HAND1 and omphalocele: To understand where the Hand1 expression domain could be contributing to omphalocele in the Hand1Hand2/Hand2 embryos beyond expression within the dorsal mesentery and gut (Fig. 1), we interrogated Hand1 expression using our Hand1lacZ/+ allele (Firulli et al., 1998) at E11.5 (Fig. S3).