the phenotype, and therefore represents a marker for early differentiation and development of the seed coat. BAN is probably involved in a metabolic channelling between the production of anthocyanins and pro-anthocyanidins in the seed coat.

Structure, organization and expression of two closely related novel Lea (late-embryogenesis-abundant) genes in Arabidopsis thaliana

We have isolated and sequenced a 9.5 kb genomic region from A. thaliana, located on chromosome 2, which contains two tandemly arranged closely related genes (AtM10 and AtM17) coding for a new family of LEA proteins. The deduced proteins have a molecular mass of 11 and 29 kDa, respectively, are extremely hydrophilic except at their N-termini and share 70% amino acid (aa) identity. A 47 aa motif containing a 6-cysteine domain is present once in AtM10 and four times in AtM17. The short intergenic region, the identical position of the intron and the overall sequence homology suggest that these two genes evolved through a duplication event. This conclusion is supported by the presence of two homologous strictosidine synthase-like (pseudo)genes downstream from AtM17 and AtM10. Expression studies, using AtM10 and AtM17 cDNAs, revealed that both transcripts accumulate exclusively in seeds from late embryogenesis until two days after imbibition. Expression of both genes in young seedlings is repressed during ABA, salt or drought treatment, whereas a cold stress induces the expression of AtM17 only. In situ hybridization revealed that AtM10 transcripts are detected throughout the embryo while those of AtM17 are more localized to cotyledon cells.

The EMB 506 gene encodes a novel ankyrin repeat containing protein that is essential for the normal development of Arabidopsis embryos

The EMB 506 gene of Arabidopsis, required for the normal development of the embryo beyond the globular stage, has been cloned. The gene encodes a protein of predicted size 35 kDa that contains five ankyrin (ANK) repeats within the C terminal moiety. ANK repeats are conserved domains of 33 amino acids involved in specific recognition of protein partners. The EMB 506 protein was detected at different stages of silique development but accumulated preferentially in the mature cauline leaves. The rescue of homozygous emb 506 embryos by complementation with the wild-type sequence cDNA demonstrated that the emb mutation is a consequence of the T-DNA insertion and that integration and expression of the transgene occurred during gametogenesis and/or early embryo development. In addition to the drastic effect of the emb 506 mutation during embryo development, complementation experiments revealed another effect of the gene: emb 506 plants transformed with the wild-type EMB 506 sequence were able to produce viable seeds but showed a reduction of apical dominance and the presence of adventitious buds or bracts along the stem. This result supports the idea that genes essential for embryogenesis may also be required at other stages of the plant life cycle.

Identification of a new exon of the brain microtubule-associated protein 2

The 5'-region of the transcripts encoding the HMW-(MAP2b) and LMW-(MAP2c) microtubule associated proteins in the brain was amplified by RT-PCR. The sequencing of cloned PCR fragments allowed to identify a new variant of brain HMW-MAP2 which contained, compared to MAP2b, an insertion of 246 bp located downstream the 5'-junction between MAP2b and MAP2c and that does not alter the open reading frame of MAP2b. The number of amino acid residues encoded by this insertion increases the molecular weight by 8.5 kDa i.e. corresponds to the difference in apparent size between MAP2a and MAP2b. A LMW-MAP2 PCR amplification product containing this insertion has been also identified. Genomic Southern blot analysis confirmed that this region belongs to the MAP2 gene and is located on a single exon.

Tau and microtubule-associated protein 2c transfection and neurite outgrowth in ND 7/23 cells

Neuronal hybrid ND 7/23 cells, which display sensorylike properties, develop neurites when cultured in the presence of either dibutyryl cyclic AMP plus nerve growth factor (DBcAMP + NGF) or retinoic acid or a phorbol ester derivative, although they express only trace amounts of the microtubule-associated tau proteins and low levels of microtubule-associated protein 2c (MAP2c). Nondifferentiated ND cells transfected with tau cDNAs did not develop neurites, whereas very short cell processes were formed in MAP2c-transfected cells. tau and MAP2 antibodies labeled microtubule bundles displayed in a ring array underneath the surface of the transfected cells and short microtubules starting from the cell center. After differentiation in the presence of DBcAMP + NGF, the same bundle organization was observed in the transfected cells. In addition, tau and MAP2 antibodies stained a short section of the formed neurites. These data demonstrate that the expression of tau protein is not sufficient to induce neurite extension and that other proteins induced by morphogens are more important to initiate morphological differentiation of this cell line.

Two novel HMW MAP2 variants with four microtubule-binding repeats and different projection domains

The brain microtubule-associated protein MAP2 is composed of two high molecular (MAP2a and b) and one low molecular (MAP2c) weight isoforms. All these forms were thought to contain three repeated microtubule-binding domains in their C-terminal region but a MAP2c variant containing four repeats has recently been identified. We report here the existence of two high molecular weight MAP2 isoforms with four microtubule-binding domains in the sensory neuronal cell line ND 7/23. A stretch of 135 bp is missing in one of these forms suggesting that several HMW MAP2 variants can be produced by alternative splicing.

