Abstract
Zebrafish caudal fin rays are used as a model system for regeneration because of their high regenerative ability, but studies on the regeneration polarity of the fin ray are limited. To investigate this regeneration polarity, we made a hole to excise part of the fin ray and analyzed the regeneration process. We confirmed that the fin rays always regenerated from the proximal margin toward the distal margin, as previously reported; however, regeneration-related genes were expressed at both the proximal and distal edges of the hole in the early stage of regeneration, suggesting that the regenerative response also occurs at the distal edge. One difference between the proximal and distal margins is a sheet-like tissue that is formed on the apical side of the regenerated tissue at the proximal margin. This sheet-like tissue was not observed at the distal edge. To investigate whether the distal margin was also capable of forming this sheet-like tissue and subsequent regeneration, we kept the distal margin separated from the proximal margin by manipulation. Consequently, the sheet-like tissue was formed at the distal margin and regeneration of the fin ray was also induced. The regenerated fin rays from the distal margin protruded laterally from the caudal fin and then bent distally, and their ends showed the same characteristics as those of the normal fin rays. These results suggest that fin rays have an ability to regenerate in both directions; however, under normal conditions, regeneration is restricted to the proximal margin because the sheet-like tissue is preferentially formed on the apical side of the regenerating tissue from the proximal margin.
Highlights
Zebrafish have a high regenerative capacity in many organs, including the retina, spinal cord, part of the heart, and fins [1,2,3,4]
When the distal margin of the hole was kept out of contact with the proximal margin by manipulation, the sheet-like tissue was autonomously formed in the distal margin, and fin ray regeneration occurred from the distal margin. These results suggest that the zebrafish fin ray has an ability to regenerate distal structures bidirectionally, but regeneration is usually restricted to the proximal margin associated with the preferential formation of the sheet-like tissue on the proximal margin
The regenerated fin ray, which was thinner than the original fin ray, was observed from the proximal margin (Figure 1H, arrow); no primordium was observed in the distal margin
Summary
Zebrafish have a high regenerative capacity in many organs, including the retina, spinal cord, part of the heart, and fins [1,2,3,4]. Regeneration proceeds in the following three stages: wound healing, blastema formation, and tissue reorganization [8,11]. Analysis of the gene expression and molecular interactions during the fin regeneration has revealed genes that are selectively expressed in the wound epithelium or regeneration blastema [6,7,9,14,15,16,17]. Expression of genes such as msxb and fgf20a has been reported in mesenchymal cells, which constitute the blastema [21,22,23,24]. The expression of these genes can be considered as an indicator of the formation of each tissue
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