Biology subjects

Marklund, U.

Publications and source records attributed to Marklund, U..

6 recordsLinked to original sources

bioRxiv2026

In utero barcoding of mouse mesoderm reveals the clonal architecture of organ mesenchyme

The mesoderm coordinates organogenesis and generates the cardiovascular, visceral and musculoskeletal systems, yet in mammals this germ layer is difficult to access, impeding its genetic manipulation and study. Here, we establish embryonic day (E) 7.5 exocoelomic cavity nano-injection as a scalable route for selective genetic targeting of mouse mesoderm. Combining in utero lentiviral barcoding with single-cell and spatial transcriptomics, we reconstructed mesodermal and neural crest clonal relationships across >590,000 cells and 31,000 multicellular clones from E9.5-E10.5 embryos and E16.5 livers and hearts. In liver, capsular mesothelium was closely related to hepatic stellate cells, whereas fibroblast and vascular smooth muscle lineages diverged earlier. In heart, epicardium was clonally coupled to three spatially restricted mesenchymal sub-lineages but not to cardiomyocytes, and lineage tracing separated epicardial- and neural crest-derived populations within transcriptionally convergent valve mesenchyme. This approach enables Cre-independent manipulation of mammalian mesoderm and resolves organ mesenchyme development at clonal resolution.

developmental biology↗

bioRxiv2026

Mapping Enteric Neural Circuits by Anterograde Transsynaptic Tracing

The diverse functions of the enteric nervous system (ENS) arise from communication between molecularly distinct neuronal populations organized into complete circuits. While recent single-cell transcriptomic studies have resolved the molecular identity of enteric neuron classes, methods for defining their synaptic connectivity remain limited. Here, we describe the implementation of mWmC, an anterograde monosynaptic tracer based on a fusion of wheat germ agglutinin (WGA) and mCherry, as a non-toxic, single-component viral tool for mapping neuronal circuits within and beyond the ENS. Following adeno-associated virus (AAV)-mediated expression in enteric neurons, mWmC was efficiently expressed and transmitted selectively to postsynaptic neurons, with no detectable transfer to enteric glia, interstitial cells of Cajal, blood vessels or other mesenchymal cell types. The method also identified postsynaptic neurons in the celiac-superior mesenteric ganglia following tracing of intestinofugal enteric neurons, demonstrating its utility for mapping inter-organ circuits. As proof of principle, we applied mWmC to two genetically defined myenteric interneuron populations and identified preferential postsynaptic targets, revealing selective connectivity with distinct enteric neuron classes. Time-course experiments showed that transsynaptic labeling occurred between 4 and 10 days and reached a plateau thereafter, consistent with monosynaptic transfer. Finally, we developed a dual-reporter version of the system that simultaneously distinguishes input and target neurons within the same tissue. Together, mWmC provides a robust approach for defining circuit architecture in the ENS, linking molecular cell atlases with neuronal connectivity and paving the way for deeper insights into the circuit mechanisms underlying gut physiology. Graphical AbstractSchematics illustrating the implementation and applications of the anterograde monosynaptic tracer mWmC for mapping enteric neuronal circuits. Parts of schematics are generated with Biorender. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=36 SRC="FIGDIR/small/741165v2_ufig1.gif" ALT="Figure 1"> View larger version (12K): org.highwire.dtl.DTLVardef@19635bborg.highwire.dtl.DTLVardef@a18ffborg.highwire.dtl.DTLVardef@f3d011org.highwire.dtl.DTLVardef@e1359c_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2026

Transmembrane aminopeptidase Q (Taqpep) is a common mechanism in the establishment of periodic patterning in skin and intestine

Periodic patterns are a frequent motif in biology that occurs across diverse tissues and species. In mammals, pigmentation patterns such as zebra stripes or tiger stripes are well-known examples of periodic patterns; more recently, the myenteric plexus (MP) of the enteric nervous system (ENS), which controls gastrointestinal motility, has been found to exhibit a striped organization in humans and laboratory mice. In domestic cats and other felids, the Transmembrane aminopeptidase Q (Taqpep) gene plays a key role in color pattern establishment during skin development, but its patterning role has not been examined in other tissues. Here, we show that, in laboratory mice, Taqpep is required for normal patterning of developing hair follicles and the MP. Using both sequencing and histologic techniques, we found Taqpep is expressed in mesenchymal cells in embryonic skin and intestine directly adjacent to where periodic patterning occurs. We generated Taqpep mutant mice, which exhibit disrupted epidermal patterning akin to the changes in periodic coat patterning observed in Taqpep mutant cats. The intestine of Taqpep mutants has irregularly periodicity of enteric neuronal stripes, and enteric neurons in Taqpep mutants exhibit disrupted Wnt signaling. This work provides new insight into the mechanism of enteric neuronal patterning and identify Taqpep as a common and conserved mediator of periodic patterning across mammalian tissues and organisms. Author summaryPeriodic patterning is a frequent motif in biology. Examples include pigmentation patterning such as tiger stripes and, as recently identified in both mouse and human, the striped organization of enteric neurons in the myenteric plexus of the intestine. In domestic and wild cats, the Transmembrane aminopeptidase Q (Taqpep) gene is essential for the establishment of periodic patterning. Whether this gene plays a conserved role in periodic patterning across other tissues and species has yet to be explored. We found that Taqpep is expressed in mesenchymal cells in embryonic mouse skin and intestine at key locations and developmental stages to instruct periodic patterning. We next generated Taqpep mutant mice that exhibit disrupted periodic patterns in both developing skin follicles and in enteric neuron organization. Thus, Taqpep is essential in establishing periodic patterning in diverse mammals and tissues.

