Roles of Notch Receptors in Epithelia Cell Fate Selection in Intestinal Development During Embryogenesis of Zebrafish

Abstract

During zebrafish embryogenesis, differentiation and specialization of intestinal epithelial cells begin at the larva stage (72 hpf). Notch signaling is used multiple times during intestinal development to specify cell fate decisions and commitment. There are four Notch receptors and five ligands in zebrafish. Notch signals transmit between adjacent cells by lateral inhibition. Activation of Notch receptors by secretory cells initiates differentiation of enterocytes, while loss of Notch signaling in zebrafish intestine results in many additional secretory cells. At Dr. Wallace's lab, they identified a group of intestinal secretory cells at the interfold base that receive Notch signaling (Notch receiving secretory cells NRSCs). The interruption of Notch signaling during embryogenesis results in the elevation of cell proliferation in the interfold region due to the interruption of NRSC production. In this work, we hypothesized that two Notch receptors work redundantly to guide epithelial cell differentiation and production towards secretory cell fate, and simultaneously, two Notch receptors work redundantly to signal NRSC differentiation. To test the hypotheses, simultaneous null mutant embryos were created using previously identified heterozygous mutant adult fish in the four zebrafish Notch genes. Screening of combined null mutant intestines and determining the average number of secretory cells in each null mutant combination allows us to decide which gene combination causes the dramatic increase of secretory cell number in intestinal development during embryogenesis. The Notch receptors control NRSCs during their development, and differentiation was identified using the same null mutants of notch genes. We created double 4 mutant embryos to determine which combination of receptors causes the most dramatic reduction in NRSC numbers during embryogenesis when unavailable. To visualize NRSCs, we used a Ncre zebrafish transgenic line with a Notch responsive Cre driver and responder transgene, which turns on nuclear mCherry to label and fate map Notch receiving cells.