Cloning, expression, and polymorphism at the 5ʹ-flanking region of the GnRH gene and their association with laying traits in Muscovy duck (Cairina moschata)

Abstract

1. Gonadotropin-releasing hormone (GnRH), a neuropeptide, plays a vital role in the hypothalamus–pituitary–gonadal (HPG) axis. In vertebrates, GnRH is crucial for the onset of sexual development and the entire reproductive process. The purpose of this study was to identify genetic factors associated with egg-laying traits of Muscovy ducks.

2. The full-length cDNA (474 bp) of Muscovy duck GnRH was obtained and characterised. It encodes 92 amino acids containing a 1-amino acid signal peptide cleavage site. Phylogenetic analysis revealed that Muscovy duck GnRH has a close relationship with Anas platyrhynchos GnRH.

3. GnRH showed significantly different expression profiles between 4 developmental periods in the hypothalamus, pituitary, and ovary. The expression of GnRH in the laying period (36 weeks) was higher than at other periods in the three tissues. GnRH was widely expressed in 12 examined tissues of nesting and laying Muscovy ducks. In the hypothalamus, pituitary and gonads, the expression of GnRH was higher than in other tissues.

4. In laying Muscovy ducks, the expression of GnRH in the hypothalamus, pituitary, ovary, muscular stomach, pancreas, heart, duodenum and spleen was significantly higher than in nesting dusks. Differences were detected in the liver and glandular stomach between laying ducks and nesting ducks. Differences between the kidney and lung were not significant.

5. In the pituitary, the GnRH and GnRH receptor (GnRHR) genes shared the same expression profiles during 4 time points. Both genes had the highest expression at 36 weeks of age.

6. A mutation (g.206G > A) in the 5ʹ-flanking region was associated with egg-laying performance. Individuals with genotype GG had better egg-laying performance than the individuals with genotype AA. GnRH may be used as a marker gene for laying performance in the Muscovy duck.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the assistance of Dr Yuanjie Hu at the University of California, Irvine, for his reviews and comments on the manuscript.

Additional information

Funding

This project was supported by the National Natural Science Foundation of China [grant number 31001005]; Fujian Provincial Natural Science Foundation of China [grant number 2013J01068]; the earmarked fund for the Modern Agro-industry Technology Research System of China [grant number CaRS-43].

Notes on contributors

X. Wu

X. Wu and X.P. Wan contributed equally to this work.