Biology subjects

Larson, G.

Publications and source records attributed to Larson, G..

At least 19 recordsLinked to original sources

bioRxiv2026

Extensive nuclear introgression accompanied ancient mitochondrial capture in the common ancestor of two sister hare species

Pleistocene climatic oscillations promoted contact and hybridization among hare species, leaving lasting genomic signatures. Two sister species, L. castroviejoi (broom hare, endemic to Iberia) and L. corsicanus (Italian hare, endemic to Italy), carry fixed mitogenomes from L. timidus (mountain hare), an Arctic species widespread in southern Europe before deglaciation. Whether such turnover was accompanied by nuclear introgression, and how it affects their genomes today, remains unclear. Here, we date the ancient mitochondrial replacement in the broom-Italian hare ancestor using whole mitogenomes incorporating Iron Age samples. Coalescent modelling of complete genomes infers a substantial mountain hare contribution (24%) to this ancestor ~900 Kya (~5N generations). Accordingly, phylogenetic segmentation identified genomic segments consistent with mountain-to-broom/Italian hare introgression, covering ~17.8% of the autosomes, close to ~18% expected under drift, given admixture's timing and magnitude. Genome polarisation corroborates this estimate, with 25-28% of the mountain hare genome polarising with broom and Italian hares rather than its sister Iberian hare, decreasing to 15-18% at diagnostic sites. The introgression segments concentrate fixed-introgression sites and show sharp transitions of ancestry at their borders. Highly introgressed regions are gene-dense, and regions of reduced introgression are repeat-rich, suggesting that recombination shapes the introgression landscape. They also harbour genes with mitochondrial function that mirror candidates linked to mito-nuclear coadaptation in the Iberian hare, hinting that mitonuclear interactions may influence which variants persist. Our study illustrates how combining demographic, phylogenomic and polarisation-based methods can quantify and localize extensive nuclear introgression, even in the absence of non-introgressed reference populations.

evolutionary biology↗

bioRxiv2025

An atlas of cell type specific regulatory effects in cattle

Understanding the genetic and molecular architecture of complex traits and artificial selection is crucial for advancing sustainable precision breeding in cattle and other livestock. Yet, how genetic variation affects cellular gene expression remains elusive in cattle. Here, by integrating 8,866 bulk RNA-seq samples and 999,192 single cells of 81 cell types in 22 bovine tissues, we presented a comprehensive atlas of regulatory variants at the cell type resolution in cattle. By colocalizing with bulk-tissue expression quantitative trait loci (beQTL), we detected 57,043 novel cell-type stratified eQTL and cell-type/state interaction eQTL in 18,153 genes, which also exhibited a stronger tissue/cell-type specificity than beQTL. By examining genome-wide associations (GWAS) of 44 complex traits, these cell-resolved eQTL were colocalized with 505 (24%) additional GWAS loci compared to beQTL. Through integrating this resource with selection signatures between dairy and beef cattle, we provided tissue/cell-specific regulatory insights into cattle breeding. Overall, the current atlas of cell-type-specific regulatory variants will serve as an invaluable resource for cattle genomics and selective breeding.

genetics↗

bioRxiv2025

Rational design of tertiary coordination sphere of a heme-based sensor for two-orders enhanced oxygen affinity

Biological O2 sensing is crucial for diverse physiological functions across all forms of life. Heme-containing proteins achieve this by binding O2 to their iron center and have been found to display O2 affinities spanning several orders of magnitude. Despite decades of investigation into the structure and function of heme-based O2 sensors, the molecular mechanisms that enable the tuning of O2 affinity to match specific physiological roles remain unclear. Here, we utilize the O2 sensing mycobacterial DosS protein as a model system to explore the role of heme irons tertiary coordination sphere in controlling its O2 affinity. By rationally and systematically modifying the tertiary coordination sphere to promote the formation of a Trp-Tyr-Asn H-bond triad within the hemes distal pocket, we have enhanced the O2 affinity of WT DosS by over 150-fold. The rationally designed DosS exhibited a Kd value of 3 {+/-} 1 nM, compared to 460 {+/-} 80 nM for WT DosS. Employing a combination of structural, biochemical, spectroscopic, and computational studies, our analysis of WT and designed DosS variants highlights how the interplay between distal H-bond networks and heme-pocket electrostatics drives large differences in their O2 sensing capabilities. Ultimately, our work shows how metalloenzymes can dramatically alter their sensitivity to diatomic signaling molecules by tuning the tertiary coordination sphere, broadly impacting how we understand related biological sensing and signaling.

