Bobe Julien, Nguyen Thaovi, Mahé Sophie, Monget Philippe
INRA, UR1337, IFR140, Ouest Genopole, Campus de Beaulieu, F-35000 Rennes, France.
BMC Genomics. 2008 Oct 23;9:499. doi: 10.1186/1471-2164-9-499.
In fish, molecular mechanisms that control follicle-enclosed oocyte progression throughout oogenesis and oocyte developmental competence acquisition remain poorly understood. Existing data in mammals have indicated that the so called "oocyte-specific" genes play an important role in oogenesis, fertilization, and early embryo development. In teleost species, very little is known about "oocyte-specific" genes. The present study therefore aimed at identifying and characterizing oocyte-specific genes in fish.
Using digital differential display PCR, mouse ESTs exhibiting an oocyte-predominant expression were identified. Those murine ESTs were subsequently used to identify cognate rainbow trout (Oncorhynchus mykiss) ESTs using a reciprocal Blast search strategy. In the present study we report the identification of five previously uncharacterized rainbow trout cDNAs exhibiting a oocyte-specific, oocyte-predominant, or gonad-specific expression: zygote arrest 1 (zar1), v-mos Moloney murine sarcoma viral oncogene-like protein (mos), B-cell translocation gene (btg3), growth differentiation factor 9 (gdf9), and mutS homolog 4 (msh4). The orthology relationship of each of these genes with vertebrate counterparts was verified by phylogenetic analysis. Among those five genes, three had never been characterized in any fish species. In addition, we report the oocyte-predominant expression of btg3 for the first time in any vertebrate species. Finally, those five genes are present in unfertilized eggs as maternally-inherited mRNAs thus suggesting that they could participate in ovarian folliculogenesis as well as early embryonic development.
The expression patterns of zar1, mos, btg3, gdf9 and msh4 in rainbow trout and the functions of their orthologs in higher vertebrates strongly suggest that they might play an important role in follicle-enclosed oocyte development, meiosis control and early embryonic development in fish. Future investigations are however required to unravel the participation of those strong candidates in the molecular processes that control folliculogenesis and/or oocyte developmental competence in fish.
在鱼类中，控制卵泡包裹的卵母细胞在整个卵子发生过程中的进程以及卵母细胞发育能力获得的分子机制仍知之甚少。哺乳动物的现有数据表明，所谓的“卵母细胞特异性”基因在卵子发生、受精和早期胚胎发育中起重要作用。在硬骨鱼类中，关于“卵母细胞特异性”基因的了解非常少。因此，本研究旨在鉴定和表征鱼类中的卵母细胞特异性基因。
使用数字差异显示PCR，鉴定出表现出卵母细胞优势表达的小鼠EST。随后使用双向Blast搜索策略，利用这些小鼠EST来鉴定同源虹鳟（Oncorhynchus mykiss）EST。在本研究中，我们报告鉴定出五个以前未表征的虹鳟cDNA，它们表现出卵母细胞特异性、卵母细胞优势或性腺特异性表达：合子阻滞1（zar1）、v-mos莫洛尼鼠肉瘤病毒癌基因样蛋白（mos）、B细胞易位基因（btg3）、生长分化因子9（gdf9）和错配修复蛋白4（msh4）。通过系统发育分析验证了这些基因中每一个与脊椎动物对应物的直系同源关系。在这五个基因中，有三个在任何鱼类物种中都从未被表征过。此外，我们首次报道了btg3在任何脊椎动物物种中的卵母细胞优势表达。最后，这五个基因以母系遗传的mRNA形式存在于未受精卵中，因此表明它们可能参与卵巢卵泡发生以及早期胚胎发育。
zar1、mos、btg3、gdf9和msh4在虹鳟中的表达模式及其在高等脊椎动物中的直系同源物的功能强烈表明，它们可能在鱼类卵泡包裹的卵母细胞发育、减数分裂控制和早期胚胎发育中起重要作用。然而，未来需要进行研究以阐明这些强有力的候选基因在控制鱼类卵泡发生和/或卵母细胞发育能力的分子过程中的参与情况。
