The innate immune system is the first line of defense against pathogens, which is initiated by the recognition of pathogen-associated molecular patterns (PAMPs) and endogenous damage-associated molecular patterns (DAMPs) by pattern recognition receptors (PRRs). Among all the PRRs identified, the toll-like receptors (TLRs) are the most ancient class, with the most extensive spectrum of pathogen recognition. Since the first discovery of Toll in Drosophila melanogaster, numerous TLRs have been identified across a wide range of invertebrate and vertebrate species. It seems that TLRs, the signaling pathways that they initiate, or related adaptor proteins are essentially conserved in a wide variety of organisms, from Porifera to mammals. Molecular structure analysis indicates that most TLR homologs share similar domain patterns and that some vital participants of TLR signaling co-evolved with TLRs themselves. However, functional specification and emergence of new signaling pathways, as well as adaptors, did occur during evolution. In addition, ambiguities and gaps in knowledge still exist regarding the TLR network, especially in lower organisms. Hence, a systematic review from the comparative angle regarding this tremendous signaling system and the scenario of evolutionary pattern across Animalia is needed. In the current review, we present overview and possible evolutionary patterns of TLRs in non-mammals, hoping that this will provide clues for further investigations in this field.

The large yellow croaker Larimichthys crocea (L. crocea) is one of the most economically important marine fish in China and East Asian countries. It also exhibits peculiar behavioral and physiological characteristics, especially sensitive to various environmental stresses, such as hypoxia and air exposure. These traits may render L. crocea a good model for investigating the response mechanisms to environmental stress. To understand the molecular and genetic mechanisms underlying the adaptation and response of L. crocea to environmental stress, we sequenced and assembled the genome of L. crocea using a bacterial artificial chromosome and whole-genome shotgun hierarchical strategy. The final genome assembly was 679 Mb, with a contig N50 of 63.11 kb and a scaffold N50 of 1.03 Mb, containing 25,401 protein-coding genes. Gene families underlying adaptive behaviours, such as vision-related crystallins, olfactory receptors, and auditory sense-related genes, were significantly expanded in the genome of L. crocea relative to those of other vertebrates. Transcriptome analyses of the hypoxia-exposed L. crocea brain revealed new aspects of neuro-endocrine-immune/metabolism regulatory networks that may help the fish to avoid cerebral inflammatory injury and maintain energy balance under hypoxia. Proteomics data demonstrate that skin mucus of the air-exposed L. crocea had a complex composition, with an unexpectedly high number of proteins (3,209), suggesting its multiple protective mechanisms involved in antioxidant functions, oxygen transport, immune defence, and osmotic and ionic regulation. Our results reveal the molecular and genetic basis of fish adaptation and response to hypoxia and air exposure. The data generated by this study will provide valuable resources for the genetic improvement of stress resistance and yield potential in L. crocea. L. crocea is a temperate-water migratory fish that belongs to the order Perciformes and the family Sciaenidae. In China, the annual yield from L. crocea aquaculture exceeds that of any other net-cage-farmed marine fish species. L. crocea also exhibits peculiar behavioral and physiological characteristics and is especially sensitive to various environmental stresses. To understand the molecular and genetic mechanisms underlying the adaptation and response of L. crocea to environmental stress, we sequenced and assembled the genome of L. crocea. Further genomic analyses showed the significant expansion of several gene families, such as vision-related crystallins, olfactory receptors, and auditory sense-related genes, and provided a genetic basis for the peculiar physiological characteristics of L. crocea. Transcriptome analyses of the hypoxia-exposed L. crocea brain revealed new aspects of neuro-endocrine-immune/metabolism regulatory networks that may help the fish to avoid cerebral inflammatory injury and maintain energy balance under hypoxia. Proteomics data demonstrate that skin mucus of the air-exposed L. crocea had a complex composition, suggesting its multiple protective mechanisms involved in antioxidant functions, oxygen transport, immune defence, and osmotic and ionic regulation. These findings provide novel insights into the mechanisms of fish stress adaptation.

