Expression Dynamics and Estrogen Response of Estrogen Receptors in Duolang Sheep During Puberty

Puberty is a critical stage in sheep development when reproductive capability is established, but the hormonal mechanisms underlying this transition remain incompletely understood. This study aimed to investigate the dynamic changes in estradiol (E2) levels and the expression patterns of estrogen receptors (ERα and ERβ) during puberty in Duolang sheep, a breed characterized by early sexual maturity and high reproductive efficiency.

A total of 18 female Duolang sheep were assigned to three developmental stages (n = 6 per group): prepuberty (145 days), puberty (within 0 h of first estrus), and postpuberty (+3 days). Serum E2 concentrations and the mRNA and protein levels of ERα and ERβ were assessed in the hypothalamus, pituitary, and ovary. Additionally, primary ovarian granulosa cells (GCs) were isolated and stimulated in vitro with increasing concentrations of E2 (0-1000 ng/mL) to evaluate the dose-dependent expression of ERα, ERβ, and gonadotropin-releasing hormone (GnRH).

E2 levels peaked at the onset of puberty and declined thereafter. ERα expression in the hypothalamus and pituitary decreased during puberty but rebounded postpuberty, indicating a role in negative feedback regulation. In contrast, ovarian ERα expression reached its highest level during puberty, while ERβ expression in the ovary gradually increased from prepuberty to postpuberty. In GCs, ERα exhibited a biphasic expression pattern, peaking at 250 ng/mL E2 and decreasing at higher concentrations. ERβ and GnRH expression levels increased in a dose-dependent manner.

These findings suggest that ERα primarily mediates E2 feedback within the hypothalamus-pituitary axis, whereas ERβ is associated with ovarian development and may regulate GnRH expression during the pubertal transition. The study provides new insights into the hormonal regulation of puberty in Duolang sheep and offers potential biomarkers for improving reproductive efficiency through targeted breeding strategies.