The murine Lin28b cDNA was inserted into the HS 21/45-vav vector containing 3' and 5' Vav1-regulatory elements. The Vav1-regulatory elements target expression of Lin28b to hematopoietic tissues. Transgenic mRNA is expressed in the bone marrow, spleen and thymus. Three lines were made, C3, D4, and D10. (J:189197)