Effect of active immunization with OPN5 on follicular development and egg production in quail under different photoperiods.

OPN5 is one of the main deep brain photoreceptors (DBPs), converting photoperiodic information into neuroendocrine signals to regulate reproduction in birds. This study investigated the mechanism of OPN5-mediated photoperiodic regulation of reproduction by active immunization against OPN5. 96 female quail were divided into OPN5-immunized and control group under the same photoperiod: 16 L:8 D (d 1 to d 35), 8 L:16 D (d 36 to d 70) and 12 L:12 D (d 71 to d 126). OPN5-immunized group was conducted with OPN5 protein vaccination and control group was given a blank vaccine. Samples were collected on d 1, d 30, d 60, and d 126. Results showed switching photoperiod to 8 L:16 D decreased the laying rate, GSI%, numbers of YFs and WFs, serum levels of PRL, P4 and E2, and pituitary PRL and TSHβ protein expressions in both groups (P < 0.05). Whereas the OPN5-immunized group exhibited higher laying rates than the control group (P < 0.05). The control group showed reduced GnRHR and TSHβ gene expressions in the pituitary and increased GnIH and DIO3 transcript and/or protein abundance in the hypothalamus. (P < 0.05). The OPN5-immunized group had lower DIO3 expression at both mRNA and protein levels. (P < 0.05). Switching photoperiod from 8 L:16 D to 12 L:12 D increased the laying rates, GSI%, numbers of YFs and WFs, serum levels of PRL, and PRL protein expression in both groups (P < 0.05), and the responses were more pronounced in OPN5-immunized group (P < 0.05). In contrast to the control group, quail with OPN5-immunization had higher OPN5 and DIO2 transcript and/or protein levels but lower DIO3 expressions in the hypothalamus along the transition photoperiods (P < 0.05). The results revealed that OPN5 responds to photoperiod transition, and its activation mediates related signaling to up-regulate TSH-DIO2/DIO3 pathway and VIP-PRL secretion to prime quail reproductive functions.