biochemistry↗

bioRxiv2025

Immunoblot-based activity assay for heme-containing histidine kinases

Histidine kinases (HKs) are essential bacterial signal transduction proteins and attractive drug targets due to their critical cellular functions. Direct measurement of their autophosphorylation activity is crucial for developing inhibitors and advancing disease treatments. While [{gamma}-32P]-ATP radiolabeling has long been a conventional method for kinase activity measurements, its reliance on 32P introduces inherent limitations. The isotopes short half-life imposes time-sensitive constraints on experiments, and stringent radiation safety and compliance requirements significantly increase operational costs and hinder scalability. Several alternative methods, including fluorescent phosphate-binding probes and fluorescence- or luminescence-based antibodies, have been developed for HKs that overcome these challenges. However, for heme-based HKs, these alternatives suffer from interference due to intrinsic heme fluorescence and luminescence. In this work, we address this interference by employing a near-IR fluorophore-labeled secondary antibody. Combined with an ATP{gamma}S immunoblot-based method, we demonstrate semi-quantitative detection of thiophosphorylation activities of Mycobacterium tuberculosis DosS (a prototypical heme-based HK) in different ligation states. Consistent with previous radiolabeling studies, we show DosSs ability for auto-thiophosphorylation is significantly enhanced with CO as compared to O2. This low-cost, easy-to-implement method simplifies and democratizes heme-based HK activity measurement.

biochemistry↗

bioRxiv2025

Functional Diversity in GII.4 Norovirus Entry: HBGA Binding and Capsid Clustering Dynamics

Human noroviruses (HuNoVs), especially GII.4 strains, are the leading cause of acute viral gastroenteritis worldwide, yet no approved vaccines or antivirals exist. The pandemic GII.4 Sydney 2012 strain enters cells via membrane wounding and clathrin-independent carrier (CLIC)-mediated endocytosis, but it is unclear whether this entry mechanism is conserved across GII.4 variants. We compared early binding and entry of multiple GII.4 variants using wildtype and mutant GII.4 virus-like particles (VLPs) and modified human intestinal enteroid (HIE) cultures. Only a subset of GII.4 variants, including GII.4 Sydney, form distinct, HBGA-dependent capsid clusters on the cell surface. Clustering strains display significantly enhanced membrane wounding and endocytosis compared to non-clustering strains and outcompete non-clustering strains in replication assays as shown by complete inhibition of GII.4 Sydney replication. Using mutant VLPs and a HBGA non-binding mutant (R345A), we identified two residues, V333 and R339, in the VP1 protruding domain as critical mediators of clustering and entry. Mutations of these residues disrupt clustering and endocytosis without affecting HBGA binding, suggesting a role in post-attachment processes. While clustering and endocytosis are contingent upon VLP binding to HBGAs, inhibitor studies show they are independent of host protein glycosylation and are driven by lipid raft remodeling regulated by cholesterol and ceramides. Quantitative analyses across multiple GII.4 variants reveal an apparent dichotomy between clustering and non-clustering phenotypes, with clustering variants exhibiting higher entry competence. This distinction offers insight into strain-specific cell entry mechanisms and may aid in identifying the elusive proteinaceous HuNoV cellular receptor(s) supporting targeted therapeutic development.

microbiology↗

bioRxiv2025

On the ancestry and evolution of the extinct dire wolf

Dire wolves (Aenocyon dirus) are extinct predators of Pleistocene North America. Although phenotypically similar to living wolves (Canis lupus), dire wolves have yet to be placed confidently in the canid family tree. We generated 3.4x and 12.8x paleogenomes from two well-preserved dire wolves dating to > 13,000 and > 72,000 years ago, and estimated consensus species trees for these and 10 canid species. Our results revealed that [~]2/3 of dire wolf ancestry is derived from a lineage sister to the clade comprising the gray wolf, coyote, and dhole, and the remaining [~]1/3 from a lineage near the base of Canini diversity. We identified 80 genes evolving under diversifying selection in dire wolves. Our results underscore the power of paleogenomes to resolve long-standing taxonomic questions and contribute to growing evidence of the role of post-speciation gene flow as an evolutionary force.

