Department of Anatomy and Histology, Faculty of Veterinary Medicine, Assiut University, Assiut71526, Egypt.
Microsc Microanal. 2020 Jun;26(3):599-608. doi: 10.1017/S1431927620001567.
The present study describes in detail the morphological characteristics of the process of ovarian follicular atresia in Redbelly tilapia (Coptodon zillii) during the nonbreeding season using light and electron microscopy and immunohistochemistry. The follicular regression process was initiated with shrinkage and disintegration of the nuclear membrane of oocytes resulting in dispersing of chromatin within the ooplasm, followed by marked hyperplasia and hypertrophy of follicular and granulosa cells, which exhibited a strong phagocytic activity to engulf the liquefied yolk particles. Rodlet cells and granulocytes were recorded on the follicular wall and invaded the regressed follicles. Rodlet cells expressed a strong immunoreactivity to matrix metalloperoxidase (MMP-9) and α-smooth muscle actin, while neutrophils expressed a strong reactivity to Myeloperoxidase-3 (MPO). In the advanced stage of follicular atresia, the yolk was almost phagocytized and resorbed and the regressed follicle lost its integrity and appeared to be formed of a cellular mass of phagocytic cells. Transmission electron microscopy revealed the presence of neutrophils, eosinophils, and dendritic cells within the atretic follicle in between these phagocytic cells. Moreover, numerous lysosomes, granules, and phagosomes were observed within the cytoplasm of both phagocytic cells and granulocytes. Telocytes were also demonstrated within the highly thickened richly vascularized theca layer during the late stages of follicular atresia. Immunohistochemical staining for caspase-3 established the participation of apoptosis in the advanced stages of follicular regression. Immune cells, rodlet cells, and telocytes in combination with follicular cells play an essential role in follicular atresia. In conclusion, the present study provides a new evidence on the role of both somatic and immune cells in the phenomenon of ovarian follicular atresia in Redbelly tilapia (Coptodon zillii) during the nonbreeding season.
本研究采用光镜和电镜结合免疫组织化学技术，详细描述了非繁殖季节红腹罗非鱼（Coptodon zillii）卵巢卵泡闭锁的形态学特征。卵泡退化过程始于卵母细胞核膜的收缩和崩解，导致染色质在卵质内弥散，随后滤泡和颗粒细胞明显增生和肥大，表现出强烈的吞噬活性，吞噬液化的卵黄颗粒。发现有杆状细胞和嗜中性粒细胞在滤泡壁上，并侵入退化的卵泡。杆状细胞对基质金属蛋白酶 9（MMP-9）和α-平滑肌肌动蛋白表达强烈的免疫反应性，而嗜中性粒细胞对髓过氧化物酶-3（MPO）表达强烈的反应性。在卵泡闭锁的晚期阶段，卵黄几乎被吞噬和吸收，退化的卵泡失去完整性，似乎由吞噬细胞的细胞团形成。透射电镜显示，在这些吞噬细胞之间，退化的卵泡内存在嗜中性粒细胞、嗜酸性粒细胞和树突状细胞。此外，在吞噬细胞和嗜中性粒细胞的细胞质内观察到大量溶酶体、颗粒和吞噬体。在卵泡闭锁的晚期阶段，还在高度增厚的富含血管的外膜层内显示出长伸细胞。Caspase-3 的免疫组织化学染色确立了细胞凋亡在卵泡退化的晚期阶段的参与。免疫细胞、杆状细胞和长伸细胞与滤泡细胞一起在卵泡闭锁中发挥重要作用。总之，本研究为非繁殖季节红腹罗非鱼（Coptodon zillii）卵巢卵泡闭锁过程中体细胞和免疫细胞的作用提供了新的证据。
