Biology subjects

Morse, D.

Publications and source records attributed to Morse, D..

7 recordsLinked to original sources

bioRxiv2026

Mesenchymal-derived neural progenitors underlie local insulin production and neuronal transdifferentiation during retina regeneration

In humans, retinal-neuron death, optic-nerve injuries, and associated neurodegenerative diseases, such as glaucoma and age-related macular degeneration, often lead to permanent vision loss. While the capacity for regeneration is low in the human nervous system, including the retina, some non-mammalian vertebrate species, including zebrafish, are capable of endogenous neuronal regeneration after injury. Unlike mammals, zebrafish do not form a scar that inhibits axonal and neuronal regeneration after injury. Rather, they harbor neural progenitor and stem-cell populations allowing regeneration of entire parts of the nervous system and restoration of tissue integrity and function. In the zebrafish retina, cycling neural progenitor cells of the ciliary marginal zone and quiescent resident neural stem cells (the latter of which are also called Muller glial cells) participate in neuronal regeneration following different types of injury. In this study, we report the identification of a novel, additional cellular source participating in neuronal regeneration of neurons in the zebrafish retina after genetic ablation of retinal ganglion cells. Before injury, these progenitor cells express molecular markers of neural-crest-cell and/or fibroblast identity, such as sox10, pdgfrb, and eya2, while after neuronal ablation they also express proneural factors including the ascl1a and olig2 genes. Combining genetic ablation of neurons with photoconversion or Cre/Lox-dependent genetic lineage tracing of sox10-expressing cells, we demonstrated that these cells can differentiate into post-mitotic retinal neurons in the ganglion cell layer (GCL) in the absence of cell proliferation. We also showed, surprisingly, that this progenitor population locally produces insulin mRNA, and that insulin signaling is involved in the accumulation of mesenchymal-derived neural progenitors in the GCL and in their subsequent transdifferentiation into RGCs. This work reveals an unexpected and novel cellular mechanism of transdifferentiation, dependent on a neural-crest-derived mesenchymal cell population, participating in neuronal regeneration in the zebrafish retina. The discovery of this plastic cell population could potentially lead to new strategies to promote the formation of new neurons in the mammalian retina.

developmental biology↗

bioRxiv2026

Reflectins form multicompartment liquid-liquid phase separated condensates that mirror and may facilitate spatial organization in squid skin Bragg lamellae

Cationic reflectin proteins transduce neuronal signals tuning skin color for dynamic camouflage and communication in Loliginid squid. Neuronally released acetylcholine (ACh) activates phosphorylation of the reflectins, triggering their condensation, folding and hierarchical assembly. This causes osmotic and Gibbs-Donnan dehydration of membrane-enclosed Bragg lamellae containing these proteins in skin cells called iridocytes, changing their refractive index and spacing to finely tune the wavelength of reflected light. Reflectins B and C are enriched in ACh-responsive iridocytes, suggesting they are critical for the neuronally tuned protein phase transitions within the Bragg lamellae. Here, using pH titration as an in vitro surrogate for phosphorylation to reduce protein net charge density, we demonstrate with confocal microscopy that reflectins A1, A2, B and C individually undergo LLPS to form protein dense liquid condensates, while physiological mixtures of these proteins exhibit coordinated phase transitions to form multicompartment condensates whose internal spatial organization is tuned by the proportions and charge densities of the different reflectins. Our findings demonstrate that (i) the charge densities of the different reflectins control their spatial organization within liquid condensates, (ii) the relative proportions of the different reflectins found in the ACh-responsive iridocytes increase the sensitivity of their proteins liquid phase transitions to changes in reflectin charge density; and (iii) the spatial segregation of reflectins A1 and C we observe in their multiphasic liquid condensate mirror their spatial segregation in the Bragg lamellae in vivo, suggesting a mechanistic explanation for the spatial segregation of these reflectins across the iridocytes Bragg lamellae.

biophysics↗

bioRxiv2025

Zebrafish genetic model of neuromuscular degeneration associated with Atrogin-1 expression

The degenerative loss of muscle associated with aging leading to muscular atrophy is called sarcopenia. Currently, practicing regular physical exercise is the only efficient way to delay sarcopenia onset. Identification of therapeutic targets to alleviate the symptoms of aging requires in vivo model organisms of accelerated muscle degeneration and atrophy. The zebrafish undergoes aging, with hallmarks including mitochondrial dysfunction, telomere shortening, and accumulation of senescent cells. However, zebrafish age slowly, and no specific zebrafish models of accelerated muscle atrophy associated with molecular events of aging are currently available. We have developed a new genetic tool to efficiently accelerate muscle-fiber degeneration and muscle-tissue atrophy in zebrafish larvae and adults. We used a gain-of-function strategy with a molecule that has been shown to be necessary and sufficient to induce muscle atrophy and a sarcopenia phenotype in mammals: Atrogin-1 (also named Fbxo32). We report the generation, validation, and characterization of a zebrafish genetic model of accelerated neuromuscular atrophy, the atrofish. We demonstrated that Atrogin-1 expression specifically in skeletal muscle tissue induces a muscle atrophic phenotype associated with locomotion dysfunction in both larvae and adult fish. We identified degradation of the myosin light chain as an event occurring prior to muscle-fiber degeneration. Biological processes associated with muscle aging such as proteolysis, inflammation, stress response, extracellular matrix (ECM) remodeling, and apoptosis are upregulated in the atrofish. Surprisingly, we observed a strong correlation between muscle-fiber degeneration and reduced numbers of neuromuscular junctions in the peripheral nervous system, as well as neuronal cell bodies in the spinal cord, suggesting that muscle atrophy could underly a neurodegenerative phenotype in the central nervous system. Finally, while atrofish larvae can recover locomotive functions, adult atrofish have impaired regenerative capacities, as is observed in mammals during muscle aging. In the future, the atrofish could serve as a platform for testing molecules aimed at treating or alleviating the symptoms of muscle aging, thereby opening new therapeutic avenues in the fight against sarcopenia.

