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.
CD1d-mediated lipid presentation by CD11c+ cells regulates intestinal homeostasis
Intestinal homeostasis requires a continuous dialogue between commensal bacteria and intestinal immune cells. Natural Killer T (NKT) cells are a population of CD1d-restricted lipid-reactive lymphocytes contributing to the regulation of mucosal immunity, but the mechanisms underlying this are poorly understood. Here we show that lipid presentation by CD1d+ intestinal dendritic cells and macrophages controls NKT cell function and activation which in turn regulates commensal bacteria and immune cell populations in the gut. These results reveal an NKT cell-dendritic cell crosstalk as a key mechanism for the regulation of intestinal homeostasis.
A protease cascade regulates release of the human malaria parasite Plasmodium falciparum from host red blood cells
This study showed that egress involves an enzyme cascade in which the serine protease SUB1 activates a second, cysteine protease called SERA6, enabling SERA6 to rapidly and precisely cleave the major red cell cytoskeletal protein β-spectrin and dismantle the cytoskeleton. It provides the first plausible model to explain how the parasite accomplishes timely rupture of its host cell membrane.
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.
Stabilization of reversed replication forks by telomerase drives telomere catastrophe
This study defined the mechanism leading to critically short telomeres in the absence of RTEL1 and showed that telomerase, which extends telomeres in normal cells, is pathological when forks encounter an obstacle within the telomere. We showed that replication forks stall and reverse at persistent t-loops, which creates a pseudo-telomere substrate that is inappropriately stabilised by telomerase. Removing telomerase or blocking replication fork reversal rescued telomere dysfunction in Rtel1 deficient cells. We proposed that when persistent t-loops stall the replisome, telomerase inhibits fork restart, triggering the excision of the t-loop by SLX1/4 and loss of a substantial part of the telomere.
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.
Nervous system regionalization entails axial allocation before neural differentiation
The prevailing view of neural induction in vertebrate embryos had been that cells are initially induced with anterior (forebrain) identity and then caudalising signals convert a proportion to posterior fates (spinal cord). Using chromatin accessibility, to define how cells adopt region-specific neural fates, combined with genetic and biochemical perturbations, we found that contrary to the established model, cells commit to a regional identity before acquiring neural identity. These findings prompt a revision to textbook models of neural induction. The study illustrates our adoption of new genomic methods (ATACseq) to address long-standing questions, and our capacity to productively collaborate with computational biologists.
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
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.
The mechanism of eukaryotic CMG helicase activation
This paper provided the first view of how the inactive MCM double hexamer is converted to two active CMG helicases. We showed MCM remains bound to ADP after loading; firing factors trigger ADP-ATP exchange; ATP rebinding causes double hexamer splitting, initial DNA melting and CMG formation. Active helicases then translocate N-terminus first.
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
α-synuclein oligomers interact with ATP synthase and open the permeability transition pore in Parkinson’s disease
Protein aggregation drives neuronal death in Parkinson’s disease, although how transition of monomeric protein structures to aggregated forms causes toxicity is unknown. We demonstrate that aggregation of the protein α-synuclein generates beta sheet-rich oligomers, which localise to the mitochondrial inner membrane, where they impair complex I-dependent respiration, induce oxidation of ATP synthase and cause mitochondrial lipid peroxidation. These oxidation events result in opening of the permeability transition pore, triggering mitochondrial swelling, and ultimately cell death. This work highlights how structural conversion of a protein changes its physiological interaction with proteins and lipids, and induces pathology in human cell models of disease.
Early-life exposure to low-dose oxidants can increase longevity via microbiome remodelling in Drosophila
This reports the first identification, in any species, of the microbiome as a key mediator of developmental stress-induced longevity. We found that mild oxidative stress during development robustly increases lifespan via the selective elimination of Acetobacter from the microbiome. This study also highlights that targeted remodelling of the early-life microbiome can provide an efficient strategy for extending healthspan and lifespan.
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.
Long-range signaling activation and local inhibition separate the mesoderm and endoderm lineages
The induction of endoderm and mesoderm by the signalling molecule Nodal has long been a textbook example of how a morphogen patterns vertebrate tissues. This study overturned the view that tissues are patterned through a single long-range morphogen gradient. Instead we demonstrated that Nodal functions in an incoherent feedforward loop with Fgf, to determine endoderm and mesoderm specification. Nodal induces long-range Fgf signaling, which is required for mesoderm induction, while simultaneously inducing a cell-autonomous Fgf signaling inhibitor within cells destined to become endoderm. This work represents a major step forward in deciphering the organising principles underlying early embryonic patterning.
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.
Plasmodium-specific atypical memory B cells are short-lived activated B cells
This paper provides strong evidence that “atypical” B cells are short-lived activated B cells, and are probably the result of chronic stimulation and not the cause of chronic malaria. This questions the commonly held view that atypical B cells are evidence of an aberrant or defective response in malaria.
Sex reversal following deletion of a single distal enhancer of Sox9
This systematic study revealed the complexity of the Sox9 regulatory region, but just one enhancer, “Enh13”, was shown by mutation studies to be essential for testis and subsequent male development. Sox9 expression is at the same very low level in XY Enh13 mutant embryos as in control XX gonads. Enh13 is efficiently bound by Sry in vivo and functions to initiate Sertoli cell fate during a short time window. This is in contrast to other redundant enhancers (e.g. TES) that bind Sry, but act later. This study helped explain Disorders of Sex Differentiation (DSDs), due to deletions and duplications mapping far upstream of Sox9, where the human Enh13 equivalent is located, as well as showing that some enhancers can be pioneering rather than redundant.
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.
Frequent loss-of-heterozygosity in CRISPR-Cas9–edited early human embryos
Crick researchers, including Kathy Niakan and James Turner, have revealed that CRISPR-Cas9 genome editing can lead to unintended mutations at the targeted section of DNA in early human embryos. The work highlights the need for greater awareness of and further research into the effects of CRISPR-Cas9 genome editing, especially when used to edit human DNA in laboratory research.