The roles of FGF and Wnt signaling during maxillary barbel regeneration in the Zebrafish (Danio rerio).

The zebrafish (Danio rerio) maxillary barbel is an integumentary sense organ that contains skin, glands, pigment cells, taste buds, nerve fibers, blood vessels and a putative lymphatic. Like other zebrafish organs, the maxillary barbel can regenerate most of its tissues after amputation. However, little is known about the molecular mechanisms that control this regeneration. Fibroblast growth factor (FGF) and wingless (Wnt) signaling are required for the control of zebrafish caudal fin regeneration; due to the similarities between the fin and the maxillary barbel, these regulatory networks may play a role in barbel regeneration as well. In this study, I explored the roles of FGF and Wnt signaling during barbel regeneration by detecting the expression of crucial genes in each pathway. These experiments revealed that many FGF and Wnt pathway members are expressed during early barbel regeneration. To test the necessity of these signaling pathways, I used a variety of in vivo molecular techniques to inhibit candidate genes in barbel regenerates. Results indicated that both pathways play important roles in barbel regrowth; however, some differences between barbel and fin regeneration were observed. Activating a dominant negative fibroblast growth factor receptor (dnfgfr1) reduced the length of barbel regenerates by 60% but completely prevented fin regeneration in the same fish. Interestingly, zebrafish homozygous recessive for a point mutation in fgf20a did not show any inhibition of barbel regeneration, although this ligand was essential for fin regeneration. When the canonical Wnt inhibitor drug IWR-1 was applied to wild type fish, barbel regenerate length decreased by nearly 50%, but was not completely prevented as in fin regenerates of the same fish. Finally, experiments transgenically overexpressing the Wnt antagonist notum1a (nom1a) dramatically inhibited regeneration in both barbels and tails, highlighting this molecule as a potential novel regulator of Wnt-dependent regeneration in zebrafish. These are the first results that describe the molecular mechanisms of zebrafish barbel regeneration. Understanding the similarities and differences between regenerating barbels and other organs could help uncover any molecular themes or, in contrast, any variations that control regeneration. Altogether, this project has established the zebrafish maxillary barbel as yet another accessible and productive model for vertebrate regeneration studies