Advancing stem cell technologies for conservation of wildlife biodiversity.

Wildlife biodiversity is essential for healthy, resilient and sustainable ecosystems. For biologists, this diversity also represents a treasure trove of genetic, molecular and developmental mechanisms that deepen our understanding of the origins and rules of life. However, the rapid decline in biodiversity reported recently foreshadows a potentially catastrophic collapse of many important ecosystems and the associated irreversible loss of many forms of life on our planet. Immediate action by conservationists of all stripes is required to avert this disaster. In this Spotlight, we draw together insights and proposals discussed at a recent workshop hosted by Revive & Restore, which gathered experts to discuss how stem cell technologies can support traditional conservation techniques and help protect animal biodiversity. We discuss reprogramming, in vitro gametogenesis, disease modelling and embryo modelling, and we highlight the prospects for leveraging stem cell technologies beyond mammalian species.

SETDB1 acts as a topological accessory to Cohesin via an H3K9me3-independent, genomic shunt for regulating cell fates.

SETDB1 is a key regulator of lineage-specific genes and endogenous retroviral elements (ERVs) through its deposition of repressive H3K9me3 mark. Apart from its H3K9me3 regulatory role, SETDB1 has seldom been studied in terms of its other potential regulatory roles. To investigate this, a genomic survey of SETDB1 binding in mouse embryonic stem cells across multiple libraries was conducted, leading to the unexpected discovery of regions bereft of common repressive histone marks (H3K9me3, H3K27me3). These regions were enriched with the CTCF motif that is often associated with the topological regulator Cohesin. Further profiling of these non-H3K9me3 regions led to the discovery of a cluster of non-repeat loci that were co-bound by SETDB1 and Cohesin. These regions, which we named DiSCs (domains involving SETDB1 and Cohesin) were seen to be proximal to the gene promoters involved in embryonic stem cell pluripotency and lineage development. Importantly, it was found that SETDB1-Cohesin co-regulate target gene expression and genome topology at these DiSCs. Depletion of SETDB1 led to localized dysregulation of Cohesin binding thereby locally disrupting topological structures. Dysregulated gene expression trends revealed the importance of this cluster in ES cell maintenance as well as at gene 'islands' that drive differentiation to other lineages. The 'unearthing' of the DiSCs thus unravels a unique topological and transcriptional axis of control regulated chiefly by SETDB1.

Engineering nucleosomes for generating diverse chromatin assemblies.

Structural characterization of chromatin is challenging due to conformational and compositional heterogeneity in vivo and dynamic properties that limit achievable resolution in vitro. Although the maximum resolution for solving structures of large macromolecular assemblies by electron microscopy has recently undergone profound increases, X-ray crystallographic approaches may still offer advantages for certain systems. One such system is compact chromatin, wherein the crystalline state recapitulates the crowded molecular environment within the nucleus. Here we show that nucleosomal constructs with cohesive-ended DNA can be designed that assemble into different types of circular configurations or continuous fibers extending throughout crystals. We demonstrate the utility of the method for characterizing nucleosome compaction and linker histone binding at near-atomic resolution but also advance its application for tackling further problems in chromatin structural biology and for generating novel types of DNA nanostructures. We provide a library of cohesive-ended DNA fragment expression constructs and a strategy for engineering DNA-based nanomaterials with a seemingly vast potential variety of architectures and histone chemistries.

Integration-free induced pluripotent stem cells from three endangered Southeast Asian non-human primate species.

Advanced molecular and cellular technologies provide promising tools for wildlife and biodiversity conservation. Induced pluripotent stem cell (iPSC) technology offers an easily accessible and infinite source of pluripotent stem cells, and have been derived from many threatened wildlife species. This paper describes the first successful integration-free reprogramming of adult somatic cells to iPSCs, and their differentiation, from three endangered Southeast Asian primates: the Celebes Crested Macaque (Macaca nigra), the Lar Gibbon (Hylobates lar), and the Siamang (Symphalangus syndactylus). iPSCs were also generated from the Proboscis Monkey (Nasalis larvatus). Differences in mechanisms could elicit new discoveries regarding primate evolution and development. iPSCs from endangered species provides a safety net in conservation efforts and allows for sustainable sampling for research and conservation, all while providing a platform for the development of further in vitro models of disease.

