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Development and regeneration of the zebrafish maxillary barbel: a novel study system for vertebrate tissue growth and repair.

LeClair EE, Topczewski J - PLoS ONE (2010)

Bottom Line: Barbels are integumentary sense organs found in fishes, reptiles and amphibians.Finally, we show that the maxillary barbel can regenerate after repeated injury and also in senescent fish (>2 years old).Although the teleost barbel has no human analog, the cell types it contains are highly conserved.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, DePaul University, Chicago, Illinois, United States of America. eleclair@depaul.edu

ABSTRACT

Background: Barbels are integumentary sense organs found in fishes, reptiles and amphibians. The zebrafish, Danio rerio, develops paired nasal and maxillary barbels approximately one month post fertilization. Small in diameter and optically clear, these adult appendages offer a window on the development, maintenance and function of multiple cell types including skin cells, neural-crest derived pigment cells, circulatory vessels, taste buds and sensory nerves. Importantly, barbels in other otophysan fishes (e.g., catfish) are known to regenerate; however, this capacity has not been tested in zebrafish.

Methodology/principal findings: We describe the development of the maxillary barbel in a staged series of wild type and transgenic zebrafish using light microscopy, histology and immunohistochemistry. By imaging transgenic zebrafish containing fluorescently labeled endothelial cells (Tg(fli1a:EGFP)), we demonstrate that the barbel contains a long ( approximately 2-3 mm) closed-end vessel that we interpret as a large lymphatic. The identity of this vessel was further supported by live imaging of the barbel circulation, extending recent descriptions of the lymphatic system in zebrafish. The maxillary barbel can be induced to regenerate by proximal amputation. After more than 750 experimental surgeries in which approximately 85% of the barbel's length was removed, we find that wound healing is complete within hours, followed by blastema formation ( approximately 3 days), epithelial redifferentiation (3-5 days) and appendage elongation. Maximum regrowth occurs within 2 weeks of injury. Although superficially normal, the regenerates are shorter and thicker than the contralateral controls, have abnormally organized mesenchymal cells and extracellular matrix, and contain prominent connective tissue "stumps" at the plane of section--a mode of regeneration more typical of mammalian scarring than other zebrafish appendages. Finally, we show that the maxillary barbel can regenerate after repeated injury and also in senescent fish (>2 years old).

Conclusions/significance: Although the teleost barbel has no human analog, the cell types it contains are highly conserved. Thus "barbology" may be a useful system for studying epithelial-mesenchymal interactions, angiogenesis and lymphangiogenesis, neural pathfinding, wound healing, scar formation and other key processes in vertebrate physiology.

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Innervation of the maxillary barbel.A) 75 µm barbel. In all panels, anterior is to the left. Whole-mount immunohistochemistry (anti-acetylated tubulin) shows a central tract of nerve fibers (arrow) within the early barbel bud (dotted white line). Smaller nerve projections are concentrated in the ventral half of the appendage. B) 200 µm barbel. Multiple fascicles of nerve fibers project distally, innervating the barbel's ventral side and distal tip. No large tracts are visible dorsally. Scale bar = 100 µm. C) 1 mm barbel. Secondary nerve fibers appear within the dorsal half of the barbel. D) Section of an adult barbel at the approximate level shown by the dotted line in C. Innervation is visible as two deep nerve tracts (dn and vn) and a ring of sub-epithelial immunoreactive punctae (p). E,F) Schematic reconstructions of maxillary barbel bud innervation based on confocal tracing of whole-mount acetylated tubulin immunostaining in multiple zebrafish juveniles. F is an enlargement of the jaw region in E.
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pone-0008737-g005: Innervation of the maxillary barbel.A) 75 µm barbel. In all panels, anterior is to the left. Whole-mount immunohistochemistry (anti-acetylated tubulin) shows a central tract of nerve fibers (arrow) within the early barbel bud (dotted white line). Smaller nerve projections are concentrated in the ventral half of the appendage. B) 200 µm barbel. Multiple fascicles of nerve fibers project distally, innervating the barbel's ventral side and distal tip. No large tracts are visible dorsally. Scale bar = 100 µm. C) 1 mm barbel. Secondary nerve fibers appear within the dorsal half of the barbel. D) Section of an adult barbel at the approximate level shown by the dotted line in C. Innervation is visible as two deep nerve tracts (dn and vn) and a ring of sub-epithelial immunoreactive punctae (p). E,F) Schematic reconstructions of maxillary barbel bud innervation based on confocal tracing of whole-mount acetylated tubulin immunostaining in multiple zebrafish juveniles. F is an enlargement of the jaw region in E.

Mentions: As a taste organ, the maxillary barbel is well supplied with nerves. To trace the ontogeny of barbel innervation, we performed whole-mount immunohistochemistry using an antibody against acetylated tubulin [42], [43] to label the neurons in a developmental series of wild types. In juveniles of the smallest size class (>10–12.5 mm SL), a small tubulin-positive branch projects into the mesodermal core of the maxillary barbel bud, apparently innervating a ventral cluster of incipient taste buds (Fig. 5A). We also observed a nerve net of small, sinuous fibers throughout the barbel's epidermal sheath.


