Nature 461, 524–528 (2009)

On page 1 of this Letter, Efna2 was inadvertently listed as Efna1 when describing the triple knockout mouse (knockout for Efna2, Efna3 and Efna5). Also, in the online-only Methods section of this Letter, the triple knockout mouse (Efna2/a3/a5) was inadvertently written as Epha2/a3/a5.