evolutionary biology↗

bioRxiv2025

Leopard Cats Occupied Human Settlements in China for 3,500 years before the Arrival of Domestic cats in 600-900 CE around the Tang Dynasty

The earliest cats in human settlements in China were not domestic cats (Felis catus), but native leopard cats (Prionailurus bengalensis). To trace when and how domestic cats arrived in East Asia, we analyzed 22 feline bones from 14 sites across China spanning 5,000 years. Nuclear and mitochondrial genomes revealed that leopard cats began occupying anthropogenic scenes around 5,400 years ago and last appeared in 150 CE. Following several centuries gap of archeological feline remains, the first known domestic cat (706-883 CE) in China was identified in Shaanxi during the Tang Dynasty. Genomic analysis suggested a white or partially white coat and a link to a contemporaneous domestic cat from Kazakhstan, indicating a likely dispersal route via the Silk Road. The two felids once independently occupied ancient anthropogenic environments in China but followed divergent paths and reached different destinations in human-animal interactions.

evolutionary biology↗

bioRxiv2024

The importance of small island populations for the long term survival of endangered large-bodied insular mammals

Island populations of large vertebrates have experienced higher extinction rates than mainland populations over long timescales due to demographic stochasticity, genetic drift and inbreeding. Conversely, small island populations often experience relatively less anthropogenic habitat degradation than populations on larger islands, making them potential targets for conservation interventions such as genetic rescue to improve their overall genetic diversity. Here we determine the consequences and conservation implications of long-term isolation and recent human activities on genetic diversity of island populations of two forest-dependent mammals endemic to the Wallacea archipelago: the anoa (Bubalus spp.) and babirusa (Babyrousa spp.). Using genomic analyses and habitat suitability models, we show that, compared to closely related species, populations on mainland Sulawesi exhibit low heterozygosity, high inbreeding, and a high proportion of deleterious alleles. In contrast, populations on smaller islands possess fewer deleterious mutations despite exhibiting lower heterozygosity and higher inbreeding. Site frequency spectra indicate that these patterns reflect stronger, long-term purging in smaller island populations. Our results thus suggest that conservation efforts should focus on protecting small island habitats and avoiding translocations from mainland populations. This study highlights the crucial role of small offshore islands for the long-term survival of Wallaceas iconic and indigenous mammals in the face of development on the mainland. Significance statementWithin tropical archipelagos, such as the Wallacea biodiversity hotspot, larger islands experience greater resource exploitation compared to smaller ones, highlighting the potential of smaller islands as refuges for conservation. To investigate the genetic health of populations on small islands, we used genomic, occurrence, and environmental data from a system of replicated populations of anoa and babirusa across islands of varying sizes. In contrast to larger islands like Sulawesi, our results demonstrate that smaller offshore islands not only provide higher-quality habitats but also support populations that have efficiently purged harmful mutations. Thus, despite their known vulnerability over geological time-frames, small island populations can provide long term insurance against human-driven extinction and conservation efforts should prioritise habitat management over translocations.

evolutionary biology↗

bioRxiv2024

Imputation of ancient canid genomes reveals inbreeding history over the past 10,000 years

The multi-millenia long history between dogs and humans has placed them at the forefront of archeological and genomic research. Despite ongoing efforts including the analysis of ancient dog and wolf genomes, many questions remain regarding their geographic and temporal origins, and the microevolutionary processes that led to the diversity of breeds today. Although ancient genomes provide valuable information, their use is hindered by low depth of coverage and post-mortem damage, which inhibits confident genotype calling. In the present study, we assess how genotype imputation of ancient dog and wolf genomes, utilising a large reference panel, can improve the resolution provided by ancient datasets. Imputation accuracy was evaluated by down-sampling high coverage dog and wolf genomes to 0.05-2x coverage and comparing concordance between imputed and high coverage genotypes. We measured the impact of imputation on principal component analyses and runs of homozygosity. Our findings show high (R2>0.9) imputation accuracy for dogs with coverage as low as 0.5x and for wolves as low as 1.0x. We then imputed a dataset of 90 ancient dog and wolf genomes, to assess changes in inbreeding during the last 10,000 years of dog evolution. Ancient dog and wolf populations generally exhibited lower inbreeding levels than present-day individuals. Interestingly, regions with low ROH density maintained across ancient and present-day samples were significantly associated with genes related to olfaction and immune response. Our study indicates that imputing ancient canine genomes is a viable strategy that allows for the use of analytical methods previously limited to high-quality genetic data.