Background: Systematic research on fish immunogenetics is indispensable in understanding the origin and evolution of immune systems. This has long been a challenging task because of the limited number of deep sequencing technologies and genome backgrounds of non-model fish available. The newly developed Solexa/Illumina RNA-seq and Digital gene expression (DGE) are high-throughput sequencing approaches and are powerful tools for genomic studies at the transcriptome level. This study reports the transcriptome profiling analysis of bacteria-challengedLateolabrax japonicususing RNA-seq and DGE in an attempt to gain insights into the immunogenetics of marine fish.Results: RNA-seq analysis generated 169,950 non-redundant consensus sequences, among which 48,987 functional transcripts with complete or various length encoding regions were identified. More than 52% of these transcripts are possibly involved in approximately 219 known metabolic or signalling pathways, while 2,673 transcripts were associated with immune-relevant genes. In addition, approximately 8% of the transcripts appeared to be fish-specific genes that have never been described before. DGE analysis revealed that the host transcriptome profile ofVibrio harveyi-challengedL. japonicusis considerably altered, as indicated by the significant up- or down-regulation of 1,224 strong infection-responsive transcripts. Results indicated an overall conservation of the components and transcriptome alterations underlying innate and adaptive immunity in fish and other vertebrate models. Analysis suggested the acquisition of numerous fish-specific immune system components during early vertebrate evolution.Conclusion: This study provided a global survey of host defence gene activities against bacterial challenge in a non-model marine fish. Results can contribute to the in-depth study of candidate genes in marine fish immunity, and help improve current understanding of host-pathogen interactions and evolutionary history of immunogenetics from fish to mammals.

Recent studies suggest that mesenchymal stem cells (MSCs) possess a greater differentiation potential than once thought and that they have the capacity to regenerate damaged tissues/organs. However, the evidence is insufficient, and the mechanism governing the recruitment and homing of MSCs to these injured sites is not well understood. We first examined the MSCs circulating in peripheral blood and then performed chemotaxis, wound healing and tubule‐formation assays to investigate the migration capability of mouse bone marrow MSCs (mBM‐MSCs) in response to liver‐injury signals. In addition, BM‐MSCs from donor enhanced green fluorescent protein transgenic male mice were transplanted into liver‐injured co‐isogenic female recipients, either by intra‐bone marrow injection or through the caudal vein, to allow in vivo tracking analysis of the cell fate after transplantation. Donor‐derived cells were analysed by in vivo imaging analysis, PCR, flow cytometry and frozen sections. Microarray and real‐time PCR were used for chemokine/cytokine and receptor analyses. We successfully isolated circulating MSCs in peripheral blood of liver‐injured mice and provided direct evidence that mBM‐MSCs could be mobilized into the circulation and recruited into the liver after stimulation of liver injury. CCR9, CXCR4 and c‐MET were essential for directing cellular migration towards the injured liver. The recruited mBM‐MSCs may play different roles, including hepatic fate specification and down‐regulation of the activity of hepatic stellate cells which inhibits over‐accumulation of collagen and development of liver fibrosis. Our results provide new insights into liver repair involving endogenous BM‐MSCs and add new information for consideration when developing clinical protocols involving the MSCs.

Macrophages originating from the yolk sac or bone marrow play essential roles in tissue homeostasis and disease. Bone marrow-derived monocytes differentiate into Ly6C^hiand Ly6C^lomacrophages according to the differential expression of the surface marker protein Ly6C. Ly6C^hiand Ly6C^locells possess diverse functions and transcriptional profiles and can accelerate the disease process or support tissue repair and reconstruction. In this review, we discuss the basic biology of Ly6C^hiand Ly6C^lomacrophages, including their origin, differentiation, and phenotypic switching, and the diverse functions of Ly6C^hiand Ly6C^lomacrophages in homeostasis and disease, including in injury, chronic inflammation, wound repair, autoimmune disease, and cancer. Furthermore, we clarify the differences between Ly6C^hiand Ly6C^lomacrophages and their connections with traditional M1 and M2 macrophages. We also summarize the limitations and perspectives for Ly6C^hiand Ly6C^lomacrophages. Overall, continued efforts to understand these cells may provide therapeutic approaches for disease treatment.