John J. Sharp

Genetic variation among 129 substrains and its importance for targeted mutagenesis in mice

Targeted mutagenesis in mice, a powerful tool for the analysis of gene function and human disease, makes extensive use of 129 mouse substrains. Although all are named 129, we document that outcrossing of these substrains, both deliberate and accidental, has lead to extensive genetic variability among substrains and embryonic stem cells derived from them. This clearer understanding of 129 substrain variability allows consideration of its negative impact on targeting technology, including: homologous recombination frequencies, preparation of inbred animals, and availability of appropriate controls. Based on these considerations we suggest a number of recommendations for future experimental design.

Identification of a ferrireductase required for efficient transferrin-dependent iron uptake in erythroid cells

The reduction of iron is an essential step in the transferrin (Tf) cycle, which is the dominant pathway for iron uptake by red blood cell precursors. A deficiency in iron acquisition by red blood cells leads to hypochromic, microcytic anemia. Using a positional cloning strategy, we identified a gene, six-transmembrane epithelial antigen of the prostate 3 (Steap3), responsible for the iron deficiency anemia in the mouse mutant nm1054. Steap3 is expressed highly in hematopoietic tissues, colocalizes with the Tf cycle endosome and facilitates Tf-bound iron uptake. Steap3 shares homology with F420H2:NADP+ oxidoreductases found in archaea and bacteria, as well as with the yeast FRE family of metalloreductases. Overexpression of Steap3 stimulates the reduction of iron, and mice lacking Steap3 are deficient in erythroid ferrireductase activity. Taken together, these findings indicate that Steap3 is an endosomal ferrireductase required for efficient Tf-dependent iron uptake in erythroid cells.