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With the aid of a dissecting microscope the small intestine was manually dissected from embryos submerged in in phosphate buffere saline (PBS). The isolation of mesenchyme was performed as described by Nagy et al (2003). The small intestines were then transferred to a Petri dish containing 200 ul of 1% trypsin in Hanks solution. The trypsin was allowed to act on the tissue for 20 minutes at room temperature. The digestion process was stopped with the addtion of ~1 ml of 20% fetal bovine serum (FBS) in Hanks solution plus a small amount of DNAse powder. Mesenchymal tissue was teased away from epithelial tissue with either tungsten needles or fine forceps. Mesenchymal tissue was then collected into Trizol. Mesenchyme from embryos of several litters was collected to obtain enough RNA for SAGE library construction.