Ben ("bursal epithelium and neuron"), a 95 to 100 kd cell surface glycoprotein functioning during chicken development, is a homophilic member of the immunoglobulin superfamily composed of 5 extracellular immunoglobulin domains, a transmembrane region and a short intracellular tail (1). Ben is transiently expressed in various cell types, including neuronal, epithelial and hemopoietic cells. In the nervous system, Ben is expressed on axonal subtypes during growth and synaptogenesis (1,2). Ben is structurally related to IrreC-rst, a neural cell adhesion molecule of Drosophila (3) that causes dominant axonal projection defects in vivo (in preparation) when misexpressed by the Gal4/UAS system (4). We wondered whether similar effects could be caused by misexpression of Ben.

Therefore a ben cDNA was cloned into the pUAST vector and transformed into the germline of Drosophila. Crossing these transformants with Gal4 lines yielded F1 individuals displaying Ben immunoreactivity in a Gal4-line specific manner. Figure shows 3rd instar larval cns of Gal41407/ UAS-ben genotype.

Ben misexpression does not mimick the effects of misexpression of IrreC-rst. In fact, no Gal4-line used so far has caused any mutant phenotype in combination with UAS-ben. This is somewhat surprising as the Ben protein is transported into the axons of Drosophila and is able to mediate homophilic adhesion in vitro (C. Corbel et al, in preparation).

The conclusion is that Ben may require co-factors for functioning that are absent in Drosophila. If such factors are detected in chicken their ability to reconstitute Ben function will be tested by co-expression. Until then, Ben is a harmless axonal marker for Gal4 expressing neurons in Drosophila.

We thank J. Urban and G.M. Technau (Mainz) for providing the Gal4-lines used in this study. Our work was supported by the DFG (Fi 336/7-1) and the Fonds der Chemischen Industrie.

(1) Pourquie, O., Corbel, C., Le Caer, J.-P., Rossier, J., and Le Douarin, N.M. (1992). BEN, a surface glycoprotein of the immunoglobulin superfamily, is expressed in a variety of developing systems. Proc. Natl. Acad. Sci. USA 89, 5261-5265.

(2) Pourquie, O., Coltey, M., Thomas, J.-L. and Le Douarin N.M. (1990). A widely distributed antigen developmentally regulated in the nervous system. Development 109, 743-752

(3) Ramos R.G.P., Igloi G.L., Lichte B., Baumann U., Maier D., Schneider T., Brandstätter J.H., Fröhlich A., and Fischbach K.-F. (1993). The irregular chiasm C-roughest locus of Drosophia, involed in axonal pathfinding and programmed cell death, encoodes a novel immunoglobulin-like protein. Genes & development 7, 2533-2547 ---> Abstract

(4) Brand, A.H., Perrimon, N. (1993). Targeted Gene Expression as a Means of Altering Cell Fates and Generating Dominant Phenotypes. Development 118, 401-415