EMX2 protein in the developing mouse brain and olfactory area

The distribution of EMX2, the protein product of the homeobox gene Emx2, wa s analyzed in the developing mouse CNS by means of a polyclonal antibody we raised against it. The protein is present in the rostral brain, the olfact ory area and a set of scattered cells lying between the nasal pits and the telencephalon. In the cortical neuroepithelium EMX2 is expressed all along the rostro-caudal axis in a graded distribution with a caudal-medial maximu m and a rostral-lateral minimum. Anti-EMX2 immunoreactivity is also detecta ble in Cajal-Retzius cells as well as in apical dendrites of marginal neuro ns of the cortical plate. We also observe that the EMX2 and EMX1 homeoprote ins display complementary expression patterns in olfactory bulbs and amygda loid complex. Here, they demarcate different neuronal populations, involved in processing olfactory information coming from the vomero-nasal organ and from the main olfactory epithelium, respectively. EMX2 is also detectable in mesencephalic structures, such as the optic tectum and tegmentum. The gr aded distribution of EMX2 along antero-posterior and medial-lateral axes of the primitive cortex prefigures a role of this protein in the subdivision of the cortex in cytoarchitectonic regions and possibly functional areas, w hereas its presence in Cajal-Retzius cells suggests a role in the process o f cortical lamination. (C) 1998 Elsevier Science Ireland Ltd. All rights re served.