Platform for in situ real-time measurement of protein-induced conformational changes of DNA.

A platform for in situ and real-time measurement of protein-induced conformational changes in dsDNA is presented. We combine electrical orientation of surface-bound dsDNA probes with an optical technique to measure the kinetics of DNA conformational changes. The sequence-specific Escherichia coli integration host factor is utilized to demonstrate protein-induced bending upon binding of integration host factor to dsDNA probes. The effects of probe surface density on binding/bending kinetics are investigated. The platform can accommodate individual spots of microarrayed dsDNA on individually controlled, lithographically designed electrodes, making it amenable for use as a high throughput assay.

HMGA2 exhibits dRP/AP site cleavage activity and protects cancer cells from DNA-damage-induced cytotoxicity during chemotherapy.

HMGA proteins are not translated in normal human somatic cells, but are present in high copy numbers in pluripotent embryonic stem cells and most neoplasias. Correlations between the degree of malignancy, patient prognostic index and HMGA levels have been firmly established. Intriguingly, HMGA2 is also found in rare tumor-inducing cells which are resistant to chemotherapy. Here, we demonstrate that HMGA1a/b and HMGA2 possess intrinsic dRP and AP site cleavage activities, and that lysines and arginines in the AT-hook DNA-binding domains function as nucleophiles. We also show that HMGA2 can be covalently trapped at genomic abasic sites in cancer cells. By employing a variety of cell-based assays, we provide evidence that the associated lyase activities promote cellular resistance against DNA damage that is targeted by base excision repair (BER) pathways, and that this protection directly correlates with the level of HMGA2 expression. In addition, we demonstrate an interaction between human AP endonuclease 1 and HMGA2 in cancer cells, which supports our conclusion that HMGA2 can be incorporated into the cellular BER machinery. Our study thus identifies an unexpected role for HMGA2 in DNA repair in cancer cells which has important clinical implications for disease diagnosis and therapy.

A divalent metal-mediated switch controlling protein-induced DNA bending.

Architectural proteins that reconfigure the paths of DNA segments are required for the establishment of functional interfaces in many genomic transactions. A single-chain derivative of the DNA architectural protein integration host factor was found to adopt two stable conformational states in complex with a specific DNA target. In the so-called open state, the degree of protein-induced DNA bending is reduced significantly compared with the closed state. The conformational switch between these states is controlled by divalent metal binding in two electronegative zones arising from the lysine-to-glutamate substitution in the protein body proximal to the phosphate backbone of one DNA arm. We show that this switch can be employed to control the efficiency of site-specific recombination catalyzed by lambda integrase. Introduction of acidic residues at the protein-DNA interface holds potential for the design of metal-mediated switches for the investigation of functional relationships.

Publisher Correction: Utf1 contributes to intergenerational epigenetic inheritance of pluripotency.

A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.

Utf1 contributes to intergenerational epigenetic inheritance of pluripotency.

Undifferentiated embryonic cell transcription factor 1 (Utf1) is expressed in pluripotent embryonic stem cells (ESCs) and primordial germ cells (PGCs). Utf1 expression is directly controlled by pluripotency factors Oct4 and Sox2, which form a ternary complex with the Utf1 enhancer. The Utf1 protein plays a role in chromatin organization and epigenetic control of bivalent gene expression in ESCs in vitro, where it promotes effective cell differentiation during exit from pluripotency. The function of Utf1 in PGCs in vivo, however, is not known. Here, we report that proper development of Utf1 null embryos almost entirely depends on the presence of functional Utf1 alleles in the parental germline. This indicates that Utf1's proposed epigenetic role in ESC pluripotency in vitro may be linked to intergenerational epigenetic inheritance in vivo. One component - or at least facilitator - of the relevant epigenetic mark appears to be Utf1 itself, since Utf1-driven tomato reporter and Utf1 are detected in mature germ cells. We also provide initial evidence for a reduced adult testis size in Utf1 null mice. Our findings thus point at unexpected functional links between the core ESC pluripotency factor network and epigenetic inheritance of pluripotency.

