Fish eggs contain carotenoids, retinals (retinal and dehydroretinal) and retinols (retinol, dehydroretinol and retinyl-esters) that are utilized during embryonic development, after fertilization. The carotenoids (mainly astaxanthins) are transported in the plasma by the low density lipoproteins, high density lipoproteins, and very high density lipoproteins (VHDL) and were found to be associated also with serum albumin. Retinals were found to be associated vitellogenin (VTG), a component of the plasma VHDL fraction that is internalized by oocytes during vitellogenesis. However, the transport of retinols and retinyl-esters that were located in the oil droplet fraction of homogenized eggs, has yet to be elucidated. Retinols are more abundant in freshwater fish eggs than in eggs of marine fish species. Since retinol is transported in the plasma of vertebrates in association with retinol binding protein (RBP), recent studies on the molecular characterization and expression sites of RBP, could contribute to determining the involvement of RBP in transporting retinol to developing oocytes in vertebrates.Recently, results from our laboratory show that RBP mRNA levels in the liver and RBP plasma levels did not significantly change with the onset and during vitellogenesis in the Rainbow trout. These results were in contrast with a dramatic elevation in the mRNA levels of VTG in the liver and an increase in VTG plasma levels that was observed in the same females. Moreover, 17beta-estradiol treatment of immature fish, resulted in relatively lower mRNA levels of RBP in the liver, concomitantly with an increase in the level of VTG transcripts and the appearance of VTG in the plasma of treated fish. In addition, RBP was localized in the cytosol of ovulated oocytes. These results for Rainbow trout are similar to those reported for the chicken but differ from those of Xenopus, where an increase in RBP mRNA was reported in the liver and higher levels of retinal and retinol were found in the plasma of 17beta-estradiol treated animals. The results, reported here for the first time in Rainbow trout, showing RBP transcripts in the ovary, oviduct (the ovarian tissue adjacent to the gonopore) and oocytes, suggest a modulating role for RBP in follicular development, as has been suggested for the bovine ovary.

中文翻译：

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类胡萝卜素和类视黄醇转运至鱼卵母细胞和卵中：视黄醇结合蛋白的作用是什么？

鱼卵含有类胡萝卜素，视网膜（视网膜和脱氢视网膜）和视黄醇（视黄醇，脱氢视黄醇和视黄酯），受精后在胚胎发育过程中使用。类胡萝卜素（主要是虾青素）在血浆中通过低密度脂蛋白，高密度脂蛋白和极高密度脂蛋白（VHDL）转运，并且还与血清白蛋白相关。发现视网膜与卵黄蛋白原（VTG）有关，卵黄蛋白原是血浆VHDL组分的一部分，在卵黄发生过程中被卵母细胞内化。然而，尚未阐明均质蛋的油滴部分中的视黄醇和视黄酯的运输。视黄醇在淡水鱼卵中比海洋鱼类物种中的丰富。由于视黄醇与视黄醇结合蛋白（RBP）一起在脊椎动物的血浆中运输，因此有关RBP分子特征和表达位点的最新研究可能有助于确定RBP在将视黄醇运输到脊椎动物发育中的卵母细胞中的作用。我们实验室的结果显示，虹鳟鱼的发病过程和卵黄形成过程中，肝脏中的RBP mRNA水平和血浆RBP血浆水平均没有显着变化。这些结果与肝脏中VTG的mRNA水平显着升高和在相同雌性中观察到的VTG血浆水平升高形成对比。此外，未成熟鱼的17β-雌二醇治疗导致肝脏中RBP的mRNA水平相对较低，伴随着VTG转录水平的增加和VTG在处理过的鱼血浆中的出现。另外，RBP位于排卵卵母细胞的胞质溶胶中。虹鳟鱼的这些结果与鸡所报告的结果相似，但与非洲爪蟾不同，后者在肝脏中RBP mRNA有所报道，在17β-雌二醇处理的动物血浆中发现较高水平的视网膜和视黄醇。在虹鳟鱼中首次报道的结果显示，卵巢，输卵管（与淋巴孔相邻的卵巢组织）和卵母细胞中的RBP转录本，暗示了RBP在卵泡发育中的调节作用，正如对牛的建议一样子房。虹鳟鱼的这些结果与鸡所报告的结果相似，但与非洲爪蟾不同，后者在肝脏中RBP mRNA有所报道，在17β-雌二醇处理的动物血浆中发现较高水平的视网膜和视黄醇。在虹鳟鱼中首次报道的结果显示，卵巢，输卵管（与淋巴孔相邻的卵巢组织）和卵母细胞中的RBP转录本，暗示了RBP在卵泡发育中的调节作用，正如对牛的建议一样子房。虹鳟鱼的这些结果与鸡所报告的结果相似，但与非洲爪蟾不同，后者在肝脏中RBP mRNA有所报道，在17β-雌二醇处理的动物血浆中发现较高水平的视网膜和视黄醇。在虹鳟鱼中首次报道的结果显示，卵巢，输卵管（与淋巴孔相邻的卵巢组织）和卵母细胞中的RBP转录本，暗示了RBP在卵泡发育中的调节作用，正如对牛的建议一样子房。