Biomedical subjects

Bettina Malnic

Publications and source records attributed to Bettina Malnic.

8 recordsLinked to original sources

PubMed2006

Identification of potential regulatory motifs in odorant receptor genes by analysis of promoter sequences.

Mouse odorant receptors (ORs) are encoded by >1000 genes dispersed throughout the genome. Each olfactory neuron expresses one single OR gene, while the rest of the genes remain silent. The mechanisms underlying OR gene expression are poorly understood. Here, we investigated if OR genes share common cis-regulatory sequences in their promoter regions. We carried out a comprehensive analysis in which the upstream regions of a large number of OR genes were compared. First, using RLM-RACE, we generated cDNAs containing the complete 5'-untranslated regions (5'-UTRs) for a total number of 198 mouse OR genes. Then, we aligned these cDNA sequences to the mouse genome so that the 5' structure and transcription start sites (TSSs) of the OR genes could be precisely determined. Sequences upstream of the TSSs were retrieved and browsed for common elements. We found DNA sequence motifs that are overrepresented in the promoter regions of the OR genes. Most motifs resemble O/E-like sites and are preferentially localized within 200 bp upstream of the TSSs. Finally, we show that these motifs specifically interact with proteins extracted from nuclei prepared from the olfactory epithelium, but not from brain or liver. Our results show that the OR genes share common promoter elements. The present strategy should provide information on the role played by cis-regulatory sequences in OR gene regulation.

5' Untranslated Regions↗

PubMed2006

Ric-8B promotes functional expression of odorant receptors.

Odorants are detected by a large family of odorant receptors (ORs) expressed in the nose. The information provided by the ORs is transmitted to specific regions of the brain, leading to odorant perception. The determination of the odorant specificities of the different ORs will contribute to the understanding of how odorants are discriminated by the olfactory system. However, to date only a few ORs have been linked to odorants they recognize, because ORs are poorly expressed on the cell surface of heterologous cells. Here we show that Ric-8B, a putative guanine nucleotide exchange factor for Galphaolf, promotes efficient heterologous expression of ORs. Our results also show that Ric-8B enhances accumulation of Galphaolf at the cell periphery, indicating that it promotes functional OR expression by improving the efficiency of OR coupling to Galphaolf. Expression systems containing Galphaolf and Ric-8B should contribute to the functional characterization of ORs.

Animals↗

PubMed2005

Ric-8B, an olfactory putative GTP exchange factor, amplifies signal transduction through the olfactory-specific G-protein Galphaolf.

The olfactory system is able to detect a large number of chemical structures with a remarkable sensitivity and specificity. Odorants are first detected by odorant receptors present in the cilia of olfactory neurons. The activated receptors couple to an olfactory-specific G-protein (Golf), which activates adenylyl cyclase III to produce cAMP. Increased cAMP levels activate cyclic nucleotide-gated channels, causing cell membrane depolarization. Here we used yeast two-hybrid to search for potential regulators for Galphaolf. We found that Ric-8B (for resistant to inhibitors of cholinesterase), a putative GTP exchange factor, is able to interact with Galphaolf. Like Galphaolf, Ric-8B is predominantly expressed in the mature olfactory sensory neurons and also in a few regions in the brain. The highly restricted and colocalized expression patterns of Ric-8B and Galphaolf strongly indicate that Ric-8B is a functional partner for Galphaolf. Finally, we show that Ric-8B is able to potentiate Galphaolf-dependent cAMP accumulation in human embryonic kidney 293 cells and therefore may be an important component for odorant signal transduction.

Animals↗

PubMed2004

Identification and complete sequencing of novel human transcripts through the use of mouse orthologs and testis cDNA sequences.

The correct identification of all human genes, and their derived transcripts, has not yet been achieved, and it remains one of the major aims of the worldwide genomics community. Computational programs suggest the existence of 30,000 to 40,000 human genes. However, definitive gene identification can only be achieved by experimental approaches. We used two distinct methodologies, one based on the alignment of mouse orthologous sequences to the human genome, and another based on the construction of a high-quality human testis cDNA library, in an attempt to identify new human transcripts within the human genome sequence. We generated 47 complete human transcript sequences, comprising 27 unannotated and 20 annotated sequences. Eight of these transcripts are variants of previously known genes. These transcripts were characterized according to size, number of exons, and chromosomal localization, and a search for protein domains was undertaken based on their putative open reading frames. In silico expression analysis suggests that some of these transcripts are expressed at low levels and in a restricted set of tissues.

