transgene insertion 6, Eric N Olson Tg(Pr2x1-Hand2)6Eno|deltabasic http://identifiers.org/mgd/MGI:2652065 deltabasic Tg(Prrx1-Hand2)6Eno O Tg(Pr2x1-Hand2)6Eno Transgene MGI:2652065 transgene