Li Jun, Zhou Yinyin, Zhou Zihua, Lin Chuanxu, Wei Jinkuan, Qin Yanpin, Xiang Zhiming, Ma Haitao, Zhang Yang, Zhang Yuehuan, Yu Ziniu
Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Science, 164 West Xingang Road, Guangzhou, 510301, China.
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 510301, China.
BMC Genomics. 2020 Dec 7;21(1):872. doi: 10.1186/s12864-020-07276-5.
Gonad development and differentiation is an essential function for all sexually reproducing species, and many aspects of these developmental processes are highly conserved among the metazoa. However, the mechanisms underlying gonad development and gametogenesis remain unclear in Tridacna squamosa, a large-size bivalve of great ecological value. They are protandrous simultaneous hermaphrodites, with the male gonad maturing first, eventually followed by the female gonads. In this study, nine gonad libraries representing resting, male and hermaphrodite stages in T. squamosa were performed to identify the molecular mechanisms.
Sixteen thousand four hundred ninety-one unigenes were annotated in the NCBI non-redundant protein database. Among the annotated unigenes, 5091 and 7328 unigenes were assigned to Gene Ontology categories and the Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway database, respectively. A total of 4763 differentially expressed genes (DEGs) were identified by comparing male to resting gonads, consisting of 3499 which were comparatively upregulated in males and 1264 which were downregulated in males. Six hundred-ninteen DEGs between male and hermaphroditic gonads were identified, with 518 DEGs more strongly expressed in hermaphrodites and 101 more strongly expressed in males. GO (Gene Ontology) and KEGG pathway analyses revealed that various biological functions and processes, including functions related to the endocrine system, oocyte meiosis, carbon metabolism, and the cell cycle, were involved in regulating gonadal development and gametogenesis in T. squamosa. Testis-specific serine/threonine kinases 1 (TSSK1), TSSK4, TSSK5, Doublesex- and mab-3-related transcription factor 1 (DMRT1), SOX, Sperm surface protein 17 (SP17) and other genes were involved in male gonadal development in Tridacna squamosal. Both spermatogenesis- (TSSK4, spermatogenesis-associated protein 17, spermatogenesis-associated protein 8, sperm motility kinase X, SP17) and oogenesis-related genes (zona pellucida protein, Forkhead Box L2, Vitellogenin, Vitellogenin receptor, 5-hydroxytryptamine, 5-hydroxytryptamine receptor) were simultaneously highly expressed in the hermaphroditic gonad to maintain the hermaphroditism of T. squamosa.
All these results from our study will facilitate better understanding of the molecular mechanisms underlying giant clam gonad development and gametogenesis, which can provided a base on obtaining excellent gametes during the seed production process for giant clams.
性腺发育和分化是所有有性生殖物种的一项基本功能，并且这些发育过程的许多方面在后生动物中高度保守。然而，大砗磲这种具有重要生态价值的大型双壳贝类，其性腺发育和配子发生的潜在机制仍不清楚。它们是雄性先熟的同步雌雄同体，雄性性腺先成熟，最终雌性性腺才成熟。在本研究中，构建了九个代表大砗磲静止期、雄性期和雌雄同体期的性腺文库，以确定其分子机制。
在NCBI非冗余蛋白质数据库中注释了16491个单基因。在注释的单基因中，分别有5091个和7328个单基因被归类到基因本体论（Gene Ontology）类别和京都基因与基因组百科全书（KEGG）通路数据库中。通过比较雄性性腺与静止期性腺，共鉴定出4763个差异表达基因（DEG），其中3499个在雄性中相对上调，1264个在雄性中下调。在雄性性腺和雌雄同体性腺之间鉴定出619个DEG，其中518个在雌雄同体中表达更强，101个在雄性中表达更强。基因本体论（GO）和KEGG通路分析表明，各种生物学功能和过程，包括与内分泌系统、卵母细胞减数分裂、碳代谢和细胞周期相关的功能，都参与了调节大砗磲的性腺发育和配子发生。睾丸特异性丝氨酸/苏氨酸激酶1（TSSK1）、TSSK4、TSSK5、双性和 mab-3相关转录因子1（DMRT1）、SOX、精子表面蛋白17（SP17）等基因参与了大砗磲雄性性腺发育。精子发生相关基因（TSSK4、精子发生相关蛋白17、精子发生相关蛋白8、精子运动激酶X、SP17）和卵子发生相关基因（透明带蛋白、叉头框L2、卵黄蛋白原、卵黄蛋白原受体、5-羟色胺、5-羟色胺受体）在雌雄同体性腺中同时高表达，以维持大砗磲的雌雄同体状态。
我们研究的所有这些结果将有助于更好地理解巨型蛤蜊性腺发育和配子发生的分子机制，这可为在巨型蛤蜊苗种生产过程中获得优质配子提供依据。
