In vertebrates, muscles of the limbs and body wall derive from the lateral compartment of the embryonic somites, and axial muscles derive from the medial compartment. Whereas the mechanisms that direct patterning of somites along the dorsoventral axis are beginning to be understood, little is known about the tissue interactions and signaling molecules that direct somite patterning along the mediolateral axis. We report the identification of a specific marker for the lateral somitic compartment and its early derivatives, cSim1, an avian homolog of the Drosophila single minded gene. Using this marker, we provide evidence that specification of the lateral somitic lineage results from the antagonistic actions of a diffusible medializing signal from the neural tube and a diffusible lateralizing signal from the lateral plate mesoderm, and we implicate bone morphogenetic protein 4(BMP4) in directing this lateralization.

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As part of the research program "WEST-COSMIC (Western Pacific Environment Study on CO 2 Ocean Sequestration for Mitigation of Climate Change)", vertical distribution and community structure of copepods were studied at Station Knot (44˚N, 155˚E) down to 4000 m depth in the western subarctic Pacific. Vertical carbon flux mediated by copepod communities was also estimated. Both abundance and biomass of copepods were greatest in the near surface layer and decreased with increasing depth. Decrease of abundance with depth was best fitted to power regression model, while that of biomass was best described by an exponential regression model. Copepod carcasses occurred throughout the layer, and carcasses/living specimens ratios were greatest in the deepest layer (the ratio was 9.3 at 3000-4000 m depth). A total of 98 calanoid copepod species belonging to 38 genera and 15 families occurred in the 0-4000 m water column (Cyclopoida, Harpacticoida and Poecilostomatoida were not identified to species). The number of genera and species showed bimodal vertical distributions with peaks at 500-1000, and at 2000-3000 m both during day and night. Based on the species similarity indices, copepod community could be classified into epipelagic, mesopelagic and bathypelagic communities. Based on the feeding pattern, copepods were divided into four types: suspension feeders, suspension feeders in diapause, detritivores and carnivores. In terms of abundance, the most dominant group was suspension feeders (mainly the cyclopoid genus Oithona) in the epipelagic zone, while detritivores (mainly Poecilostomatoida genus Oncaea) were dominant in the meso-and bathypelagic zones. In terms of biomass, suspension feeders in diapause (calanoid genera Neocalanus and Eucalanus) were the major component (ca. 70%), especially at 200-2000 m depth. Comparison of vertical flux of particulate carbon with estimated copepod ingestion/egestion rates suggests that the suspension feeding copepods receive sufficient food. For detritivorous copepods, copepod carcasses, a possible food source, are not abundant enough, so other food sources need to be considered. As a food source for carnivorous copepods, the abundance of suspension feeding and detritivorous copepods appears to be high enough to meet their demand. Our calculation showed that an average of 32% of the particulate carbon flux is consumed by copepods in the 0-4000 m water column.

It remained very difficult to manipulate gene expression in chick embryos until the advent of in ovo electroporation which enabled the induction of both gain-of-function, and recently loss-of-function, of a gene of interest at a specific developmental stage. Gain-of-function by electroporation is so effective that it has become widely adopted in developmental studies in the chick. Recently, it became possible to induce loss-of-function by introducing an siRNA expression vector by electroporation. In this review, the methods of electroporation for gain-of-function and for loss-of-function by siRNA are discussed.

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BMP-4 is a transforming growth factor beta (TGF- beta) superfamily member which plays important roles in various developmental processes in vertebrate embryogenesis. In this study the expression pattern of BMP-4 was examined during early chick and quail embryonic development. Transcripts were found in the lateral ridges of the neural plate during neurulation and in dorsal regions of the neural tube after its closure along the whole length of the neural axis. To investigate the role of BMP-4 expressed in dorsal regions of the neural tube, cells producing BMP4 were grafted ectopically in the paraxial mesoderm in E2 chick embryos at the level of somites 16-22. Ectopic BMP4 induced Msx-1 and Msx-2 gene expression in superficial ectoderm and superficial mesodermal cells which normally do not express these transcription factors. Moreover, it could be seen that in the E9 operated embryos, additional cartilage had been induced at the level of the graft. These results suggest that BMP4 produced by dorsal regions of the neural tube acts as an endogenous inducing signal in the activation of the genes of the Msx family which are likely to be part of the cascade of molecular events leading to subcutaneous cartilage formation. Therefore, BMP-4 expression in the tissues located dorsally in the neural tube and superficial ectoderm is proposed to be involved in the development of the spinous process of the vertebra.

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