Bio-morphological studies of apoptotic with non-apoptotic dying cells in developing inner ear of mouse embryos.

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Dying cells studied the TdT-mediated dUTP nick end-labeling (TUNEL) method have been classified as ‘apoptotic' and ‘non-apoptotic' cells. In this study, in which 12-day-old mouse embryos were used because of a high frequency of ‘natural cell death' due to changing inner ear morphology, the percentages of ‘apoptotic' and ‘non-apoptotic' dying cells (ADC and NADC) among total dying cells in the inner ear were calculated.Observation of consecutive paraffin sections showed 90% of the dying inner ear cells to be ADC and 10% to by NADC in the control group. 70% of the inner ear dying cells were ADC and 30% were NADC in the cis-diammine-dichloroplatinum (CDDP) group ADC and NADC TUNEL positive dying cells in resin sections observed by light microscopy were examined again by transmission electron microscopy using a re-embedding procedure. ADC and NADC were then analyzed based on the classification of dying cells (type 1,2,3A and 3B) as described by Clarke. It was clear that ADC were the equivalent of type 1(apoptotic) dying cells and NADC were the equivalent of type 2(autophagic) dying cells. No type 3A or 3B cell death occurred. It was suggested that ADC essential to development of inner ear, and increased NADC might be defensive phenomenon against CDDP toxicity. We consider these finding to be important baselines for determining the process underlying abnormal development of the inner ear and its functional disorders such as hearing loss.