Apoptosis in the development of the mouse olfactory epithelium

Apoptotic cells were detected in the mouse olfactory epithelium (OE) at dif ferent embryonic and postnatal stages by in situ nick translation (ISNT) an d Tdt-mediated dUTP nick end-labeling (TUNEL) techniques. During developmen t, the apoptotic process presented two peaks. One at E12 during the invagin ation of the olfactory placode and the second at E16 corresponding to olfac tory axon synaptogenesis. Then, from E18, a sharp decrease in the number of apoptotic cells was observed and at E19 the apoptotic index reached low va lues that were maintained in postnatal stages, pi and P8, and in the adult. Apoptotic nuclei belonged to mature as well as immature olfactory receptor neurons (ORNs). Indeed, double-labeling experiments evidenced apoptotic ne urons immunopositive for olfactory marker protein (OMP), carnosine and GAP- 43. According to our data, two apoptotic phases occur during early developm ent. One is involved in the morphogenesis of the OE when this last is not y et, or poorly, connected to its target, the olfactory bulb (OB). The second peak of apoptosis is more closely dependent on the interplay between OE an d OB. (C) 1999 Elsevier Science B.V. All rights reserved.