Identification, characterization and functional analysis of regulatory region of nanos gene from half-smooth tongue sole ( Cynoglossus semilaevis )

Identification and Characterization of Dimorphic Expression of Sex-Related Genes in Rock Bream, a Fish With Multiple Sex Chromosomes

The rock bream (Oplegnathus fasciatus) is a typical fish with a unique multiple sex chromosome system. In this study, we investigated the gene expression profiling in the gonads and brains of both males and females using RNA-Seq to identify sex-related genes and pathways. In accordance with the dimorphic expression profiles, combined with Gene ontology and KEGG enrichment analyses, a number of potential genes and pathways associated with sex determination were obtained from transcriptional analysis, especially some sex-biased genes and pathways. Next, we selected 18 candidate genes and analyzed their expression in different tissues and developmental stages. We found that the expression levels of Amh, Dmrt1, Sox9, Dmrtb1, and Nanos2 were significantly higher in the testis than those in the ovary or other tissues, whereas the expression levels of ZP4, Bouncer, RNF208, FoxH1, and TOB were significantly higher in the ovary than those in the testis. Furthermore, the expression levels of these genes in different developmental stages of gonads also showed sexually dimorphic patterns, suggesting that they might play important roles during gonadal development. These genes are useful markers for investigating sex determination and differentiation in rock bream. The findings of this study can provide insights into the molecular mechanisms of sex determination and differentiation in fish with multiple sex chromosome systems.

Transcriptome Dynamics During Turbot Spermatogenesis Predicting the Potential Key Genes Regulating Male Germ Cell Proliferation and Maturation

Spermatogenesis is a dynamic developmental process in which spermatogonial stem cells proliferate, differentiate and mature into functional spermatozoa. These processes require an accurate gene regulation network. Here, we investigated the dynamic changes that occur during spermatogenesis through a combination of histological and transcriptome analyses of different developmental stages of the testis. We constructed 18 testis transcriptome libraries, and the average length, N50, and GC content of the unigenes were 1,795 bp; 3,240 bp and 49.25%, respectively. Differentially expressed genes (DEGs) that were related to germ cell proliferation and maturation, such as NANOS3, RARs, KIFs, steroid hormone synthesis-related genes and receptor genes, were identified between pairs of testis at different developmental stages. Gene ontology annotation and pathway analyses were conducted on DEGs with specific expression patterns involved in the regulation of spermatogenesis. Nine important pathways such as steroid hormone biosynthesis related to spermatogenesis were identified. A total of 21 modules that ranged from 49 to 7,448 genes were designed by a weighted gene co-expression network analysis. Furthermore, a total of 83 candidate miRNA were identified by computational methods. Our study provides the first transcriptomic evidence for differences in gene expression between different developmental stages of spermatogenesis in turbot (Scophthalmus maximus).

Oocyte maturation and origin of the germline as revealed by the expression of Nanos-like in the Pacific oyster Crassostrea gigas

Nanos gene plays an important role in germline development in animals. However, the molecular mechanisms involved in germline development in Mollusca, the second largest animal phylum, are still poorly understood. Here we identified the Nanos orthologue from the Pacific oyster Crassostrea gigas (Cg-Nanos-like), and investigated the expression patterns of Nanos during gametogenesis and embryogenesis in C. gigas. Tissue expression analysis showed that Cg-Nanos-like was specifically expressed in female gonads. During the reproductive cycle, the expression of Cg-Nanos-like mRNA increased matching the seasonal development of the ovarian tissues in diploids, while the expression levels were significantly lower in the ovaries of sterile triploids compared to diploids. High expression of Cg-Nanos-like transcripts were detected in early embryonic stages, while the expression significantly dropped at gastrulation and was barely detectable in veliger stages. In situ hybridization showed that Cg-Nanos-like was expressed at different stages of developing oocytes, whereas positive signals were detected only in spermatogonia during the spermatogenic cycle. These findings indicated that Cg-Nanos-like was involved in the development of germ cells, and maintenance of oocyte maturation. In early embryogenesis, the transcripts were broadly expressed; following gastrulation, the expression was restricted to two cell clumps, which might be the putative primordial germ cells (PGCs) or their precursors. Based on the results, the formation of the PGCs in C. gigas was consistent with the model of transition from epigenesis to preformation.