Echiuran Hox genes provide new insights into the correspondence between Hox subcluster organization and collinearity pattern.

In many bilaterians, Hox genes are generally clustered along the chromosomes and expressed in spatial and temporal order. In vertebrates, the expression of Hox genes follows a whole-cluster spatio-temporal collinearity (WSTC) pattern, whereas in some invertebrates the expression of Hox genes exhibits a subcluster-level spatio-temporal collinearity pattern. In bilaterians, the diversity of collinearity patterns and the cause of collinearity differences in Hox gene expression remain poorly understood. Here, we investigate genomic organization and expression pattern of Hox genes in the echiuran worm Urechis unicinctus (Annelida, Echiura). Urechis unicinctus has a split cluster with four subclusters divided by non-Hox genes: first subcluster (Hox1 and Hox2), second subcluster (Hox3), third subcluster (Hox4, Hox5, Lox5, Antp and Lox4), fourth subcluster (Lox2 and Post2). The expression of U. unicinctus Hox genes shows a subcluster-based whole-cluster spatio-temporal collinearity (S-WSTC) pattern: the anterior-most genes in each subcluster are activated in a spatially and temporally colinear manner (reminiscent of WSTC), with the subsequent genes in each subcluster then being very similar to their respective anterior-most subcluster gene. Combining genomic organization and expression profiles of Hox genes in different invertebrate lineages, we propose that the spatio-temporal collinearity of invertebrate Hox is subcluster-based.

Genome-Wide Analyses of Heat Shock Protein Superfamily Provide New Insights on Adaptation to Sulfide-Rich Environments in Urechis unicinctus (Annelida, Echiura).

The intertidal zone is a transitional area of the land-sea continuum, in which physical and chemical properties vary during the tidal cycle and highly toxic sulfides are rich in sediments due to the dynamic regimes. As a typical species thriving in this habitat, Urechis unicinctus presents strong sulfide tolerance and is expected to be a model species for sulfide stress research. Heat shock proteins (HSPs) consist of a large group of highly conserved molecular chaperones, which play important roles in stress responses. In this study, we systematically analyzed the composition and expression of HSPs in U. unicinctus. A total of eighty-six HSP genes from seven families were identified, in which two families, including sHSP and HSP70, showed moderate expansion, and this variation may be related to the benthic habitat of the intertidal zone. Furthermore, expression analysis revealed that almost all the HSP genes in U. unicinctus were significantly induced under sulfide stress, suggesting that they may be involved in sulfide stress response. Weighted gene co-expression network analysis (WGCNA) showed that 12 HSPs, including 5 sHSP and 4 HSP70 family genes, were highly correlated with the sulfide stress response which was distributed in steelblue and green modules. Our data indicate that HSPs, especially sHSP and HSP70 families, may play significant roles in response to sulfide stress in U. unicinctus. This systematic analysis provides valuable information for further understanding of the function of the HSP gene family for sulfide adaptation in U. unicinctus and contributes a better understanding of the species adaptation strategies of marine benthos in the intertidal zone.

TRAF6 is a critical factor in fish immune response to virus infection.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is one of the key adaptor molecule in Toll-like receptor signal transduction that triggers downstream cascades involved in innate immunity. In our previous study, the molecular characteristics of EtTRAF6 (TRAF6 from Epinephelus tauvina), the tissue distributions, expression patterns after challenging with bacterial and viral pathogens were investigated. Here we identified EtTRAF6 as an important regulator of virus-triggered signaling pathway. Overexpression of EtTRAF6-ORF and truncated forms of EtTRAF6, including EtTRAF6-C (delete the MATH domain), EtTRAF6-N (delete the RING domain) and EtTRAF6-MATH, inhibited IFN-ß activity strongly in grouper spleen (GS) cells. Overexpression of EtTRAF6 repressed virus-induced production of type I IFNs. When EtTRAF6 cotransfected with EcIRF3 or EcIRF7, EtTRAF6 inhibited IRF-induced activation of IFN-ß. Over-expressed EtTRAF6 inhibited the transcription of SGIV genes significantly in GS cells. Although TRAF6 has a role in apoptosis regulation, it is not known if EtTRAF6 has any role in apoptosis regulation. Strikingly, when over-expressed in fathead minnow (FHM) cells, EtTRAF6 protected them from cell death induced by SGIV. Therefore, these results suggest that TRAF6 may play a critical role in their response to SGIV infection, through regulation of a cell death pathway that is common to fish and humans.