INTRODUCTION Fatty acid binding proteins (FABPs) constitute a multigene family of small intracellular proteins that bind hydrophobic ligands such as fatty acids, eicosanoids and retinoids. More than 12 different FABPs have been described (Börchers and Spener, 1994) and by sequence homology they can be classi- fied into 4 major subfamilies: heart-, liver- and intestinal type FABPs as well as the group of cellular retinoid binding proteins (CRtBPs). FABPs, in general, are synthesised in specific differentiated tissues (Matarese et al., 1989; Veerkamp et al., 1991). The physiological roles of FABPs remain imperfectly understood while structural diversity, tissue and ligand specificity suggest distinct functional specializations (Kaikaus et al., 1990). Evidence supports a dual function: alleviation of intracellular transport and metabolism of their hydrophobic ligands and sequestration of ligands in a manner that limits their associa- tion with alternative binding sites, in particular with members of the nuclear hormone receptor superfamily such as the retinoic acid receptors (RAR, RXR), and the peroxisome pro- liferator activated receptors (PPAR). In the case of CRtBPs, evidence has been provided that the binding protein-ligand complexes act as direct substrates in several steps of retinoid conversion (Napoli, 1993; Posch et al., 1992). Thereby, these proteins may be implicated in the generation of retinoic acid gradients. It was suggested that other FABPs might fulfill a similar role with respect to hydrophobic ligands, such as fatty acids or their metabolites, for other members of the large nuclear hormone receptor family such as PPAR or one of the ‘orphan’ receptors (Bass, 1993; Issemann et al., 1992). This hypothesis is based on observations that expression of liver- and adipocyte-FABP is induced by fatty acids in hepatocytes and adipocytes (Kaikaus et al., 1993; Grimaldi et al., 1992), respectively, that PPAR induces FABP expression in hepato- cytes (Brandes et al., 1990), that overexpression of liver-FABP in hepatoma cells increased their growth response to linoleic acid (Keler and Sorof, 1993), and that fatty acids and eicosanoids may activate PPAR and RXR (Eager et al., 1992; Keller et al., 1993). We have been studying the function of mammary derived growth inhibitor (MDGI) (Böhmer et al., 1987), which is 2637 Development 120, 2637-2649 (1994) Printed in Great Britain © The Company of Biologists Limited 1994 Fatty acid binding proteins (FABPs) are a multigene family of small intracellular proteins that bind hydrophobic ligands. In this report we describe the cloning and expression pattern of a novel member of this gene family that is specifically expressed in the developing and adult nervous system and thus was designated brain (B)-FABP. B-FABP is closely related to heart (H)-FABP with 67% amino acid identity. B-FABP expression was first detected at mouse embryonic day 10 in neuroepithelial cells and its pattern correlates with early neuronal differentiation. Upon further development, B-FABP was confined to radial glial cells and immature astrocytes. B-FABP mRNA and protein were found in glial cells of the peripheral nervous system such as satellite cells of spinal and cranial ganglia and ensheathing cells of the olfactory nerve layer from as early as embryonic day 11 until adulthood. In the adult mouse brain, B-FABP was found in the glia limitans, in radial glial cells of the hippocampal dentate gyrus and Bergman glial cells. These findings suggest a function of B- FABP during neurogenesis or neuronal migration in the developing nervous system. The partially overlapping expression pattern with that of cellular retinoid binding proteins suggests that B-FABP is involved in the metabo- lism of a so far unknown hydrophobic ligand with potential morphogenic activity during CNS development. Key words: fatty acid binding protein, gene isolation, radial glia, ensheathing cells, satellite cells, neuroepithelium, CNS development, mouse SUMMARY The expression pattern of a novel gene encoding brain-fatty acid binding protein correlates with neuronal and glial cell development Andreas Kurtz 1 , Andreas Zimmer 1 , Frank Schnütgen 2 , Gerold Brüning 3 , Friedrich Spener 2 and Thomas Müller 4, * 1 Unit on Developmental Biology, National Institute of Mental Health, Bethesda, USA 2 Department of Biochemistry, University of Münster, Germany 3 Department of Anatomy, Free University of Berlin, Berlin, Germany 4 Max-Delbrück-Center for Molecular Medicine, Berlin, Germany *Author for correspondence at his present address: Laboratory of Molecular Biology, NINDS, Bldg. 36, Room 3D02, National Institutes of Health, Bethesda, MD 20892, USA