High molecular weight tau distribution and microtubule stability in neuroblastoma N115 cells

The localization of high molecular weight (HMW) tau proteins in neuroblastoma N115 cells and of their transcripts was compared to that of non-tyrosinated and tyrosinated tubulin before and after treatment with depolymerizing drugs. Microtubules stained by tau antibodies were present both in a limited region of the cell center and in the cell processes, whereas tau transcripts were detected only in the cell body. The microtubules localized in the cell center and labeled by tau antibodies resisted colcemid treatment, whereas those in the neurites were completely depolymerized by the drug. Microtubules containing stable and unstable microtubule tracts were identified in the neurites after colcemid treatment. These composite microtubules were not labeled by tau antibodies. It is concluded that stable and unstable polymers--localized in the cell center and in the neurites, respectively--contain HMW tau proteins, whereas composite microtubules displayed in the cell processes do not. Microtubule stability in this cell line does not therefore seem to be related to the association of tau proteins to the polymers but, rather, to posttranslational modifications of the tubulin subunits.

Heterogeneity of the high molecular weight tau proteins in N115 neuroblastoma cells

The sequence of a high molecular weight (HMW) tau cDNA cloned from a neuroblastoma N115 library contains, in addition to the C- and N-terminal and middle regions present in the low molecular weight mouse brain tau proteins, a 711-bp nonhomologous domain (exon 4a) and a region of 198 bp corresponding to exon 6 of the tau gene. Protein immunoblot analysis, performed with antibodies specific either for a sequence present in the N-terminal region of all the tau variants or for exon 4a revealed several bands suggesting that more than one tau form is expressed in this cell line. Northern blot experiments performed with a number of cDNA probes spanning domains common and uncommon to low molecular weight and HMW tau allowed the identification of four tau transcripts differing in the size of their coding and noncoding regions. All these transcripts contain the sequence encoded by exon 6, but two of them lack exon 4a. As shown by RNase protection assays, the N-terminal region of these transcripts is also variable and contains either exon 1, or exons 1 and 2, or exons 1-3. Yet all these HMW tau forms contain four homologous repeats in their C-terminal domain both in the differentiated and nondifferentiated cells, i.e., have adult characteristics. In conclusion, the data reported in this article demonstrate that several HMW tau variants are expressed in neuroblastoma N115 cells and that the transition between immature to mature tau forms occurring during brain development is not required for neurite outgrowth during morphological differentiation of this cell line.

A tau-related protein of 130 kDa is present in Alzheimer brain

Two abnormal entities of 69 and 130 kDa, immunologically related to the microtubule-associated tau proteins, are present in the hippocampus and the frontal cortex of the Alzheimer brain, which contain a large number of neurofibrillary tangles (NFTs), but are absent in the cerebellum, which does not contain these structures. Epitope mapping with antibodies spanning domains present in the N-terminal, middle, and C-terminal tau sequence demonstrated that the 69- and 130-kDa entities belong to the tau family. Both the 69- and the 130-kDa proteins were found in an insoluble form and were the major tau species present in purified NFTs. A procedure was devised that allowed us to prepare from Alzheimer hippocampi two NFT fractions differing in size (20 and 3 microns), both of which contained the tau entities of 130 and 69 kDa.

Expression of Tau protein and Tau mRNA in the cerebellum during axonal outgrowth

"In situ" hybridization and immunohistochemical analysis of the expression of Tau mRNAs and Tau proteins in the developing cerebellum showed that: 1. At early postnatal stages Tau mRNAs are expressed in the deeper region of the external granular layer (EGL II) i.e. in the cells that begin to migrate from the proliferative zone. Little labeling was seen in the upper layer (EGL I) where the cerebellar interneurons actively proliferate during the first two postnatal weeks. Anti-Tau antibodies failed to detect Tau proteins both in EGL I and II. 2. Tau transcripts were also clearly detected in the migrating cells present in the molecular layer; no Tau immunoreactivity was seen in this layer. This suggests that Tau mRNAs remain very poorly translated in the migrating granule cells and in the other interneurons. 3. Tau proteins begin to be detected at postnatal day 8 in the molecular layer but only at the level of the parallel fibers that are present in the Purkinje cell dendritic field. This suggests that the Tau mRNAs transcribed in the migrating cells are not actively translated for several days and that Tau proteins accumulate only in the more mature sections of their axons, the parallel fibers.

IN CONCLUSION

Tau mRNAs are transcribed in the migrating cells several days before Tau proteins are actively translated and transported to their axons. Tau proteins accumulation occurs only at the end of granule cell migration i.e. when the parallel fibers interact with their post-synaptic counterparts, the dendrites of the Purkinje cells. Thus, axonal outgrowth and differentiation seem to be a multistep process.

Protein TAU variants present in paired helical filaments (PHFs) of Alzheimer brains

Polyclonal anti-TAU antisera directed against native Tau protein and the NH2-terminal side of the mouse TAU sequence were used to determine the nature of the TAU variants present in Alzheimer brains and in PHFs. These antibodies labelled specifically neurofibrillary tangles and plaque neurites in Alzheimer brains. On immunoblots of PHF extracts, two entities of 69 and 130 kDa were identified. These TAU-related species were absent from control brains. Protein immunoblot of total Alzheimer and control supernatants were shown to contain the same 4-5 TAU variants but none of the 69 and 130 TAU-related entities found in PHFs. These data suggest that specific TAU species are present in PHFs.

