Programmed cell death in the development of the mouse external auditory canal

Abstract

Programmed cell death (PCD) is an essential event for development. The purpose of this work was to ascertain how PCD, in vivo designated apoptosis, is involved in the development of the external auditory canal. We performed a time sequence study of the distribution of apoptosis during the development of external auditory canal (EAC) of the mouse. ICR mice ranging in age from embryonic day 11.5 (E11.5) to 12 days after birth (DAB) were used in the present study. A part of each head including both ears was removed and was processed according to its purpose. Light and electron microscopy for morphological studies and TUNEL method (Gavrieli et al. [1992] J Cell Biol., 119:493-501) for histochemical studies were used. On E11.5, distinct TUNEL-positive staining occurred in the branchial arch. Between E15.5 and 1DAB, TUNEL-positive cells were observed throughout the EAC and the number of these cells decreased with age. On E15.5 and E16.5, numerous TUNEL-positive cells were observed in a cavity remained in the epithelial plate. Transmission electron microscopy revealed that these cells had the features of apoptosis. From 3-12 DAB, no apoptosis was observed in the EAC except for the terminal differentiation of the skin of the EAC. Apoptosis was not observed during recanalization of the EAC, but occurred during the formation of the epithelial plate. The investigation established that PCD is involved in the formation of the epithelial plate, whereas only cornification of the epithelium of the EAC is associated with recanalization.

The development of the mammalian outer and middle ear

“…(); Nishizaki et al. () and unpublished observations. E,embryonic day; EAM, external auditory meatus; gd, gestational days; gw, gestational weeks; P, postnatal day.…”

“…Keratin squames can be seen in the forming cavity during this opening process (Michaels & Soucek, ; Nishimura & Kumoi, ; Nishizaki et al. ; Schoenwolf et al. ; Fig.…”

“…Programmed cell death in the epithelium of the EAM may be important for the development of the meatal plug, as seen by terminal deoxynucleotidyl transferase dUTP nick‐end labelling (TUNEL) analysis (Nishizaki et al. ). However, extensive TUNEL‐positive cell death is not seen during the opening of the ear canal (Nishizaki et al.…”

Dominant negative connexin26 mutation R75W causing severe hearing loss influences normal programmed cell death in postnatal organ of Corti

“…The enlarged GER that characterizes caspase 3 (−/−) mice may result from diminished apoptosis and/or elevated levels of cell proliferation during embryogenesis. Most apoptosis within the developing cochlear system of the mouse occurs during embryogenesis [11]. We have demonstrated, however, that apoptosis of GER cells during postnatal stages is essential for normal development of the cochlea [13,32].…”

“…Present at birth, the GER typically disappears by postnatal day 10 (P10) [9,10]. In the mouse, most apoptosis in the developing cochlear system occurs during embryogenesis [11]. In the developing spiral ganglion cells of rats, however, 22% of programmed cell death was measured between P5 and P6 [12].…”