Phenotypic abnormalities observed in aged cloned mice from embryonic stem cells after long-term maintenance

Somatic/embryonic stem cell cloning has made it possible to produce an individual genomically identical to another individual. However, the cloned animals have a variety of abnormalities caused by the aberrant gene modification, with insufficient reprogramming in cloning. We previously reported abnormalities in cloned mice at birth. In this study, we examined what abnormalities could be seen in cloned mice after long-term maintenance. The aged cloned mice showed multiple abnormalities: increase of body weight, some phenotypic abnormalities in the kidneys, testes and thymus, and lower urea nitrogen in their serum biochemical values. The kidneys of all cloned mice were hypertrophied, with a metamorphic or whitish appearance. The multiple lesions, including the enlarged renal pelvis and distension of the renal veins in histology, might be the result of urine accumulation by urinary tract obstruction. The testes of the cloned mice were atrophied, and showed no sperm formation in histology. In contrast, the thymus was rather hypertrophied, and a comparably increased number of lymphocytes were observed in the medulla, consisting mainly of T cells. By conducting a progeny test between the cloned mice, it was confirmed that these abnormalities in the aged cloned mice were not transmitted to their offspring, indicating that the incomplete reprogramming in clones might be in part responsible for the abnormalities detected in aged clones. These results indicate that the postnatal abnormalities observed in aged cloned mice are varied and can be restored through the germ line.