There was an error published in Development137, 2329-2339.

In the RT-PCR and in situ hybridization section on p. 2330, the primer pair for xMID1 was incorrect. The correct primer pair is shown below.

5′-AGTGTGGTTTCCTATGAGCTA-3′ and 5′-TGTATAATGGTTCTGTTTGAT-3′

The authors apologise to readers for this mistake.