Correction

INAUGURAL ARTICLE, DEVELOPMENTAL BIOLOGY. For the article “Nuclear cloning of embryonal carcinoma cells,” by Robert H. Blelloch, Konrad Hochedlinger, Yasuhiro Yamada, Cameron Brennan, Minjung Kim, Beatrice Mintz, Lynda Chin, and Rudolf Jaenisch, which appeared in issue 39, September 28, 2004, of Proc. Natl. Acad. Sci. USA (101, 13985–13990; first published August 11, 2004; 10.1073/pnas.0405015101), all authors agree to this correction. The mouse embryonal carcinoma cell line referred to in the publication as METT-1 was in fact a derivative designated METT-1a, and it should have been referred to as such throughout the paper. The METT-1 cell line was isolated from an induced teratocarcinoma and found to be karyotypically normal (29). When injected into blastocysts, the cells contributed to all somatic tissues and to the germ line (25). The cells in the present study were grown from a thawed aliquot of the METT-1 line, previously tested in vivo and frozen at culture passage 12 (25). In the experiments we performed, the cells were grown in a medium different from the one to which they had been adapted, and they were passaged repeatedly to obtain the data reported in the present study. Genetic and developmental differences, relative to METT-1, may have arisen during these passages. This correction does not change the conclusions in the present study.