Biology subjects

Wu, W.

Publications and source records attributed to Wu, W..

At least 253 records · Page 14Linked to original sources

bioRxiv2021

MLC Seq: De novo sequencing of full-length tRNA isoforms by mass ladder complementation

tRNAs can exist in distinct isoforms because of different chemical modifications, which confounds attempts to accurately sequence individual tRNA species using next generation sequencing approaches or to quantify different RNA modifications at specific sites on a tRNA strand. Herein, we develop a mass spectrometric (MS) ladder complementation sequencing (MLC-Seq), allowing for direct and simultaneous sequencing of full-length tRNA molecules, including those with low abundance. MLC-seq is achieved by improved instrumentation, and advanced algorithms that identify each tRNA species and related isoforms in an RNA mixture, and assemble full MS ladders from partial ladders with missing ladder components. Using MLC-Seq, we successfully obtained the sequence of tRNA-Phe from yeast and tRNA-Glu from mouse hepatocytes, and simultaneously revealed new tRNA isoforms derived from nucleotide modifications. Importantly, MLC-Seq pinpointed the location and stoichiometry changes of RNA modifications in tRNA-Glu upon the treatment of dealkylated enzyme AlkB, which confirmed its known enzymatic activity and suggested previously unidentified effects in RNA editing.

biochemistry↗

bioRxiv2021

LIN37-DREAM Prevents DNA End Resection and Homologous Recombination at DNA Double Strand Breaks in Quiescent Cells

DNA double strand break (DSB) repair by homologous recombination (HR) is thought to be restricted to the S- and G2- phases of the cell cycle in part due to 53BP1 antagonizing DNA end resection in G1-phase and non-cycling quiescent (G0) cells. Here, we show that LIN37, a component of the DREAM transcriptional repressor, functions in a 53BP1-independent manner to prevent DNA end resection and HR in G0 cells. Loss of LIN37 leads to expression of HR proteins, including BRCA1, BRCA2, PALB2 and RAD51, and DNA end resection in G0 cells even in the presence of 53BP1. In contrast to 53BP1-deficiency, DNA end resection in LIN37-deficient G0 cells depends on BRCA1 and leads to RAD51 filament formation and HR. LIN37 is not required to protect DNA ends in cycling cells at G1-phase. Thus, LIN37 regulates a novel 53BP1-independent cell phase-specific DNA end protection pathway that functions uniquely in quiescent cells.

cell biology↗

bioRxiv2021

Antibody Cocktail Exhibits Broad Neutralization against SARS-CoV-2 and SARS-CoV-2 variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has precipitated multiple variants resistant to therapeutic antibodies. In this study, 12 high-affinity antibodies were generated from convalescent donors in early outbreaks using immune antibody phage display libraries. Of them, two RBD-binding antibodies (F61 and H121) showed high affinity neutralization against SARS-CoV-2, whereas three S2-target antibodies failed to neutralize SARS-CoV-2. Following structure analysis, F61 identified a linear epitope located in residues G446 -S494, which overlapped with angiotensin-converting enzyme 2 (ACE2) binding sites, while H121 recognized a conformational epitope located on the side face of RBD, outside from ACE2 binding domain. Hence the cocktail of the two antibodies achieved better performance of neutralization to SARS-CoV-2. Importantly, F61 and H121 exhibited efficient neutralizing activity against variants B.1.1.7 and B.1.351, those showed immune escape. Efficient neutralization of F61 and H121 against multiple mutations within RBD revealed a broad neutralizing activity against SARS-CoV-2 variants, which mitigated the risk of viral escape. Our findings defined the basis of therapeutic cocktails of F61 and H121 with broad neutralization and delivered a guideline for the current and future vaccine design, therapeutic antibody development, and antigen diagnosis of SARS-CoV-2 and its novel variants.

