线纹海马(Hippocampus erectus)性腺特异性结构与生殖细胞发育特征研究

Distinct structures of gonads and germ cell development of lined seahorse,Hippocampus erectus

海马属(Hippocampus)鱼类具有独特的雄性育儿繁殖方式,其卵巢和精巢结构也极其独特。本研究系统阐明了线纹海马(Hippocampuserectus)的性腺及生殖细胞的发育特征,根据组织学结构和细胞形态学变化特征,将线纹海马的精巢和卵巢发育过程均分为6个时期。其中,卵巢发育方式为不同步成熟型,Ⅰ期卵巢只包含第Ⅰ时相卵母细胞,包括卵原细胞和早期初级卵母细胞(d<20μm);Ⅱ期卵巢开始出现第Ⅱ时相卵母细胞(d=20~140μm);Ⅲ期卵巢卵母细胞数量显著增多,体积增大,并开始出现第Ⅲ时相卵母细胞(d=140~260μm),此时细胞内开始出现皮质小泡、卵黄颗粒和卵黄膜;Ⅳ期卵巢开始出现第Ⅳ时相卵母细胞(d=260~1100μm),卵黄颗粒充满整个细胞质,形成过渡期的卵黄球;Ⅴ期卵巢出现大量第Ⅴ时相成熟卵母细胞(d=1100~2000μm),细胞内形成流动性卵黄囊;Ⅵ期卵巢为排卵不久后的卵巢,卵母细胞数量显著减少。线纹海马精巢属于非限制型小叶精巢,Ⅰ期精巢主要含精原细胞,核大,含一到多个核仁;Ⅱ期精巢开始形成精小囊,囊内出现初级精母细胞;Ⅲ期精巢呈乳白色,开始出现次级精母细胞;Ⅳ期精巢体积较Ⅲ期时显著增大,开始出现精子细胞,并逐渐移向中央生精腔;Ⅴ期精巢内含大量的成熟精子,随时准备释放。精子释放后精巢进入Ⅵ期,残留少量精细胞在生精腔中。组织化学反应结果显示,氨基酸、蛋白质和脂肪的信号在卵母细胞的细胞质、卵黄囊中呈阳性,且随着卵母细胞的发育而增强。本研究结果为进一步探索海马属鱼类雄性繁殖策略提供了重要的基础数据。

Seahorses(Genus Hippocampus)have not only peculiar reproductive strategy of male pregnancy but also unique ovarian and testis structures.Developmental characteristics of the ovary and testis as well as the germ cells of the lined seahorse(Hippocampus erectus)were clarified in the present study.Based on the histological structure and morphological features,we described six stages of gonadal development of lined seahorse.Seahorses have an asynchronous ovarian developmental characteristic.The stageⅠovary contained only oogonia and early meiotic oocytes(d<20μm).In the stageⅡovary,phaseⅡoocytes(d=20-140μm)began to appear.In the stageⅢovary,the number and volume of the phaseⅢoocytes(d=140-260μm)were increased remarkably.The vitellogenic oocytes(d=260-1100μm),in which transitional yolk sphere was accumulated,could be observed in the stageⅣovary.PhaseⅤmaturational oocytes(d=1100-2000μm),which were characterized by highly compact vitelline envelope and fluid yolk mass,were observed in the stageⅤovary.The ovary shortly after ovulation with decrement of the number of oocytes was stageⅥovary.The testis of the lined seahorse is of the unrestricted lobular type.StageⅠtestis mainly contained spermatogonia with large nuclear and one or more nucleolus.In the stageⅡtestis,the spermatocyst began to appear,inside of which were the primary spermatocytes with smaller nuclear.The secondary spermatocytes were first present in the stageⅢtestis.In the stageⅣtestis,the volume of testis was increased significantly and the matured spermatids appeared.Large scale of mature spermatozoa was restricted into the testicular lumen and ready to be released in the stageⅤtestis.The stageⅥtestis was vascularized with few spermatozoa or spermatocytes in the lumen.Further histochemical analysis showed that the amino acid and fat were positive in the cytoplasm and yolk mass of oocytes,and accumulated with the oocytes development.Generally,our results provide basic evidence for further understanding of male pregnancy strategies of seahorses.