Survival motor neuron: motor neuron insurance for a whole lifespan?

The SMN (survival motor neuron) gene plays an important role in ontogenesis and its dysfunction leads to immatu-rity of skeletal muscles and motor neurons in the spinal cord. As a result of SMN mutations the affected cells die and clinical symptoms of spinal muscular atrophy (SMA) develop. Physiologically, SMN together with gemins is part of a multiprotein complex of particular importance to motor neuron development. Since the SMN gene is necessary for normal motor neuron maturity, a question arises whether its expression is preserved in postnatal life or finishes with the end of ontogenesis. To answer this question we examined expression of SMN and gemins 2, 3 and 4 in spinal cords of Wistar rats at age 1-350 days using immunofluorescence and immunohistochemical methods. In the examined animals expression of SMN appeared in neurons in 20-day old rats and increased with animal age. In rats aged 30-350 days SMN immunoreactivity was similar in all the examined animals. The same phenomenon was observed in assessment of gemin expression. Our study revealed that in rat spinal cord expression of SMN and gemins 2, 3 and 4 is present through a whole animal lifespan and not only in motor but also in sensory and autonomic neurons.