OTX2 HOMEOPROTEIN IN THE DEVELOPING CENTRAL-NERVOUS-SYSTEM AND MIGRATORY CELLS OF THE OLFACTORY AREA

We analyzed the distribution of OTX2 during mouse development. OTX2 is a homeoprotein encoded by Otx2, a vertebrate homeobox gene expressed in the developing brain and anterior head regions. The protein is alre ady detectable in pre-streak embryos, in nuclei of embryonic ectoderm or epiblast and primitive endoderm or hypoblast. Its distribution is u niform along the entire epiblast, while showing an antero-posterior gr adient along the hypoblast at the time when primitive streak first for ms. Between embryonic day 7 (E7) and E7.5 there is a progressive confi nement of the protein to the anterior ectoderm corresponding to the fo rming headfold. At E7.5-E7.8, the protein is mainly confined in this r egion but is still present, though at lower level, in more posterior e ctoderm. Starting from day 8 of development it is essentially confined to anterior neuroectoderm corresponding to presumptive fore- and midb rain. Its subsequent distribution in forebrain, midbrain, developing i sthmo-cerebellum and posterior central nervous system is analyzed in d etail. Of particular interest is the presence of OTX2 in nuclei of cel ls of the olfactory system starting from its origin in the olfactory p lacode. OTX2 protein is present in some cells of the olfactory epithel ium, in both the major olfactory epithelium and the vomero-nasal organ , and in scattered migratory cells present in the mesenchyme outside i t. These cells surround the axon bundles of the olfactory nerve along its path from the olfactory epithelium in the nasal cavities to the ol factory bulb in rostral telencephalon and include both ensheathing gli al cells and luteinizing hormone-releasing hormone (LHRH)-positive cel ls.