Annabelle Monnier

Although hepcidin expression was shown to be induced by the BMP/Smad signaling pathway, it is not yet known how iron regulates this pathway and what its exact molecular targets are. We therefore assessed genome-wide liver transcription profiles of mice of 2 genetic backgrounds fed iron-deficient, -balanced, or -enriched diets. Among 1419 transcripts significantly modulated by the dietary iron content, 4 were regulated similarly to the hepcidin genes Hamp1 and Hamp2. They are coding for Bmp6, Smad7, Id1, and Atoh8 all related to the Bmp/Smad pathway. As shown by Western blot analysis, variations in Bmp6 expression induced by the diet iron content have for functional consequence similar changes in Smad1/5/8 phosphorylation that leads to formation of heteromeric complexes with Smad4 and their translocation to the nucleus. Gene expression variations induced by secondary iron deficiency or iron overload were compared with those consecutive to Smad4 and Hamp1 deficiency. Iron overload developed by Smad4- and Hamp1-deficient mice also increased Bmp6 transcription. However, as shown by analysis of mice with liver-specific disruption of Smad4, activation of Smad7, Id1, and Atoh8 transcription by iron requires Smad4. This study points out molecules that appear to play a critical role in the control of systemic iron balance.

Allopolyploidy results from two events: the merger of divergent genomes and genome duplication. Both events have important functional consequences for the evolution and adaptation of newly formed allopolyploid species. In spite of the significant progress made in recent years, few studies have decoupled the effects of hybridization from genome duplication in the observed patterns of expression changes accompanying allopolyploidy in natural conditions. We used Agilent rice oligomicroarrays to explore gene expression changes following allopolyploidy in Spartina that includes a classic example of recent allopolyploid speciation: S. anglica formed during the 19th century following genome duplication of the hybrid S. x townsendii. Our data indicate important, but different, effects of hybridization and genome duplication in the expression patterns of the hybrid and allopolyploid. Deviation from parental additivity was most important following hybridization and was accompanied by maternal expression dominance, although transgressively expressed genes were also encountered. Maternal dominance was attenuated following genome duplication in S. anglica, but this species exhibits an increased number of transgressively overexpressed genes. These results reflect the decoupled effects of the 'genomic shock' following hybridization and genome redundancy on the genetic, epigenetic and regulatory mechanisms characterizing transcriptomic evolution in allopolyploids.

Development of the sporophyte and gametophyte generations of the brown alga E. siliculosus involves two different patterns of early development, which begin with either a symmetric or an asymmetric division of the initial cell, respectively. A mutant, immediate upright (imm), was isolated that exhibited several characteristics typical of the gametophyte during the early development of the sporophyte generation. Genetic analyses showed that imm is a recessive, single-locus Mendelian factor and analysis of gene expression in this mutant indicated that the regulation of a number of life-cycle-regulated genes is specifically modified in imm mutant sporophytes. Thus, IMM appears to be a regulatory locus that controls part of the sporophyte-specific developmental programme, the mutant exhibiting partial homeotic conversion of the sporophyte into the gametophyte, a phenomenon that has not been described previously.

BACKGROUND: Picoeukaryotes represent an important, yet poorly characterized component of marine phytoplankton. The recent genome availability for two species of Ostreococcus and Micromonas has led to the emergence of picophytoplankton comparative genomics. Sequencing has revealed many unexpected features about genome structure and led to several hypotheses on Ostreococcus biology and physiology. Despite the accumulation of genomic data, little is known about gene expression in eukaryotic picophytoplankton. RESULTS: We have conducted a genome-wide analysis of gene expression in Ostreococcus tauri cells exposed to light/dark cycles (L/D). A Bayesian Fourier Clustering method was implemented to cluster rhythmic genes according to their expression waveform. In a single L/D condition nearly all expressed genes displayed rhythmic patterns of expression. Clusters of genes were associated with the main biological processes such as transcription in the nucleus and the organelles, photosynthesis, DNA replication and mitosis. CONCLUSIONS: Light/Dark time-dependent transcription of the genes involved in the main steps leading to protein synthesis (transcription basic machinery, ribosome biogenesis, translation and aminoacid synthesis) was observed, to an unprecedented extent in eukaryotes, suggesting a major input of transcriptional regulations in Ostreococcus. We propose that the diurnal co-regulation of genes involved in photoprotection, defence against oxidative stress and DNA repair might be an efficient mechanism, which protects cells against photo-damage thereby, contributing to the ability of O. tauri to grow under a wide range of light intensities.

To evaluate the genetic diversity of viral haemorrhagic septicaemia virus (VHSV), the sequence of the glycoprotein genes (G) of 11 North American and European isolates were determined. Comparison with the G protein of representative members of the family Rhabdoviridae suggested that VHSV was a different virus species from infectious haemorrhagic necrosis virus (IHNV) and Hirame rhabdovirus (HIRRV). At a higher taxonomic level, VHSV, IHNV and HIRRV formed a group which was genetically closest to the genus Lyssavirus. Compared with each other, the G genes of VHSV displayed a dissimilar overall genetic diversity which correlated with differences in geographical origin. The multiple sequence alignment of the complete G protein, showed that the divergent positions were not uniformly distributed along the sequence. A central region (amino acid position 245-300) accumulated substitutions and appeared to be highly variable. The genetic heterogeneity within a single isolate was high, with an apparent internal mutation frequency of 1.2 x 10(-3) per nucleotide site, attesting the quasispecies nature of the viral population. The phylogeny separated VHSV strains according to the major geographical area of isolation: genotype I for continental Europe, genotype II for the British Isles, and genotype III for North America. Isolates from continental Europe exhibited the highest genetic variability, with sub-groups correlated partially with the serological classification. Neither neutralizing polyclonal sera, nor monoclonal antibodies, were able to discriminate between the genotypes. The overall structure of the phylogenetic tree suggests that VHSV genetic diversity and evolution fit within the model of random change and positive selection operating on quasispecies.