A Powerful Method for Transcriptional Profiling of Specific Cell Types in Eukaryotes: Laser-Assisted Microdissection and RNA Sequencing

The acquisition of distinct cell fates is central to the development of multicellular organisms and is largely mediated by gene expression patterns specific to individual cells and tissues. A spatially and temporally resolved analysis of gene expression facilitates the elucidation of transcriptional networks linked to cellular identity and function. We present an approach that allows cell type-specific transcriptional profiling of distinct target cells, which are rare and difficult to access, with unprecedented sensitivity and resolution. We combined laser-assisted microdissection (LAM), linear amplification starting from <1 ng of total RNA, and RNA-sequencing (RNA-Seq). As a model we used the central cell of the Arabidopsis thaliana female gametophyte, one of the female gametes harbored in the reproductive organs of the flower. We estimated the number of expressed genes to be more than twice the number reported previously in a study using LAM and ATH1 microarrays, and identified several classes of genes that were systematically underrepresented in the transcriptome measured with the ATH1 microarray. Among them are many genes that are likely to be important for developmental processes and specific cellular functions. In addition, we identified several intergenic regions, which are likely to be transcribed, and describe a considerable fraction of reads mapping to introns and regions flanking annotated loci, which may represent alternative transcript isoforms. Finally, we performed a de novo assembly of the transcriptome and show that the method is suitable for studying individual cell types of organisms lacking reference sequence information, demonstrating that this approach can be applied to most eukaryotic organisms

A tissue-specific landscape of sense/antisense transcription in the mouse intestine

<p>Abstract</p> <p>Background</p> <p>The intestinal mucosa is characterized by complex metabolic and immunological processes driven highly dynamic gene expression programs. With the advent of next generation sequencing and its utilization for the analysis of the RNA sequence space, the level of detail on the global architecture of the transcriptome reached a new order of magnitude compared to microarrays.</p> <p>Results</p> <p>We report the ultra-deep characterization of the polyadenylated transcriptome in two closely related, yet distinct regions of the mouse intestinal tract (small intestine and colon). We assessed tissue-specific transcriptomal architecture and the presence of novel transcriptionally active regions (nTARs). In the first step, signatures of 20,541 NCBI RefSeq transcripts could be identified in the intestine (74.1% of annotated genes), thereof 16,742 are common in both tissues. Although the majority of reads could be linked to annotated genes, 27,543 nTARs not consistent with current gene annotations in RefSeq or ENSEMBL were identified. By use of a second independent strand-specific RNA-Seq protocol, 20,966 of these nTARs were confirmed, most of them in vicinity of known genes. We further categorized our findings by their relative adjacency to described exonic elements and investigated regional differences of novel transcribed elements in small intestine and colon.</p> <p>Conclusions</p> <p>The current study demonstrates the complexity of an archetypal mammalian intestinal mRNA transcriptome in high resolution and identifies novel transcriptionally active regions at strand-specific, single base resolution. Our analysis for the first time shows a strand-specific comparative picture of nTARs in two tissues and represents a resource for further investigating the transcriptional processes that contribute to tissue identity.</p

Maternal epigenetic pathways control parental contributions to Arabidopsis early embryogenesis

Defining the contributions and interactions of paternal and maternal genomes during embryo development is critical to understand the fundamental processes involved in hybrid vigor, hybrid sterility, and reproductive isolation. To determine the parental contributions and their regulation during Arabidopsis embryogenesis, we combined deep-sequencing-based RNA profiling and genetic analyses. At the 2-4 cell stage there is a strong, genome-wide dominance of maternal transcripts, although transcripts are contributed by both parental genomes. At the globular stage the relative paternal contribution is higher, largely due to a gradual activation of the paternal genome. We identified two antagonistic maternal pathways that control these parental contributions. Paternal alleles are initially downregulated by the chromatin siRNA pathway, linked to DNA and histone methylation, whereas transcriptional activation requires maternal activity of the histone chaperone complex CAF1. Our results define maternal epigenetic pathways controlling the parental contributions in plant embryos, which are distinct from those regulating genomic imprinting

