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Cetaceans have evolved elongated soft-tissue flipper with digits made of hyperphalangy. Cetaceans were found to have 2-3 more alanine residues in Hoxd13 than other mammals, which were suggested to be related to their flipper. However, how Hoxd13 regulates other genes and induces hyperphalangy in cetaceans remain poorly understood. Here, we overexpressed the bottlenose dolphin Hoxd13 in zebrafish (Danio rerio). Combined with transcriptome data and evolutionary analyses, our results revealed that the Wingless/Integrated (Wnt) and Hedgehog signaling pathways and multiple genes might regulate hyperphalangy development in cetaceans. Meanwhile, the Notch and mitogen-activated protein kinase (Mapk) signaling pathways and Fibroblast growth factor receptor 1 (Fgfr1) are probably correlated with interdigital tissues retained in the cetacean flipper. In conclusion, this is the first study to use a transgenic zebrafish to explore the molecular evolution of Hoxd13 in cetaceans, and it provides new insights into cetacean flipper formation.

Background: Large, long-lived organisms typically have a higher risk of cancer, but cetaceans, which include the largest and longest-living mammals, may have evolved a mechanism to counter this. However, little is known about the genetic basis underlying this mechanism. Cetaceans, which include the largest and longest-lived mammals, may have evolved effective anticancer mechanisms in response to a high risk of cancer caused by massive somatic cell divisions.Results: The p53 pathway is ideal for studying the mechanisms behind cancer resistance, as nearly all types of cancer have evolved ways to evade this suppressive mechanism. Here, comparative genetic analyses of the 73 genes involved in the p53 pathway were examined in cetaceans to explore potential anticancer mechanisms behind natural longevity. We found that long-lived species have three positively selected genes (APAF1, CASP8, TP73) and three duplicated genes (IGFBP3, PERP, CASP3) involved in the regulation of apoptosis, suggesting that apoptosis regulation may be an important strategy for cancer resistance in these long-lived cetaceans. Inhibition of angiogenesis may be another strategy for protecting cetaceans from cancer because the evolutionary rates of three angiogenesis-regulated genes (SERPINE1, CD82 and TSC2) were significantly related to longevity traits (longevity quotient and maximum lifespan). Interestingly, some tumor suppressor genes were determined to be under positive selection (APAF1 and TP73), have high copy numbers (CASP3 and CCNG1), and be related to body size in the large-bodied and long-lived cetacean lineages. The above is all molecular evidence for Peto's paradox. Conclusions: Our study identified several candidate genes for the p53 pathway with different evolutionary paths in the large, long-lived cetaceans and suggested that tumor suppression in cetaceans might be mediated through multiple synergistic effects rather than a single pathway/target.

The cetacean hindlimb skeleton massively decreased to only vestigial limb elements as cetaceans evolved from land to aquatic lifestyles; however, the molecular mechanism underlying this major morphological transition remains unclear. In this study, four deletions and specific substitutions were detected in cetacean hindlimb enhancer A (HLEA), an enhancer that can regulate Tbx4 expression in hindlimb tissues to control hindlimb development. Transcriptional activation of HLEA was significantly weaker in bottlenose dolphin than mice, and this was found to be closely associated with cetacean-specific deletions. Furthermore, deletions in cetacean HLEA might disrupt HOX and PITX1 binding sites, which are required for enhancer activation. The ancestral state of these deletions was investigated, and all four specific deletions were found to have occurred after the species diverged from their common ancestor, suggesting that the deletion occurred recently, during a secondary aquatic adaptation. Taking these findings together, we suggest that cetacean-specific sequence changes reduced the Tbx4 gene expression pattern, and consequently drove the gradual loss of hindlimb in cetaceans.

Most of Alvinocaridid shrimps live in hydrothermal vents, where is a wicked environment with highly toxic chemistry, hypoxia, acidic pH, and sulfide deposits. In order to adapt to this environment, change in energy metabolism may be one of the primary factors. However, the genetic basis of energy metabolism underlying this environment remains unexplored. Here, we present the first systematic investigation of mitochondrial genes in Alvinocarididae. The analysis demonstrated that ATP6, ND4 and ND6 were subjected to strong positive selection leading to last common ancestors of Alvinocarididae, and ATP8, ND5, COX1 and COX2 were determined to have undergone positive selection in the interior lineages of Alvinocarididae. Considering that about 95% of ATP is supplied by mitochondria via oxidative phosphorylation, and body detoxification process associated with cytochrome c. Positive selection in these genes suggested that Alvinocaridid shrimps might have acquired an enhanced capacity for energy metabolism and detoxification in extreme hydrothermal vent field.

