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Biology subjects

Lin, C. P.

Publications and source records attributed to Lin, C. P..

11 recordsLinked to original sources

Intermittent parathyroid hormone employs autonomous and non-autonomous mechanisms to drive osteogenesis from Ebf3-expressing skeletal progenitor cells

How systemic hormonal signals coordinate stem cell fate decisions in adult tissues remains incompletely understood. In bone marrow, Cxcl12-abundant reticular (CAR) cells, marked by Early B-cell Factor 3 (Ebf3) expression, are multipotent mesenchymal progenitors that maintain the hematopoietic stem cell niche and serves as a major osteoblast progenitor source during adult bone remodeling. Using inducible lineage tracing coupled with single-cell transcriptomics and conditional genetics in mice, we show that intermittent parathyroid hormone (iPTH; teriparatide) drives osteogenesis from CAR cells by simultaneously engaging cell-intrinsic and cell-extrinsic mechanisms. Directly, iPTH suppresses lineage-enforcing transcription factors Ebf3, Ebf1, and Foxc1, thereby destabilizing progenitor identity and priming CAR cells for osteogenic commitment. Simultaneously, iPTH stimulates osteoclastic bone resorption, releasing TGF{beta} which recruits these primed progenitors to bone surfaces, a process abolished by osteoclast depletion. Preventing CAR cell maturation via Sp7 deletion abrogates iPTH-induced bone gain, establishing these progenitors as essential mediators of bone anabolism. This coupled mechanism, in which intrinsic transcriptional priming converges with extrinsic niche remodeling, is conserved in human CAR cells from teriparatide-treated postmenopausal women, which show concordant suppression of EBF3 and FOXC1 and elevated TGF{beta}-responsive gene signatures. These findings reveal a general principle by which a systemic hormone orchestrates tissue remodeling through simultaneous reprogramming of progenitor identity and remodeling of the niche microenvironment.

physiology↗

The Mechanism of Histone Ubiquitylation by the ASB9-CUL5 Ubiquitin Ligase

The E3 ligase substrate receptor ankyrin and SOCS box protein 9 (ASB9) was shown to bind over 10 different proteins including metabolic enzymes such as creatine kinase, filament proteins such as vimentin, and histones. In previous work, we characterized the ASB9-Cullin 5 E3 ligase (ASB9-CRL) ubiquitylation of creatine kinase and showed that ubiquitylation required the ring-between-ring ligase, ARIH2. Here we characterize the ASB9-CRL ubiquitylation of histones and show that histones H3 and H4 are polyubiquitylated by the ASB9-CRL whereas histones H2A and H2B are not. Many, but not all lysines in the histones are ubiquitylated suggesting some substrate specificity. Binding experiments show that the ligase-histone interaction is highly electrostatic and the neddylated ASB9-CRL binds with highest affinity. Only free histones are ubiquitylated. When the histones are in nucleosomes or in complex with the chaperone Asf1, they are not ubiquitylated. Only K48 and K63 polyubiquitin chains were observed, suggesting that the ubiquitylation probably drives protein degradation. The presence of ASB9 in specific cell types correlates with situations in which free histones H3 and H4 need to be degraded. In this work, we demonstrate that the ASB9-CRL is the ligase that facilitates degradation of histones H3 and H4. In addition, this work represents the first example of Cullin 5 mediated ubiquitylation that does not require a ring-between-ring "helper" ligase.

biochemistry↗

CRISPR-RNA binding drives structural ordering that primes Cas7-11 for target cleavage

Type III-E CRISPR-Cas effectors, referred to as Cas7-11 of gRAMPs, are single proteins that cleave target RNAs without nonspecific collateral cleavage, opening new possibilities for RNA editing. Here, biochemical assays combined with amide hydrogen-deuterium exchange (HDX-MS) experiments provide a first glimpse of the conformational dynamics of apo Cas7-11. HDX-MS revealed the backbone comprising the four Cas7 zinc-binding RRM folds are well-folded but insertion sequences are highly dynamic and fold upon binding crRNA. The crRNA causes folding of disordered catalytic loops and {beta}-hairpins, stronger interactions at domain-domain interfaces, and folding of the Cas7.1 processing site. Target RNA binding causes only minor ordering around the catalytic loops of Cas7.2 and Cas7.3. We show that Cas7-11 cannot independently process the CRISPR array and that binding of partially processed crRNA induces multiple states in Cas7-11 and reduces target RNA cleavage. The insertion domain shows the most ordering upon binding of mature crRNA. Finally, we show a crRNA-induced conformational change in one of the TPR-CHAT binding sites providing an explanation for why crRNA binding facilitates TPR-CHAT binding. The results provide the first glimpse of the apo state of Cas7-11 and reveal how its structure and function are regulated by crRNA binding.