immunology↗

bioRxiv2021

"Evolution of Nuclear Receptors in Platyhelminths

Since the first complete set of Platyhelminth nuclear receptors (NRs) from Schistosoma mansoni were identified a decade ago, more flatworm genome data is available to identify their NR complement and to analyze the evolutionary relationship of Platyhelminth NRs. NRs are important transcriptional modulators that regulate development, differentiation and reproduction of animals. In this study, NRs are identified in genome databases of thirty-three species including in all Platyhelminth classes (Rhabditophora, Monogenea, Cestoda and Trematoda). Phylogenetic analysis shows that NRs in Platyhelminths follow two different evolutionary lineages: 1) NRs in a free-living freshwater flatworm (Schmidtea mediterranea) and all parasitic flatworms share the same evolutionary lineage with extensive gene loss. 2) NRs in a free-living intertidal zone flatworm (Macrostomum lignano) follow a different evolutionary lineage with a feature of multiple gene duplication and gene divergence. The DNA binding domain (DBD) is the most conserved region in NRs which contains two C4-type zinc finger motifs. A novel zinc finger motif is identified in parasitic flatworm NRs: the second zinc finger of parasitic Platyhelminth HR96b possesses a CHC2 motif which is not found in NRs of all other animals. In this study, novel NRs (members of NR subfamily 3 and 6) are identified in flatworms, this result demonstrates that members of all six classical NR subfamilies are present in the Platyhelminth phylum. NR gene duplication, loss and divergence in Platyhelminths are analyzed along with the evolutionary relationship of Platyhelminth NRs.

evolutionary biology↗

bioRxiv2021

Caspase-dependent cleavage of DDX21 suppresses host innate immunity

DEAD (Glu-Asp-Ala-Glu)-box RNA helicases have been proven to contribute to antiviral innate immunity. DDX21 RNA helicase was identified as a nuclear protein involved in ribosomal RNA processing and RNA unwinding. DDX21 was also proved to be the scaffold protein in the complex of DDX1-DDX21-DHX36 which senses double strand RNA and initiates downstream innate immunity. Here, we identified that DDX21 undergoes caspase-dependent cleavage after virus infection and treatment with RNA/DNA ligands, especially for RNA virus and ligands. Caspase-3/6 cleave DDX21 at D126 and promotes its translocation from the nucleus to the cytoplasm in response to virus infection. The cytoplasmic cleaved DDX21 negatively regulates the IFN-{beta} signaling pathway by suppressing the formation of DDX1-DDX21-DHX36 complex. Thus, our data identify DDX21 as a regulator of immune balance and most importantly uncover a potential role of DDX21 cleavage in the innate immunity response towards virus. ImportanceInnate immunity serves as the first barrier against virus infection. DEAD (Glu-Asp-Ala-Glu)-box RNA helicases, originally considered to be involved RNA processing and RNA unwinding, have been shown to play an important role in anti-viral innate immunity. The precise regulation of innate immunity is critical for the host because the aberrant production of cytokines leads to unexpected pathological consequences. Here, we identified DDX21 was cleaved at D126 by virus infection and treatment with RNA/DNA ligands via the caspase-3/6-dependent pathway. The cytoplasmic cleaved DDX21 negatively regulates the IFN-{beta} signaling pathway by suppressing the formation of DDX1-DDX21-DHX36 complex. In sum, our data identify DDX21 as a regulator of immune balance and most importantly uncover a potential role of DDX21 cleavage in the innate immunity response towards virus.

microbiology↗

bioRxiv2021

Anti-GD2 antibody disrupts GD2:Siglec-7 interactions and synergizes with CD47 blockade to mediate tumor eradication

The disialoganglioside GD2 is consistently overexpressed in neuroblastoma and osteosarcoma, and is variably expressed in other sarcomas, gliomas, neuroendocrine tumors, and epithelial cancers. Anti-GD2 antibodies have improved the survival rates of patients with neuroblastoma only when administered as part of intense chemotherapy-based cytotoxic regimens, which are associated with debilitating late effects including hearing loss, growth retardation, and secondary leukemias. Despite broad expression of GD2 on osteosarcoma, anti-GD2 antibody has not mediated significant antitumor activity in that disease or any other GD2+ cancers. CD47 is a checkpoint molecule overexpressed on tumor cells that inhibits macrophage activity, and CD47 blockade has demonstrated promising clinical activity in early human trials. We investigated whether anti-CD47 antibody could enhance the efficacy of anti-GD2 antibody in neuroblastoma and other GD2+ malignancies. We demonstrate substantial synergy of these two agents, resulting in the recruitment of tumor associated macrophages (TAMs) to mediate robust and durable anti-tumor responses. The responses are driven by GD2-specific factors that reorient the balance of macrophage activity towards phagocytosis of tumor cells, including disruption of a newly described GD2:Siglec-7 axis. These results demonstrate the unique synergy of combining anti-GD2 with anti-CD47, which has the potential to significantly enhance outcomes for children with neuroblastoma and osteosarcoma and will soon be investigated in a first-in-human clinical trial.

immunology↗

bioRxiv2021

Case study of a rhizosphere microbiome assay on a bamboo rhizome with excessive shoots

