The tissue-specific transcription factor Pit-1 is expressed in the spinal cord of the lancelet, Branchiostoma lanceolatum

The spinal cord of the lancelet Branchiostoma lanceolatum was studied by using a monoclonal antibody to the rat tissue-specific transcription factor, Pit-1. Our previous studies have demonstrated Pit-1 immunoreactivity in different nervous and endocrine structures of the head region of adults and in the rostral central nervous system (CNS) of larval lancelet. Our present results show the presence of Pit-1-like protein in dorso-lateral nerve cells and ependymocytes of the adult spinal cord. Using double immunofluorescence techniques, we have revealed the coexistence of the glial fibrillary acidic protein (GFAP) with Pit-1 in groups of laterally located ependymocytes. The occurrence of GFAP, a specific marker of mammalian astrocytes and radial glia, in some lancelet ependymocytes confirms that glial elements are also present in protochordates. Furthermore, other ependymocytes, located in the roof of the central canal and containing Pit-1-like protein exclusively, could be considered as ependymal tanycytes.