Nat. Genet. 47, 353–360 (2015); published online 2 March 2015; corrected after print 16 April 2015

In the version of this article initially published, an accession number was not provided for RNA-seq data sets. The RNA-seq data sets that passed quality control are available at the Sequence Read Archive (SRA) under accession SRP056236. The error has been corrected in the HTML and PDF versions of the article.