The tissue-specific transcription factor Pit-1 is expressed in the spinal cord of the lancelet, Branchiostoma lanceolatum Simona Candiani, Mario Pestarino* Institute of Comparative Anatomy, University of Genova, viale Benedetto XV 5, 16132 Genova, Italy Received 14 October 1998; received in revised form 13 November 1998; accepted 16 November 1998 Abstract 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.  1999 Elsevier Science Ireland Ltd. All rights reserved Keywords: Pit-1; Glial fibrillary acidic protein; Immunocytochemistry; Lancelet (Branchiostoma lanceolatum); Spinal cord; Glia; Evolution The central nervous system of the lancelet Branchios- toma lanceolatum (Cephalochordata, Protochordata) con- sists of a cerebral vesicle and a spinal cord. The dorsal spinal cord overlies the notochord. The central canal of the spinal cord is cylindrical ventrally and tapers dorsally. Typically, dorsal roots go from the dorsolateral side of the spinal cord into each myocomma. They then extend to the outer surface of the muscle blocks, and reaching the ventral region they divide into dorsal and ventral branches. The dorsal roots alternate along the cord and contain somatic- sensory, visceral-sensory and viscero-motor fibers. In the lancelet, true ventral roots are absent, but segmentally dis- tributed ventral neuromuscular junctions can be considered the equivalent of the ventral roots [6]. The dorsal spinal roots originate from different types of nerve cells: (1) the most anterior Rohde cells (2) the so-called visceral moto- neurons ventrally located and (3) the Retzius bipolar cells forming a double column along the cord roof. Commissural cells of several types link the dorsal somatic-sensory col- umn. Different glial cell types are present in the lancelet spinal cord. The most abundant type is the ependymal glial cell that lines the central canal and sends processes in bun- dles to the cord periphery [1]. Photoreceptors known as Hesse eyecups, consisting of two types of cells, receptor and pigment elements, respectively, are ventrally distribu- ted in groups along the spinal cord [14]. Cephalochordates and vertebrates show common ances- tral patterns from many points of view [10,18]. Neverthe- less, the extant cephalochordates cannot be considered primitive even if they are classified the sister group of ver- tebrates. Recently, the increasing number of molecular phy- logenetic studies together with the expression analysis of some gene families such as Otx, Pax and Hox in urochor- dates, cephalochordates and vertebrates may allow to deter- mine which features are primitive or derived [20]. The vertebrate spinal nerve organization seems to be evolved from an ancestral state. In particular, the spinal cord of the lampreys could be derived from a lancelet-like organization by the addition of ventral roots, neural crest- Neuroscience Letters 260 (1999) 25–28 0304-3940/99/$ - see front matter  1999 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00933-1 * Corresponding author. Tel.: +39 010 3538043; fax: +39 010 3538047; e-mail: e-mail: pesta@unige.it