biophysics↗

Synthetic type III-E CRISPR-Cas effectors for programmable RNA-targeting

The recent discovery of the type III-E CRISPR-Cas effector class has reshaped our fundamental understanding of CRISPR-Cas evolution and classification. Type III-E effectors are composed of several Cas7-like domains and a single Cas11-like domain naturally fused together to create a single polypeptide capable of programmably targeting and degrading RNA. Here we identify a novel composition of a type III-E-like effector composed of Cas7-like and a Cas1-like domain, that can be engineered into an active chimeric RNA-targeting Cas effector and presents a new function of Cas1 in RNA-targeting. Furthermore, we demonstrate a unique modularity of type III-E effectors by methodically substituting domains between orthogonal type III-E proteins to engineer compact synthetic Cas effectors. We refine our methods to generate several compact effectors for programmable RNA-targeting in mammalian cells. Cas7-S represents a new understanding of type III-E architecture and modularity, and provides a platform for engineering genome engineering technologies from the blueprint of nature.

molecular biology↗

MACROPHAGES COORDINATE IMMUNE RESPONSE TO LASER-INDUCED INJURY VIA EXTRACELLULAR TRAPS

Macrophages/monocytes, the primary contributors to chronic inflammation in degenerated retinas, orchestrate intricate immune responses. They remain enigmatic in their local coordination and activation mechanisms. Innovations in experimental systems enable real-time exploration of immune cell interactions and temporal dimensions in response. In preclinical mouse models, we use in vivo microscopy to unravel how macrophages/monocytes govern microglia and PL responses spatio-temporally. Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. Innate immune cells, when activated, release chromatin and granular proteins, forming extracellular traps (ETs), critical for tissue repair by modulating neutrophil and T-cell responses. Our investigations demonstrate that pharmacological inhibition of ETosis with Cl-amidine enhances retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, Cl-amidine treatment reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to cluster primarily in the superficial capillary plexus, affecting retinal microvasculature perfusion. Our data offer novel insights into innate immunitys role in responding to retinal damage, potentially informing more effective immunotherapeutic strategies for neurodegenerative diseases.

neuroscience↗

Label free autofluorescence imaging permits comprehensive and simultaneous assignment of cell type identity and reveals the existence of airway secretory cell associated antigen passages (SAPs).

The specific functional properties of a tissue are distributed amongst its component cell types. The various cells act coherently, as an ensemble, in order to execute a properly orchestrated physiologic response. Thus, modern approaches to dissect physiologic mechanism would benefit from an ability to identify specific cell types in live tissues and image them in real time. Current techniques require the use of fluorescent genetic reporters that are not only cumbersome, but which only allow the simultaneous study of 2 or 3 cell types. We report a non-invasive imaging modality that capitalizes on the endogenous autofluorescence signatures of the metabolic cofactors NAD(P)H and FAD. By marrying morphological characteristics with autofluorescence signatures, all seven of the airway epithelial cell types can be distinguished simultaneously in real time. Furthermore, we find that this methodology for direct cell type specific identification avoid potential pitfalls with the use of ostensibly cell type-specific markers that can be altered by clinically relevant physiologic stimuli. Finally, we utilize this methodology to interrogate real-time physiology using a clinically relevant model of cholinergic stimulation and identify dynamic secretory cell associated antigen passages (SAPs) that are highly reminiscent of previously reported goblet cell associated antigen passages (GAPs) in the intestine. eLifes Review ProcesseLife works to improve the process of peer review so that it more effectively conveys the assessment of expert reviewers to authors, readers and other interested parties. In the future we envision a system in which research is first published as a preprint and the outputs of peer review are the primary way research is assessed, rather than journal title. Our editorial process produces two outputs: i) an assessment by peers designed to be posted alongside a preprint for the benefit of the readers; i) detailed feedback on the manuscript for the authors, including requests for revisions and suggestions for improvement. Therefore we want to change how we construct and write peer reviews to make themuseful to both authors and readers in a way that better reflects the work you put into reading and thinking about a paper. eLife reviews now have three parts: O_LIAn evaluation summary (in two or three sentences) that captures the major conclusions of the review in a concise manner, accessible to a wide audience. C_LIO_LIA public review that details the strengths and weaknesses of the manuscript before you, and discusses whether the authors claims and conclusions are justified by their data. C_LIO_LIA set of private recommendations for the authors that outline how you think the science and its presentation could be strengthened. C_LI All three sections will be used as the basis for an eLife publishing decision, which will, as always, be made after a consultation among the reviewers and editor. Each of the public reviews will be published (anonymously) alongside the preprint, together with a response from the authors if they choose. In the case of papers we reject after review, the authors can choose to delay posting until their paper has been published elsewhere. If this is your first time going through this new process, we ask that you take some time to read our Reviewer Guide, which discusses how we see each section will be used, what it should contain, and what we hope it accomplishes. And we remind you that, with the shift of reviews from private correspondence to public discourse, it is more important than ever that reviews are written in a clear and constructive manner appropriate for a public audience and mindful of the impact language choices might have on the authors.

