EX-1, A SURFACE-ANTIGEN OF MOUSE NEURONAL PROGENITOR CELLS AND MATURENEURONS

Using membrane fragments of PCC7-Mz1 embryonal carcinoma cells, an est ablished in vitro model of neural differentiation (Lang et al., J. Cel l Biol., 109 (1989) 2481-2493), we have raised monoclonal antibodies ( mAb) against developmental stage-specific cell surface antigens. As sh own by double-immunofluorescence labeling studies, employing different iating PCC7-Mz1 cells, primary cultures of mouse cerebellum cells and cryosections of mouse brain and other tissues, rat mAb anti-mouse EX-1 recognizes a membrane protein which is exclusively expressed by cells of the neuronal cell lineage. EX-1-expressing neuronal precursor cell s were identified by double labeling with antibodies directed against stem cell markers or BrdU, EX-1-expressing postmitotic neurons by labe ling with antibodies directed against phenotypic markers. In the devel oping mouse brain, the EX-1 antigen is expressed in the neuroepitheliu m already at prenatal day 8, i.e. clearly before the onset of mature n euron-specific marker expression. Increasing co-expression with the la tter is observed from embryonic day E10 throughout neuronal maturation , but not with markers of other cell types tested. From these studies, the EX-1 antigen is the earliest marker for the mouse brain neuronal cell lineage so far discovered.