Ethylene responses are negatively regulated by a receptor gene family in Arabidopsis thaliana

Disseminated neuroblastoma frequently show a very poor prognosis. N-myc gene amplification, 1p deletion and lack of CD44 gene expression, are all genetic factors associated with the disease's dissemination. Human neuroblastoma xenografts in nude mice has permitted to characterize, in disseminated neuroblasts, oncogenes overexpression, inactivation of tumor suppressor genes as well as detoxifying genes activation which contributes to increase cellular resistance to chemotherapy. These genetic abnormalities permit to propose a nosology of this very aggressive pediatric solid tumor. Hopefully, this genetic classification could be of great value for new therapeutic approaches.     

Members of the Arabidopsis actin gene family are widely dispersed in the genome

Plant genomes are subjected to a variety of DNA turnover mechanisms that are thought to result in rapid expansion and presumable contraction of gene copy number. The evolutionary history of the 10 actin genes in Arabidopsis thaliana is well characterized and can be traced to the origin of vascular plant genomes. Knowledge about the genomic position of each actin gene may be the key to tracing landmark genomic duplication events that define plant families or genera and facilitate further mutant isolation. All 10 actin genes were mapped by following the segregation of cleaved amplified polymorphisms between two ecotypes and identifying actin gene locations among yeast artificial chromosomes. The Arabidopsis actin genes are widely dispersed on four different chromosomes (1, 2, 3, and 5). Even the members of three closely related and recently duplicated pairs of actin genes are unlinked. Several other cytoskeletal genes (profilins, tubulins) that might have evolved in concert with actins were also mapped, but showed few patterns consistent with that evolutionary history. Thus, the events that gave rise to the actin gene family have been obscured either by the duplication of very small genic fragments or by extensive rearrangement of the genome.     

Large multi-chromosomal duplications encompass many members of the olfactory receptor gene family in the human genome

The human genome contains thousands of genes that encode a diverse repertoire of odorant receptors (ORs). We report here on the identification and chromosomal localization of 74 OR-containing genomic clones. Using fluorescence in situ hybridization (FISH), we demonstrate a striking homology among a set of approximately 20 OR locations, illustrating a history of duplications that have distributed OR sequences across the genome. Half of the OR-containing BACs cloned from total genomic DNA and 86% of cosmids derived from chromosome 3 cross-hybridize to a subset of these locations, many to 17 of them. These paralogous regions are distributed on 13 chromosomes, and eight lie in terminal bands. By analyzing clones from an approximately 250 kb clone-walk across one of these sites (3p13), we show that the homology among these sites is extensive (>150 kb) and encompasses both OR genes and intergenic genomic sequences. The FISH signals appear significantly larger at some sites than at the native location, indicating that portions of some duplicons have undergone local amplification/attrition. More restricted duplications involving pairs of other genomic locations are detected with 12% of the OR-BACs. Only a small subset of OR locations is sufficiently diverged from the others that clones derived from them behave as single-copy FISH probes. We estimate that duplications encompassing members of the OR gene family account for >0.1% of the human genome. A comparison of FISH signals at orthologous locations in other primates indicates that a portion of this OR 'subgenome' has been in flux during the divergence of primates, possibly as a mechanism for evolving the repertoire of olfactory receptors.     

ETR2 is an ETR1-like gene involved in ethylene signaling in Arabidopsis

The plant hormone ethylene regulates a variety of processes of growth and development. To identify components in the ethylene signal transduction pathway, we screened for ethylene-insensitive mutants in Arabidopsis thaliana and isolated a dominant etr2-1 mutant. The etr2-1 mutation confers ethylene insensitivity in several processes, including etiolated seedling elongation, leaf expansion, and leaf senescence. Double mutant analysis indicates that ETR2 acts upstream of CTR1, which codes for a Raf-related protein kinase. We cloned the ETR2 gene on the basis of its map position, and we found that it exhibits sequence homology to the ethylene receptor gene ETR1 and the ETR1-like ERS gene. ETR2 may thus encode a third ethylene receptor in Arabidopsis, transducing the hormonal signal through its "two-component" structure. Expression studies show that ETR2 is ubiquitously expressed and has a higher expression in some tissues, including inflorescence and floral meristems, petals, and ovules.     

Different members of the fibroblast growth factor receptor family are specific to distinct cell types in the developing chicken embryo

Single-stranded RNA probes for the three chicken fibroblast growth factor (FGF) receptors, cek-1, cek-2, and cek-3, in conjunction with in situ hybridization were used to characterize the distribution of the corresponding mRNAs in the developing chicken embryo. Cek-1 was expressed diffusely in most tissues examined, whereas the expression of cek-2 and cek-3 was more restricted. The highest levels of FGF receptor expression were seen in the developing bones; in skeletal, cardiac, and smooth muscle; and in some areas of the brain. Although all three receptors were expressed in a number of the same tissues, the expression of each receptor within a given tissue was generally specific for different cell types. In addition, the distribution of each of these receptors did not correlate with the previously characterized distributions of individual FGFs. These results suggest that the members of the FGF receptor family may represent cell-type-specific receptors rather than ligand-specific receptors. Thus, the interaction between a growth factor of the FGF family and a given FGF receptor is likely to be controlled to a large extent by spatial constraints, rather than exclusively by high binding affinities.     

