213 Calcium‐calmodulin‐dependent cyclic nucleotide phosphodiesterase in cultured spinal cord neurons: modulation of expression by factors present in muscle extract

Several in vitro studies aimed at deciphering F3 function showed that it is a multifunctional molecule involved in different types of effects, depending on its physical form and its cellular context of expression. In a first series of studies we isolated F3-containing membrane microdomains from cerebellum on the basis of their resistance to Triton Xl00 at 4’C. Immunoprecipitation experiments indicated that in these microdomains enriched in GPI-anchored molecules F3, but not NCAM120 or Thyl, was physically associated in a complex with both Ll and fyn tyrosine kinase. This observation supports a functional interaction between these three molecules. In a second series of experiments we prepared a soluble F3Fc chimeric molecule and used it as a probe to isolate molecules binding to F3 Ig domains in cerebellum membrane homogenates. Among these we could identify several molecules bearing HNKI epitope such as tenascin-R, and chondroitine-sulfate bearing molecules, but not the receptor phosphatase 0. F3 contracts different interactions involving both its Ig and FNIII domains. Which physiological effect results from these interactions remain to be identified. 212