cell biology↗

Thymic mesenchymal niche cells drive T cell immune regeneration

Thymic atrophy and the progressive immune decline that accompanies it is a major health problem, chronically with age and acutely with immune injury. No solution has been defined. Here we demonstrate that one of the three mesenchymal cell subsets identified by single-cell analysis of human and mouse thymic stroma is a critical niche component for T lymphopoiesis. The Postn+ subset is located perivascularly in the cortical-medullary junction, medulla and subcapsular regions. Cell depletion demonstrated that it recruits T competent cells to the thymus and initiates T lymphopoiesis in vivo. This subset distinctively expresses the chemokine Ccl19 necessary for niche functions. It markedly declines with age and in the acute setting of hematopoietic stem cell transplant conditioning. When isolated and adoptively transferred, these cells durably engrafted the atrophic thymus, recruited early T progenitors, increased T cell neogenesis, expanded TCR complexity and enhanced T cell response to vaccination. These data define a thymus lymphopoietic niche cell type that may be manipulated therapeutically to regenerate T lymphopoiesis.

immunology↗

Cerebrospinal fluid outflow through skull channels instructs cranial hematopoiesis

Interactions between the immune and central nervous systems strongly influence brain health. Although the blood-brain barrier restricts this crosstalk, we now know that meningeal gateways through brain border tissues, particularly dural lymphatic vessels that allow cerebrospinal fluid outflow, facilitate intersystem communication. Here we observe that cerebrospinal fluid exits into the skull bone marrow. Fluorescent tracers injected into the cisterna magna of mice travel through hundreds of sub-millimeter skull channels into the calvarial marrow. During meningitis, bacteria usurp this perivascular route to infect the skulls hematopoietic niches and initiate cranial hematopoiesis ahead of remote tibial sites. Because skull channels also directly provide leukocytes to meninges, the privileged sampling of brain-derived danger signals in cerebrospinal fluid by regional marrow has broad implications for neurological disorders. One-Sentence SummarySkull channels transport cerebrospinal fluid from the subarachnoid space to the cranial bone marrow via a perivascular route, which bacteria use during meningitis.

immunology↗

Control of osteocyte dendrite formation by Sp7 and its target gene osteocrin

Osteocytes use an elaborate network of dendritic connections to control bone remodeling. Some osteoblasts embed within mineralized bone matrix, change shape, and become osteocytes. The molecular circuitry that drives dendrite formation during "osteocytogenesis" is poorly understood. Here we show that deletion of Sp7, a gene linked to rare and common skeletal disease, in mature osteoblasts and osteocytes causes severe defects in osteocyte dendrites. Unbiased profiling of Sp7 target genes and binding sites reveals unexpected repurposing of this transcription factor to drive dendrite formation. Osteocrin is a Sp7 target gene that promotes osteocyte dendrite formation and rescues phenotypic and molecular defects in Sp7-deficient mice. Single-cell RNA-sequencing demonstrates overt defects in osteocyte maturation in vivo in the absence of Sp7. Sp7-dependent gene networks enriched in developing osteocytes are associated with rare and common human skeletal traits. Moreover, humans homozygous for the osteogenesis imperfecta-causing SP7R316C mutation show dramatic defects in osteocyte morphology. Genes that mark osteocytes in vivo and that are regulated by Sp7 in vitro are highly enriched in neurons, highlighting shared features between osteocytic and neuronal connectivity. Taken together, these findings reveal a crucial role for Sp7 and its target gene Osteocrin in osteocytogenesis, demonstrating that pathways that control osteocyte development influence human bone diseases.

molecular biology↗

In Vivo Monitoring of Rare Circulating Tumor Cell and Cluster Dissemination in a Multiple Myeloma Xenograft Model

We recently developed Diffuse in vivo Flow Cytometry (DiFC), a new pre-clinical research tool for enumerating extremely rare fluorescently-labeled circulating cells directly in vivo. In this paper, we developed a green fluorescent protein (GFP) compatible version of DiFC, and used it to non-invasively monitor the circulating tumor cell (CTC) burden over time in a multiple myeloma disseminated xenograft model. We show that DiFC allowed counting of CTCs at estimated concentrations below 1 cell per mL in peripheral blood with a negligible false alarm rate. DiFC also revealed the presence of CTC clusters in circulation to our knowledge for the first time in this model, and allowed us to calculate their size, kinetics, and frequency of shedding. We anticipate that the unique capabilities of DiFC will have many applications in the study of hematogenous metastasis, and as a powerful complementary methodology to liquid biopsy assays.

bioengineering↗

In Vivo Flow Cytometry of Extremely Rare Circulating Cells

Circulating tumor cells (CTCs) are of great interest in cancer research, but methods for their enumeration remain far from optimal. We developed a new small animal research tool called \"Diffuse in vivo Flow Cytometry\" (DiFC) for detecting extremely rare fluorescently-labeled circulating cells directly in the bloodstream. The technique exploits near-infrared diffuse photons to detect and count cells flowing in large superficial arteries and veins without drawing blood samples. DiFC uses custom-designed, dual fiber optic probes that are placed in contact with the skin surface approximately above a major vascular bundle. In combination with a novel signal processing, algorithm DiFC allows counting of individual cells moving in arterial or venous directions, as well as measurement of their speed and depth. We show that DiFC allows sampling of the entire circulating blood volume of a mouse in under 10 minutes, while maintaining a false alarm rate of 0.014 per minute. Hence, the unique capabilities of DiFC are highly suited to biological applications involving very rare cell types such as the study of hematogenic cancer metastasis.

bioengineering↗