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Fig. S1 A splice-blocking morpholino targeted to dll4. (a) Schematic representation of the region spanning exon 4 through exon 7 of dll4. Target sites for MODll4 and the PCR primers used for RT-PCR are indicated. (b) RT-PCR analysis of dll4 splicing upon injection with 5 or 10 ng MODll4. In embryos injected with 10 ng MODll4, the normal transcript is undetectable and replaced by a predominant splice variant lacking exon 6 and with a frame-shift introducing a stop codon in exon 7. A total of 10 ng of the morpholino was used for all subsequent experiments. EF-1α was used as a loading control. The sequence for MODll4 is 5′-TAGGGTTTAGTCTTACCTTGGTCAC-3′. PCR was performed in two rounds using heminested primers. The first reaction was performed using the primer 5′-CATTGATTATTGAGGCCTGG-3′ (located 5′ of the region shown in a) and PCR-rev (5′-CTGTCACACTCTCGCACCTG-3′). A small amount of the resulting product was then amplified using PCR-for (5′-GTTTCGGCCACTACACCTGC-3′) and PCR-rev.