evolutionary biology↗

bioRxiv2023

Unraveling the Global Proteome and Phosphoproteome of Prostate Cancer Patient-Derived Xenografts

Resistance to androgen deprivation therapies leads to metastatic castration-resistant prostate cancer (mCRPC) of adenocarcinoma (AdCa) origin that can transform to emergent aggressive variant prostate cancer (AVPC) which has neuroendocrine (NE)-like features. To this end, we used LuCaP patient-derived xenograft (PDX) tumors, clinically relevant models that reflects and retains key features of the tumor from advanced prostate cancer patients. Here we performed proteome and phosphoproteome characterization of 48 LuCaP PDX tumors and identified over 94,000 peptides and 9,700 phosphopeptides corresponding to 7,738 proteins. When we compared 15 NE versus 33 AdCa PDX samples, we identified 309 unique proteins and 476 unique phosphopeptides that were significantly altered and corresponded to proteins that are known to distinguish these two phenotypes. Assessment of protein and RNA concordance from these tumors revealed increased dissonance in transcriptionally regulated proteins in NE and metabolite interconversion enzymes in AdCa.

cancer biology↗

bioRxiv2023

The ChickenGTEx pilot analysis: a reference of regulatory variants across 28 chicken tissues

Chicken is a valuable model for understanding fundamental biology, vertebrate evolution and diseases, as well as a major source of nutrient-dense and lean-protein-enriched food globally. Although it is the first non-mammalian amniote genome to be sequenced, the chicken genome still lacks a systematic characterization of functional impacts of genetic variants. Here, through integrating 7,015 RNA-Seq and 2,869 whole-genome sequence data, the Chicken Genotype- Tissue Expression (ChickenGTEx) project presents the pilot reference of regulatory variants in 28 chicken tissue transcriptomes, including millions of regulatory effects on primary expression (including protein-coding genes, lncRNA and exon) and post-transcriptional modifications (alternative splicing and 3 untranslated region alternative polyadenylation). We explored the tissue-sharing and context-specificity of these regulatory variants, their underlying molecular mechanisms of action, and their utility in interpreting adaptation and genome-wide associations of 108 chicken complex traits. Finally, we illustrated shared and lineage-specific features of gene regulation between chickens and mammals, and demonstrated how the ChickenGTEx resource can further assist with translating genetic findings across species. One-Sentence SummaryThe ChickenGTEx provides a multi-tissue reference of regulatory variants for chicken genetics and genomics, functional genomics, precision breeding, veterinary medicine, vertebrate evolution and even human biomedicine.

genetics↗

bioRxiv2023

Understanding ATP binding to DosS catalytic domain with a short ATP-lid

DosS is a heme-sensor histidine kinase that responds to redox-active stimuli in mycobacterial environments by triggering dormancy transformation. Sequence comparison of the catalytic ATP-binding (CA) domain of DosS to other well-studied histidine kinases suggests that it possesses a rather short ATP-lid. This feature has been thought to inhibit DosS kinase activity by blocking ATP binding in the absence of interdomain interactions with the dimerization and histidine phospho-transfer (DHp) domain of full-length DosS. Here, we use a combination of computational modeling, structural biology, and biophysical studies to re-examine ATP-binding modalities in DosSs CA domain. We show that the closed lid conformation observed in protein crystal structures of DosS CA is caused by the presence of a zinc cation in the ATP binding pocket that coordinates with a glutamate residue on the ATP-lid. Furthermore, circular dichroism (CD) studies and comparisons of DosS CA crystal structure with its AlphaFold model and homologous DesK reveal that a key N-box alpha-helix turn of the ATP pocket manifests as a random coil in the zinc-coordinated protein crystal structure. We note that this closed lid conformation and the random-coil transformation of an N-box alpha-helix turn are artifacts arising from the millimolar zinc concentration used in DosS CA crystallization conditions. In contrast, in the absence of zinc, we find that the short ATP-lid of DosS CA has significant conformational flexibility and can bind ATP (Kd = 53 {+/-} 13 M). We conclude that DosS CA is almost always bound to ATP under physiological conditions (1-5 mM ATP, sub-nanomolar free zinc) in the bacterial environment. Our findings elucidate the conformational adaptability of the short ATP-lid, its relevance to ATP binding in DosS CA and provide insights that extends to 2988 homologous bacterial proteins containing such ATP-lids.