Young Moso bamboo shoots are a very popular seasonal food. Bamboo is an important source of income for farmers and the value for cultivation has recently been estimated to $30,000 per hectare. A rare and valuable phenomenon has recently appeared where dozens of adjacent buds within a single Moso bamboo rhizome have grown into shoots. Due to its rarity, this phenomenon, which is of practical importance for the production of edible shoots, has not been scientifically studied. We report the occurrence of a rhizome with 18 shoots, of which the microbiome were analyzed, using rhizomes having one or no shoots as controls. The community of prokaryotes, but not fungi, correlated with the shoot numbers. Burkholderia was the most abundant genus, which negatively correlated with rhizome shoot number, while Clostridia and Ktedonobacteria positively correlated with many shoots. Two Burkholderia strains were isolated and their plant-growth promoting activity was tested. The isolated Burkholderia strains attenuated the growth of bamboo seedlings. Analysis of collected events of enhanced shoot production in China showed no evidence that enhanced shoot development was heritable. Overall, our data provides a firsthand study on excessive shoot development of bamboo.

plant biology↗

bioRxiv2021

Comparative genome analysis revealed gene inversions, boundary expansion and contraction, and gene loss in Stemona sessilifolia (Miq.) Miq. chloroplast genome

Stemona sessilifolia (Miq.) Miq., commonly known as Baibu, is one of the most popular herbal medicines in Asia. In Chinese Pharmacopoeia, Baibu has multiple authentic sources, and there are many homonym herbs sold as Baibu in the herbal medicine market. The existence of the counterfeits of Baibu brings challenges to its identification. To assist the accurate identification of Baibu, we sequenced and analyzed the complete chloroplast genome of Stemona sessilifolia using next-generation sequencing technology. The genome was 154,039 bp in length, possessing a typical quadripartite structure consisting of a pair of inverted repeats (IRs: 27,094 bp) separating by a large single copy (LSC: 81,950 bp) and a small single copy (SSC: 17,901 bp). A total of 112 unique genes were identified, including 80 protein-coding, 28 transfer RNA, and four ribosomal RNA genes. Besides, 45 tandem, 27 forward, 23 palindromic, and 72 simple sequence repeats were detected in the genome by repeat analysis. Compared with its counterfeits (Asparagus officinalis and Carludovica palmate), we found that IR expansion and SSC contraction events of Stemona sessilifolia resulted in two copies of the rpl22 gene in the IR regions and partial duplication of the ndhF gene in the SSC region. Secondly, an approximately 3-kb-long inversion was identified in the LSC region, leading to the petA and cemA gene presented in the complementary strand of the chloroplast DNA molecule. Comparative analysis revealed some highly variable regions, including trnF-GAA_ndhJ, atpB_rbcL, rps15_ycf1, trnG-UCC_trnR-UCU, ndhF_rpl32. Finally, gene loss events were investigated in the context of phylogenetic relationships. In summary, the complete plastome of Stemona sessilifolia will provide valuable information for the molecular identification of Baibu and assist in elucidating the evolution of Stemona sessilifolia.

genomics↗

bioRxiv2021

Targeted RNA-seq improves efficiency, resolution, and accuracy of allele specific expression for human term placentas

Genomic imprinting is an epigenetic mechanism that results in allele specific expression (ASE) based on parent of origin. It is known to play a role in the prenatal and postnatal allocation of maternal resources in mammals. ASE detected by whole transcriptome RNA-seq (wht-RNAseq) has been widely used to analyze imprinted genes using reciprocal crosses in mice to generate large numbers of informative SNPs. Studies in humans are more challenging due to the paucity of SNPs and the poor preservation of RNA in term placentas and other tissues. Targeted RNA-seq (tar-RNAseq) can potentially mitigate these challenges by focusing sequencing resources on the regions of interest in the transcriptome. Here we compared tar-RNAseq and wht-RNAseq in a study of ASE in known imprinted genes in placental tissue collected from a healthy human cohort in Mali, West Africa. As expected, tar-RNAseq substantially improved the coverage of SNPs. Compared to wht-RNAseq, tar-RNAseq produced on average four times more SNPs in twice as many genes per sample and read depth at the SNPs increased 4-fold. In previous research on humans, discordant ASE values for SNPs of the same gene have limited the ability to accurately quantify ASE. We show that tar-RNAseq reduces this limitation as it unexpectedly increased the concordance of ASE between SNPs of the same gene, even in cases of degraded RNA. Studies aimed at discovering associations between individual variation in ASE and phenotypes in mammals and flowering plants will benefit from the improved power and accuracy of tar-RNAseq.

