Biology subjects

Horst, S. G.

Publications and source records attributed to Horst, S. G..

3 recordsLinked to original sources

bioRxiv2025

Sonic hedgehog signaling promotes basal epidermal fibrillin 3 expression for zebrafish fin ray branching

Zebrafish robustly regenerate amputated fins, including restoring branched bony ray skeletons. During fin outgrowth, sonic hedgehog a (shha)-expressing basal epidermal cells (bEps) signal to themselves and adjacent progenitor osteoblasts (pObs) to progressively split pObs into daughter ray pools. Collectively moving bEps pass through a shha-expressing state to define distal shha- positive bEp domains that themselves separate laterally ahead of ray branching. As such, Shh/Smo signaling may promote transient associations between bEps and pObs that gradually splits pOb pools. We used bulk RNA sequencing of caudal fin regenerates after Smoothened (Smo) inhibition followed by a CRISPant screen to identify fibrillin 3 (fbn3) as a candidate Shh/Smo target gene for ray branching. Homozygous fbn3 mutant zebrafish regenerated caudal fins with fewer branched rays and increased distances to branch points. Shh/Smo signaling was required specifically for full fbn3 induction in bEps but not pObs. Double mutants showed that fibrillin 2 (fbn2; FBN2 ortholog) redundantly supports fbn3-promoted ray branching. Fbn1-containing microfibrils accumulated at the bEp/pOb interface in fbn3 and, more so, fbn3/2 mutant regenerating caudal fins. Shh/Smo signaling may activate bEp fbn3 expression to locally modify microfibril abundance, facilitating bEp-pOb interactions and/or movements underlying ray branching morphogenesis.

developmental biology↗

bioRxiv2024

Early exercise disrupts a pro-repair extracellular matrix program during zebrafish fin regeneration

Mechanical stimulation effects on cell behaviors that restore organ form and function during tissue repair are unresolved. We applied swim flume-mediated exercise during zebrafish caudal fin regeneration to explore mechanical loading impacts on a robust model of organ regeneration. Exercise initiated during but not after blastema establishment compromised fin regeneration, including outgrowth and skeletal pattern. Long-term tracking of fluorescently labeled fibroblasts showed exercise loading disrupted blastemal mesenchyme formation. Transcriptomic profiling and section staining indicated loading reduced an extracellular matrix (ECM) gene expression program, including for hyaluronic acid (HA) synthesis. As with exercise loading, HA synthesis inhibition or blastemal HA depletion impaired blastema formation. We considered if injury-upregulated HA establishes a pro-regenerative environment facilitating mechanotransduction. HA density across the blastema correlated with nuclear localization of the mechanotransducer Yes-associated protein (Yap). Exercise loading or HA depletion decreased nuclear Yap, and culturing primary fin fibroblasts on HA-coated surfaces induced Yap nuclear localization. We conclude early exercise during fin regeneration disrupts expression of an HA-rich ECM supporting Yap-promoted blastema expansion. These findings reveal that fin regeneration is acutely sensitive to the timing and intensity of mechanical loading, underscoring how biomechanical forces integrate with regenerative programs to guide robust tissue repair.

developmental biology↗

bioRxiv2023

The Fraser complex interconnects tissue layers to support basal epidermis and osteoblast integrated morphogenesis underlying fin skeletal patterning

Fraser Syndrome is a rare, multisystemic autosomal recessive disorder characterized by disrupted epithelial-mesenchymal associations upon loss of Fraser Complex genes. Disease manifestation and affected organs are highly variable. Digit malformations such as syndactyly are common but of unclear developmental origins. We explored if zebrafish fraser extracellular matrix complex subunit 1 (fras1) mutants model Fraser Syndrome-associated appendicular skeleton patterning defects. Approximately 10% of fras1 mutants survive to adulthood, displaying striking and varied fin abnormalities, including endochondral bone fusions, ectopic cartilage, and disrupted caudal fin symmetry. The fins of surviving fras1 mutants frequently have fewer and unbranched bony rays. fras1 mutant fins regenerate to their original size but with exacerbated ray branching and fin symmetry defects. Single cell RNA-Seq analysis, in situ hybridizations, and antibody staining show specific Fraser complex expression in the basal epidermis during regenerative outgrowth. Fras1 and Fraser Complex component Frem2 accumulate along the basal side of distal-most basal epidermal cells. Greatly reduced and mislocalized Frem2 accompanies loss of Fras1 in fras1 mutants. The Sonic hedgehog signaling between distal basal epidermis and adjacent mesenchymal pre-osteoblasts that promotes ray branching persists upon Fraser Complex loss. However, fras1 mutant regenerating fins exhibit extensive sub-epidermal blistering associated with a disorganized basal epidermis and adjacent pre-osteoblasts. We propose Fraser Complex-supported tissue layer adhesion enables robust integrated tissue morphogenesis involving the basal epidermis and osteoblasts. Further, we establish zebrafish fin development and regeneration as an accessible model to explore mechanisms of Fraser Syndrome-associated digit defects and Fraser Complex function at epithelial-mesenchymal interfaces.

developmental biology↗