494 research outputs found

    An improved apparent polar wander path for southwest Japan: post-Cretaceous multiphase rotations with respect to the Asian continent

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    To construct the Mesozoic apparent polar wander path (APWP) for the inner arc of the southwestern Japanese islands (referred to as southwest Japan) and compare it to that of East Asia, a 110 Ma paleomagnetic pole for southwest Japan was determined. Mudstone and sandstone samples were collected from 16 sites for paleomagnetic analysis in the Lower Cretaceous Inakura Formation of the Inakura area in the central part of southwest Japan. A high-temperature magnetization component, with unblocking temperatures of 670-695 degrees C, was isolated from 12 sites of red mudstone. Of these, 11 sites revealed a primary remanent magnetization during the Early Cretaceous. The primary directions combined with the previously reported ones provide a new mean direction (D = 79.7 degrees, I = 47.4 degrees, alpha(95) = 6.5 degrees, N = 17), and a corresponding paleomagnetic pole that is representative of southwest Japan (24.6 degrees N, 203.1 degrees E, A(95) = 6.8 degrees). The Early Cretaceous paleomagnetic pole, together with the Late Cretaceous and Cenozoic poles, constitute a new APWP for southwest Japan. The new APWP illustrates a standstill polar position during 110-70 Ma, suggesting tectonic quiescence of this region. This standstill was followed by two large tracks during the Cenozoic. We interpret these tracks as clockwise tectonic rotations of southwest Japan that occurred twice during the Cenozoic. The earlier tectonic rotation occurred for a tectonic unit positioned below northeast China, the Liaodong and Korean Peninsulas, and southwest Japan (East Tan-Lu Block) during the Paleogene. The later rotation took place only under southwest Japan during the Neogene. Cenozoic multiphase rifting activity in the eastern margin of the Asian continent was responsible for the tectonic rotations that are observed from the paleomagnetic studies. Intermittent rifting may constitute a series of phenomena due to asthenospheric convection, induced by the growth of the Eurasian mega-continent in the Mesozoic

    Absence of Cretaceous hairpin in the apparent polar wander path of southwest Japan: consistency in paleomagnetic pole positions

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    To test the hypothesis that a Cretaceous hairpin turn is absent in the apparent polar wander path (APWP) of the inner arc of southwestern Japanese island (southwest Japan), we refined a mid-Cretaceous (100 Ma) paleomagnetic pole from southwest Japan. Red mudstone samples from the 100 Ma Hayama Formation were collected for paleomagnetic analysis from eight sites in the Hayama area in the central part of southwest Japan. A high-temperature remanent magnetization component carried by hematite was isolated from these sites and was found to be of primary mid-Cretaceous origin. The primary nature of the magnetization is supported by the detrital character of the magnetic carrier. The primary directions provided a paleomagnetic pole (35.0 degrees N, 209.6 degrees E, A(95) = 6.1 degrees, N = 8), which represented southwest Japan at 100 Ma. This pole falls into a cluster of Cretaceous poles in southwest Japan. An APWP for southwest Japan between 110 and 70 Ma was updated to ascertain the stationarity of the pole positions for this region. Therefore, it is unlikely that the APWP for southwest Japan experienced a hairpin turn during the Cretaceous

    Cloning and characterization of mr-s, a novel SAM domain protein, predominantly expressed in retinal photoreceptor cells

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    BACKGROUND: Sterile alpha motif (SAM) domains are ~70 residues long and have been reported as common protein-protein interaction modules. This domain is found in a large number of proteins, including Polycomb group (PcG) proteins and ETS family transcription factors. In this work, we report the cloning and functional characterization of a novel SAM domain-containing protein, which is predominantly expressed in retinal photoreceptors and the pineal gland and is designated mouse mr-s (major retinal SAM domain protein). RESULTS: mr-s is evolutionarily conserved from zebrafish through human, organisms through which the mechanism of photoreceptor development is also highly conserved. Phylogenetic analysis suggests that the SAM domain of mr-s is most closely related to a mouse polyhomeotic (ph) ortholog, Mph1/Rae28, which is known as an epigenetic molecule involved in chromatin modifications. These findings provide the possibility that mr-s may play a critical role by regulating gene expression in photoreceptor development. mr-s is preferentially expressed in the photoreceptors at postnatal day 3–6 (P3-6), when photoreceptors undergo terminal differentiation, and in the adult pineal gland. Transcription of mr-s is directly regulated by the cone-rod homeodomain protein Crx. Immunoprecipitation assay showed that the mr-s protein self-associates mainly through the SAM domain-containing region as well as ph. The mr-s protein localizes mainly in the nucleus, when mr-s is overexpressed in HEK293T cells. Moreover, in the luciferase assays, we found that mr-s protein fused to GAL4 DNA-binding domain functions as a transcriptional repressor. We revealed that the repression activity of mr-s is not due to a homophilic interaction through its SAM domain but to the C-terminal region. CONCLUSION: We identified a novel gene, mr-s, which is predominantly expressed in retinal photoreceptors and pineal gland. Based on its expression pattern and biochemical analysis, we predict that mr-s may function as a transcriptional repressor in photoreceptor cells and in pinealocytes of the pineal gland

    Deformation of rhyolite lava crust associated with intermittent inner flow of lava: palaeomagnetic evidence

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    A palaeomagnetic study has been conducted to examine the deformation of thick crusts of rhyolite lava while its inner portions continue to flow. The Sanukayama rhyolite lava, which erupted in the Pleistocene in Kozushima Island, Japan, was chosen as the investigation site because of its well-exposed vertical lithofacies variations classified into three distinct zones (pumiceous, obsidian and crystalline). The targets of this study are the pumiceous and obsidian zones, which constitute the crust of the lava. Thermal demagnetization reveals three remanent magnetization components from the pumiceous and obsidian samples but only a single magnetization component from the inner crystalline rhyolite samples. Alternating field demagnetization is ineffective in isolating the magnetization components in the pumiceous and obsidian samples. The multiple components of remanent magnetization of the crust are interpreted to have been acquired during cooling as thermoremanent magnetizations. We suspect intermittent lava transport of the inner portions, the primary mode of rhyolite lava advancement, to be responsible for the presence of multiple components in pumice and obsidian of the lava crust. When the inner portions of the lava retain mobility to flow out of the crust, the solidified crust of the lava surface below the magnetite Curie temperature remains susceptible to deformation. Analysis of palaeomagnetic directions from the crust allows the deformation of the crust to be described in terms of rotation. Although the mode of rhyolite lava advancement is not well understood, because of its infrequent occurrence, our observations offer an important insight on how the mobile part of the lava is associated with the deformation of the crust during continued lava advance
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