[Report] Plasticity of Animal Genome Architecture Unmasked by Rapid Evolution of a Pelagic Tunicate

[Report] Plasticity of Animal Genome Architecture Unmasked by Rapid Evolution of a Pelagic Tunicate: "A metazoan genome departs from the organization that appears rigidly established in other animal phyla.

Authors: France Denoeud, Simon Henriet, Sutada Mungpakdee, Jean-Marc Aury, Corinne Da Silva, Henner Brinkmann, Jana Mikhaleva, Lisbeth Charlotte Olsen, Claire Jubin, Cristian Cañestro, Jean-Marie Bouquet, Gemma Danks, Julie Poulain, Coen Campsteijn, Marcin Adamski, Ismael Cross, Fekadu Yadetie, Matthieu Muffato, Alexandra Louis, Stephen Butcher, Georgia Tsagkogeorga, Anke Konrad, Sarabdeep Singh, Marit Flo Jensen, Evelyne Huynh Cong, Helen Eikeseth-Otteraa, Benjamin Noel, Véronique Anthouard, Betina M. Porcel, Rym Kachouri-Lafond, Atsuo Nishino, Matteo Ugolini, Pascal Chourrout, Hiroki Nishida, Rein Aasland, Snehalata Huzurbazar, Eric Westhof, Frédéric Delsuc, Hans Lehrach, Richard Reinhardt, Jean Weissenbach, Scott W. Roy, François Artiguenave, John H. Postlethwait, J. Robert Manak, Eric M. Thompson, Olivier Jaillon, Louis Du Pasquier, Pierre Boudinot, David A. Liberles, Jean-Nicolas Volff, Hervé Philippe, Boris Lenhard, Hugues Roest Crollius, Patrick Wincker, Daniel Chourrout"

The three-dimensional architecture of Hox cluster silencing

The three-dimensional architecture of Hox cluster silencing: "

Spatial chromatin organization is emerging as an important mechanism to regulate the expression of genes. However, very little is known about genome architecture at high-resolution in vivo. Here, we mapped the three-dimensional organization of the human Hox clusters with chromosome conformation capture (3C) technology. We show that computational modeling of 3C data sets can identify candidate regulatory proteins of chromatin architecture and gene expression. Hox genes encode evolutionarily conserved master regulators of development which strict control has fascinated biologists for over 25 years. Proper transcriptional silencing is key to Hox function since premature expression can lead to developmental defects or human disease. We now show that the HoxA cluster is organized into multiple chromatin loops that are dependent on transcription activity. Long-range contacts were found in all four silent clusters but looping patterns were specific to each cluster. In contrast to the Drosophila homeotic bithorax complex (BX-C), we found that Polycomb proteins are only modestly required for human cluster looping and silencing. However, computational three-dimensional Hox cluster modeling identified the insulator-binding protein CTCF as a likely candidate mediating DNA loops in all clusters. Our data suggest that Hox cluster looping may represent an evolutionarily conserved structural mechanism of transcription regulation.

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Genomic repertoires of DNA-binding transcription factors across the tree of life

Genomic repertoires of DNA-binding transcription factors across the tree of life: "

Sequence-specific transcription factors (TFs) are important to genetic regulation in all organisms because they recognize and directly bind to regulatory regions on DNA. Here, we survey and summarize the TF resources available. We outline the organisms for which TF annotation is provided, and discuss the criteria and methods used to annotate TFs by different databases. By using genomic TF repertoires from ~700 genomes across the tree of life, covering Bacteria, Archaea and Eukaryota, we review TF abundance with respect to the number of genes, as well as their structural complexity in diverse lineages. While typical eukaryotic TFs are longer than the average eukaryotic proteins, the inverse is true for prokaryotes. Only in eukaryotes does the same family of DNA-binding domain (DBD) occur multiple times within one polypeptide chain. This potentially increases the length and diversity of DNA-recognition sequence by reusing DBDs from the same family. We examined the increase in TF abundance with the number of genes in genomes, using the largest set of prokaryotic and eukaryotic genomes to date. As pointed out before, prokaryotic TFs increase faster than linearly. We further observe a similar relationship in eukaryotic genomes with a slower increase in TFs.

