Expression of Nurr1 during rat brain and spinal cord development

Nurr1 is a member of the nuclear receptor superfamily and is a regulatory factor of differentiation, migration and maturation of mesencephalic dopaminergic neurons. The present study was designed to observe the dynamic changes in the protein expression of Nurr1 and the relationship between Nurr1 and proliferating cell nuclear antigen (PCNA) during rat brain and spinal cord development. And we also investigated the significance of Nurr1 in differentiation and migration of nerve cells. Paraffin-embedded sections, immunohistochemistry, immunohistochemical double staining and Western blot techniques were used. The results demonstrate that the presence of Nurr1-positive cells increased during embryo development and that these cells slowly migrated to locations far from the lateral ventricle. In postnatal rats, the presence of Nurr1-positive cells surrounding the lateral ventricle decreased markedly. The expression of Nurr1 in the cerebral cortex peaked at postnatal days 1-5 (P1-P5) and then decreased as the cells matured, becoming rare in the mature cerebral cortex. As the cells matured, a staircase-shaped migration of Nurr1-positive cells from dorsal areas to ventral areas of the spinal cord could be observed. As maturation continued, the presence of Nurr1-positive cells in the spinal cord decreased, and no Nurr1-positive cells were found in the mature spinal cord. The comparative observation of Nurr1 and PCNA showed that the two proteins were expressed in different regions and in different cells. Nurr1 was confined to differentiated and migrating immature cells and was not present in proliferating cells. We suggest that Nurr1 may play a regulatory role in the differentiation, migration and maturation of nerve cells in the rat brain and spinal cord.