APOPTOSIS IN CAVITATION OF MIDDLE-EAR SPACE

Mesenchyme cells surround early ossicles in the developing middle ear, then are replaced by space that is created by what has been described as an expansion of the pharyngeal pouch. Cell death has not been cons idered important in cavitation of chick middle ear (Jaskoll and Maders on [1978] Anat. Rec., 190.177-200), but an uncharacterized form of cel l death has been reported to play a major role in cavitation of mouse middle ear (Jaskoll [1977] PhD thesis, CUNY). We investigated whether this uncharacterized cell death is the non-random form known as apopto sis. We examined the middle ear cavitation process using an in situ im munomarker for apoptosis. CBy RF mice during prenatal days 15-20 and p ostnatal days 1-3 and chick embryos representing HH stages 33-38 were investigated. Apoptotic cells were marked in mouse postnatal day 1. No indication of apoptosis was present in other prenatal and postnatal d ays of development included in this study, although morphology showed that cavitation proceeds over several perinatal days in the mouse. Apo ptosis was not marked in the chick middle ear.Previously observed cell death in murine middle ear is the non-random form of cell death known as apoptosis. Cell death has not been reported in avian middle ear, a nd lack of apoptotic marker supports those observations. The limited o ccurrence of apoptosis in mice and apparent absence of apoptosis in ch icks suggest that several mechanisms contribute to cavitation of verte brate middle ear space. Anat. Rec. 251:286-289, 1998. (C) 1998 Wiley-L iss, Inc.