Transcriptome Analysis on Single Small Yellow Follicles Reveals That Wnt4 Is Involved in Chicken Follicle Selection.

Yiya Wang,Zemin Liu,Yunliang Jiang,Qiuyue Chen,Li Kang,Yanzhi Du,Xiaoli Guo,Yi Sun,Zhenjie Yuan,Miao Guo

doi:10.3389/fendo.2017.00317

Abstract

Ovarian follicle selection is an important process impacting the laying performance and fecundity of hens, and is regulated by follicle-stimulating hormone (FSH) through binding to its receptor [follicle-stimulating hormone receptor (FSHR)]. In laying hens, the small yellow follicle (6–8 mm in diameter) with the highest expression of FSHR will be recruited into the preovulatory hierarchy during ovarian follicle development. The study of molecular mechanism of chicken follicle selection is helpful for the identification of genes underlying egg-laying traits in chicken and other poultry species. Herein, the transcriptomes of chicken small yellow follicles differing in the mRNA expression of FSHR were compared, and a total of 17,993 genes were identified in 3 pairs of small yellow follicles. The Wnt signaling pathway was significantly enriched in the follicles with the greatest fold change in FSHR expression. In this pathway, the expression level of Wnt4 mRNA was significantly upregulated with a log2(fold change) of 2.12. We further investigated the expression, function, and regulation of Wnt4 during chicken follicle selection and found that Wnt4 mRNA reached its peak in small yellow follicles; Wnt4 stimulated the proliferation of follicular granulosa cells (GCs), increased the expression of StAR and CYP11A1 mRNA in prehierarchical and hierarchical follicles, increased the expression of FSHR mRNA, and decreased the expression of anti-Müllerian hormone and OCLN mRNA. Treatment with FSH significantly increased Wnt4 expression in GCs. Moreover, Wnt4 facilitated the effects of FSH on the production of progesterone (P4) and the mRNA expression of steroidogenic enzyme genes in the GCs of hierarchical follicles, but inhibited the effects of FSH in the GCs of prehierarchical follicles. Collectively, these data suggest that Wnt4 plays an important role in chicken follicle selection by stimulating GC proliferation and steroidogenesis. This study provides a theoretical basis for improving the egg-laying performance of chicken and a reference for the elucidation of the molecular mechanism of follicular selection in mammals.

Highlights

The chicken ovary is a dynamic organ and a key component of the female reproductive system
As the Wingless-Type MMTV Integration Site Family Member 4 (Wnt4) expression level changed during follicle development and was affected by the concentration of follicle-stimulating hormone (FSH), we further focused on the function of Wnt4 in follicular selection and development
Recent studies have shown that all of the small yellow follicles isolated from the same ovary in a laying hen can express follicle-stimulating hormone receptor (FSHR) and respond to stimulation by FSH [25,26,27], and one of them contains significantly higher FSHR mRNA expression levels than the others, and this follicle will be selected to the hierarchical follicles [14]

Summary

Introduction

The chicken ovary is a dynamic organ and a key component of the female reproductive system. Wnt Involved in Chicken Follicle Selection in diameter approximately once a day, a process termed follicle selection. The selected follicle will undergo rapid development from an F5 follicle to an F1 follicle until ovulation [2]. This process is regulated by the hypothalamic–pituitary axis and the paracrine and autocrine factors from ovarian follicles [3]. It is estimated that there are approximately 12,000 oocytes in a sexually mature hen, but only a few hundred of them are selected to mature and reach the ovulation stage [4]; most small yellow follicles are not selected and undergo atresia [5, 6]

Methods

Results

Conclusion