In the eel ovary, the expression of growth differentiation factor-9 (Gdf9) appears to be largely confined to the germ cell in early stages of oogenesis. However, both the target tissue and the function of Gdf9 in fish remain unknown. This study aimed to describe the abundance and localization of activin receptor-like kinase-5 (Alk5) and bone morphogenetic protein receptor type II (Bmpr2), which together mediate the Gdf9 signal, in the ovary of a basal teleost, the shortfinned eel, Anguilla australis, during early folliculogenesis. The cDNA encoding eel alk5 and bmpr2 genes were cloned, characterized and the transcript abundances of these receptors quantified by quantitative real-time PCR. Ovarian transcript abundance for both receptors, along with that of gdf9 and of its paralogue bmp15, increased from the previtellogenic to early vitellogenic stage. Localization of receptor mRNAs by in situ hybridization revealed that these receptors are located in the somatic cells surrounding the oocyte. Furthermore, tissue distribution analysis showed that the expression of alk5 and bmpr2 were highest in ovary and thyroid, respectively. Unexpectedly, however, bmpr2 mRNA levels were lower in the ovary than in any of the other 17 tissues examined, and indeed, lower than ovarian gdf9 transcript abundance. These findings, together with the ovarian expression pattern of Gdf9, suggest that Gdf9, and conceivably, Bmp15, from the oocyte can signal through receptors that are located on the somatic cells surrounding the oocyte; this, in turn, facilitates elucidation of the function of these growth factors during oogenesis in teleost fish.

在鳗鱼卵巢中，在成卵早期，生长分化因子9（Gdf9）的表达似乎主要局限于生殖细胞。但是，目标组织和鱼中Gdf9的功能仍然未知。这项研究旨在描述激活素受体样激酶5（Alk5）和II型骨形态发生蛋白受体（Bmpr2）的丰度和定位，它们共同介导基底硬骨鱼，短鳍鳗鱼卵巢中的Gdf9信号，南极的安圭拉（Anguilla australis），在早期卵泡形成过程中。克隆，表征了编码鳗鱼alk5和bmpr2基因的cDNA，并通过实时定量PCR定量了这些受体的转录本丰度。两种受体的卵巢转录本丰度以及gdf9及其旁系同源物bmp15，从玻璃体形成前增加到卵黄形成早期。通过原位杂交对受体mRNA的定位表明这些受体位于卵母细胞周围的体细胞中。此外，组织分布分析表明，alk5和bmpr2的表达分别在卵巢和甲状腺中最高。但是，出乎意料的是，卵巢中的bmpr2 mRNA水平低于其他17个组织中的任何一个，并且确实低于卵巢gdf9笔录丰富。这些发现与Gdf9的卵巢表达模式一起表明，来自卵母细胞的Gdf9和Bmp15可以通过位于卵母细胞周围体细胞上的受体发出信号。反过来，这有助于阐明硬骨鱼在卵子发生过程中这些生长因子的功能。