Investigation of insulin-like growth factor-1 gene with egg-laying traits in the Muscovy duck (Cairina moschata)

Muscovy duck (Cairina moschata) is characterized by broodiness, and egg-laying traits in this species should be of primary concern. As a member of the IGF superfamily of proteins, insulin-like growth factor-1 (IGF-1) is an important positive regulator of growth and gonad development in vertebrates. To explore the effect of IGF-1 on the growth hormone/insulin-like growth factors (GH/IGF) axis, we cloned and characterized IGF-1 of Muscovy duck. The expression level of IGF-1 was widely expressed in all the tested tissues, and the highest level was detected in the liver. In laying ducks, IGF-1 expression levels in the hypothalamus, pituitary, and ovary were very significantly higher (P < 0.01) than that in the tissues of nesting duck, and IGF-1 expression levels in the heart and liver were significantly higher (P < 0.05) than that in nesting duck tissues. Furthermore, a single nucleotide polymorphism (SNP) (A/G) was found and significantly (P < 0.05) associated with age at first egg and egg number at 300 d. This study provides the first evidence that IGF-1 promote egg-laying traits of Muscovy duck through two axes, involving GH/IGF and hypothalamic–pituitary–gonadal axes. These findings enrich the information of IGF-1 of Muscovy duck and demonstrate for the first time the ability of IGF-1 to promote reproduction, indicating that IGF-1 could be used as an important marker gene.