Distribution and Restoration of Serotonin-Immunoreactive Paraneuronal Cells During Caudal Fin Regeneration in Zebrafish

Abstract

Aquatic vertebrates possess diverse types of sensory cells in their skin to detect stimuli in the water. In the adult zebrafish, a common model organism, the presence of such cells in fins has only rarely been studied. Here, we identified scattered serotonin (5-HT)-positive cells in the epidermis of the caudal fin. These cells were distinct from keratinocytes as revealed by their low immunoreactivity for cytokeratin and desmosome markers. Instead, they were detected by Calretinin (Calbindin-2) and Synaptic vesicle glycoprotein 2 (SV2) antibodies, indicating a calcium-regulated neurosecretory activity. Consistently, electron microscopy revealed abundant secretory organelles in desmosome-negative cells in the fin epidermis. Based on the markers, 5-HT, Calretinin and SV2, we referred to these cells as HCS-cells. We found that HCS-cells were spread throughout the entire caudal fin at an average density of 140 cells per mm2 on each fin surface. These cells were strongly enriched at ray bifurcations in wild type fins, as well as in elongated fins of another longfin mutant fish. To determine whether hydrodynamics play a role in the distribution of HCS-cells, we used an interdisciplinary approach and performed kinematic analysis. Measurements of particle velocity with a fin model revealed differences in fluid velocities between bifurcated rods and adjacent non-bifurcated regions. Therefore the accumulation of HCS-cells near bone bifurcations may be a biological adaptation for sensing of water parameters. The significance of this HCS-cell pattern is reinforced by the fact, that it is reestablished in the regenerated fin after amputation. Regeneration of HCS-cells was not impaired by the chemical inhibition of serotonin synthesis, suggesting that this neurotransmitter is not essential for the restorative process. In conclusion, our study identified a specific population of solitary paraneurons in the zebrafish fin, whose distribution correlates with fluid dynamics.

Continuouscis-regulatory changes in an advantageous gene are linked with adaptive radiation in cichlid fishes

“…This robust nature is not unexpected for immune and brain network system 26,27 , as the DE genes of the lg KO line are mainly neurons and immunity related genes. Besides, lineage-specific new genes initially usually located at the edge of the gene network 28 29 ; in pharyngeal cartilages, the wellknown tissues related to feeding and ecological niche exploration, are key to cichlid fish adaptive radiation [30][31][32] ; in scattered epidermal serotonin-positive cells which are neuroepithelia cells related to environmental stimuli, such as water flow, pheromone and hormone 33,34 ; in the olfactory epithelium which is well-known for detection of odorants, such as amino acid, hormone and pheromone 35 . Considering that some of these tissues are derived from a key vertebrate innovation, the neural crest cells 36 , lg can be also causally linked to neural crest cell development and differentiation.…”

Sensory cutaneous papillae in the sea lamprey (Petromyzon marinus L.): II. Ontogeny and immunocytochemical characterization of solitary chemosensory cells

“…While an earlier study showed 5HT immunoreactive cells on gill papillar epithelium (Suntres, ), this localization was not confirmed in later experiments. While SCCs were not 5‐HT‐immunoreactive in the sea lamprey, 5HT is localized in the gustatory taste cells (Barreiro‐Iglesias et al, ) and 5HT, calretinin and SV2 immunoreactive cells are present in the epidermis of zebrafish fins (Konig et al, ).…”

Hydrodynamic stress maps on the surface of a flexible fin-like foil

“…Moreover, the tangential shear stress may have a particular significance in certain hydrodynamic problems, even when the flow is dominated by the fluid inertial forces. For instance, resolving the viscous shear stress maps on the surface of fin models might be informative in problems related to flow sensing in the skin of fish [ 111 ]. In other words, despite the lower order of magnitude of the measured viscous tangential stress, these components may be of special interest for certain biological applications, which is why we retained them in our analysis.…”

“…In the present work, the focus is on providing an estimate of both hydrodynamic stress contributions (shear stress and pressure) from instantaneous captures of the three-dimensional flow field, which requires a compromise between the size of the measurement volume and the vector field spatial resolution. In a recent study, we showed that it is possible to resolve the velocity field inside the shear layer forming over a flat plate pitching in a similar flow regime using the same volumetric PTV experimental setup [ 111 ]. In that case, the boundary layer thickness, defined as the distance at which the velocity reaches 99% of the free-stream value, varied dynamically between ∼2 and 6 mm.…”

“…The shear stress profile remains fairly well captured (with a slight offset in magnitude) as long as the reconstructed surface stands sufficiently close to the real object (distance below 1 mm according to [ 110 ]). Using volumetric PTV experiments, we recently showed the feasibility of resolving the velocity field over a rigid plate pitching inside a water tunnel, with a spatial resolution of 0.75 mm, and we measured the thickness of the boundary layer within a dynamic range of about [ 2 , 6 ] mm [ 111 ].…”