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EVOLUTION AND INHERITANCE OF EARLY EMBRYONIC PATTERNING IN D. SIMULANS AND D. SECHELLIA.

EVOLUTION AND INHERITANCE OF EARLY EMBRYONIC PATTERNING IN D. SIMULANS AND D. SECHELLIA.: "

ABSTRACT

Pattern formation in Drosophila is a widely studied example of a robust developmental system. Such robust systems pose a challenge to adaptive evolution, as they mask variation which selection may otherwise act upon. Yet we find variation in the localization of expression domains (henceforth ‘stripe allometry’) in the pattern formation pathway. Specifically, we characterize differences in the gap genes giant and Kruppel, and the pair-rule gene even-skipped, which differ between the sibling species D. simulans and D. sechellia. In a double-backcross experiment, stripe allometry is consistent with maternal inheritance of stripe positioning and multiple genetic factors, with a distinct genetic basis from embryo length. Embryos produced by F1 and F2 backcross mothers exhibit novel spatial patterns of gene expression relative to the parental species, with no measurable increase in positional variance among individuals. Buffering of novel spatial patterns in the backcross genotypes suggests that robustness need not be disrupted in order for the trait to evolve, and perhaps the system is incapable of evolving to prevent the expression of all genetic variation. This limitation, and the ability of natural selection to act on minute genetic differences that are within the “margin of error” for the buffering mechanism, indicates that developmentally buffered traits can evolve without disruption of robustness

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Is Transcription Factor Binding Site Turnover a Sufficient Explanation for Cis-Regulatory Sequence Divergence?

Is Transcription Factor Binding Site Turnover a Sufficient Explanation for Cis-Regulatory Sequence Divergence?: "

The molecular evolution of cis-regulatory sequences is not well understood. Comparisons of closely related species show that cis-regulatory sequences contain a large number of sites constrained by purifying selection. In contrast, there are a number of examples from distantly related species where cis-regulatory sequences retain little to no sequence similarity but drive similar patterns of gene expression. Binding site turnover, whereby the gain of a redundant binding site enables loss of a previously functional site, is one model by which cis-regulatory sequences can diverge without a concurrent change in function. To determine whether cis-regulatory sequence divergence is consistent with binding site turnover, we examined binding site evolution within orthologous intergenic sequences from 14 yeast species defined by their syntenic relationships with adjacent coding sequences. Both local and global alignments show that nearly all distantly related orthologous cis-regulatory sequences have no significant level of sequence similarity but are enriched for experimentally identified binding sites. Yet, a significant proportion of experimentally identified binding sites that are conserved in closely related species are absent in distantly related species and so cannot be explained by binding site turnover. Depletion of binding sites depends on the transcription factor but is detectable for a quarter of all transcription factors examined. Our results imply that binding site turnover is not a sufficient explanation for cis-regulatory sequence evolution.

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Neighbourhood Continuity Is Not Required for Correct Testis Gene Expression in Drosophila

Neighbourhood Continuity Is Not Required for Correct Testis Gene Expression in Drosophila: "

Disrupting the linear organization of testis gene expression neighborhoods in the Drosophila genome does not affect gene expression, suggesting that neighborhood organization is not primarily driven by gene expression requirements.

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Co-Evolution of Transcriptional Silencing Proteins and the DNA Elements Specifying Their Assembly

Co-Evolution of Transcriptional Silencing Proteins and the DNA Elements Specifying Their Assembly: "

As shown by genetic assays in Saccharomyces interspecies hybrids, the co-evolution of heterochromatin assembly proteins with silencer elements allows transcriptional silencing functions to be maintained in rapidly evolving regions of the genome.

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