@unpublished{21291, abstract = {The complexity and specificity of movement in vertebrates is driven by a rich diversity of spinal motor and interneuron cell types. During development, eleven spinal cord progenitor domains generate an equivalent number of cardinal neuron types. How progenitor domains, individual progenitors, and post-mitotic diversity relate is still unknown. We performed high-resolution, single-progenitor cell lineage tracing in the embryonic mouse spinal cord using mosaic analysis with double markers (MADM). Our quantitative study of lineage progression revealed that spinal cord progenitors undergo highly variable numbers of proliferative, neurogenic, and gliogenic cell divisions. The nascent clonally-related neurons migrate radially over large distances, span the dorsoventral axis, and even cross the midline, demonstrating striking bilaterality. Molecular and morphometric analysis indicate high levels of progenitor multipotency, with an individual progenitor capable of producing several molecularly and morphologically distinct neuron types, as well as astrocytes. These findings redefine spinal cord development as a process in which lineage variability — rather than rigid progenitor identity — drives the generation of cellular diversity.}, author = {Gobeil, Sophie A and Da Silveira Neto, Francisco and Silvestrelli, Giulia and Smits, Matthijs Geert and Streicher, Carmen and Cheung, Giselle T and Hippenmeyer, Simon and Sweeney, Lora Beatrice Jaeger}, booktitle = {bioRxiv}, title = {{Lineage origin of spinal cord cell type diversity}}, doi = {10.64898/2026.02.12.705305}, year = {2026}, } @inbook{22926, abstract = {Adeno-associated viruses (AAVs) provide a versatile tool for labeling neurons in the Xenopus central nervous system across developmental stages. AAV-mediated transgene expression is long-lasting and stable, enabling robust labeling of neuronal populations without genomic integration and without the need to generate transgenic lines. The choice of AAV capsid and promoter can restrict expression to a population of interest, and depending on the route and timing of delivery, AAVs can selectively target either progenitor-derived neuronal cohorts or mature neuronal populations. Here, we have outlined two labeling strategies. First, intraventricular injections in tadpoles transduce neural progenitor cells lining the ventricular system, resulting in cohort-based labeling of neurons as they differentiate during development. Second, direct intraparenchymal injections in post-metamorphic frogs enable spatially restricted labeling and anterograde or retrograde tracing of connectivity within defined brain regions. Together, these approaches provide selective access to developing and mature neural circuits in X. laevis, supporting applications ranging from anatomical tracing to functional imaging and manipulation of neural circuits.}, author = {Vijatovic, David and Sweeney, Lora Beatrice Jaeger}, booktitle = {Xenopus}, editor = {Beck, Caroline W.}, issn = {1940-6029}, pages = {219--229}, publisher = {Springer}, title = {{Adeno-Associated Virus (AAV) for tracking neural development and connectivity in Xenopus}}, doi = {10.1007/978-1-0716-5360-9_9}, volume = {3049}, year = {2026}, } @inbook{22925, abstract = {Hybridization Chain Reaction (HCR) enables highly sensitive and multiplexed detection of mRNA with subcellular spatial resolution. It employs fluorophore-tagged DNA hairpins that self-assemble on target-bound probe pairs, amplifying the signal without enzymatic reactions. Here, we describe a protocol for performing HCR fluorescence in situ hybridization (FISH) on Xenopus tissue sections. We also outline a semi-automated image analysis pipeline that enables per-cell quantification of probe expression and co-localization. This method provides a robust and quantitative approach for visualizing gene expression patterns in situ.}, author = {Vijatovic, David and Papadopoulos, Stavros and Dalla Vecchia, Marco and Sweeney, Lora Beatrice Jaeger}, booktitle = {Xenopus}, editor = {Beck, Caroline W.