The entire open reading frame of mouse Tbx18 was fused to a mesodermal specific promoter containing a 1495 bp mesodermal element from the 5' untranslated region of the Dll1 gene fused to the Dll1 minimal promoter. Two lines were generated, Tg(Dll1-Tbx18)2Akis and Tg(Dll1-Tbx18)20Akis, with the latter showing a more severe homozygous phenotype. The mesodermal specific promoter was first described in J:63760 (J:63760, J:90513)