FoxL2 combined with Cyp19a1a regulate the spawning upstream migration in Coilia nasus

FoxL2 is a member of the forkhead/HNF-3-related family of transcription factors which provides tissue specific gene regulation. It is known to regulate ovarian aromatase, which plays a crucial role in ovarian development and mature. To understand the role of FoxL2/ovarian aromatase encoded gene Cyp19a1a during ovarian development and recrudescence, we identified cDNA characteristics of FoxL2 and Cyp19a1a, analyzed its temporal expression both at transcript and protein levels in the anadromous fish, Coilia nasus. Tissue distribution pattern revealed that FoxL2 mRNA expression level was highest in ovary, while Cyp19a1a mRNA was highest in brain. During the upstream migration cycle, in ovary, the FoxL2 mRNA temporal expression peaked at the multiplication stage (stage III in May), the Cyp19a1a mRNA expression peaked at the onset stage (stage I in March). It was found that their mRNA transcripts were maintained at high level during the migration stage (from stage I in March to stage VI in July). Additionally, the strongest immunolabeling positive signals of Cyp19a1a and FoxL2 proteins were mainly found in the cytoplasm of olfactory bulb cell, stratum granulare and neurogliocyte cells and development stage oocytes. Data indicated that FoxL2 and Cyp19a1a were inducible and functional in the C. nasus ovary development and migration process. Therefore, the present results can be regarded as evidence for indispensable roles of FoxL2 and Cyp19a1a in the ovary development and migratory behavior at gene expression patterns and encoded protein distribution level.

New insights on geographical/ecological populations within Coilia nasus (Clupeiformes: Engraulidae) based on mitochondrial DNA and microsatellites

The Coilia nasus is an important fish species, which is of commercial values in China. In order to manage the fisheries resources and the development of sustainable fishing strategies to protect this species, 11 microsatellite loci polymorphisms and mtDNA COI sequences were used to examine the genetic diversity of C. nasus in Japan and China. In total, the 40 COI haplotypes and 93 microsatellite alleles were detected. The mtDNA phylogeny did not support population grouping, but the distribution patterns of mtDNA haplotypes and the results of STRUCTURE analysis based on microsatellite indicated a degree of genetic isolation in this species. Our study suggested that the lack of a population genetic structure might result in its amphidromous life cycle, and the geographical distance and habitat fragments might cause isolated populations. Thus, the sampling populations of C. nasus in Japan and China could be divided as four geographical/ecological populations.

Ovary transcriptome profiling of Coilia nasus during spawning migration stages by Illumina sequencing

Coilia nasus is an anadromous kind of small to moderate size fish species, and limited transcriptomics research has been performed. In the present study, we performed Illumina sequencing to produce a 22,996,612 clean reads representing with a total of 4,599,079,601 (4.5Gb) nucleotides comprehensive transcript dataset for ovary of C. nasus. Over 20 million total reads were assembled into 63,141 unigenes, and 27,027 annotated genes were predicted by Blastx and ESTScan, respectively. Applying Blast analysis and functional annotation (e.g., GO, COG, Swissprot and KEGG), we have sampled an extensive and diverse expressed gene catalog for C. nasus representing a large proportion of the genes expressed in the ovary development process. This approach will assist in the discovery and annotation of novel genes that play key roles in anadromous fish spawning migration process.

Genetic structure of Scomber japonicus (Perciformes: Scombridae) along the coast of China revealed by complete mitochondrial cytochrome b sequences

The phylogeography history and contemporary agents of selection for many marine fisheries, characterized by widespread species distributions in the face of significant harvest, remains poorly understood. Chub mackerel (Scomber japonicus) are a widespread species in the Indo-Pacific and represent one of the top five commercially fished species in the world, yet their phylogeographic history remains unknown. We characterized the genetic diversity, structure and demographic history of S. japonicus throughout adjacent Chinese seas (from the Yellow Sea to the South China Sea). Using 220 individuals from 11 sites, we inferred 55 distinct haplotypes from complete mitochondrial cytochrome b gene sequences. Haplotype diversity ranged from 0.505 to 0.967 and nucleotide diversity ranged from 0.00056 to 0.01042. Genetic differentiation (F_st) statistics suggested that the highest level of differentiation existed between the SanYa and SanSha localities (F_st = 0.86977), while the lowest levels of differentiation occurred between the DongGang and ShiDao localities (F_st∼ 0). Kimura's genetic distances ranged from 0.001 to 0.011 within and from 0.001 to 0.018 between populations. Hierarchical analysis of molecular variance, Neighbor-joining and median-joining network analyses identified significant phylogeographic structure with two localities (SanYa, Hainan of the South China Sea and LianYunGang, Jiangsu of the East China Sea) explaining most of the genetic variation observed, while the remaining populations were poorly differentiated.