Abstract
Simple SummarySuccessive follicle selection is important for egg production and reproductive performance in chickens. The molecular mechanisms of follicle selection in chickens are unclear. In the present study, the histological characteristics, reproductive hormone concentration, and transcriptional profiles of follicles were measured to identify the key genes and regulatory pathways for follicle selection. The results provide deep insights into the crucial molecular mechanism of follicle development and egg-laying performance in chickens.Ovarian follicle selection largely depends on the transition of granulosa cells from an undifferentiated to a fully differentiated state, which is accompanied by morphological and functional changes in follicles. The processes and transcriptional regulation of follicles during follicle selection are unclear; we thus used follicles from the prehierarchal to the hierarchal stage to investigate histology, reproductive endocrinology, and transcription. The morphology of follicles changed markedly during follicle selection. The numbers of large white, small yellow, and large yellow follicles (LWF, SYF, and LYF, respectively) were 11.83 ± 2.79, 6.83 ± 2.23, and 1.00, respectively, per ovary. LYF showed thicker granulosa cell layers than those of other prehierarchal follicles. Progesterone concentrations were significantly higher in LYF than that in LWF and SYF. In total, 16,823 genes were positively expressed in LWF, SYF, and LYF. Among follicle types, 1290 differentially expressed genes were enriched regarding cell differentiation, blood vessel morphogenesis, and response to steroid hormones. Candidate genes associated with follicle selection participated in the Wnt signaling pathway, steroid hormone biosynthesis, and the TGF-β signaling pathway. We produced insights into crucial morphological characteristics of transcriptional regulation in follicle development. Our results provide an important basis for revealing the mechanism of follicle selection and potential impact on the poultry industry.
Highlights
We focused on the morphological characteristics and transcriptome of large white follicles (LWF), small yellow follicles (SYF), and large yellow follicles (LYF; termed F5)
The results revealed that the granulosa layer was significantly thicker in LYF than in LWF and SYF during follicle selection
Our results showed that FZD4 receptors and the downstream target gene NFATC1 were highly expressed in LYF
Summary
A sexually mature hen carries approximately 12,000 oocytes, but only a few hundred follicles are selected to mature and reach ovulation [2]. The chicken ovary undergoes a dynamic development process, and during the laying period, a series of follicles at different developmental stages occur on the ovary. Follicles can be divided into prehierarchal and hierarchal follicles ( termed preovulatory follicles) [3]. Prehierarchal follicles grow slowly and incorporate protein–rich yolk over several weeks [3]. During the egg–laying period, a single small yellow follicle (SYF) is recruited almost every day from a cohort of SYFs to develop into a hierarchal follicle; this process is termed follicle selection [4]. The selected follicles will develop rapidly and form a mature yolk within a few days, after which, they can ovulate and enter the oviduct [5]
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