There was an error published in Development141, 1971-1980. The correct funding information is given below.


This research was funded largely by a Wellcome Trust Senior Investigator Award [100329/Z/12/Z to W.A.H.]. S.C.S. is funded by a grant [EY14358 to R. O. Wong] from the National Institutes of Health. Deposited in PMC for immediate release.

The authors apologise to readers for this mistake.