developmental biology↗

bioRxiv2026

In utero transduction resolves gut cell lineages and enables conditional gene perturbation in the developing enteric nervous system

How diverse cell lineages emerge and are genetically regulated during organogenesis are central questions in understanding the developmental origins of disease. However, the mouse gut, including its intrinsic enteric nervous system (ENS) derived from migratory neural crest, has remained difficult to experimentally target. Here, we introduce an in utero lentiviral nano-injection strategy that enables early and efficient access to progenitor cells of all major cell types within the developing gut as well as gut-innervating ganglia. Leveraging this approach in combination with DNA barcoding and single cell transcriptomics, we resolve clonal relationships in all gut lineages, including epithelial, neural, immune, and mesenchymal cell types. Clonal coupling between distinct subsets of fibroblasts and either pericytes, mesothelial cells, or interstitial cells of Cajal, suggested a developmental logic whereby the mesenchymal compartment arises from a set of fate-biased progenitors. Yet, mesenchymal regionalization along the anterior-posterior axis establishes early, whereas the ENS displays broad clonal dispersion across gut regions and acquires subsequent regional identities. We further adapted the platform for temporally controlled cell-type specific gene manipulation and, as a proof-of-principle, show that induced expression of the proneural factor Ascl1 biases ENS progenitor cells toward neuronal differentiation. Together, this work provides insights into refined spatiotemporal lineage relationships within a multigerm-layer organ and establishes a broadly applicable in vivo framework for probing gene function during gastrointestinal and neural crest development. SIGNIFICANCEThe gastrointestinal tract comprises diverse cell types originating from all three germ layers and includes the neural crest-derived enteric nervous system (ENS). Progress in defining these lineages and their gene regulation is challenged by the limited experimental access to the developing gut. Here, we establish in utero lentiviral transduction as an efficient approach to resolve clonal lineages and address gene functions in defined gut cell types. We show that mesenchyme assumes positional allocation early and differentiates through fate-restricted progenitors, linking specialized mesenchymal cell types to different fibroblasts. In contrast, the ENS differentiates stochastically and acquires late regional identities. Our study reveals fundamental principles of multi-lineage organogenesis and provides a framework to dissect the contribution of developmental programs to visceral dysfunction.

developmental biology↗

bioRxiv2020

Diversification of molecularly defined myenteric neuron classes revealed by single cell RNA-sequencing

Autonomous functions of the gastrointestinal tract require the combined activity of functionally distinct neurons of the enteric nervous system (ENS). However, the range of enteric neuron diversity and how it emerges during development remain largely unknown. We here make a novel molecular definition of 12 enteric neuron classes (ENCs) within the myenteric plexus of the mouse small intestine. We identify communication features and provide histochemical markers for discrete motor, sensory, and interneurons together with genetic tools for class-specific targeting. Transcriptome analysis of embryonic ENS reveals a largely post-mitotic principle of diversification, where only ENC1 or ENC8 phenotypic traits arise through a binary neurogenic trajectory, and other identities form through subsequent differentiation. We propose generic and class-specific transcriptional regulators and functionally connect the transcription factor Pbx3 to one post-mitotic identity conversion. Our results offers a conceptual and molecular resource for dissecting ENS circuits, and predicting key regulators for the directed differentiation of distinct enteric neuron classes.

neuroscience↗

bioRxiv2018

Molecular architecture of the mouse nervous system

The mammalian nervous system executes complex behaviors controlled by specialised, precisely positioned and interacting cell types. Here, we used RNA sequencing of half a million single cells to create a detailed census of cell types in the mouse nervous system. We mapped cell types spatially and derived a hierarchical, data-driven taxonomy. Neurons were the most diverse, and were grouped by developmental anatomical units, and by the expression of neurotransmitters and neuropeptides. Neuronal diversity was driven by genes encoding cell identity, synaptic connectivity, neurotransmission and membrane conductance. We discovered several distinct, regionally restricted, astrocytes types, which obeyed developmental boundaries and correlated with the spatial distribution of key glutamate and glycine neurotransmitters. In contrast, oligodendrocytes showed a loss of regional identity, followed by a secondary diversification. The resource presented here lays a solid foundation for understanding the molecular architecture of the mammalian nervous system, and enables genetic manipulation of specific cell types.

neuroscience↗