Project description:Among small photosynthetic eukaryotes that play a key role in oceanic food webs, picoplanktonic Mamiellophyceae such as Bathycoccus, Micromonas, and Ostreococcus are particularly important in coastal regions. By using a combination of cell sorting by flow cytometry, whole genome amplification (WGA), and 454 pyrosequencing, we obtained metagenomic data for two natural picophytoplankton populations from the coastal upwelling waters off central Chile. About 60% of the reads of each sample could be mapped to the genome of Bathycoccus strain from the Mediterranean Sea (RCC1105), representing a total of 9 Mbp (sample T142) and 13 Mbp (sample T149) of non-redundant Bathycoccus genome sequences. WGA did not amplify all regions uniformly, resulting in unequal coverage along a given chromosome and between chromosomes. The identity at the DNA level between the metagenomes and the cultured genome was very high (96.3% identical bases for the three larger chromosomes over a 360 kbp alignment). At least two to three different genotypes seemed to be present in each natural sample based on read mapping to Bathycoccus RCC1105 genome.
Project description:Bathycoccus is a cosmopolitan green micro-alga belonging to the Mamiellophyceae, a class of picophytoplankton that contains important contributors to oceanic primary production. A single species of Bathycoccus has been described while the existence of two ecotypes has been proposed based on metagenomic data. A genome is available for one strain corresponding to the described phenotype. We report a second genome assembly obtained by a single cell genomics approach corresponding to the second ecotype. The two Bathycoccus genomes are divergent enough to be unambiguously distinguishable in whole DNA metagenomic data although they possess identical sequence of the 18S rRNA gene including in the V9 region. Analysis of 122 global ocean whole DNA metagenome samples from the Tara-Oceans expedition reveals that populations of Bathycoccus that were previously identified by 18S rRNA V9 metabarcodes are only composed of these two genomes. Bathycoccus is relatively abundant and widely distributed in nutrient rich waters. The two genomes rarely co-occur and occupy distinct oceanic niches in particular with respect to depth. Metatranscriptomic data provide evidence for gain or loss of highly expressed genes in some samples, suggesting that the gene repertoire is modulated by environmental conditions.
Project description:Background: Ependymomas encompass multiple, clinically relevant tumor types based on localization and molecular profiles. Although tumors of the methylation class “spinal ependymoma” (SP-EPN) represent the most common intramedullary neoplasms in children and adults, their developmental origin is ill-defined, molecular data are scarce, and the potential heterogeneity within SP-EPN remains unexplored. The only known recurrent genetic events in SP-EPN are loss of chromosome 22q and NF2 mutations, but neither types and frequency of these alterations nor their clinical meaning have been described in a large, epigenetically defined series. Methods: We mapped SP-EPN transcriptomes (n=76) to developmental atlases of the developing and adult spinal cord to uncover potential developmental origins of these tumors. In addition, transcriptomic, epigenetic (n=234), genetic (n=140), and clinical analyses (n=115) were integrated for a detailed overview on this entity. Results: Integration of transcriptomic ependymoma data with single-cell atlases of the spinal cord identified mature adult ependymal cells to display highest similarities to SP-EPN. Unsupervised hierarchical clustering of tumor data together with integrated analysis of methylation profiles identified two molecular SP-EPN subtypes. Subtype 1 predominantly contained NF2 wild type sequences with regular NF2 expression but revealed more extensive copy number alterations. Subtype 2 harbored previously known germline or sporadic NF2 mutations and was NF2-deficient in most cases, more often showed multilocular disease, and demonstrated a significantly reduced progression-free survival. Conclusion: Based on integrated molecular profiling of a large tumor series we identify two distinct SP-EPN subtypes with important implications for genetic counseling, patient surveillance, and drug development priorities.