Histidine kinase activity of the ETR1 ethylene receptor from Arabidopsis

ETR1 represents a prototypical ethylene receptor. Homologues of ETR1 have been identified in Arabidopsis as well as in other plant species, indicating that ethylene perception involves a family of receptors and that the mechanism of ethylene perception is conserved in plants. The amino-terminal half of ETR1 contains a hydrophobic domain responsible for ethylene binding and membrane localization. The carboxyl-terminal half of the polypeptide contains domains with homology to histidine kinases and response regulators, signaling motifs originally identified in bacteria. The putative histidine kinase domain of ETR1 was expressed in yeast as a fusion protein with glutathione S-transferase and affinity purified. Autophosphorylation of the purified fusion protein was observed on incubation with radiolabeled ATP. The incorporated phosphate was resistant to treatment with 3 M NaOH, but was sensitive to 1 M HCl, consistent with phosphorylation of histidine. Autophosphorylation was abolished by mutations that eliminated either the presumptive site of phosphorylation (His-353) or putative catalytic residues within the kinase domain. Truncations were used to delineate the region required for histidine kinase activity. An examination of cation requirements indicated that ETR1 requires Mn2+ for autophosphorylation. These results demonstrate that higher plants contain proteins with histidine kinase activity. Furthermore, these results indicate that aspects of ethylene signaling may be regulated by changes in histidine kinase activity of the receptor.     

mRNAS for one, two or three members of trk receptor family are expressed in single rat trigeminal ganglion neurons

We have studied the effects of the neuroleptic haloperidol and the non-benzodiazepine anxiolytics buspirone and lesopitron on the expression of c-Fos immunoreactivity in the rat forebrain. Haloperidol and buspirone administration resulted in a significant quantitative increase in the number of Fos-immunoreactive neurons in the lateral striatum and a presumable qualitative increase in the nucleus accumbens. In contrast, lesopitron did not lead to a significant increase in the c-Fos expression in the striatum. The induction of c-Fos immunoreactivity by buspirone is compatible with an interaction of this compound with D2 dopamine receptors, as documented for haloperidol. The lack of effects after lesopitron administration suggests that, in contrast with buspirone, this compound has no dopaminergic blocking activity.     

MtENOD16 and 20 are members of a family of phytocyanin-related early nodulins

We have identified two single-copy genes from the model legume. Medicago truncatula (MtENOD16 and 20) whose expression can be correlated with early stages of root nodulation and whose predicted coding sequences are partially homologous to both pea/vetch ENOD5 and soybean N315/ENOD55. Database searching and sequence alignment have defined the encoded early nodulins as a distinct sub-family of phytocyanin-related proteins, although the absence of key ligands implies that they are unlikely to bind copper. Molecular modelling based on known phytocyanin structure has been used to predict the 3-dimensional conformation of the principle globular domain of MtENOD16/20. Additional structural features common to both early nodulin and phytocyanin precursors include an N-terminal transit peptide, a highly variable (hydroxy)proline-rich sequence which probably undergoes extensive post-translational modification, and a hydrophobic C-terminal tail.     

Expression of several members of the TNF-ligand and receptor family on tonsillar lymphoid B cells

Although the expression patterns of the members of the tumour necrosis factor receptor and ligand families have extensively been studied by flow-cytometry on stimulated peripheral blood mononuclear cells (PBMNC), little or no flow-cytometric or immunohistological data exist about their expression in lymphoid tissue. According to the data obtained from stimulated PBMNC, several members of these molecule families (e.g. CD40 ligand [CD40L], CD30, CD27, hOX40) have been considered to be either T-cell restricted or strongly T-cell associated. The present study on samples from palatine tonsils revealed that most of these molecules are also expressed by tonsillar B cells. The additional analysis of the co-expression of these molecules also disclosed the existence of CD40+/CD40L+ and CD27+/CD70+ (CD27L+) lymphoid cells in tonsillar tissue.     

Xanthophyll cycle enzymes are members of the lipocalin family, the first identified from plants

Violaxanthin de-epoxidase and zeaxanthin epoxidase catalyze the addition and removal of epoxide groups in carotenoids of the xanthophyll cycle in plants. The xanthophyll cycle is implicated in protecting the photosynthetic apparatus from excessive light. Two new sequences for violaxanthin de-epoxidase from tobacco and Arabidopsis are described. Although the mature proteins are well conserved, the transit peptides of these proteins are divergent, in contrast to transit peptides from other proteins targeted to the thylakoid lumen. Sequence analyses of both violaxanthin de-epoxidase and zeaxanthin epoxidase establish the xanthophyll cycle enzymes as members of the lipocalin family of proteins. The lipocalin family is a diverse group of proteins that bind small hydrophobic (lipophilic) molecules and share a conserved tertiary structure of eight beta-strands forming a barrel configuration. This is the first reported identification of lipocalin proteins in plants.     

Characterization of an Arabidopsis thaliana gene that defines a new class of putative plant receptor kinases with an extracellular lectin-like domain

We have characterized an Arabidopsis receptor-like serine/threonine kinase gene, Ath.lecRK1 (Arabidopsis thaliana lectin-receptor kinase), defining a new and putatively important class of plant receptor kinases. Structural features of the predicted polypeptide include an amino-terminal membrane-targeting signal sequence, a legume lectin-like extracellular domain, a single membrane-spanning domain, and a characteristic serine/threonine protein kinase domain. A recombinant protein containing the kinase domain can be autophosphorylated on a serine residue. Ath.lecRK1 is a member of a gene family of at least two closely related genes. Northern blot analysis indicates that the Ath.lecRK1 gene is weakly expressed in a variety of organs and is regulated in Arabidopsis cell suspension cultures according to the growth phase of cells. The role this new class of plant receptor kinase could play is discussed with regard to the transduction of oligosaccharide and plant hormone signals.