genomics↗

bioRxiv2021

Distinct mutations and lineages of SARS-CoV-2 virus in the early phase of COVID-19 global pandemic and subsequent global expansion

A novel coronavirus, SARS-CoV-2, has caused over 190 million cases and over 4 million deaths worldwide since it occurred in December 2019 in Wuhan, China. Here we conceptualized the temporospatial evolutionary and expansion dynamics of SARS-CoV-2 by taking a series of cross-sectional view of viral genomes from early outbreak in January 2020 in Wuhan to early phase of global ignition in early April, and finally to the subsequent global expansion by late December 2020. Based on the phylogenetic analysis of the early patients in Wuhan, Wuhan/WH04/2020 is supposed to be a more appropriate reference genome of SARS-CoV-2, instead of the first sequenced genome Wuhan-Hu-1. By scrutinizing the cases from the very early outbreak, we found a viral genotype from the Seafood Market in Wuhan featured with two concurrent mutations (i.e. M type) had become the overwhelmingly dominant genotype (95.3%) of the pandemic one year later. By analyzing 4,013 SARS-CoV-2 genomes from different continents by early April, we were able to interrogate the viral genomic composition dynamics of initial phase of global ignition over a timespan of 14-week. 11 major viral genotypes with unique geographic distributions were also identified. WE1 type, a descendant of M and predominantly witnessed in western Europe, consisted a half of all the cases (50.2%) at the time. The mutations of major genotypes at the same hierarchical level were mutually exclusive, which implying that various genotypes bearing the specific mutations were propagated during human-to-human transmission, not by accumulating hot-spot mutations during the replication of individual viral genomes. As the pandemic was unfolding, we also used the same approach to analyze 261,323 SARS-CoV-2 genomes from the world since the outbreak in Wuhan (i.e. including all the publicly available viral genomes) in order to recapitulate our findings over one-year timespan. By 25 December 2020, 95.3% of global cases were M type and 93.0% of M-type cases were WE1. In fact, at present all the four variants of concern (VOC) are the descendants of WE1 type. This study demonstrates the viral genotypes can be utilized as molecular barcodes in combination with epidemiologic data to monitor the spreading routes of the pandemic and evaluate the effectiveness of control measures. Moreover, the dynamics of viral mutational spectrum in the study may help the early identification of new strains in patients to reduce further spread of infection, guide the development of molecular diagnosis and vaccines against COVID-19, and help assess their accuracy and efficacy in real world at real time.

genomics↗

bioRxiv2020

A high-quality genome of the mangrove Aegiceras corniculatum aids investigation of molecular adaptation to intertidal environments

Mangroves have colonized extreme intertidal environments characterized by high salinity, hypoxia, and other abiotic stresses. During millions of years of evolution, mangroves have adapted to these habitats, evolving a series of highly specialized traits. Aegiceras corniculatum, a pioneer mangrove species that evolved salt secretion and crypto-vivipary, is an attractive ecological model to investigate molecular mechanisms underlying adaptation to intertidal environments. Here we report a high-quality reference genome of A. corniculatum using the PacBio SMRT sequencing technology, comprising 827 Megabases (Mb) and containing 32,092 protein-coding genes. The longest scaffold and N50 for the assembled genome are 13.76 Mb and 3.87 Mb. Comparative and evolutionary analyses revealed that A. corniculatum experienced a whole-genome duplication (WGD) event around 35 million years ago after the divergence between Aegiceras and Primula. We inferred that maintenance of cellular environmental homeostasis is an important adaptive process in A. corniculatum. The 14-3-3 protein-coding genes were retained after the recent WGD event, decoding a calcium signal to regulate Na+ homeostasis. A. corniculatum has more H+-ATPase coding genes, essential for the maintenance of low Na+ concentration in the cells, than its relatives. Photosynthesis and oxidative-phosphorylation pathways are overrepresented among significantly expanded gene families and might supply the energy needed for salt secretion. Genes involved in natural antioxidant biosynthesis, contributing to scavenging reactive oxygen species against high salinity, have also increased in copy number. We also found that all homologs of DELAY OF GERMINATION1 (DOG1), a pivotal regulator of seed dormancy, lost their heme-binding ability in A. corniculatum. This loss may contribute to crypto-vivipary. Our study provides a valuable resource to investigate molecular adaptation to extreme environments in mangroves.