Dendritic and axonal distribution of the microtubule-associated proteins MAP2 and tau in the cerebellum of the nervous mutant mouse

The fate of the different types of axons and dendrites in the nervous mutant mouse has been studied with antibodies raised against the two major microtubule-associated proteins, MAP2 and tau. These proteins are specific markers of dendrites and axons, respectively. (1) Immunoblot analysis of cerebellar extracts showed that MAP2 concentration is markedly reduced (by approximately 90%) in the adult mutant. A 60% decrease was already noticed at day 20 postnatal, i.e., when all the Purkinje cells are present in their normal location and in apparent normal number. (2) Immunohistochemical studies performed at an adult stage with anti MAP2 antibodies showed marked alterations in the shape of the dendrites of the rare surviving Purkinje cells present in the lateral sections of the cerebellum of the mutant. In the vermis, where 50% of the cells survive in adulthood, the MAP2 antibody revealed both clusters of cells with a normal density and an intricated and extensive pattern of dendritic arborization and isolated cells showing either an apparently normal or an altered dendritic tree. (3) At day 20 postnatal the same antibody revealed, in the lateral sections severe abnormalities of the dendrites of the Purkinje cells which were different from those seen in adulthood in the vermis. Thus, although few or any Purkinje cells are dead at this stage, a large proportion of them have already profound dendritic alterations. In contrast, in the vermis the Purkinje cells and their dendritic tree are undistinguishable at this stage from those of the unaffected normal mice. (4) Immunoblot and immunohistochemical studies performed with the anti Tau antibody suggested that the majority of the axonal fibers of the cerebellum were present both at day 20 postnatal and at later adult stages. This suggests that, although deprived of their postsynaptic targets these axons can survive for a long time after Purkinje cell death. However, an anti-neurofilament monoclonal antibody which stains specifically the axons of the basket cells, revealed an altered morphology of the basket cell nest in the regions devoid of Purkinje cells. (5) In conclusion the alterations in the morphology of dendrites seem to represent an early event of Purkinje cell degeneration and to be correlated with a marked decrease in expression of MAP2. It remains unclear, however, whether such changes in expression of MAP2 represent a primary effect of the mutation or if it is only a precocious result of Purkinje cell degeneration.

Both adult and juvenile tau microtubule-associated proteins are axon specific in the developing and adult rat cerebellum

Several antibodies directed against the heterogeneous microtubule-associated protein group tau have been used to determine the immunocytochemical localization of these proteins in the developing rat cerebellum. Immunoblot analysis of brain extracts showed that both monoclonal and polyclonal anti-tau antibodies revealed not only the adult tau proteins (50,000-70,000 mol. wt) but also the immature (48,000 mol. wt) tau form. Immunocytochemical studies showed that, whatever the stage of development, anti-tau antibodies stained several types of axonal fibres. The Purkinje cell bodies and their dendrites were never significantly labelled. This means that immature tau is, as adult tau, localized essentially in axons. Axonal labelling seems to follow the cerebellar developmental pattern. For instance, the climbing fibres which reach the cerebellum during the embryonic life were stained soon after birth by the anti-tau antibodies. In contrast, the parallel fibres, that begin to develop perinatally, do not express tau at early (5 days) postnatal stages; a clear labelling of the deeper parallel fibres (which are more mature than the superficial ones) was seen at day 10 after birth in the vicinity of the developing dendrites of the Purkinje cells. This suggests that (1) the appearance of tau immunoreactivity reflects a certain stage of maturity of the parallel fibre; (2) both immature and mature tau microtubule-associated proteins seem to be axon specific in the developing rat cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of microtubule-associated proteins during the early stages of neurite extension by brain neurons cultured in a defined medium

Immunoblotting analysis was used to identify the microtubule-associated proteins (MAPs) present in cultures of mouse brain neurons. Polyclonal antibodies were raised against the two main adult brain MAPs, i.e., MAP2 (300 kDa) and tau (60-70 kDa). Whatever the stage of the culture, which was performed in a defined medium (3 or 6 days), the anti-MAP2 serum detected several high-molecular-weight components (including MAP2) and an entity with 62-65 kDa. Anti-tau revealed essentially a major peak of 48 kDa (young tau) but also slightly cross-reacted with the 62-65 kDa entity. During the culture period (0-6 days) the cells developed progressively a dense neuritic network; the concentration of the different MAPs increased in parallel but at different rates depending on the different species. The increase in concentration of the high-molecular-weight components occurred before that of 48-kDa tau. This suggests that high-molecular-weight MAPs and 48-kDa tau might be involved respectively in the initiation and elongation of neurites. In contrast, and since the main developmental changes in tau composition seen in vivo did not occur during the time course of the culture, this transition might be related to later events of neuronal differentiation.