biochemistry↗

bioRxiv2021

Differential neutralization and inhibition of SARS-CoV-2 variants by antibodies elicited by COVID-19 mRNA vaccines

IntroductoryThe evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in the emergence of many new variant lineages that have exacerbated the COVID-19 pandemic. Some of those variants were designated as variants of concern/interest (VOC/VOI) by national or international authorities based on many factors including their potential impact on vaccines. To ascertain and rank the risk of VOCs and VOIs, we analyzed their ability to escape from vaccine-induced antibodies. The variants showed differential reductions in neutralization and replication titers by post-vaccination sera. Although the Omicron variant showed the most escape from neutralization, sera collected after a third dose of vaccine (booster sera) retained moderate neutralizing activity against that variant. Therefore, vaccination remains the most effective strategy to combat the COVID-19 pandemic.

microbiology↗

bioRxiv2021

SARS-CoV-2 susceptibility of cell lines and substrates commonly used in diagnosis and isolation of influenza and other viruses

Coinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other viruses is inevitable as the COVID-19 pandemic continues. This study aimed to evaluate cell lines commonly used in virus diagnosis and isolation for their susceptibility to SARS-CoV-2. While multiple kidney cell lines from monkeys were susceptible and permissive to SARS-CoV-2, many cell types derived from human, dog, mink, cat, mouse, or chicken were not. Analysis of MDCK cells, which are most commonly used for surveillance and study of influenza viruses, demonstrated that they were insusceptible to SARS-CoV-2 and that the cellular barrier to productive infection was due to low expression level of the angiotensin converting enzyme 2 (ACE2) receptor and lower receptor affinity to SARS-CoV-2 spike, which could be overcome by over-expression of canine ACE2 in trans. Moreover, SARS-CoV-2 cell tropism did not appear to be affected by a D614G mutation in the spike protein.

microbiology↗

bioRxiv2021

Extracellular endosulfatase Sulf-2 harbours a chondroitin/dermatan sulfate chain that modulates its enzyme activity

Sulfs represent a class of unconventional sulfatases, which differ from all other members of the sulfatase family by their structures, catalytic features and biological functions. Through their specific endosulfatase activity in extracellular milieu, Sulfs provide an original post-synthetic regulatory mechanism for heparan sulfate complex polysaccharides and have been involved in multiple physiopathological processes, including cancer. However, Sulfs remain poorly characterized enzymes, with major discrepancies regarding their in vivo functions. Here we show that human Sulf-2 (HSulf-2) features a unique polysaccharide post-translational modification. We identified a chondroitin/dermatan sulfate glycosaminoglycan (GAG) chain, attached to the enzyme substrate binding domain. We found that this GAG chain affects enzyme/substrate recognition and tunes HSulf-2 activity in vitro and in vivo using a mouse model of tumorigenesis and metastasis. In addition, we showed that mammalian hyaluronidase acted as a promoter of HSulf-2 activity by digesting its GAG chain. In conclusion, our results highlight HSulf-2 as a unique proteoglycan enzyme and its newly-identified GAG chain as a critical non-catalytic modulator of the enzyme activity. These findings contribute in clarifying the conflicting data on the activities of the Sulfs and introduce a new paradigm into the study of these enzymes.

biochemistry↗

bioRxiv2020

HAYSTAC: A Bayesian framework for robust and rapid species identification in high-throughput sequencing data