Activation of site-specific DNA integration in human cells by a single chain integration host factor.

The heterodimeric integration host factor (IHF) is a site-specific DNA-binding and DNA-bending protein from Escherichia coli. It plays essential roles in a variety of DNA transactions including recombination, transcription and DNA replication. IHF's ability for concerted binding and bending of DNA is key to its biological function. Here we report the design, characterization and application of a single polypeptide chain IHF, termed scIHF2. In a novel approach for protein engineering, we inserted almost the entire alpha-subunit of IHF into the beta-subunit. DNA binding and DNA bending assays revealed that purified wild-type IHF and scIHF2 behave very similarly. Further, scIHF2 is required for site-specific integrative recombination by phage lambda integrase and for pSC101 replication in a DeltaIHF E.coli host. It also triggers site-specific integrative and excisive recombination in vitro to the same extent as the wild-type protein. We also demonstrate that scIHF2 is stably expressed in HeLa cells, that it is localized primarily in the cell nucleus and that it triggers integrative recombination in mammalian cells by wild-type integrase. Hence, scIHF2 may be used as a novel regulatory cofactor for recombination or other DNA transactions in mammalian cells that require or benefit from sequence-specific high precision DNA bending.

Single-chain integration host factors as probes for high-precision nucleoprotein complex formation.

Integration host factor (IHF) is a heterodimeric, site-specific DNA-binding and DNA-bending protein from Escherichia coli. It is involved in high-precision DNA transactions where it serves as a key architectural component of specialized nucleoprotein structures (snups). We described recently a novel approach for protein engineering using a single polypeptide chain IHF, termed scIHF2, as a first example. ScIHF2 is made up of the alpha subunit of IHF which was inserted into the beta subunit at peptide bond Q39/G40 via two short linkers. The monomer behaves very similarly to the heterodimeric, parental IHF in biochemical and functional assays. Here, we describe an extension of this approach in which we shortened either one or both linkers by one amino acid, thereby generating three new variants termed scIHF1, 3, and 4. These variants exhibit distinct DNA-binding properties, different phenotypes in site-specific integrative and excisive recombination by phage lambda integrase in vitro, as well as in pSC101 replication assays in a DeltaIHF E. coli host. We also introduced a K45E substitution within the alpha domain of scIHF3 and based on electrophoretic mobility shift assays (EMSAs), argue that it significantly changes the DNA trajectory within the protein-DNA complex. Our results indicate that IHF's pleiotropic roles in DNA transactions inside E. coli require different types of high-precision DNA architectural activities. The scIHF variants described here will help to explore further how flexible these requirements are.

Optimization of coliphage HK022 Integrase activity in human cells.

The Integrase (Int) site-specific recombinase of coliphage HK022 catalyzes integrative and excisive DNA recombination between two attachment (att) sites in human cells without the need to supply the accessory proteins Integration Host Factor (IHF) and Excisionase (Xis). Previous work has shown that under these conditions, reactions in cis, i.e. both att sites are located on the same chromosome, can be detected without selection. However, recombination in trans, i.e. one att site positioned on a chromosome and the other on an episomal vector, was detected only after selection. Here we show that optimization of the int-HK022 gene for human codon usage according to the GeneOptimizer software algorithm, as well as addition of accessory proteins IHF and Xis improve the recombination efficiencies in human cells, such that recombinants in a trans reaction could be detected without selection.