Researchers at the Crick are tackling the big questions about human health and disease, and new findings are published every week. Our faculty have picked some of the most significant papers published by Crick scientists, all of which are freely available thanks to our open science policy.
Phospho-dependent regulation of SAMHD1 oligomerisation couples catalysis and restriction
This study explained the mechanism of SAMHD1 regulation by phosphorylation/tetramerisation and correlated restriction activity with the capacity of SAMHD1 to form long lived, stable tetramers. These data form the basis of the prevailing model for SAMHD1 restriction of HIV-1 where dNTP-stabilised SAMHD1 tetramers deplete and maintain low levels of dNTPs in the non-permissive cells resistant to HIV-1 infection.
Autocatalytic activation of a malarial egress protease is druggable and requires a protein cofactor
A study led by the Blackman lab has shed new light on a key pathway that allows the malaria parasite to escape from the host’s red blood cells. Their findings identify a target that could be used to develop a new class of antimalarial drug designed to prevent disease progression.
Versatile humanized niche model enables study of normal and malignant human hematopoiesis
Immunodeficient mouse models have been instrumental in improving our understanding of human healthy haemopoietic stem cells and their hierarchical organisation as well as of the functional and phenotypic heterogeneity of leukaemic stem cells in acute myeloid leukaemia. However, xenotransplantation models failed at reconstituting the human bone marrow niche which remains of mouse origin. Using a bioengineered scaffold, we developed a new versatile humanised bone marrow niche which supports the engraftment of both normal and leukaemia stem cells in vivo. This 3D scaffold represents a suitable model to study and dissect the human bone marrow composition and test the effect of specific stroma cell types and niche factor functions during both normal human haemopoiesis and leukaemia.
Rad51 paralogs remodel pre-synaptic Rad51 filaments to stimulate homologous recombination
This study was the first to demonstrate that RAD51 paralogues bind to and structurally remodel the pre-synaptic RAD-51-ssDNA filament to a stabilised, “open”, and flexible conformation, which facilitates strand exchange with the template duplex. We showed that RAD51 paralogues act by binding the end of the presynaptic filament, which induces a conformational change that stabilises RAD-51 bound to ssDNA and primes the filament for strand exchange. These observations established for the first time the underlying mechanism of HR stimulation by Rad51 paralogues and revealed a new paradigm for the action of HR mediator proteins.
TRF2-independent chromosome end protection during pluripotency
This work revealed that telomere protection is solved by distinct mechanisms in pluripotent and somatic tissues. In somatic cells, TRF2 sequesters the telomere within a t-loop, preventing telomere end-to-end fusions and inviability. In contrast, TRF2 is dispensable for telomere protection in pluripotent cells; ESCs lacking TRF2 grow normally, do not fuse their telomeres and form functional t-loops. Upon differentiation this unique attribute of stem cells is lost and TRF2 assumes its full role in end protection. The retention of end protection in the presence of t-loops, but absence of TRF2, confirmed that t-loops are a key mediator of telomere end protection irrespectively of how they form.
Decoding of position in the developing neural tube from antiparallel morphogen gradients
Like many developing tissues, the vertebrate neural tube is patterned by antiparallel morphogen gradients. Using quantitative gene expression and signalling measurements we derived and validated a characteristic decoding map that relates morphogen input to the positional identity of neural progenitors. This revealed a strategy that minimises patterning errors in response to the joint input of noisy opposing gradients. The study illustrates how we integrate quantitative data, developmental and microfluidic experiments with phenological and mechanistic models.
Permissive selection followed by affinity-based proliferation of GC light zone B cells dictates cell fate and ensures clonal breadth
Memory B cells (MBCs) and plasma cells (PCs) are formed during the so-called germinal center (GC) B cell reaction. In the GC reaction B cells mutate their B cell receptor (BCR) genes and those that acquire a higher-affinity BCR for a pathogen antigen are presumably selected to survive and differentiate, whereas B cells carrying a lower-affinity BCR die. However, this cannot explain retention of GC B cells with varied BCR affinities and the formation of MBCs that normally carry lower-affinity BCRs. This work re-defines selection of GC B cells as permissive to ensure clonal diversity and broad protection.
Published in Proceedings of the National Academy of Sciences of USA
A supramolecular assembly mediates lentiviral DNA integration
Lentiviral IN proteins are notoriously poorly behaved in vitro, and the HIV 1 intasome has eluded structural biologists for over two decades. Prior research resulted in a collection of partial crystal and NMR structures that did not explain how lentiviral integrase synapses viral DNA ends. This paper described the first structure of the lentiviral intasome, solving the long-standing mystery and reconciling years of HIV-1 integrase structural biology and biochemistry.
Structural basis for retroviral integration into nucleosomes
Here, we described a cryo-EM structure of a retroviral intasome in a functional complex with a nucleosome. The structure revealed a multivalent interface of the viral integration machinery and chromatin, involving both gyres of nucleosomal DNA and histones. Whilst the histone octamer remains intact, the DNA is lifted from its surface to allow for strand transfer at highly preferred integration sites. These data provided a unique snapshot of an enzyme recognizing and acting upon nucleosomal DNA. The structure was the first to illustrate nucleosome flexibility facilitating a biological process and, as such, had far-reaching implications for chromosome biology.
