Substrate selectivity APPLies to Akt.

The protein kinase Akt occupies a central position in multiple signaling pathways. Although numerous Akt substrates have been identified, less is known about the factors that regulate specific cellular responses to Akt signaling. In this issue, Schenck et al. (2008) demonstrate that the endosomal protein Appl1 modulates Akt's substrate selectivity to promote cell survival during zebrafish development.