Investigation of ciliated cell types and ciliary gene expression during heart regeneration in zebrafish (Danio rerio)

Abstract

Unlike the adult mammalian heart, the adult zebrafish (Danio rerio) heart can regenerate after injury. In a series of regenerative processes, the zebrafish can regenerate their hearts after up to 20% of their ventricle apex is resected. The process of regeneration is directed via highly coordinated cell signaling pathways. Primary cilia act as directors of cell signaling pathways. Important ciliary signaling pathways have been implicated in zebrafish heart regeneration, but the direct link between regeneration and cilia has not been fully elucidated. Previous studies have found cilia present in the outer region of the regenerating zone during zebrafish heart regeneration. This led to the first hypothesis that cilia were present in the epicardium in zebrafish heart regeneration because the epicardium is believed to cover the outer region of the ventricle apex during regeneration. To test this hypothesis, the present study used immunofluorescence of transgenic zebrafish to label the different cell types of the regenerating heart. It was revealed that cilia were present in the outer region regenerating zone but not on the myocardium. There was indirect evidence that the cilia are not on the epicardium. Previous studies also found a change in abundance and length of cilia during zebrafish heart regeneration. This led to the second hypothesis that ciliary genes were differentially expressed during zebrafish heart regeneration. To test this hypothesis, the present study used DESeq2 in R to determine differential gene expression of ciliary genes. A total of 196 ciliary transcripts were found to be differentially expressed in at least one time point in zebrafish heart regeneration. Overall, the ciliated cell types and ciliary gene expression may provide further evidence of the importance of cilia in zebrafish heart regeneration. Continuing to gain insight the mechanisms of zebrafish heart regeneration may lead to clinical applications for human cardiac injury.