The evolutionary conservation of the core components necessary for the extrinsic apoptotic signaling pathway, in Medaka fish

<p>Abstract</p> <p>Background</p> <p>Death receptors on the cell surface and the interacting cytosolic molecules, adaptors and initiator caspases, are essential as core components of the extrinsic apoptotic signaling pathway. While the apoptotic machinery governing the extrinsic signaling pathway is well characterized in mammals, it is not fully understood in fish.</p> <p>Results</p> <p>We identified and characterized orthologs of mammalian Fas, FADD and caspase-8 that correspond to the death receptor, adaptor and initiator caspase, from the Medaka fish (<it>Oryzias latipes</it>). Medaka Fas, caspase-8 and FADD exhibited protein structures similar to that of their mammalian counterparts, containing a death domain (DD), a death effector domain (DED) or both. Functional analyses indicated that these molecules possess killing activity in mammalian cell lines upon overexpression or following activation by apoptotic stimuli, suggesting similar pro-apoptotic functions in the extrinsic pathway as those in mammals. Genomic sequence analysis revealed that the Medaka <it>fas </it>(<it>tnfrsf6</it>), <it>fadd </it>and <it>caspase-8 </it>(<it>casp8</it>) genes are organized in a similar genomic structure as the mammalian genes. Database search and phylogenetic analysis revealed that the <it>fas </it>gene, but not the <it>fadd </it>and <it>casp8 </it>genes, appear to be present only in vertebrates.</p> <p>Conclusion</p> <p>Our results indicate that the core components necessary for the extrinsic apoptotic pathway are evolutionarily conserved in function and structure across vertebrate species. Based on these results, we presume the mechanism of apoptosis induction via death receptors was evolutionarily established during the appearance of vertebrates.</p

CO2 efflux from leaf litter focused on spatial and temporal heterogeneity of moisture

Leaf litter respiration (R [LL]) was directly measured in situ to evaluate relationships with the water content in leaf litter (WC), which is distributed heterogeneously under natural conditions. To do so, we developed a small, closed static chamber system using an infrared gas analyzer, which can measure instantaneous R [LL]. This study focuses on the measurement of CO2 effluxes from leaf litter using the chamber system in the field and examines the relationship between R [LL] and WC among seven broadleaf species in a temperate forest. The measurements focused on the position of leaves within the litter layer, finding that both R [LL] and WC were significantly higher in the lower layer. The value of R [LL] increased with increasing WC, and the response of R [LL] to WC was similar among all seven species. Moreover, the temporal variation in WC differed among three species and was associated with leaf litter thickness. The observed heterogeneity in WC induced by the physical environment (e.g., position and thickness of leaf litter) affects the variation in WC and, therefore, both R [LL] and the decomposition rates of organic matter in the litter layer