Ultra-Structural Identification of the Interstitial Cells of Cajal in the Zebrafish Danio rerio

Abstract

The interstitial cells of Cajal (ICCs) are important mediators of gastrointestinal motility due to their role as pacemakers in the GI tract. In addition to their function, ICCs are also structurally distinct cells most easily identified by their ultra-structural features and expression of the tyrosine kinase receptor c-KIT. ICCs have been described in mammals, rodents, birds, reptiles and amphibians ; there are no reports at the ultra-structural level of ICC’s within the GI tract of an organism from the teleost lineage. This report describes the presence of cells in the muscularis of the zebrafish intestine with similar features to ICCs in other vertebrates. ICC-like cells were associated with the muscularis, were more electron dense than surrounding smooth muscle cells, possessed long cytoplasmic processes and mitochondria, and were situated opposing to enteric nervous structures. In addition, immunofluorescent and immunoelectron microscopic studies using antibodies targeting the zebrafish ortholog of a putative ICC marker, c-KIT (kita), demonstrated c-kit immunoreactivity in zebrafish ICCs. Taken together, these data represent the first ultra-structural characterization of cells in the muscularis of the zebrafish Danio rerio and suggest ICC differentiation in vertebrate evolution may date back to the teleost lineage.