Fluorescent micrograph showing healthy spinal cord neurons of mice with a mutation that causes amyotrophic lateral sclerosis (ALS). ALS is a disease that causes the degeneration of motor neurons. The mice had a mutation that made the enzyme CDK-5 overactive. This enzyme phosphorylates cytoskeletal proteins p35 and p25. However, when CDK-5 phosphorylates p25, CDK-5 becomes overactive and kills neurons. Researchers have now found a peptide called CDK-5 inhibitory peptide (CIP) that can deregulate CDK-5 activity and rescue spinal cord neurons.