The mudflat crab Helice tientsinensis is one of the most commercially valuable species for crabmeat production due to its delicious taste. These crabs are mainly found in coastal wetland where they are seriously threatened by toxic heavy metal pollution. In crustaceans, the hepatopancreas is an important organ for detoxification, and metal toxic substances can be converted to non-toxic or less toxic compounds in this organ. To develop a better understanding of the molecular response of H. tientsinensis to the toxic metal cadmium (Cd) and provide a molecular basis for the toxic metal tolerance of H. tientsinensis. In this study, we performed comparative hepatopancreas transcriptome analysis between H. tientsinensis unexposed (as control) and exposed to the toxic metal Cd for 48 h. We identified 1089 Cd stress significantly-upregulated and 1560 Cd stress significantly-downregulated unigenes. Functional categorization and annotation of these differentially-expressed genes (DEGs) demonstrated that the response to Cd stress in the hepatopancreas of H. tientsinensis mainly involves “antioxidant activity”, “detoxification”, “toxin degradation activity” and “immune system process”. In addition, five genes (ABCC1, NDUFAF5, ASTL, DES1, CYP27A) were identified as possible major targets for toxic metal tolerance. This is the first time reporting that the response of H. tientsinensis to Cd exposure at the transcriptome level, and it lays the foundation for understanding the molecular mechanisms of the response of H. tientsinensis to environmental toxic metal stress.

Background The swimming crab Portunus trituberculatus is one of the most commonly farmed crustaceans in China. As one of the most widely known and high-value edible crabs, it crab supports large crab fishery and aquaculture in China. Only large and sexually mature crabs can provide the greatest economic benefits, suggesting the considerable effect of reproductive system development on fishery. Studies are rarely conducted on the molecular regulatory mechanism underlying the development of the reproductive system during the mating embrace stage in this species. In this study, we used high-throughput sequencing to sequence all transcriptomes of the P. trituberculatus reproductive system. Results Transcriptome sequencing of the reproductive system produced 81,688,878 raw reads (38,801,152 and 42,887,726 reads from female and male crabs, respectively). Low-quality (quality

qRT-PCR was performed for 4 genes that were identified as differentially expressed between the immature and mature male reproductive systems. The Y axis shows the relative mRNA expression levels. * p

qRT-PCR was performed for 4 genes that were identified as differentially expressed between the immature and mature female reproductive systems. The Y axis shows the relative mRNA expression levels. * p

Passeriformes is the largest group within aves and the phylogenetic relationships between Passeriformes have caused major disagreement in ornithology. Particularly, the phylogenetic relationships between muscicapoidea and sylvioidea are complex, and their taxonomic boundaries have not been clearly defined. Our aim was to study the status of two bird species: Tarsiger cyanurus and Phoenicurus auroreus. Furthermore, we analyzed the phylogenetic relationships of Passeriformes. Complete mitochondrial DNA (mtDNA) sequences of both species were determined and the lengths were 16,803 (T. cyanurus) and 16,772 bp (P. auroreus), respectively. Thirteen protein-coding genes, 22 tRNA genes, two rRNA genes, and one control region were identified in these mtDNAs. The contents of A and T at the base compositions was significantly higher than the content of G and C, and this AT skew was positive, while the GC skew was negative. The monophyly of Passeriformes is divided into four major clades: Corvoidea, Sylvioidea, Passeroidea, and Musicicapoidea. Paridae should be separated from the superfamily Sylvioidea and placed within the superfamily Muscicapoidea. The family Muscicapidae and Corvida were paraphyly, while Carduelis and Emberiza were grouped as a sister taxon. The relationships between some species of the order passeriformes may remain difficult to resolve despite an effort to collect additional characters for phylogenetic analysis. Current research of avian phylogeny should focus on adding characters and taxa and use both effectively to obtain a better resolution for deeper and shallow nodes.