Development and regeneration of the zebrafish maxillary barbel: a novel study system for vertebrate tissue growth and repair.

LeClair EE, Topczewski J - PLoS ONE (2010)

Innervation of the maxillary barbel.A) 75 µm barbel. In all panels, anterior is to the left. Whole-mount immunohistochemistry (anti-acetylated tubulin) shows a central tract of nerve fibers (arrow) within the early barbel bud (dotted white line). Smaller nerve projections are concentrated in the ventral half of the appendage. B) 200 µm barbel. Multiple fascicles of nerve fibers project distally, innervating the barbel's ventral side and distal tip. No large tracts are visible dorsally. Scale bar = 100 µm. C) 1 mm barbel. Secondary nerve fibers appear within the dorsal half of the barbel. D) Section of an adult barbel at the approximate level shown by the dotted line in C. Innervation is visible as two deep nerve tracts (dn and vn) and a ring of sub-epithelial immunoreactive punctae (p). E,F) Schematic reconstructions of maxillary barbel bud innervation based on confocal tracing of whole-mount acetylated tubulin immunostaining in multiple zebrafish juveniles. F is an enlargement of the jaw region in E.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2806924&req=5

pone-0008737-g005: Innervation of the maxillary barbel.A) 75 µm barbel. In all panels, anterior is to the left. Whole-mount immunohistochemistry (anti-acetylated tubulin) shows a central tract of nerve fibers (arrow) within the early barbel bud (dotted white line). Smaller nerve projections are concentrated in the ventral half of the appendage. B) 200 µm barbel. Multiple fascicles of nerve fibers project distally, innervating the barbel's ventral side and distal tip. No large tracts are visible dorsally. Scale bar = 100 µm. C) 1 mm barbel. Secondary nerve fibers appear within the dorsal half of the barbel. D) Section of an adult barbel at the approximate level shown by the dotted line in C. Innervation is visible as two deep nerve tracts (dn and vn) and a ring of sub-epithelial immunoreactive punctae (p). E,F) Schematic reconstructions of maxillary barbel bud innervation based on confocal tracing of whole-mount acetylated tubulin immunostaining in multiple zebrafish juveniles. F is an enlargement of the jaw region in E.
Mentions: As a taste organ, the maxillary barbel is well supplied with nerves. To trace the ontogeny of barbel innervation, we performed whole-mount immunohistochemistry using an antibody against acetylated tubulin [42], [43] to label the neurons in a developmental series of wild types. In juveniles of the smallest size class (>10–12.5 mm SL), a small tubulin-positive branch projects into the mesodermal core of the maxillary barbel bud, apparently innervating a ventral cluster of incipient taste buds (Fig. 5A). We also observed a nerve net of small, sinuous fibers throughout the barbel's epidermal sheath.

Bottom Line: Barbels are integumentary sense organs found in fishes, reptiles and amphibians.Finally, we show that the maxillary barbel can regenerate after repeated injury and also in senescent fish (>2 years old).Although the teleost barbel has no human analog, the cell types it contains are highly conserved.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, DePaul University, Chicago, Illinois, United States of America. eleclair@depaul.edu

ABSTRACT

Background: Barbels are integumentary sense organs found in fishes, reptiles and amphibians. The zebrafish, Danio rerio, develops paired nasal and maxillary barbels approximately one month post fertilization. Small in diameter and optically clear, these adult appendages offer a window on the development, maintenance and function of multiple cell types including skin cells, neural-crest derived pigment cells, circulatory vessels, taste buds and sensory nerves. Importantly, barbels in other otophysan fishes (e.g., catfish) are known to regenerate; however, this capacity has not been tested in zebrafish.

Methodology/principal findings: We describe the development of the maxillary barbel in a staged series of wild type and transgenic zebrafish using light microscopy, histology and immunohistochemistry. By imaging transgenic zebrafish containing fluorescently labeled endothelial cells (Tg(fli1a:EGFP)), we demonstrate that the barbel contains a long ( approximately 2-3 mm) closed-end vessel that we interpret as a large lymphatic. The identity of this vessel was further supported by live imaging of the barbel circulation, extending recent descriptions of the lymphatic system in zebrafish. The maxillary barbel can be induced to regenerate by proximal amputation. After more than 750 experimental surgeries in which approximately 85% of the barbel's length was removed, we find that wound healing is complete within hours, followed by blastema formation ( approximately 3 days), epithelial redifferentiation (3-5 days) and appendage elongation. Maximum regrowth occurs within 2 weeks of injury. Although superficially normal, the regenerates are shorter and thicker than the contralateral controls, have abnormally organized mesenchymal cells and extracellular matrix, and contain prominent connective tissue "stumps" at the plane of section--a mode of regeneration more typical of mammalian scarring than other zebrafish appendages. Finally, we show that the maxillary barbel can regenerate after repeated injury and also in senescent fish (>2 years old).

Conclusions/significance: Although the teleost barbel has no human analog, the cell types it contains are highly conserved. Thus "barbology" may be a useful system for studying epithelial-mesenchymal interactions, angiogenesis and lymphangiogenesis, neural pathfinding, wound healing, scar formation and other key processes in vertebrate physiology.

Show MeSH
Related in: MedlinePlus