Common Carp mef2 Genes: Evolution and Expression.

The MEF2 (myocyte enhancer factor 2) family belongs to the MADS-box superfamily of eukaryotic transcription factors. The vertebrate genes compose four distinct subfamilies designated MEF2A, -B, -C, and -D. There are multiple mef2 genes in the common carp (Cyprinus carpio). So far, the embryonic expression patterns of these genes and the evolution of fish mef2 genes have been barely investigated. In this study, we completed the coding information of C. carpio mef2ca2 and mef2d1 genes via gene cloning and presented two mosaic mef2 sequences as evidence for recombination. We also analyzed the phylogenetic relationship and conserved synteny of mef2 genes and proposed a new evolutionary scenario. In our version, MEF2B and the other three vertebrate subfamilies were generated in parallel from the single last ancestor via two rounds of whole genome duplication events that occurred at the dawn of vertebrates. Moreover, we examined the expression patterns of C. carpio mef2 genes during embryogenesis, by using whole-mount in situ hybridization, and found the notochord to be a new expression site for these genes except for mef2ca1&2. Our results thus provide new insights into the evolution and expression of mef2 genes.

Evolution of the viral hemorrhagic septicemia virus: divergence, selection and origin.

Viral hemorrhagic septicemia virus (VHSV) is an economically significant rhabdovirus that affects an increasing number of freshwater and marine fish species. Extensive studies have been conducted on the molecular epizootiology, genetic diversity, and phylogeny of VHSV. However, there are discrepancies between the reported estimates of the nucleotide substitution rate for the G gene and the divergence times for the genotypes. Herein, Bayesian coalescent analyses were conducted to the time-stamped entire coding sequences of the six VHSV genes. Rate estimates based on the G gene indicated that the marine genotypes/subtypes might not all evolve slower than their major European freshwater counterpart. Age calculations on the six genes revealed that the first bifurcation event of the analyzed isolates might have taken place within the last 300 years, which was much younger than previously thought. Selection analyses suggested that two codons of the G gene might be positively selected. Surveys of codon usage bias showed that the P, M and NV genes exhibited genotype-specific variations. Furthermore, we proposed that VHSV originated from the Pacific Northwest of North America.

Dating the divergence of the infectious hematopoietic necrosis virus.

Infectious hematopoietic necrosis virus (IHNV) is an economically significant rhabdovirus that can cause severe disease to most salmonid fish. Phylogenetic analyses of worldwide IHNV isolates have defined five major genogroups. Herein, to further the understanding of the molecular epidemiology and evolution of IHNV, Bayesian coalescent analyses were conducted to the time-stamped coding sequences of the N, G and NV genes. The nucleotide substitution rates and the divergence times were assessed. Among the three genes, NV, the smallest one coding for a non-virion protein, was conferred the highest mean rate. Estimates for the G subsets based upon the five genogroups indicated that L and U evolved much slower than the others. Age calculations suggested that the first diversification event of the IHNV isolates analyzed might have happened before the notification of the disease during the early 1950s. Selection analyses suggested that the three genes were mainly subject to purifying selection. In addition, surveys of codon usage variation showed that the three genes had influences other than mutational bias.

[Regulation of zebrafish development by microRNAs].

MicroRNAs (miRNAs) are a class of non-coding small RNAs at the length about 22nt, which are found in the cells of both unicellular and multicellular eukaryotes, and highly conserved in many processes of biological evolution. miRNAs play important roles in the regulation of animal development, physiological functions, and pathological processes. As a model organism, zebrafish has been widely used in the modern biological researches. The studies on miRNAs in zebrafish are capable of revealing the function of miRNAs in vertebrate. This paper reviews the effects of total miRNA deletion and the individual miRNAs on the embryonic development of zebrafish in order to provide the clues for the functional researches of miRNAs on vertebrate and breeding in fish.