The disruption of the nerve growth factor (NGF) gene in transgenic mice leads to a lethal phenotype (Crowley et al., 1994) and hinders the study of NGF functions in the adult. In this study the phenotypic knockout of NGF in adult mice was achieved by expressing transgenic anti-NGF antibodies, under the control of the human cytomegalovirus promoter. In adult mice, antibody levels are 2000-fold higher than in newborns. Classical NGF targets, including sympathetic and sensory neurons, are severely affected. In the CNS, basal forebrain and hippocampal cholinergic neurons are not affected in the early postnatal period, whereas they are greatly reduced in the adult (55 and 62% reduction, respectively). Adult mice show a reduced ability in spatial learning behavioral tasks. Adult, but not neonatal, transgenic mice further show a new phenotype at the level of peripheral tissues, such as apoptosis in the spleen and dystrophy of skeletal muscles. The analysis of this novel comprehensive transgenic model settles the controversial issue regarding the NGF dependence of cholinergic neurons in adult animals and reveals new NGF functions in adult non-neuronal tissues. The results demonstrate that the decreased availability of NGF in the adult causes phenotypic effects via processes that are at least partially distinct from early developmental effects of NGF deprivation.

The crystal structures of the regulated Src and Hck tyrosine kinases show intramolecular interactions between the phosphorylated tail and the SH2 domain as well as between the SH3 domain, the SH2–catalytic domain linker (SH2‐CD linker) and the catalytic domain. The relative contribution of these interactions to regulation of activity is poorly understood. Mutational analysis of Src and Lck revealed that interaction of the SH2‐CD linker with the SH3 domain is crucial for regulation. Moreover, three sites of interaction of the linker with the catalytic domain, one at the beginning (Trp260) and two at the back of the small lobe, opposite the catalytic cleft (β2/β3 loop; αC/β4 loop), impinge on Src activity. Other activating mutations map to the front of the catalytic domain in the loop preceding the αC‐helix (β3/αC loop). SH2‐CD linker mutants are deregulated in mammalian cells but transform fibroblasts weakly, suggesting that the linker may bind cellular components. Interpretation of our results on the basis of the crystal structure of Src favours a model in which the correctly positioned SH2‐CD linker exerts an inhibitory function on catalysis of Src family members by facilitating displacement of the αC‐helix. This study may provide a template for the generation of deregulated versions of other protein kinases.