Doctor of Philosophy, Universiteit Utrecht (2014)
Bachelor of Science, Nanyang Technological University (2006)
Roeland Nusse, Postdoctoral Faculty Sponsor
In the healthy adult liver, most hepatocytes proliferate minimally. However, upon physical or chemical injury to the liver, hepatocytes proliferate extensively in vivo under the direction of multiple extracellular cues, including Wnt and pro-inflammatory signals. Currently, liver organoids can be generated readily in vitro from bile-duct epithelial cells, but not hepatocytes. Here, we show that TNFα, an injury-induced inflammatory cytokine, promotes the expansion of hepatocytes in 3D culture and enables serial passaging and long-term culture for more than 6 months. Single-cell RNA sequencing reveals broad expression of hepatocyte markers. Strikingly, in vitro-expanded hepatocytes engrafted, and significantly repopulated, the injured livers of Fah-/- mice. We anticipate that tissue repair signals can be harnessed to promote the expansion of otherwise hard-to-culture cell-types, with broad implications.
View details for PubMedID 30500539
Here we present a compendium of single-cell transcriptomic data from the model organism Mus musculus that comprises more than 100,000 cells from 20 organs and tissues. These data represent a new resource for cell biology, reveal gene expression in poorly characterized cell populations and enable the direct and controlled comparison of gene expression in cell types that are shared between tissues, such as T lymphocytes and endothelial cells from different anatomical locations. Two distinct technical approaches were used for most organs: one approach, microfluidic droplet-based 3'-end counting, enabled the survey of thousands of cells at relatively low coverage, whereas the other, full-length transcript analysis based on fluorescence-activated cell sorting, enabled the characterization of cell types with high sensitivity and coverage. The cumulative data provide the foundation for an atlas of transcriptomic cell biology.
View details for DOI 10.1038/s41586-018-0590-4
View details for PubMedID 30283141
Lgr5 was originally discovered as a common Wnt target gene in adult intestinal crypts and colon cancer. It was subsequently identified as an exquisite marker of multiple Wnt-driven adult stem cell types. Lgr5 and its homologs, Lgr4 and Lgr6, constitute the receptors for R-spondins, potent Wnt signal enhancers and stem cell growth factors. The Lgr5/R-spondin complex acts by neutralizing Rnf43 and Znrf3, two transmembrane E3 ligases that remove Wnt receptors from the stem cell surface. Rnf43/Znrf3 are themselves encoded by Wnt target genes and constitute a negative Wnt feedback loop. Thus, adult stem cells are controlled by an intricate interplay of potent Wnt agonists, antagonists, and anti-antagonists.
View details for DOI 10.1101/gad.235473.113
View details for Web of Science ID 000331616100001
View details for PubMedID 24532711
Zinc RING finger 3 (ZNRF3) and its homolog RING finger 43 (RNF43) antagonize Wnt signaling in adult stem cells by ubiquitinating Frizzled receptors (FZD), which leads to endocytosis of the Wnt receptor. Conversely, binding of ZNRF3/RNF43 to LGR4-6 - R-spondin blocks Frizzled ubiquitination and enhances Wnt signaling. Here, we present crystal structures of the ZNRF3 ectodomain and its complex with R-spondin 1 (RSPO1). ZNRF3 binds RSPO1 and LGR5-RSPO1 with micromolar affinity via RSPO1 furin-like 1 (Fu1) domain. Anonychia-related mutations in RSPO4 support the importance of the observed interface. The ZNRF3-RSPO1 structure resembles that of LGR5-RSPO1-RNF43, though Fu2 of RSPO1 is variably oriented. The ZNRF3-binding site overlaps with trans-interactions observed in 2:2 LGR5-RSPO1 complexes, thus binding of ZNRF3/RNF43 would disrupt such an arrangement. Sequence conservation suggests a single ligand-binding site on ZNRF3, consistent with the proposed competing binding role of ZNRF3/RNF43 in Wnt signaling.
