Morpholino knockdown reveals a specific requirement of notch1b for embryonic mast cell development in zebrafish. Morpholinos to zebrafish notch gene homologs were injected in 1 to 4 cell stage wild-type embryos followed by WISH for cpa5, gata2, pu.1, and gata1. notch1b morphants demonstrate a dramatic decrease in the level of cpa5 expression and reduced gata2 expression at 28 hpf, implicating a key role for notch1b in mast cell development mediated through gata2. Bar graphs represent the percent of embryos categorized by WISH expression levels. The table summarizes the predominant phenotype observed for each probe with each morpholino. The numbers of wild-type embryos, notch1a, notch1b, notch2, and notch3 morphants analyzed for each probe were n = 37, 17, 33, 19, and 11 for cpa5; n = 13, 9, 5, 10, and 9 for pu.1; n = 36, 9, 8, 23, and 24 for gata1; and n = 19, 12, 10, 22, and 16 for gata2. MO indicates morpholino; N1a, notch1a; N1b, notch1b; N2, notch2; and N3, notch3. 5× objective, MZ6 microscope (Leica).