In the last two decades, the zebrafish has emerged as an important model species for heart regeneration studies. Various approaches to model loss of cardiac myocytes and myocardial infarction in the zebrafish have been devised, and have included resection, genetic ablation, and cryoinjury. However, to date, the response of the zebrafish ventricle to cautery injury has not been reported. Here, we describe a simple and reproducible method using cautery injury via a modified nichrome inoculating needle as a probe to model myocardial infarction in the zebrafish ventricle. Using light and electron microscopy, we show that cardiac cautery injury is attended by significant inflammatory cell infiltration, accumulation of collagen in the injured area, and the reconstitution of the ventricular myocardium. Additionally, we document the ablation of cardiac nerve fibers, and report that the re-innervation of the injured zebrafish ventricle is protracted, compared to other repair processes that accompany the regeneration of the cauterized ventricle. Taken together, our study demonstrates that cautery injury is a simple and effective means for generating necrotic tissue and eliciting a remodeling and regenerative response in the zebrafish heart. This approach may serve as an important tool in the methods toolbox for regeneration studies in the zebrafish.

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Protein epitope tags play an important role in protein characterization, allowing for easy detection, tracking and isolation in cellular and biochemical experiments. A polyhistidine tag is an amino acid motif that consists of at least six histidine (His) residues, often located at the N‐ or C‐terminus of the protein. Affinity tags, like His tags, are routinely employed as convenient means of purifying recombinantly expressed proteins. However there have been increasing reports suggesting that His tags interfere with the structure and function of proteins. We hypothesize that His tags affect the energy landscape of proteins. Acyl Co‐A Binding Protein (ACBP) is a single‐domain protein that is thought to fold in a two‐state process To test our hypothesis we studied the stability and folding kinetics of ACBP with differentially located His tags in the presence of buffers with varying pHs with a fluorimeter and a stopped‐flow spectrometer. First, we found that buffer pH differentially affected the charge of the His tag: At a pH of 5.3 Histidine is protonated and at 7 Histidine is deprotonated. Second, we observed a significant difference in the kinetics and thermodynamics of the C‐Terminus His tagged ACBP relative to the taglesss ACBP. In a pH of 5.3, the C‐Term His tagged ACBP was less stable whereas in a pH of 7 it was more stable. On the other hand, there was no significant difference in the thermodynamics or the kinetics of the N‐term ACBP to the tagless ACBP. Taken together our studies suggest that the location of the His tag (and ionic environment) markedly affected the energy landscape of ACBP. Support or Funding Information DePauw University‐PDF