Development and Regeneration of the Zebrafish Maxillary Barbel: A Novel Study System for Vertebrate Tissue Growth and Repair

Abstract

BackgroundBarbels 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 FindingsWe 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 (∼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 (∼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/SignificanceAlthough 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.

Coevolutionary patterning of teeth and taste buds

“…Preplacode stage represents the model of placode recruitment from a bipotent epithelium. These interactions are consistent with reports in the mouse for taste bud (9,11,70) and tooth (8,21,38,47,49) patterning networks, when studied independently. Based on cichlid expression and treatment data, Wnts drive the formation of taste placodes proximally and tooth placodes distally, whereas BMPs and Hhs are inhibitory of taste bud differentiation and permissive for tooth germs.…”

“…6, red), a marker of innervation (38), and (ii) calretinin/Calb2 (Fig. 6, green) and visualized fluorescence using nonlinear optics in conjunction with multiphoton microscopy.…”

Regeneration of the adult zebrafish brain from neurogenic radial glia-type progenitors

“…A common principle in the regeneration of tissues such as appendages, heart or barbel in adult axolotl and zebrafish is the generation of a population of progenitor cells within the wound blastema, which are generated at least partly through dedifferentiation of differentiated cells (Jopling et al, 2010;Kikuchi et al, 2010;Kragl et al, 2009;LeClair and Topczewski, 2010). By contrast, in our stab-lesion paradigm, most proliferating cells belong to either the RG-or the leukocyte lineage, and the formation of a typical regeneration blastema consisting of undifferentiated mesenchymal cells is not evident.…”

Genetic lineage labeling in zebrafish uncovers novel neural crest contributions to the head, including gill pillar cells

“…Barbels are tentacle-like chemosensory structures that arose independently many times during actinopterygian evolution (LeClair and Topczewski, 2010). Poor homology in terms of embryonic development and cellular composition across different vertebrate taxa complicates phylogenetic comparisons and makes it difficult to trace the evolutionary history of these sensory structures (Fox, 1999).…”

“…These two cell types are likely to be involved in the production of the connective tissue of the supporting central rod. Barbels are an attractive model for understanding tissue regeneration in adult organs (LeClair and Topczewski, 2010). That central components of these structures have a NC origin raises the intriguing possibility of studying the potential role of NC-derived adult tissues in organ repair.…”