View details for DOI 10.1371/journal.pone.0083110
View details for Web of Science ID 000328731800094
View details for PubMedID 24349440
Leucine-rich repeat-containing G protein-coupled receptors 4-6 (LGR4-LGR6) are receptors for R-spondins, potent Wnt agonists that exert profound trophic effects on Wnt-driven stem cells compartments. We present crystal structures of a signaling-competent fragment of R-spondin 1 (Rspo1) at a resolution of 2.0 Å and its complex with the LGR5 ectodomain at a resolution of 3.2 Å. Ecto-LGR5 binds Rspo1 at its concave leucine-rich-repeat (LRR) surface, forming a dimeric 2:2 complex. Fully conserved residues on LGR4-LGR6 explain promiscuous binding of R-spondins. A phenylalanine clamp formed by Rspo1 Phe106 and Phe110 pinches Ala190 of LGR5 and is critical for binding. Mutations related to congenital anonychia reduce signaling, but not binding of Rspo1 to LGR5. Furthermore, antibody binding to the extended loop of the C-terminal LRR cap of LGR5 activates signaling in a ligand-independent manner. Thus, our data reveal binding of R-spondins to conserved sites on LGR4-LGR6 and, in analogy to FSHR and related receptors, suggest a direct signaling role for LGR4-LGR6 in addition to its formation of Wnt receptor and coreceptor complexes.
View details for DOI 10.1016/j.celrep.2013.06.009
View details for Web of Science ID 000321901200016
View details for PubMedID 23809763
The fibroblast growth factor receptor 3 (FGFR3) is a member of the FGFR subfamily of the receptor tyrosine kinases (RTKs) involved in signaling across the plasma membrane. Generally, ligand binding leads to receptor dimerization and activation. Dimerization involves the transmembrane (TM) domain, where mutations can lead to constitutive activation in certain cancer types and also in skeletal malformations. Thus, it has been postulated that FGFR homodimerization must be inherently weak to allow regulation, a feature reminiscent of alpha and beta integrin TM interactions. However, we show herein that in FGFR3-TM, four C-terminal residues, CRLR, have a profound destabilizing effect in an otherwise strongly dimerizing TM peptide. In the absence of these four residues, the dimerizing propensity of FGFR3-TM is comparable to glycophorin, as shown using various detergents. In addition, the expected enhanced dimerization induced by the mutation associated to the Crouzon syndrome A391E, was observed only when these four C-terminal residues were present. In the absence of these four residues, A391E was dimer-destabilizing. Finally, using site specific infrared dichroism and convergence with evolutionary conservation data, we have determined the backbone model of the FGFR3-TM homodimer in model lipid bilayers. This model is consistent with, and correlates with the effects of, most known pathological mutations found in FGFR-TM.
View details for DOI 10.1002/pro.65
View details for Web of Science ID 000264941500019
View details for PubMedID 19165726
The first low resolution solution structure of the soluble domain of subunit b (b (22-156)) of the Escherichia coli F(1)F(O) ATPsynthase was determined from small-angle X-ray scattering data. The dimeric protein has a boomerang-like shape with a total length of 16.2 +/- 0.3 nm. Fluorescence correlation spectroscopy (FCS) shows that the protein binds effectively to the subunit delta, confirming their described neighborhood. Using the recombinant C-terminal domain (delta(91-177)) of subunit delta and the C-terminal peptides of subunit b, b (120-140) and b (140-156), FCS titration experiments were performed to assign the segments involved in delta-b assembly. These data identify the very C-terminal tail b (140-156) to interact with delta(91-177). The novel 3D structure of this peptide has been determined by NMR spectroscopy. The molecule adopts a stable helix formation in solution with a flexible tail between amino acid 140 to 145.
View details for DOI 10.1007/s10863-008-9154-x
View details for Web of Science ID 000260957000005
View details for PubMedID 18668355