Glial Fibrillary Acidic Protein and Vimentin Immunoreactivity of Astroglial Cells in the Central Nervous System of the African Lungfish, Protopterus annectens (Dipnoi: Lepidosirenidae) Maurizio Lazzari* and Valeria Franceschini Department of Biology, University of Bologna, 40126 Bologna, Italy ABSTRACT The distribution of glial intermediate fila- ment molecular markers, glial fibrillary acidic protein (GFAP), and vimentin, in the brain and spinal cord of the African lungfish, Protopterus annectens, was examined by light microscopy immunoperoxidase cytochemistry. Glial fibrillary acidic protein immunoreactivity is clear and is evident in a radial glial system. It consists of fibers of different lengths and thicknesses that are arranged in a regular radial pattern throughout the central nervous sys- tem (CNS). They emerge from generally immunopositive radial ependymoglia (tanycytes), lining the ventricular surface, and are directed from the ventricular wall to the meningeal surface. These fibers give rise to endfeet that are apposed to the subpial surface and to blood vessel walls forming the glia limitans externa and the perivas- cular glial layer, respectively. GFAP-immunopositive star-shaped astrocytes were not found in P. annectens CNS. In the gray matter of the spinal cord, cell bodies of immunopositive radial glia are displaced from the ependy- mal layer. Vimentin-immunopositive structures are rep- resented by thin fibers mostly localized in the peripheral zones of the brain and the spinal cord. While a few stained fibers appear in the gray matter, the ependymal layer shows no antivimentin immunostaining. In P. annectens the immunocytochemical response of the astroglial inter- mediate filaments is typical of a mature astroglia cell lineage, since they primarily express GFAP immunoreac- tivity. This immunocytochemical study shows that the glial pattern of the African lungfish resembles that found in tetrapods such as urodeles and reptiles. The glial pat- tern of lungfishes is comparable to that of urodeles and reptiles but is not as complex as that of teleosts, birds, and mammals. J. Morphol. 262:741–749, 2004. © 2004 Wiley-Liss, Inc. KEY WORDS: GFAP; vimentin; immunoreactivity; astro- glial cells; CNS; lungfish; Protopterus Radial glia include pear- or spindle-shaped cells with bodies located in the ependymal or periependy- mal layer constituting ependymal or periependymal radial glia, respectively. They are characterized by long cytoplasmic processes radially oriented to the meningeal surface and the vascular wall, where they terminate as endfeet forming the membrana gliae limitans externa and the perivascular glial layer, respectively (Elmquist et al., 1994; Lazzari et al., 1997; Lazzari and Franceschini, 2001). Radial glia not only represent the most phylogenetically primi- tive form of glia (Onteniente et al., 1983; Miller and Liuzzi, 1986), but also an ontogenetically immature type of glia since they are the first to appear during ontogeny of vertebrates that show a complex glial organization (Levitt and Rakic, 1980; Monzon- Mayor et al., 1990). Moreover, in mammals radial glia become progressively reduced as development proceeds and therefore are virtually absent in adults (Pixley and De Vellis, 1984; Elmquist et al., 1994). In the other vertebrates radial glia are retained in the adult (Ebner and Colonnier, 1975; Lazzari et al., 1997; Lazzari and Franceschini, 2001). Glial fibrillary acidic protein (GFAP) is the main component of gliofilaments that belong to the inter- mediate filament class and it is present in mature cells of the astroglial lineage. It is widely considered a reliable molecular marker for this cellular type (Dahl and Bignami, 1985). This protein is expressed in gliofilaments of all astrocyte types: star-shaped fibrous and protoplasmic astrocytes, Bergmann glia, periependymal radial glia, and ependymal radial glia or tanycytes (see Wasowicz et al., 1994; Wicht et al., 1994; Naujoks-Manteuffel and Meyer, 1996, for reviews). Glial fibrillary acidic protein shows considerable stability in its molecular and antigenic characteris- tics across vertebrate phylogeny, as indicated by the observation that in each vertebrate group GFAP shows cross-reactivity to antimammalian GFAP an- tibodies (Onteniente et al., 1983; Dahl et al., 1985; Contract grant sponsor: Ministero dell’Istruzione, dell’Universita `e della Ricerca. *Correspondence to: Maurizio Lazzari, Department of Biology, Uni- versity of Bologna, Via Selmi 3, 40126 Bologna, Italy. E-mail: maurizio.lazzari@unibo.it Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10274 JOURNAL OF MORPHOLOGY 262:741–749 (2004) © 2004 WILEY-LISS, INC.