A 425 T>C polymorphism in complement C7 association with resistance to Aeromonas hydrophila in grass carp.

Aeromonas hydrophila, a widespread bacterium in the aquatic environment, causes hemorrhagic septicemia in fish. In the last decade, the disease has caused mass mortalities and tremendous economic loss in cultured fish. The complement component C7 is a terminal component of complement that interacts in a sequence of polymerization reactions with other terminal complement components to form a membrane attack complex. The formation of the membrane attack complex creates a pore in the membranes of certain pathogen that can lead to their death. The objective of this study was to identify single nucleotide polymorphisms (SNPs) in the C7 gene and to assess their association with A. hydrophila resistance in grass carp. A resource population consisting of 186 susceptible and 191 resistant grass carp was constructed. We sequenced a total of 7826 bp of the C7 gene and identified 6 SNPs that were genotyped in the resource population. The SNP -1575 A>C was positioned in the promoter region of the gene. The SNP 425 C>T identified in the coding exon was a synonymous substitution in the fourth exon. Statistical analysis showed that SNP 425 C>T was associated with the incidence of hemorrhagic septicemia. The SNPs -1575 A>C, -688 T>C, and -266 A>C were highly linked together (r(2) > 0.85). No haplotypes generated with these 3 SNPs were associated with resistance to A. hydrophila in grass carp. These findings suggest that the 425 C>T polymorphism in C7 gene may be a significant molecular marker for resistance to A. hydrophila in grass carp.

Novel polymorphic microsatellite markers in Odontobutis potamophila.

We characterized 16 novel polymorphic loci isolated from a partial genomic DNA library of Odontobutis potamophila enriched for CA repeats. We tested the variability of these microsatellites on 51 unrelated individuals collected in China. All loci were polymorphic. The average allele number was 14.6 per locus, ranging from 2 to 27. The observed heterozygosity ranged from 0.35 to 0.90, with an average of 0.70, whereas the average expected heterozygosity was 0.76. Twelve of the 16 microsatellites conformed to Hardy-Weinberg equilibrium and were inherited independently. These developed microsatellites will be useful in studies of population genetics and other genetic studies on this important food species.

Differential expression of interleukin-12 p35 and p40 subunits in response to Aeromonas hydrophila and Aquareovirus infection in grass carp, Ctenopharyngodon idella.

The grass carp (Ctenopharyngodon idella) aquaculture industry in Asia is prone to bacterial and viral hemorrhagic diseases. Effective adjuvants for vaccine formulation are the need of the hour for control of these diseases and long-term sustainability of grass carp farming. In this study, the involvement of interleukin-12 (IL-12) from grass carp (gcIL­12) in anti-bacterial and anti-viral immune responses was demonstrated via expression profiles of gcIL-12 subunits in immune tissues of the fish, following infection by Aeromonas hydrophila and Aquareovirus. Additionally, cDNA of the gcIL-12 subunits, p35 and p40 was cloned and characterized. We found that most of the structurally and functionally important features of vertebrate orthologues were conserved in gcIL-12 subunits, p35 and p40, with some features specific to grass carp. High levels of gcIL-12 p35 expression in the brain and gills suggest that IL-12 plays an important role in neural and immune systems. High expression levels in the heart, blood, and immune-related tissues suggest an important role in circulation and the immune system as well. Infections by both, A. hydrophila and Aquareovirus stimulated the mRNA expression of gcIL-12 subunits, p35 and p40 in most immune tissues. Significant upregulation or downregulation of gcIL-12 subunits, p35 and p40 by bacterial and viral infection confirms their potential role in anti-bacterial and anti-viral immune responses in fish.