Abstract
Simple SummaryIn highly efficient laying hens, such as in commercial layer lines, the development of follicles is mainly characterized by an organized follicular hierarchy. Leptin has been implicated in the modulation of female reproduction in vertebrate animals. Forkhead box L2 (FOXL2) and R-spondin1 (RSPO1) have also been implicated in the regulation of ovarian functions and the development of follicles. In this study, using a laying hen model, we observed abundant mRNA expression of FOXL2 and RSPO1 in small (prehierarchical) and large (hierarchical) follicles, respectively. FOXL2 mRNA expression was stable in granulosa cells harvested from 3–5 mm to F4 follicles, and exhibited a significantly higher expression in large hierarchical follicles. However, theca cells exhibited a significantly higher mRNA expression of RSPO1 in F4 to F1 follicles. In subsequent experiment, we observed that 100 ng/mL leptin significantly modulated FOXL2 and RSPO1 expression in cultured granulosa cells harvested from large hierarchical and small prehierarchical follicles. These findings reasonably suggest that FOXL2 and RSPO1 genes may have a role in modulating the ovarian mechanisms, possibly affecting follicle growth and selection in laying hens. In addition, we demonstrated that leptin administration to granulosa cells in vitro modulated FOXL2 and RSPO1 expression, suggesting an implication of leptin in the follicular development and steroidogenesis in laying hens. However, further focused studies are warranted to improve our understanding of the exact roles played by these genes in follicle development and selection in laying hens.In this study, using a laying hen model, we determined the expression of FOXL2 and RSPO1 in different central and peripheral tissue and ovarian follicles at different stages of development. At the same time, mRNA expression of both genes in granulosa and theca cells harvested from follicles at different stages of folliculogenesis was also evaluated. Finally, we assessed the effect of leptin treatment on expression of FOXL2 and RSPO1 in in vitro cultured granulosa cells harvested from 1–5 mm to F3–F1 follicles. Our RT-qPCR results revealed that a comparatively higher expression of FOXL2 and RSPO1 was observed in ovary, hypothalamus, and pituitary. Abundant mRNA expression of FOXL2 was observed in small prehierarchical follicles (1–1.9 and 2–2.9 mm follicles; p < 0.05), whereas mRNA expression of RSPO1 showed an increasing trend in large hierarchical follicles (F5–F1), and its abundant expression was observed in post-ovulatory follicles. FOXL2 mRNA expression was stable in granulosa cells harvested from 3–5 mm to F4 follicles, and exhibited a significantly higher expression in large hierarchical follicles. Conversely, relatively low mRNA expression of FOXL2 was observed in theca cells. RSPO1 mRNA expression was relatively lower in granulosa cells; however, theca cells exhibited a significantly higher mRNA expression of RSPO1 in F4 to F1 follicles. In the next experiment, we treated the in vitro cultured granulosa cells with different concentrations (1, 10, 100, and 1000 ng/mL) of exogenous leptin. Compared to the control group, a significant increase in the expression of FOXL2 was observed in groups treated with 1, 10, and 100 ng/mL leptin, whereas expression of RSPO1 was increased in all leptin-treated groups. When treated with 100 ng/mL leptin, FOXL2 and RSPO1 expression was upregulated in cultured granulosa cells harvested from both large hierarchical (F3–F1) and small prehierarchical follicles (1–5 mm). Based on these findings and evidence from mainstream literature, we envisage that FOXL2 and RSPO1 genes (in connection with hypothalamic-hypophysis axis) and leptin (via modulation of FOXL2 and RSPO1 expression) might have significant physiological roles, at least in part, in modulating the ovarian mechanisms, such as follicle development, selection, and steroidogenesis in laying hens.
Highlights
The reproductive strategy of avian species is unique compared to mammals, in that they usually produce a clutch of eggs that is dependent upon the maintenance of a small cohort of viable prehierarchical follicles [1,2]
We evaluated the expression patterns of Forkhead box L2 (FOXL2) and RSPO1 in granulosa cells and theca cells obtained from follicles at different stages of development
Our results revealed that mRNA expression of FOXL2 was stable in granulosa cells harvested from 3–5 mm to F4 follicles, and exhibited a significantly higher (p < 0.05) expression in large hierarchical follicles
Summary
The reproductive strategy of avian species is unique compared to mammals, in that they usually produce a clutch of eggs that is dependent upon the maintenance of a small cohort of viable (undifferentiated) prehierarchical follicles [1,2]. On a day-to-day basis, a single follicle is recruited from the pool, which undergoes a rapid growth phase and differentiation before ovulation [1] These growing ovarian follicles are usually classified on the basis of their size (for example: 3–5 or 6–9 mm) or their color (as large white follicles or small yellow follicles). The stage of development of ovarian follicles is associated with the initiation of steroidogenic competence in granulosa cell layers. This process seems to be complex and highly coordinated, involving a number of divergent biological effects on the maturation of oocytes and differentiation and proliferation of granulosa and theca cells within the ovarian follicles [8]. Follicle stimulating hormone receptors (FSHR) are reportedly expressed on the granulosa layer of developing follicles, and mRNA expression of these receptors (FSHR) changes with progressing follicular maturation [3,6,13]
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