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Abstract:
Olfactory epithelium is known for neuronal turnover throughout life by a tight regulation of proliferation and apoptosis. However, proliferation density decreases postnatally (Weiler \& Farbman, J Neurosci 1997, 17, 3610-22) and thus apoptosis should be inhibited to retain the olfactory sheet. Therefore we asked, whether apoptosis
inhibitors are expressed in olfactory tissues, especially in older animals. Using RT-PCR and duplex-RT-PCR we investigated the expression of the apoptosis inhibitor survivin, also known as Birc5, in olfactory mucosa of rats at different postnatal ages (P10-900). We describe here, that survivin is expressed in olfactory mucosa at all
postnatal ages and furthermore, at much higher levels in young animals compared to older ones; survivin expression decreases postnatally as does proliferation density. The question arises, what function does survivin fulfill in the olfactory system, why is the expression much higher in young animals, where there is a backup by high proliferation? In young animals, where proliferation is high, many olfactory sensory neurons compete for the target cells in the
olfactory bulb, and we know that synaptic input is essential for neurons to survive. So it seems reasonable for a neuron to express an apoptosis inhibitor. On the other hand, when proliferation density is decreased in older animals, the turnover pressure is low and apoptosis inhibitors are not necessary as much. Thus we conclude, that the apoptosis inhibitor survivin is expressed to help neurons to survive
during their competition for target contacts until they adjust enough stable synapses, which then take over the survival function.
