Shixi Chen

Why does the mudskipper Boleophthalmus pectinirostris form territories in farming ponds

The mudskipper Boleophthalmus pectinirostris maintained territories in farming ponds during the cold season between November and February. There were two types of territory, one was surrounded by mud-walls, and the other was without mud-walls. Both types of territory were entirely covered by shallow water. The area of walled territories was significantly bigger than that of non-walled ones. The nearest neighbour distance of walled territories was significantly shorter than that of non-walled territories. In January, fish surface activity occurred between 1200 and 1500 hours at which time the territorial water temperature reached a maximum, being significantly higher than that of the air, mud surface or deep burrow. The territorial sediments exhibited a significantly greater benthic microalgal biomass (chlorophyll- a and total chlorophyll- a ) as compared to the non-territorial sediments. The present study indicates that B. pectinirostris forms a territory during the cold season to keep a pool of water that encourages diatom growth and enables the fish to engage in surface activity.

Population genetic structure and demographic history of the mudskipper Boleophthalmus pectinirostris on the northwestern pacific coast

The genetic structure and demographic history of nine mudskipper Boleophthalmus pectinirostris populations on the Northwestern Pacific coast were investigated using the complete mitochondrial cytochrome b sequences. Among the 248 individuals examined, 118 haplotypes were detected. As a whole, high haplotype diversity and moderate nucleotide diversity were observed within the populations. The topology of the neighbor-joining tree of B. pectinirostris haplotypes was assigned into two closely related lineages (A and B) that appeared to have strong geographic genetic structure. Lineage A included the populations from Jiangsu, Zhejiang, Fujian, Taiwan, Guangdong, Guangxi and Vietnam while Lineage B included populations from Japan and Korea. The pairwise comparisons of FST were all statistically significant (Pu2009<0.05) between populations while the analysis of molecular variance showed that most of the variances were found between the two lineages. Neutrality tests and mismatch distribution analyses revealed that B. pectinirostris had undergone population expansion during the late Pleistocene. Population expansion occurred approximately 170,000xa0years ago for Lineage A, and 80,000xa0years ago for Lineage B. Sea level changes during the late Pleistocene might have been responsible for this population expansion and lineage isolation.

Transcriptomic signatures for ovulation in vertebrates

The central roles of luteinizing hormone (LH), progestin and their receptors for initiating ovulation have been well established. However, signaling pathways and downstream targets such as proteases that are essential for the rupture of follicular cells are still unclear. Recently, we found anovulation in nuclear progestin receptor (Pgr) knockout (Pgr-KO) zebrafish, which offers a new model for examining genes and pathways that are important for ovulation and fertility. In this study, we examined expression of all transcripts using RNA-Seq in preovulatory follicular cells collected following the final oocyte maturation, but prior to ovulation, from wild-type (WT) or Pgr-KO fish. Differential expression analysis revealed 3567 genes significantly differentially expressed between WT and Pgr-KO fish (fold change⩾2, p<0.05). Among those, 1543 gene transcripts were significantly more expressed, while 2024 genes were significantly less expressed, in WT than those in Pgr-KO. We then retrieved and compared transcriptional data from online databases and further identified 661 conserved genes in fish, mice, and humans that showed similar levels of high (283 genes) or low (387) expression in animals that were ovulating compared to those with no ovulation. For the first time, ovulatory genes and their involved biological processes and pathways were also visualized using Enrichment Map and Cytoscape. Intriguingly, enrichment analysis indicated that the genes with higher expression were involved in multiple ovulatory pathways and processes such as inflammatory response, angiogenesis, cytokine production, cell migration, chemotaxis, MAPK, focal adhesion, and cytoskeleton reorganization. In contrast, the genes with lower expression were mainly involved in DNA replication, DNA repair, DNA methylation, RNA processing, telomere maintenance, spindle assembling, nuclear acid transport, catabolic processes, and nuclear and cell division. Our results indicate that a large set of genes (>3000) is differentially regulated in the follicular cells in zebrafish prior to ovulation, terminating programs such as growth and proliferation, and beginning processes including the inflammatory response and apoptosis. Further studies are required to establish relationships among these genes and an ovulatory circuit in the zebrafish model.

Hypoxic tolerance of Chinese black sleeper Bostrichthys sinensis embryos at heartbeat stage

Tolerance of hypoxia in Chinese black sleeper ( Bostrichthys sinensis ) embryos at heartbeat stage was examined at different oxygen concentrations. Embryonic response to hypoxic conditions was expressed in terms of the intensity of variation in heartbeat rate ( V ). Exposure of the embryos at 25°C to 0.5, 1.0 and 1.5 mg/l dissolved oxygen (DO), caused bradycardia, which was developed within the first 10 min of hypoxia, followed by a plateau, and lasted until termination of the hypoxia. The V values were significantly affected by DO concentrations ( P P P V values were significantly lower than the V values of average heartbeat rates ( P V values were not significantly different between primary heartbeat rate and average heartbeat rate after 90 min exposure ( P >0.05).

