PROTEIN TARGETING IN THE ANALYSIS OF LEARNING AND MEMORY - A POTENTIAL ALTERNATIVE TO GENE TARGETING

Gene targeting using homologous recombination in embryonic stem (ES) c ells offers unprecedented precision with which one may manipulate sing le genes and investigate the in vivo effects of defined mutations in t he mouse. Geneticists argue that this technique abrogates the lack of highly specific pharmacological tools in the study of brain function a nd behavior. However, by now it has become clear that gene targeting h as some limitations too. One problem is spatial and temporal specifici ty of the generated mutation, which map appear in multiple brain regio ns or even in other organs and may also he present throughout developm ent, giving rise to complex, secondary phenotypical alterations. This may be a disadvantage in the functional analysis of a number of genes associated with learning and memory processes. For example, several pr oteins, including neurotrophins cell-adhesion molecules - and protein kinases, that play a significant developmental role have recently been suggested to be also involved in neural and behavioral plasticity. Kn ocking out genes of such proteins may lead to developmental alteration s or even embryonic lethality in the mouse, making it difficult to stu dy their function in neural plasticity, learning, and memory. Therefor e, alternative strategies to gene targeting may be needed. Here, we su ggest a potentially useful in vivo strategy based on systemic applicat ion of immunoadhesins, genetically engineered fusion proteins possessi ng the Fe portion of the human IgG molecule and, for example, a bindin g domain of a receptor of interest. These proteins are stable in vivo and exhibit high binding specificity and affinity for the endogenous l igand of the receptor, but lack the ability to signal. Thus, if delive red to the brain, immunoadhesins may specifically block signalling of the receptor of interest. Using osmotic minipumps, the protein can be infused in a localized region of the brain for a specified period of t ime (days or weeks). Thus, the location and timing of delivery are con trolled. Here, we present methodological details of this novel approac h and argue that infusion of immunoadhesins will be useful for studyin g the role particular receptors play in behavioral and neural plastici ty.