developmental biology↗

bioRxiv2025

The small molecule ML233 is a direct inhibitor of tyrosinase function

Melanogenesis is the biological process regulating the synthesis of melanin pigments in melanocytes. Defective melanogenesis is associated with numerous human skin diseases, including, but not limited to, albinism, vitiligo, melasma, and hypo- and hyperpigmentation disorders. Tyrosinase is the rate-limiting enzyme controlling melanogenesis, and hence tremendous efforts have been made to identify potent and safe inhibitors of tyrosinase function. However, despite decades of research, currently there is no effective treatment that inhibits melanogenesis or tyrosinase activity with no adverse side effects. In this study, we report characterization of the ML233 chemical as a potent inhibitor of tyrosinase activity in vivo and in vitro. We demonstrate that ML233 reduces melanin production in the zebrafish model with no observable significant toxic side effects, and in murine melanoma cells. We also predict that these effects are mediated through direct tyrosinase-ML233 interaction, i.e., binding of the ML233 molecule to the active site of the protein to inhibit its function. Together, our results reveal that ML233 plays roles in both healthy and pathological skin cells via inhibition of melanin production. ML233-mediated tyrosinase inhibition is a potentially safe and effective approach to alleviate the symptoms of melanocyte-associated diseases and thereby substantially improve human health.

pharmacology and toxicology↗

bioRxiv2024

Charge screening and hydrophobicity drive progressive assembly and liquid-liquid phase separation of reflectin protein

The intrinsically disordered reflectin proteins drive tunable reflectivity for dynamic camouflage and communication in the recently evolved Loliginidae family of squid. Previous work revealed that reflectin A1 forms discrete assemblies whose size is precisely predicted by protein net charge density (NCD) and charge screening by the local anion concentration. Using dynamic light scattering (DLS), Forster resonant energy transfer (FRET) and confocal microscopy, we show that these assemblies, of which 95-99% of bulk protein in solution is partitioned into, are dynamic intermediates to liquid protein-dense condensates formed by liquid-liquid phase separation (LLPS). Increasing salt concentration drives this progression by anionic screening of the cationic proteins Coulombic repulsion, and by increasing the hydrophobic effect which tips the balance between short-range attraction and long-range repulsion (SALR) to drive protein assembly and ultimately LLPS. Measuring fluorescence recovery after photobleaching (FRAP) and droplet fusion dynamics, we demonstrate that reflectin diffusivity in condensates is tuned by salt concentration and protein NCD. These results illuminate the physical processes governing reflectin A1 assembly and LLPS, and demonstrate the potential for reflectin A1 condensate-based tunable biomaterials. They also compliment previous observations of liquid phase separation in the Bragg lamellae of activated iridocytes and suggest that LLPS behavior may serve a critical role in governing the tunable and reversible dehydration of the membrane-bounded Bragg lamellae and vesicles containing reflectin in biophotonically active cells.

biophysics↗

bioRxiv2024

Differential gene expression analysis identifies a group of defensin like peptides from Solanum chacoense ovules with in vitro pollen tube attraction activity

Solanum chacoense is a wild potato species with superior genetic resistance to diseases and pests that has been extensively used for introgression into cultivated potato. One determinant of crossing success between wild and cultivated potato species is the effective ploidy of the parents. However, little is known about whether other, prezygotic level, breeding barriers exist. We hypothesize ovular pollen tube guidance may serve as such a checkpoint. Tests for species-specific pollen tube guidance using semi-in vivo assays suggested a positive correlation between species-specificity and taxonomic distance. RNA-seq of ovules hand dissected from wild type plants at anthesis and two days before anthesis, as well as from a frk1 mutant lacking an embryo sac identified a list of 284 embryo sac-dependent genes highly expressed in mature ovules and poorly expressed in all other samples. Among these are 17 Solanum chacoense cysteine-rich proteins (ScCRPs), considered to be good candidates since CRPs are ovular pollen tube attractants in other species. A group of three cloned and purified ScCRP2 sequences belonging to the DEFL protein family showed moderate levels of in vitro pollen tube attraction activity in functional assays. We conclude that ScCRP2s are good candidates for ovular pollen tube guidance in S. chacoense. HighlightsThis work introduces key characteristics of pollen tube guidance in Solanum chacoense, identifies candidate attractants through transcriptome subtraction and reports in vitro pollen tube attraction activity for three defensin-like peptides.

plant biology↗

bioRxiv2023

spinDrop: a droplet microfluidic platform to maximise single-cell sequencing information content

Droplet microfluidic methods have massively increased the throughput of single-cell sequencing campaigns. The benefit of scale-up is, however, accompanied by increased background noise when processing challenging samples and the overall RNA capture efficiency is lower. These drawbacks stem from the lack of strategies to enrich for high-quality material or specific cell types at the moment of cell encapsulation and the absence of implementable multi-step enzymatic processes that increase capture. Here we alleviate both bottlenecks using fluorescence-activated droplet sorting to enrich for droplets that contain single viable cells, intact nuclei, fixed cells or target cell types and use reagent addition to droplets by picoinjection to perform multi-step lysis and reverse transcription. Our methodology increases gene detection rates fivefold, while reducing background noise by up to half. We harness these unique properties to deliver a high-quality molecular atlas of mouse brain development, despite starting with highly damaged input material, and provide an atlas of nascent RNA transcription during mouse organogenesis. Our method is broadly applicable to other droplet-based workflows to deliver sensitive and accurate single-cell profiling at a reduced cost.

developmental biology↗