Complete mitochondrial genome and phylogenetic analysis of the barred mudskipper Periophthalmus argentilineatus (Perciformes, Gobiidae).

Abstract The complete mitochondrial genome sequence of the barred mudskipper Periophthalmus argentilineatus was first determined in this study. The circle genome was 16u2009509u2009bp long and consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region. The nucleotide composition of the heavy strand of P. argentilineatus is 28.28% for A, 27.83% for C, 16.01% for T, and 27.88% for G, with a slight Gu2009+u2009C bias of 55.71%. Only the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes were encoded on the light strand, other mitochondrial genes were all encoded on the heavy strand. The mitochondrial gene arrangement of P. argentilineatus is similar to those of most other gobies. The phylogenetic analysis using the neighbor-joining method showed that the kinship between Periophthalmus and Boleophthalmus is closer than those between Periophthalmus and other selected genera. Periophthalmus argentilineatus was clustered into one branch with other four species from the same genus Periophthalmus.

Cardiac performance of Chinese black sleeper (Bostrichthys sinensis) at early stages of development under hypoxic conditions

Cardiac performance of the Chinese black sleeper (Bostrichthys sinensis) was examined at early stages of development (the heartbeat, blood circulation and newly hatched larval stages) under different hypoxic oxygen concentrations. Exposure of the embryos at 25°C to 0.2 mg/l dissolved oxygen (DO) indicated periodic heartbeat at both the heartbeat stage and the blood circulation stage, but it started sooner after exposure at the blood circulation stage than at the heartbeat stage. With the appearance of the gill slits, the tolerance of the newly hatched larvae to hypoxia was improved. The larvae did not display periodic heartbeat at 0.2 mg/L DO, but periodic heartbeat occurred at 0.1 mg/L DO and 0.02 mg/L DO after 23.3 ± 6.2 minutes and 13.2 ± 3.4 minutes of exposure. With exposure of the embryos to hypoxia, the occurrence of periodic heartbeat of excised embryos was earlier than that of whole egg embryos at both the blood circulation and heartbeat stages. These results indicated that the tolerance of embryos to hypoxia decreased with the progress of embryogenesis and suggested that the perivitelline liquid can protect the embryos by conserving oxygen. In this study, we also found that a breakdance performance (an arrhythmic heart beat) occurred in the newly hatched larvae at 0.02 mg/l DO. The breakdance performance lasted about 10 minutes, and then the heartbeat became normal.

Complete mitochondrial genome and phylogenetic analysis of the serpent mudskipper Parapocryptes serperaster (Perciformes, Gobiidae): repetitive sequences in the control region

Abstract The complete mitochondrial genome sequence of the serpent mudskipper Parapocryptes serperaster was first determined in this study. The circle genome was 17u2009243u2009bp long and consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region. The nucleotide composition of the heavy strand of P. serperaster is 28.65% for A, 30.07% for C, 25.31% for T, and 15.97% for G, with a slight Au2009+u2009T bias of 53.96%. Only the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes were encoded on the light strand, all other mitochondrial genes were encoded on the heavy strand. A 178-bp tandem repeat, which started from the 827-bp site of the control region, was identified. Like most other gobies, P. serperaster also has the typical vertebrate mitochondrial gene arrangement. The phylogenetic analysis showed that the kinship between Parapocryptes and Boleophthalmus is closer than those between Parapocryptes and other selected genera.

Complete mitochondrial genome and phylogenic analysis of the mudskipper Scartelaos gigas (Perciformes, Gobiidae)

Abstract In this paper, the complete mitochondrial genome sequence of Scartelaos gigas was firstly determined. The circular genome (16u2009717 bp) comprises 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 control region. The overall base composition of S. gigas is 28.9% for C, 28.3% for A, 26.4% for T, 16.4% for G, with a slight Au2009+u2009T bias of 54.7%. In the control region, the termination-associated sequence and conserved sequence block domains were found, but the tandem repeat structure was not found. It has the typical vertebrate mitochondrial gene arrangement. The phylogenic analysis using the Neighbor-Joining method showed that the fishes belonging to Gobiidae, Odontoburidae, and Eleotridae formed three branches grouped with other fishes into one clade which separated from the mammals. We hope that the results from the present study will provide useful molecular information for the further studies on genetic structure and demographic history of S. gigas.