Floor plate descendants in the ependyma of the adult mouse Central Nervous System

During embryonic development of the Central Nervous System (CNS), the expression of the bHLH transcription factor Nato3 (Ferd3l) is unique and restricted to the floor plate of the neural tube. In mice lacking Nato3 the floor plate cells of the spinal cord do not fully mature, whereas in the midbrain floor plate, progenitors lose some neurogenic activity, giving rise to a reduced population of dopaminergic neurons. Since the floor plate is considered to be disintegrated at the time of birth, Nato3 expression was never tested postnatally and in adult mice. Here, we utilized a Nato3 knockout mouse model in which a LacZ reporter precisely replaced the coding region under the endogenous regulatory elements, so that its expression recapitulates the spatiotemporal pattern of Nato3 expression. Nato3 was found to be expressed in the CNS throughout life in a highly restricted manner along the medial cavities: in subpopulations of cells in the III^rd ventricle, the cerebral aqueduct, the IV^th ventricle, the central canal of the spinal cord, and the subcommissural organ, a gland located in the midbrain. A few unifying themes are shared among all Nato3-positive cells: all are positioned in the midline, are of an ependymal type, and contact the cerebrospinal fluid (CSF) similarly to the embryonic position of the floor plate bordering the lumen of the neural tube. Taken together, Nato3 defines an unrecognized subpopulation of medial cells positioned at only one side of circular ependymal structures, and it may affect their regulatory activities and neuronal stem cell function.