The HRN™ nude mouse was developed by backcrossing the HRN™ mouse to Taconic's NCr nude strain. The HRN™ mouse was developed in the laboratory of C. Roland Wolf of the Ninewells Hospital & Medical School. The model was created by targeting the Por gene to generate a floxed allele in GK129/1 embryonic stem cells derived from 129P2 mice and injecting the targeted cells into C57BL/6 blastocysts. Resultant chimeras were backcrossed to C57BL/6 for one generation. Mice heterozygous for the floxed Por allele were intercrossed to generate mice homozygous for the floxed Por allele on a mixed B6;129P2 background. The Alb-cre transgene was developed in the laboratory of Mark A. Magnuson at Vanderbilt University School of Medicine by microinjecting Cre recombinase gene under the control of the rat albumin enhancer/promoter into B6D2F2 zygotes. Mice homozygous for the floxed Por allele were bred to carriers for the Alb-cre transgene to generate HRN™ mice. The HRN™ model was backcrossed to C57BL/6J a total of 6 generations (N6). Taconic received stock from CXR Biosciences in April 2007. The mice were backcrossed to C57BL/6NTac (N7) and embryo transfer derived. In 2009, a large scale backcross to the outbred NCr nude strain commenced. After three backcrosses to NCr nudes from representative rotational breeding groups, an intracross was performed. The colony is maintained through rotational outbred mating of females that are homozygous for the floxed Por allele, heterozygous for the nude mutation and carriers for the Alb-cre transgene to males that are homozygous for the floxed Por allele, homozygous for the nude mutation and carriers for the Alb-cre transgene.