PROGRAMMED CELL-DEATH IN THE DEVELOPMENT OF THE MOUSE EXTERNAL AUDITORY-CANAL

Programmed cell death (PCD) is an essential event for development. The purpose of this work was to ascertain how PCD, in vivo designated apo ptosis, is involved in the development of the external auditory canal. We performed a time sequence study of the distribution of apoptosis d uring the development of external auditory canal (EAC) of the mouse. I CR mice ranging in age from embryonic day 11.5 (E11.5) to 12 days afte r birth (DAB) were used in the present study. A Dart of each head incl uding both ears was removed and was processed according to its purpose . Light and electron microscopy for morphological studies and TUNEL me thod (Gavrieli et al. [1992] J Cell Biol., 119:493-501) for histochemi cal studies were used. On E11.5, distinct TUNEL-positive staining occu rred in the branchial arch. Between E15.5 and 1DAB, TUNEL-positive cel ls were observed throughout the EAC and the number of these cells decr eased with age. On E15.5 and E16.5, numerous TUNEL-positive cells were observed in a cavity remained in the epithelial plate. Transmission e lectron microscopy revealed that these cells had the features of apopt osis. From 3-12 DAB, no apoptosis was observed in the EAC except for t he terminal differentiation of the skin of the EAC. Apoptosis was not observed during recanalization of the EAC, but occurred during the for mation of the epithelial plate. The investigation established that PCD is involved in the formation of the epithelial plate, whereas only co rnification of the epithelium of the EAC is associated with recanaliza tion. Anat. Rec. 252:378-382,1998. (C) 1998 Wiley-Liss, Inc.