SARS-CoV-2 can recruit a haem metabolite to evade antibody immunity
A team led by the Cherepanov lab has found a molecule that can block the binding of a subset of human antibodies to SARS-CoV-2. This could explain patients who, despite having high levels of antibodies, become ill.
Bidirectional eukaryotic DNA replication is established by quasi-symmetrical helicase loading
This paper shows that loading of the MCM double hexamer is a quasi-symmetrical reaction: two ORC molecules bound at two opposing sites of different affinity each recruit and load a single hexamer. The distance between the ORC binding sites is not critical. Subsequent work has provided further evidence for this from cryo-EM.
Chromatin controls DNA replication origin selection, lagging-strand synthesis, and replication fork rates
In this and the accompanying paper (Yeeles et al. 2017 Mol Cel 65, 105-116) we describe the reconstitution of full chromatin replication. We first identified all of the factors required for complete and rapid replication of naked DNA. Then we identified and characterised factors required to replicate chromatinised templates. We showed FACT is essential for chromatin replication, whilst nucleosome remodellers and histone acetylases help chromatin replication. In addition, chromatin enforces origin specificity and Okazaki fragment processing. Finally, we found that histones are efficiently transferred to nascent DNA.
Oncogenic RAS signaling promotes tumor immunoresistance by stabilizing PD-L1 mRNA
This work establishes for the first time a link between oncogenic RAS signalling and increased immuno-suppressive expression of the immune checkpoint protein PD-L1. RAS signalling results in phosphorylation and inactivation of TTP, a factor involved in degrading PD-L1 mRNA transcripts. As TTP inactivation causes accumulation of PD-L1 mRNA, interfering with the RAS pathway increases TTP binding to AU-rich elements of the transcripts, decreases PD-L1 protein production, and leads to enhanced antitumor immunity.
The effect of the D614G substitution on the structure of the spike glycoprotein of SARS-CoV-2
Research from the Gamblin lab has compared the original SARS-CoV-2 spike protein with a mutated version which arose last spring. They have found structural differences that could help to explain why the mutated version remains the dominant form circulating in all recent variants of concern.
Published in Proceedings of the National Academy of Sciences of USA
aPKC cycles between functionally distinct PAR protein assemblies to drive cell polarity
Through the use of aPKC inhibitors and genetic mutations, we demonstrate that aPKC cycles between distinct PAR-3 and CDC-42 dependent states, which define, respectively, the ability of the aPAR network to respond to spatial cues and to displace pPAR proteins from the membrane. We further show that cue sensing depends crucially on the oligomeric nature of the PAR-3 state, that the integrity of this cycle is required for coupling of cue-sensing and effector functions of the aPAR network, and that this cycle is enforced by activity of aPKC.
Antioxidant role for lipid droplets in a stem cell niche of Drosophila
This paper is a continuation of our major research theme on how dividing stem cells in the CNS are able to resist environmental stresses that shut down proliferation in most other developing tissues. It reports the first identification, in any species, of lipid droplets as protectors of stem cells. We discovered that hypoxia induces lipid droplets in the neural stem cell niche and that these protect the neural stem cells themselves from damaging polyunsaturated fatty acid (PUFA) peroxidation reactions. This study laid the foundation for our current mechanistic studies into the antioxidant functions of lipid droplets during development and tumorigenesis.
Coordinated changes in cellular behavior ensure the lifelong maintenance of the hippocampal stem cell population
Stem cell numbers in the hippocampus of young adults stabilise due to coordinated changes in stem cell behaviour which ensures lifelong hippocampal neurogenesis, according to new research from the Guillemot lab.
A temporal window for signal activation dictates the dimensions of a nodal signaling domain
This paper shows how temporal information in the zebrafish embryo is transformed into a spatial pattern. We demonstrate how the Nodal signalling gradient is formed in the early zebrafish embryo and show that its size and shape are determined by a temporal signal activation window created by a microRNA-mediated delay in the translation of Lefty, a Nodal antagonist. This paper was important as it not only challenged the long-held view in the field that the Nodal gradient was formed by a reaction–diffusion mechanism, but highlighted the importance of signalling duration in gradient formation.
Mutations in SKI in Shprintzen-Goldberg syndrome lead to attenuated TGF-β responses through SKI stabilization
Using a combination of structural biology, genome editing, and biochemistry, a new study from the Hill lab showed that Shprintzen–Goldberg syndrome is associated with an attenuation of TGF-β-induced transcriptional responses, and not enhancement, as previously predicted.
SOX2 is required independently in both stem and differentiated cells for pituitary tumorigenesis in p27-null mice
Tumour development depends on cell intrinsic dysfunction, but extrinsic factors can also be important drivers. Deletion of p27, which is downregulated in many tumours, predominantly gives pituitary tumours in mice. Sox2, which is transcriptionally derepressed in the absence of P27, is also important for tumorigenesis in this and other systems. Using various approaches, we establish the regulatory interaction in vivo of SOX2 and p27 and show that SOX2 is required independently, both cell-autonomously in the endocrine cells that form the tumours and non-cell-autonomously, in adjacent pituitary stem cells, to orchestrate tumorigenesis in the absence of P27.