The microinjection of messenger RNA encoding the eukaryotic translatio
n initiation factor 4E (elF-4E) into early embryos of Xenopus laevis l
eads to the induction of mesoderm in ectodermal explants. This inducti
on occurs without a stimulation of overall protein synthesis and is bl
ocked by the co-expression of a dominant negative mutant of the proto-
oncogene ras or a truncated activin type II receptor. Although other t
ranslation factors have been studied in vertebrate and invertebrate em
bryos, none have been shown to play a direct role in development. The
results here suggest a mechanism for relaying and amplifying signals f
or mesoderm induction.