Janus-a comprehensive tool investigating the two faces of transcription

Motivation: Protocols to generate strand-specific transcriptomes with next-generation sequencing platforms have been used by the scientific community roughly since 2008. Strand-specific reads allow for detection of antisense events and a higher resolution of expression profiles enabling extension of current transcript annotations. However, applications making use of this strandedness information are still scarce. Results: Here we present a tool (Janus), which focuses on the identification of transcriptional active regions in antisense orientation to known and novel transcribed elements of the genome. Janus can compare the antisense events of multiple samples and assigns scores to identify mutual expression of either transcript in a sense/antisense pair, which could hint to regulatory mechanisms. Janus is able to make use of single-nucleotide variant (SNV) and methylation data, if available, and reports the sense to antisense ratio of regions in the vicinity of the identified genetic and epigenetic variation. Janus interrogates positions of heterozygous SNVs to identify strand-specific allelic imbalance

Molecular signatures of the three stem cell lineages in Hydra and the emergence of stem cell function at the base of multicellularity

How distinct stem cell populations originate and whether there is a clear stem cell “genetic signature” remain poorly understood. Understanding the evolution of stem cells requires molecular profiling of stem cells in an animal at a basal phylogenetic position. In this study, using transgenic Hydra polyps, we reveal for each of the three stem cell populations a specific signature set of transcriptions factors and of genes playing key roles in cell type-specific function and interlineage communication. Our data show that principal functions of stem cell genes, such as maintenance of stemness and control of stem cell self-renewal and differentiation, arose very early in metazoan evolution. They are corroborating the view that stem cell types shared common, multifunctional ancestors, which achieved complexity through a stepwise segregation of function in daughter cells

Transcriptomic resilience to global warming in the seagrass Zostera marina, a marine foundation species

Large-scale transcription profiling via direct cDNA sequencing provides important insights as to how foundation species cope with increasing climatic extremes predicted under global warming. Species distributed along a thermal cline, such as the ecologically important seagrass Zostera marina, provide an opportunity to assess temperature effects on gene expression as a function of their long-term adaptation to heat stress. We exposed a southern and northern European population of Zostera marina from contrasting thermal environments to a realistic heat wave in a common-stress garden. In a fully crossed experiment, eight cDNA libraries, each comprising ∼125 000 reads, were obtained during and after a simulated heat wave, along with nonstressed control treatments. Although gene-expression patterns during stress were similar in both populations and were dominated by classical heat-shock proteins, transcription profiles diverged after the heat wave. Gene-expression patterns in southern genotypes returned to control values immediately, but genotypes from the northern site failed to recover and revealed the induction of genes involved in protein degradation, indicating failed metabolic compensation to high sea-surface temperature. We conclude that the return of gene-expression patterns during recovery provides critical information on thermal adaptation in aquatic habitats under climatic stress. As a unifying concept for ecological genomics, we propose transcriptomic resilience, analogous to ecological resilience, as an important measure to predict the tolerance of individuals and hence the fate of local populations in the face of global warming

Protein cofactor competition regulates the action of a multifunctional RNA helicase in different pathways

<p>A rapidly increasing number of RNA helicases are implicated in several distinct cellular processes, however, the modes of regulation of multifunctional RNA helicases and their recruitment to different target complexes have remained unknown. Here, we show that the distribution of the multifunctional DEAH-box RNA helicase Prp43 between its diverse cellular functions can be regulated by the interplay of its G-patch protein cofactors. We identify the orphan G-patch protein Cmg1 (YLR271W) as a novel cofactor of Prp43 and show that it stimulates the RNA binding and ATPase activity of the helicase. Interestingly, Cmg1 localizes to the cytoplasm and to the intermembrane space of mitochondria and its overexpression promotes apoptosis. Furthermore, our data reveal that different G-patch protein cofactors compete for interaction with Prp43. Changes in the expression levels of Prp43-interacting G-patch proteins modulate the cellular localization of Prp43 and G-patch protein overexpression causes accumulation of the helicase in the cytoplasm or nucleoplasm. Overexpression of several G-patch proteins also leads to defects in ribosome biogenesis that are consistent with withdrawal of the helicase from this pathway. Together, these findings suggest that the availability of cofactors and the sequestering of the helicase are means to regulate the activity of multifunctional RNA helicases and their distribution between different cellular processes.</p