Expression of aquaporin 4 in the chicken ovary in relation to follicle development

Contents In the mammalian ovary, aquaporins ( AQP s) are thought to be involved in the regulation of fluid transport within the follicular wall and antrum formation. Data concerning the AQP s in the avian ovary is very limited. Therefore, the present study was designed to examine whether the AQP 4 is present in the chicken ovary, and if so, what is its distribution in the ovarian compartment of the laying hen. Localization of AQP 4 in the ovarian follicles at different stage of development was also investigated. After decapitation of hens the stroma with primordial follicles and white (1–4 mm), yellowish (4–8 mm), small yellow and the three largest yellow pre‐ovulatory follicles F3‐F1 (F3 < F2 < F1; 20–36 mm) were isolated from the ovary. The granulosa and theca layers were separated from the pre‐ovulatory follicles. The AQP 4 mRNA and protein were detected in all examined ovarian compartments by the real‐time PCR and Western blot analyses, respectively. The relative expression of AQP 4 was depended on follicular size and the layer of follicular wall. It was the lowest in the granulosa layer of pre‐ovulatory follicles and the highest in the ovarian stroma as well as white and yellowish follicles. Along with approaching of the largest follicle to ovulation the gradual decrease in AQP 4 protein level in the granulosa layer was observed. Immunoreactivity for AQP 4 was present in the granulosa and theca cells (theca interna ≥ theca externa > granulosa). The obtained results suggest that AQP 4 may take part in the regulation of water transport required for follicle development in the chicken ovary.