Localization and phosphorylation of Ab1-interactor proteins, Abi-1 and Abi-2, in the developing nervous system

Abl-interactor (Abi) proteins are targets of Abl-family nonreceptor tyrosin e kinases and are required for Rac-dependent cytoskeletal reorganization in response to growth factor stimulation. We asked if the expression, phospho rylation, and cellular localization of Abi-1 and Abi-2 supports a role for these proteins in Abl signaling in the developing and adult mouse nervous s ystem. In mid- to late-gestation embryos, abi-2 message is elevated in the central and peripheral nervous systems (CNS and PNS). Abi-1 mRNA is present , but not enhanced, in the CNS, and is not observed in PNS structures. Abi proteins from brain lysates undergo changes in apparent molecular weight an d phosphorylation with increasing age. In the postnatal brain, abi-1 and ab i-2 are expressed most prominently in cortical layers populated by projecti on neurons. In cultured neurons, Abi-1 and Abi-2 are concentrated in puncta throughout the cell body and processes. Both Abi and Abl proteins are pres ent in synaptosomes and growth cone particles. Therefore, the Abi adaptors exhibit proper expression patterns and subcellular localization to particip ate in Abl kinase signaling in the nervous system.