We synthesized the 60-amino acid polypeptide corresponding to the sequence of the Drosophia antennapedia gene homeobox. This peptide (pAntp) recognized the consensus motif for binding to the promoter region ofHox-1.3. pAntp mechanically introduced into mammalian nerve cells provoked a dramatic morphological differentiation of the neuronal cultures. Moreover, pAntp directly added to already differentiated neuronal cultures penetrated the cells and further augmented their morphological differentiation. Examination of live and fixed neurons in classical and confocal fluorescence microscopy demonstrated that pAntp was captured at all regions of the nerve cells and accumulated in the nuclei. In addition, the effect of pAntp on neurite extension was blocked in the presence of the protein synthesis inhibitor cycloheximide. Thus, our results demonstrate that neurons possess an efficient uptake system for the antennapedia homeobox peptide and suggest that binding of pAntp to consensus motifs present in nerve cell nuclei influences neuronal morphogenetic programs.Studies on developmental mutants in Drosophila have demonstrated that several DNA binding proteins encoded by homeotic genes are endowed with morphogenetic functions (1, 2). In Drosophila at least, the expression of specific homeotic genes is responsible for the formation of cell assemblies exhibiting precise and defined morphologies. The DNA binding properties ofthese proteins is due to a sequence of about 60 amino acids called the homeobox.The homeobox sequences have been highly conserved during evolution and genes containing homeobox sequences are present in all vertebrates, including mammals (3, 4). In vertebrates, as in Drosophila, homeobox gene expression is not limited to the period during which the general features of body organization are established. In particular, a number of these genes are expressed in the nervous system rather late during development and, in some cases, through adulthood (5-7).In vitro studies have shown that the regulatory effect of homeotic proteins on gene expression depends on the specific binding of the homeobox domain to consensus DNA sequences found in the promotors or enhancers of several reporter genes and homeobox-containing genes (8-10). It has also been clearly demonstrated that the 60-amino acid homeobox polypeptide alone, isolated from the flanking regions, which are necessary for the activation or repression of transcription, has per se a high affinity for such consensus motifs (11).Thus, one possible way to study directly, within the live cell, the role of a homeotic protein family, as defined by the primary structure of the homeobox (e.g., antennapedia-or engrailed-like) and by the recognition of identical binding sites, on neural development would be to synthesize and inject the 60-amino acid homeotic polypeptides into the cells. In fact, such peptides could act as competitive inhibitors of endogeneous homeotic proteins with similar binding specificities.In the experiments presented herein we have used this...

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Interactions between neural cell surfaces seem to be of prime importance during neuroontogenesis, and responsible for the guidance of migrating neuroblasts and growing axons and for the formation of synapses. Little is known about the underlying molecular mechanisms, but most hypotheses imply the existence of cell-surface molecules that mediate the formation of transient or permanent bonds between neural cells. Recently, a membrane glycoprotein called neural cell adhesion molecule (N-CAM) has been characterized in chick and rodent nervous tissue that appears to act as a ligand in adhesion among neural cell bodies or neurites. We have identified a mouse neural surface glycoprotein, named BSP-2 (ref. 7), which by criteriaof electrophoretic migration, developmental changes, amino acid and sugar composition seems to be closely related or identical to N-CAM. Both BSP-2 (refs 8, 9) and N-CAM undergo conversion from an embryonic to an adult form during brain development and it has been suggested that this transition changes the adhesive properties or the binding specificity of the molecule. Using a neuroblastoma line to study functional differences between embryonic and adult BSP-2/N-CAM molecules, we show here that liposomes bearing adult BSP-2 but not those bearing the embryonic form adhere to neuroblastoma cells, demonstrating that the two forms do indeed possess different binding properties.