EX-1, a surface antigen of mouse neuronal progenitor cells and mature neurons

Using membrane fragments of PCC7-Mz1 embryonal carcinoma cells, an established in vitro model of neural differentiation (Lang et al., J. Cell Biol., 109 (1989) 2481-2493), we have raised monoclonal antibodies (mAb) against developmental stage-specific cell surface antigens. As shown by double-immunofluorescence labeling studies, employing differentiating 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 cells were identified by double labeling with antibodies directed against stem cell markers or BrdU, EX-1-expressing postmitotic neurons by labeling with antibodies directed against phenotypic markers. In the developing mouse brain, the EX-1 antigen is expressed in the neuroepithelium already at prenatal day 8, i.e. clearly before the onset of mature neuron-specific marker expression. Increasing co-expression with the latter 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.