genomics↗

bioRxiv2020

Single point mutations can potentially enhance infectivity of SARS-CoV-2 revealed by in silico affinity maturation and SPR assay

The RBD (receptor binding domain) of the SARS-CoV-2 virus S (spike) protein mediates the viral cell attachment and serves as a promising target for therapeutics development. Mutations on the S-RBD may alter its affinity to cell receptor and affect the potency of vaccines and antibodies. Here we used an in-silico approach to predict how mutations on RBD affect its binding affinity to hACE2 (human angiotensin-converting enzyme2). The effect of all single point mutations on the interface was predicted. SPR assay result shows that 6 out of 9 selected mutations can strengthen binding affinity. Our prediction has reasonable agreement with the previous deep mutational scan results and recently reported mutants. Our work demonstrated in silico method as a powerful tool to forecast more powerful virus mutants, which will significantly benefit for the development of broadly neutralizing vaccine and antibody.

bioinformatics↗

bioRxiv2020

CTCF is a Barrier for Totipotent-like Reprogramming

Totipotent cells have the ability of generating embryonic and extra-embryonic tissues1,2. Interestingly, a rare population of cells with totipotent-like potential was identified within ESC cultures3. These cells, known as 2 cell (2C)-like cells, arise from ESC and display similar features to those found in the totipotent 2 cell embryo2-4. However, the molecular determinants of 2C-like conversion have not been completely elucidated. Here, we show that CTCF is a barrier for 2C-like reprogramming. Indeed, forced conversion to a 2C-like state by DUX expression was associated with DNA damage at a subset of CTCF binding sites. Endogenous or DUX-induced 2C-like ESC showed decreased CTCF enrichment at known binding sites, suggesting that acquisition of a totipotent-like state is associated with a highly dynamic chromatin architecture. Accordingly, depletion of CTCF in ESC efficiently promoted spontaneous and asynchronous conversion to a totipotent-like state. This phenotypic reprogramming was reversible upon restoration of CTCF levels. Furthermore, we showed that transcriptional activation of the ZSCAN4 cluster was necessary for successful 2C-like reprogramming. In summary, we revealed the intimate relation between CTCF and totipotent-like reprogramming.

developmental biology↗

bioRxiv2020

High-resolution Cell Atlas of Pig Lung and Online Platform Exploring for Lung Single Cell

Due to the comparable organ sizes and physiology to human beings, genetically engineered pig is gradually regarded as an optimal source of human for transplantation and an excellent model for human diseases research. The major barrier between pig and human is mainly cellular heterogeneity and immune incompatibilities. Myriad scRNA-seq data of human has been reported, but the counterpart in pig is scarce. Here, we applied scRNA-seq technology to study the cellular heterogeneity of 3 months old pig lungs, generating the single-cell atlas of 13,580 cells covering 16 major cell types. Based on this data, we systematically characterized transcription factor regulatory networks, cell-cell communications in each cell type, and comparison of them and those in human lung. We first presented a comprehensive and openly accessible online platform, ScdbLung, which was composed of three functional modules (Marker, Cluster, and Download) and dedicated to exploiting the valuable resources of lung scRNA-seq data across four mammalian species. Overall, our scRNA-seq atlas of domestic pig lung, conserved transcription factor regulatory networks and cell-cell communications between domestic pig and human, and ScdbLung could provide guidance for porcine lung research and clinical applicability.

cell biology↗

bioRxiv2020

Targeted cancer therapy induces APOBEC fuelling the evolution of drug resistance

Introductory paragraphThe clinical success of targeted cancer therapy is limited by drug resistance that renders cancers lethal in patients1-4. Human tumours can evolve therapy resistance by acquiring de novo genetic alterations and increased heterogeneity via mechanisms that remain incompletely understood1. Here, through parallel analysis of human clinical samples, tumour xenograft and cell line models and murine model systems, we uncover an unanticipated mechanism of therapy-induced adaptation that fuels the evolution of drug resistance. Targeted therapy directed against EGFR and ALK oncoproteins in lung cancer induced adaptations favoring apolipoprotein B mRNA-editing enzyme, catalytic polypeptide (APOBEC)-mediated genome mutagenesis. In human oncogenic EGFR-driven and ALK-driven lung cancers and preclinical models, EGFR or ALK inhibitor treatment induced the expression and DNA mutagenic activity of APOBEC3B via therapy-mediated activation of NF-{kappa}B signaling. Moreover, targeted therapy also mediated downregulation of certain DNA repair enzymes such as UNG2, which normally counteracts APOBEC-catalyzed DNA deamination events. In mutant EGFR-driven lung cancer mouse models, APOBEC3B was detrimental to tumour initiation and yet advantageous to tumour progression during EGFR targeted therapy, consistent with TRACERx data demonstrating subclonal enrichment of APOBEC-mediated mutagenesis. This study reveals how cancers adapt and drive genetic diversity in response to targeted therapy and identifies APOBEC deaminases as future targets for eliciting more durable clinical benefit to targeted cancer therapy.