Amino Acid Sequence↗

PubMed2004

A novel human G protein-coupled receptor is over-expressed in prostate cancer.

G protein-coupled receptors (GPCRs) are involved in a large variety of physiological functions. The number of known members that belong to this large family of receptors has been rapidly increasing. Now, with the availability of the human genome sequence databases, further family members are being identified. We describe the identification of a novel GPCR that shows no significant amino acid identity to any one of the known members of the GPCR superfamily. The gene expression pattern of this receptor is restricted: in normal tissues it is confined to the nervous system and testis, but we also detected gene expression in several tumor types, most notably prostate cancer, suggesting a potential role for this gene as a marker for this disease.

Amino Acid Sequence↗

PubMed2004

A transcript finishing initiative for closing gaps in the human transcriptome.

We report the results of a transcript finishing initiative, undertaken for the purpose of identifying and characterizing novel human transcripts, in which RT-PCR was used to bridge gaps between paired EST clusters, mapped against the genomic sequence. Each pair of EST clusters selected for experimental validation was designated a transcript finishing unit (TFU). A total of 489 TFUs were selected for validation, and an overall efficiency of 43.1% was achieved. We generated a total of 59,975 bp of transcribed sequences organized into 432 exons, contributing to the definition of the structure of 211 human transcripts. The structure of several transcripts reported here was confirmed during the course of this project, through the generation of their corresponding full-length cDNA sequences. Nevertheless, for 21% of the validated TFUs, a full-length cDNA sequence is not yet available in public databases, and the structure of 69.2% of these TFUs was not correctly predicted by computer programs. The TF strategy provides a significant contribution to the definition of the complete catalog of human genes and transcripts, because it appears to be particularly useful for identification of low abundance transcripts expressed in a restricted set of tissues as well as for the delineation of gene boundaries and alternatively spliced isoforms.

Alternative Splicing↗

PubMed2004

The human olfactory receptor gene family.

Humans perceive an immense variety of chemicals as having distinct odors. Odor perception initiates in the nose, where odorants are detected by a large family of olfactory receptors (ORs). ORs have diverse protein sequences but can be assigned to subfamilies on the basis of sequence relationships. Members of the same subfamily have related sequences and are likely to recognize structurally related odorants. To gain insight into the mechanisms underlying odor perception, we analyzed the human OR gene family. By searching the human genome database, we identified 339 intact OR genes and 297 OR pseudogenes. Determination of their genomic locations showed that OR genes are unevenly distributed among 51 different loci on 21 human chromosomes. Sequence comparisons showed that the human OR family is composed of 172 subfamilies. Types of odorant structures that may be recognized by some subfamilies were predicted by identifying subfamilies that contain ORs with known odor ligands or human homologs of such ORs. Analysis of the chromosomal locations of members of each OR subfamily revealed that most subfamilies are encoded by a single chromosomal locus. Moreover, many loci encode only one or a few subfamilies, suggesting that different parts of the genome may, to some extent, be involved in the detection of different types of odorant structural motifs.

Animals↗

PubMed2004

The mouse olfactory receptor gene family.

In mammals, odor detection in the nose is mediated by a diverse family of olfactory receptors (ORs), which are used combinatorially to detect different odorants and encode their identities. The OR family can be divided into subfamilies whose members are highly related and are likely to recognize structurally related odorants. To gain further insight into the mechanisms underlying odor detection, we analyzed the mouse OR gene family. Exhaustive searches of a mouse genome database identified 913 intact OR genes and 296 OR pseudogenes. These genes were localized to 51 different loci on 17 chromosomes. Sequence comparisons showed that the mouse OR family contains 241 subfamilies. Subfamily sizes vary extensively, suggesting that some classes of odorants may be more easily detected or discriminated than others. Determination of subfamilies that contain ORs with identified ligands allowed tentative functional predictions for 19 subfamilies. Analysis of the chromosomal locations of members of each subfamily showed that many OR gene loci encode only one or a few subfamilies. Furthermore, most subfamilies are encoded by a single locus, suggesting that different loci may encode receptors for different types of odorant structural features. Comparison of human and mouse OR subfamilies showed that the two species have many, but not all, subfamilies in common. However, mouse subfamilies are usually larger than their human counterparts. This finding suggests that humans and mice recognize many of the same odorant structural motifs, but mice may be superior in odor sensitivity and discrimination.

Animals↗