GnRHr, LHr, and Vg gene expression levels and ovarian development of G5 transgenic mutiara female catfish (Clarias gariepinus) after exposure photoperiod induction

Abstract

This study aimed to determine the relative expression ratios of the genes gonadotrophin-releasing hormone receptor (GnRHr), luteinizing hormone receptor (LHr), vitellogenin (Vg) and β-actin genes as expression control internal of the G5 fish using real-time PCR in a photoperiod experiment with designed treatments (A: 8L-16D; B: 12L-12D; C: 16L-8D for transgenic fish; and A*: 8L-16D; B*: 12L-12D; C*: 16L-8D for nontransgenic fish) for 60 days of rearing period. Ovary maturation was evaluated in G5 transgenic mutiara catfish during different photoperiod induction. A short photoperiod (8L-16D) induced an high expression of GnRHr, LHr, and Vg genes (mean, 4.42 ± 0.53, 5.63 ± 0.42, and 6.67 ± 0.31, respectively), indicating the role of dark cycle in increasing the gene expressions involved in ovarian maturation of G5 transgenic mutiara catfish. The lowest GnRHr, LHr, and Vg gene expression levels were found in nontransgenic fish (C*) (mean, 1.27 ± 0.13, 1.38 ± 0.24, and 2.42 ± 0.33, respectively). The exposure of transgenic fish (CgGH insert content) to a long photoperiod (16L-8D) resulted in lower expression levels of GnRHr, LHr, and Vg (mean, 2.31 ± 0.27, 2.34 ± 0.25, and 4.49 ± 0.30, respectively) and lower levels of hormones Vg and E2 (mean, 295.16 ± 21.71 μg/mL and 0.25 ± 0.03 ng/mL, respectively) and in non-transgenic fish (mean, 163.54 µg/mL and 0.14 ng/mL, respectively). Short photoperiods (8L-16D and 12l-12D) led to oocyte maturation and higher GSI values (mean, 12.24 ± 0.53 and 10.24 ± 0.38, respectively) compared to long photoperiods (16L-8D). Conversely, a long photoperiod led to decreased GnRHr, LHr, and Vg expression levels, and Vg and E2 hormone levels, leading to the growth of immature oocytes and decreased GSI (mean, 3.93 ± 0.29) in nontransgenic fish. The presence of CgGH in G5 transgenic mutiara female catfish can maintain the growth of primary oocytes to secondary oocytes during the 16L-8D photoperiod induction.