cancer biology↗

bioRxiv2020

Neuronal Enhancers are Hotspots For DNA Single-Strand Break Repair

Genome stability is essential for all cell types. However, defects in DNA repair frequently lead to neurodevelopmental and neurodegenerative diseases, underscoring the particular importance of DNA repair in long-lived post-mitotic neurons. The neuronal genome is subjected to a constant barrage of endogenous DNA damage due to high levels of oxidative metabolism in the central nervous system. Surprisingly, we know little about the identity of the lesion(s) that accumulate in neurons and whether they accrue throughout the genome or at specific loci. Here, we show that neurons, but not other post-mitotic cells, accumulate unexpectedly high numbers of DNA single-strand breaks (SSBs) at specific sites within the genome. These recurrent SSBs are found within enhancers, and trigger DNA repair through recruitment and activation of poly(ADP-ribose) polymerase-1 (PARP1) and XRCC1, the central SSB repair scaffold protein. Notably, deficiencies in PARP1, XRCC1, or DNA polymerase {beta} elevate the localized incorporation of nucleotides, suggesting that the ongoing DNA synthesis at neuronal enhancers involves both short-patch and long-patch SSB repair processes. These data reveal unexpected levels of localized and continuous DNA single-strand breakage in neurons, suggesting an explanation for the neurodegenerative phenotypes that occur in patients with defective SSB repair.

neuroscience↗

bioRxiv2020

Phenotypic plasticity of ER+ breast cancer in the bone microenvironment

ER+ breast cancer exhibits a strong bone-tropism in metastasis. How the bone microenvironment impacts the ER signaling and endocrine therapies remains poorly understood. Here, we discover that the osteogenic niche transiently reduces ER expression and activities specifically in bone micrometastases (BMMs), leading to endocrine resistance. This is mediated by gap junctions and paracrine FGF/PDGF signaling, which together generate a stable "memory": cancer cells extracted from bone remain resistant to endocrine therapies for several generations. Using single cell-derived populations (SCPs), we demonstrated that this process is independent of clonal selection, and represents an EZH2-mediated epigenomic reprogramming. EZH2 drives ER+ BMMs toward a basal and stem-like state. EZH2 inhibition reverses endocrine resistance. Our data demonstrates how epigenomic adaptation to the bone microenvironment drives phenotypic plasticity of metastatic seeds and alters their therapeutic responses together with clonal selection, and provides insights into the clinical enigma of ER+ metastatic recurrences despite endocrine therapies.

cancer biology↗

bioRxiv2020

DIffusion-Prepared Phase Imaging (DIPPI): quantifying myelin in crossing fibres

PurposeMyelin has long been the target of neuroimaging research due to its importance in brain development, plasticity, and disease. However, most available techniques can only provide a voxel-averaged estimate of myelin content. In the human brain, white matter fibre pathways connecting different brain areas and carrying different functions often cross each other in the same voxel. A measure that can differentiate the degree of myelination of crossing fibres would provide a more specific marker of myelination. Theory & MethodsOne MRI signal property sensitive to myelin is the phase accumulation, which to date has also been limited to voxel-averaged myelin estimates. We use this sensitivity by measuring the phase accumulation of the signal remaining after diffusion weighting, which we call DIffusion-Prepared Phase Imaging (DIPPI). Including diffusion weighting before estimating the phase accumulation has two distinct advantages for estimating the degree of myelination: (1) it increases the relative contribution of intra-axonal water, whose phase is related linearly to the amount of myelin surrounding the axon (in particular the log g-ratio) and (2) it gives directional information, which can be used to distinguish between crossing fibres. ResultsUsing simulations and phantom data we argue that other sources of phase accumulation (i.e., movement-induced phase shift during the diffusion gradients, eddy currents, and other sources of susceptibility) can be either corrected for or are sufficiently small to still allow the g-ratio to be reliably estimated. ConclusionsThis new sequence is capable of providing a g-ratio estimate per fibre population crossing within a voxel.

neuroscience↗