Apoptotic mechanism behind the testicular atrophy in photorefractory and scotosensitive quail: Involvement of GnIH induced p-53 dependent Bax-Caspase-3 mediated pathway.

In most of the avian species, daylength or photoperiod is the main environmental factor regulating reproduction. During their annual gonadal cycle, birds once sensitive to short or long day effect develop refractoriness to the same daylength and gonad develop or regress accordingly. The present study investigated the effects of photoperiodic alterations on apoptosis mediated testicular responses of photosensitive/photorefractory and scotosensitive/scotorefractory quail, Coturnix coturnix japonica. Testicular apoptosis in the quail of different photoperiodic conditions was assessed by monitoring the alterations in the local testicular expression of GnRH-I, GnIH, pro-apoptotic proteins (p53 and Bax), inactive caspase (pro-Caspase-3), executioner active-Caspase-3 and inactive/uncleaved PARP-1 (DNA repair enzyme) and TUNEL analysis. Alterations in these parameters indicate that testicular quiescence/regression in scotosensitive and photorefractory quail is mediated by apoptosis of testicular cells and hence apoptosis appears to be the key mechanism of testicular regression in Japanese quail. Present findings demonstrated the underlying molecular mechanism of how avian testes respond differentially to same photoperiodic conditions and exhibit scoto-/photo-sensitivity and refractoriness. It is concluded that photoperiod induced testicular stimulation in photosensitive/scotorefractory quail may be due to apoptotic inhibition and testicular regression in scotosensitive/photorefractory quail is guided by apoptosis, an effect invariably regulated by local action of GnRH and GnIH.