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.

T-type Ca2+ currents have been detected in cells from the external muscular layers of gastrointestinal smooth muscles and appear to contribute to the generation of pacemaker potentials in interstitial cells of Cajal from those tissues. However, the Ca2+ channel subunit responsible for these currents has not been determined. We established that the ? subunit of the ?1H Ca2+ channel is expressed in single myocytes and interstitial cells of Cajal using reverse transcription and polymerase chain reaction from whole tissue, laser capture microdissected tissue and single cells isolated from the mouse jejunum. Whole-cell voltage clamp recordings demonstrated that a nifedipine and Cd2+ resistant, mibefradil-sensitive current is present in myocytes dissociated from the jejunum. Electrical recordings from the circular muscle layer demonstrated that mibefradil reduced the frequency and initial rate of rise of the electrical slow wave. Gene targeted knockout of both alleles of the cacna1h gene, which encodes the ? 1H Ca2+ channel subunit, resulted in embryonic lethality because of death of the homozygous knockouts prior to E13.5 days in utero. We conclude that a channel with the pharmacological and molecular characteristics of the ? 1H Ca2+ channel subunit is expressed in interstitial cells of Cajal and myocytes from the mouse jejunum, and that ionic conductances through the ? 1H Ca2+ channel contribute to the upstroke of the pacemaker potential. Furthermore, the survival of mice that do not express the ? 1H Ca2+ channel protein is dependent on the genetic background and targeting approach used to generate the knockout mice.

The enhancer of rudimentary, e(r), gene encodes a small highly conserved protein, enhancer of rudimentary homolog (ERH), which has been shown to have a regulatory function in cell division, Notch signaling, and cancer progression. Human and Drosophila ERH, both 104 amino acids in length, are 76% identical and 84% similar. The high sequence identity translates into nearly identical tertiary structures. Previous studies on the expression of the human and Drosophila e(r) genes reveal that the two genes are similarly regulated. Data in the present study using an e(r)-eGFP reporter gene confirm these results, showing a high expression of the reporter in the ovaries, testes, and brain. The high structural and regulatory conservation of e(r) and ERH argue that human and Drosophila ERH may be biochemically and functionally equivalent. To test this hypothesis, a chimeric transgene containing the Drosophila e(r) non-coding regions and the human e(r) coding region was constructed and used to establish transgenic Drosophila stocks. This transgene can rescue all of the mutant phenotypes of an e(r) deletion, and Drosophila stocks in which the fly ERH has been replaced with the human ERH are fully healthy and viable. These studies demonstrate that the human and Drosophila ERH are functionally equivalent, suggesting that studies on the activity of the human ERH can be done in Drosophila, where a multitude of genetic and developmental tools are available.