13-P141 The role of paf and p53 during embryonic diapause in a marsupial

lates with the maturational stage of these cells. We have studied cyclin D1 expression in the inner ear. Besides its well known function in the cell cycle control, cyclin D1 has also been implicated in other cellular processes like cell death, cellular differentiation and cancer. During early embryogenesis cyclin D1 is widely expressed in the developing sensory epithelia, but it becomes downregulated at the onset of morphological differentiation of both cochlear and vestibular hair cells. Interestingly, cyclin D1 expression transiently returns to cochlear hair cells at P3 and stays until P9. This postnatal period corresponds to the period of functional maturation of hair cells. Cyclin D1 is not expressed in differentiated vestibular hair cells, but is strongly expressed in vestibular supporting cells. After first postnatal week cyclin D1 expression is downregulated from vestibular supporting cells, but persists in a small population of these cells until adulthood. Thus, cyclin D1 might be one of the factors that determine the proliferative capacity of hair cells.