A cell system with targeted disruption of the SMN gene - Functional conservation of the SMN protein and dependence of gemin2 on SMN

The motor neuron degenerative disease spinal muscular atrophy is caused by reduced expression of the survival motor neuron (SMN) protein. Here we repo rt a genetic system developed in the chicken pre-B cell line DT40, in which the endogenous SMN gene is disrupted by homologous recombination, and SMN protein is expressed from a chicken SMN cDNA under control of a tetracyclin e (tet)-repressible promoter. Addition of tet results in depletion of SMN p rotein and consequent cell death, which directly demonstrates that SMN is r equired for cell viability. The tet-induced lethality can be rescued by exp ression of human SMN, indicating that the function of SMN is highly conserv ed between the two species. Cells expressing low levels of SMN display slow growth proportional to the amount of SMN they contain. Interestingly, the level of the SMN-interacting protein Gemin2 decreases significantly followi ng depletion of SMN, supporting the conclusion that SMN and Gemin2 form a s table complex in vivo, This system provides a powerful setting for studying the function of SMN in vivo and for screening for potential therapeutics f or spinal muscular atrophy.