}, issn = {1940-6029}, keywords = {mRNA FISH, Hybridization chain reaction, In situ hybridization, Fluorescence microscopy}, pages = {245--259}, publisher = {Springer}, title = {{Fluorescent in situ mRNA hybridization (FISH) using Hybridization Chain Reaction (HCR) in Xenopus cryosections}}, doi = {10.1007/978-1-0716-5360-9_11}, volume = {3049}, year = {2026}, } @article{21746, abstract = {As vertebrates transitioned from water to land, locomotion shifted from undulatory swimming to limb-based movement. How spinal circuits and their cell types evolved to support this transition remains unclear. We leverage frog metamorphosis, which recapitulates this transition within a single organism, to define how spinal circuits generate aquatic versus terrestrial motor patterns. At swim stages, spinal architecture is uniform, with a transcriptionally and anatomically homogeneous motor and interneurons. As limbs develop and their movement complexifies, spinal circuits expand in neuron number and subtype diversity. This expansion is most pronounced for V1 inhibitory neurons, which increase ∼70-fold and diversify into transcriptionally distinct subtypes. Disrupting transcription factors defining emerging motor and V1 populations reveals molecular segregation between swim and limb circuits, highlighting the role of subtype diversity in motor coordination. A multifold increase in inhibitory neuron diversity thus underlies the tail-to-limb locomotor transition, providing a framework for spinal circuit adaptation during vertebrate evolution.}, author = {Vijatovic, David and Toma, Florina Alexandra and Ignatyev, Y and Harrington, Zoe P and Sommer, Christoph M and Hauschild, Robert and Smits, Matthijs Geert and Dalla Vecchia, Marco and Trevisan, Alexandra J. and Chapman, Phillip and Julseth, Mara and Brenner-Morton, Susan and Gabitto, Mariano I. and Dasen, Jeremy S. and Bikoff, Jay B. and Sweeney, Lora Beatrice Jaeger}, issn = {2211-1247}, journal = {Cell Reports}, number = {4}, publisher = {Cell Press}, title = {{Multifold increase in spinal inhibitory cell types with emergence of limb movement}}, doi = {10.1016/j.celrep.2026.117227}, volume = {45}, year = {2026}, } @article{15016, abstract = {Amphibians, by virtue of their phylogenetic position, provide invaluable insights on nervous system evolution, development, and remodeling. The genetic toolkit for amphibians, however, remains limited. Recombinant adeno-associated viral vectors (AAVs) are a powerful alternative to transgenesis for labeling and manipulating neurons. Although successful in mammals, AAVs have never been shown to transduce amphibian cells efficiently. We screened AAVs in three amphibian species—the frogs Xenopus laevis and Pelophylax bedriagae and the salamander Pleurodeles waltl—and identified at least two AAV serotypes per species that transduce neurons. In developing amphibians, AAVs labeled groups of neurons generated at the same time during development. In the mature brain, AAVrg retrogradely traced long-range projections. Our study introduces AAVs as a tool for amphibian research, establishes a generalizable workflow for AAV screening in new species, and expands opportunities for cross-species comparisons of nervous system development, function, and evolution.}, author = {Jaeger, Eliza C.B. and Vijatovic, David and Deryckere, Astrid and Zorin, Nikol and Nguyen, Akemi L. and Ivanian, Georgiy and Woych, Jamie and Arnold, Rebecca C and Ortega Gurrola, Alonso and Shvartsman, Arik and Barbieri, Francesca and Toma, Florina-Alexandra and Gorbsky, Gary J. and Horb, Marko E. and Cline, Hollis T. and Shay, Timothy F. and Kelley, Darcy B. and Yamaguchi, Ayako and Shein-Idelson, Mark and Tosches, Maria Antonietta and Sweeney, Lora Beatrice Jaeger}, issn = {1878-1551}, journal = {Developmental Cell}, number = {5}, pages = {794--812.e6}, publisher = {Cell Press}, title = {{Adeno-associated viral tools to trace neural development and connectivity across amphibians}}, doi = {10.1016/j.devcel.2024.10.025}, volume = {60}, year = {2025}, }