Identification of specific species in metagenomic samples is critical for several key applications, yet many tools available require large computational power and are often prone to false positive identifications. Here we describe High-AccuracY and Scalable Taxonomic Assignment of MetagenomiC data (HAYSTAC), which can estimate the probability that a specific taxon is present in a metagenome. HAYSTAC provides a user-friendly tool to construct databases, based on publicly available genomes, that are used for competitive reads mapping. It then uses a novel Bayesian framework to infer the abundance and statistical support for each species identification and provide per-read species classification. Unlike other methods, HAYSTAC is specifically designed to efficiently handle both ancient and modern DNA data, as well as incomplete reference databases, making it possible to run highly accurate hypothesis-driven analyses (i.e., assessing the presence of a specific species) on variably sized reference databases while dramatically improving processing speeds. We tested the performance and accuracy of HAYSTAC using simulated Illumina libraries, both with and without ancient DNA damage, and compared the results to other currently available methods (i.e., Kraken2/Bracken, KrakenUniq, MALT/HOPS, and Sigma). HAYSTAC identified fewer false positives than both Kraken2/Bracken, KrakenUniq and MALT in all simulations, and fewer than Sigma in simulations of ancient data. It uses less memory than Kraken2/Bracken, KrakenUniq as well as MALT both during database construction and sample analysis. Lastly, we used HAYSTAC to search for specific pathogens in two published ancient metagenomic datasets, demonstrating how it can be applied to empirical datasets. HAYSTAC is available from https://github.com/antonisdim/HAYSTAC Author summaryThe emerging field of paleo-metagenomics (i.e., metagenomics from ancient DNA) holds great promise for novel discoveries in fields as diverse as pathogen evolution and paleoenvironmental reconstruction. However, there is presently a lack of computational methods for species identification from microbial communities in both degraded and nondegraded DNA material. Here, we present "HAYSTAC", a user-friendly software package that implements a novel probabilistic model for species identification in metagenomic data obtained from both degraded and non-degraded DNA material. Through extensive benchmarking, we show that HAYSTAC can be used for accurately profiling the community composition, as well as for direct hypothesis testing for the presence of extremely low-abundance taxa, in complex metagenomic samples. After analysing simulated and publicly available datasets, HAYSTAC consistently produced the lowest number of false positive identifications during taxonomic profiling, produced robust results when databases of restricted size were used, and showed increased sensitivity for pathogen detection compared to other specialist methods. The newly proposed probabilistic model and software employed by HAYSTAC can have a substantial impact on the robust and rapid pathogen discovery in degraded/shallow sequenced metagenomic samples while optimising the use of computational resources.

bioinformatics↗

bioRxiv2020

Revealing interspecies transmission barriers of avian influenza A viruses

Influenza A virus (IAV) pandemics result from interspecies transmission events within the avian reservoir and further to mammals including humans. Investigating molecular virus-host interactions dictating this process and the adaptations to the new hosts that follow is vital to understand zoonotic IAV spread. Receptor incompatibility has been suggested to limit zoonotic IAV transmission from the wild bird reservoir. Other barriers to interspecies transmission, particularly within the avian system, largely remain elusive. Through assessment of infection dynamics of mallard origin IAV in two different avian hosts, coupled with studies of receptor expression and host response we aimed to reveal the host-pathogen interactions in a cross-species transmission event. We found that shedding patterns and innate immune responses were highly dependent on viral genotypes, host species and inoculation routes, but less dependent on receptor expression. Further, in contrary to the prevailing dogma we demonstrate that birds can produce a wide range of different sialylated structures also found in mammals, e.g. extended N- and O-linked Neu5Ac2,6 terminated glycans. Overall, receptor incompatibility is not the sole transmission barrier for IAV between birds and to humans, but other host-pathogen factors deserve dedicated studies to achieve proper pandemic preparedness.

microbiology↗

bioRxiv2020

b3galt6 knock-out zebrafish recapitulate β3GalT6-deficiency disorders in human and reveal a trisaccharide proteoglycan linkage region

Proteoglycans are structurally and functionally diverse biomacromolecules found abundantly on cell membranes and in the extracellular matrix. They consist of a core protein linked to glycosaminoglycan chains via a tetrasaccharide linkage region. Here, we show that CRISPR/Cas9-mediated b3galt6 knock-out zebrafish, lacking galactosyltransferase II, which adds the third sugar in the linkage region, largely recapitulate the phenotypic abnormalities seen in human {beta}3GalT6-deficiency disorders. These comprise craniofacial dysmorphism, generalized skeletal dysplasia, skin involvement and indications for muscle hypotonia. In-depth TEM analysis revealed disturbed collagen fibril organization as the most consistent ultrastructural characteristic throughout different affected tissues. Strikingly, despite a strong reduction in glycosaminoglycan content, as demonstrated by anion-exchange HPLC, subsequent LC-MS/MS analysis revealed a small amount of proteoglycans containing a unique linkage region consisting of only three sugars. This implies that formation of glycosaminoglycans with an immature linkage region is possible in a pathogenic context. Our study therefore unveils a novel rescue mechanism for proteoglycan production in the absence of galactosyltransferase II, hereby opening new avenues for therapeutic intervention.

genetics↗