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

Abl-interactor (Abi) proteins are targets of Abl-family nonreceptor tyrosine kinases and are required for Rac-dependent cytoskeletal reorganization in response to growth factor stimulation. We asked if the expression, phosphorylation, 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 system. 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 and phosphorylation with increasing age. In the postnatal brain, abi-1 and abi-2 are expressed most prominently in cortical layers populated by projection 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 present in synaptosomes and growth cone particles. Therefore, the Abi adaptors exhibit proper expression patterns and subcellular localization to participate in Abl kinase signaling in the nervous system.