Difference in Sexual Maturation Ages and Levels of Hypothalamic GnRH-I, POMC and NPY mRNA in Shaoxing Ducks During Long- or Short-day Photoperiods

Shaoxing ducks raised in long-day (LD) or short-day photoperiods (SD) matured at different ages. The aim of this study was to investigate the central mechanisms behind this difference. The results were as follows: Ducks raised in LD grew faster and matured earlier than those raised in SD. LD and SD ducks attained puberty at 120 and 150 days of age, respectively. Additionally, the hypothalamic gonadotropinreleasing hormone-I (GnRH-I) pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) mRNA abundance were detected by semi-quantitative RT-PCR using β-actin or 18S rRNA as an internal standard. The results showed that, even though the profile of GnRH-I mRNA expression was similar between two groups, which increased progressively during sexual maturation, the level was higher in LD ducks than in SD ducks of corresponding ages, especially at 120 days of age (P<0.05). The levels of hypothalamic POMC and NPY gene expression showed different patterns compared with GnRH-I gene. POMC and NPY mRNA reached the highest level on D60 or D90, then decreased significantly till D150. Multi-factor ANOVA analysis showed that the LD photoperiod stimulated the expression of hypothalamic GnRH-I and POMC mRNA, but had no effect on NPY gene expression. These results suggest that the hypothalamic GnRH-I gene is the key factor for the onset of puberty and earlier maturation for ducks raised in the LD photoperiod. Additionally, right before or at the onset of laying, the coincidence of down-regulation of POMC and NPY mRNA and up-regulation in GnRH-I gene expression in hypothalamus indicates that GnRH-I, POMC and NPY gene work synergistically underlying the onset of puberty in Shaoxing ducks.

Keywords
Gonadotrophin-releasing hormone-I (GnRH-I), Pro-opiomelanocortin (POMC), Neuropeptide Y (NPY), Sexual maturation, Photoperiod, Reverse transcription-polymerase chain reaction (RT-PCR), Shaoxing ducks