Phenomenology of the Lense-Thirring effect in the Solar System

Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate the present and future perspectives in directly measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in Astrophysics and Space Science (ApSS). Some uncited references in the text now correctly quoted. One reference added. A footnote adde

Does the high gene density in the Sponge NK Homeobox gene cluster reflect limited regulatory capacity?

A huge discrepancy in morphological diversity exists between poriferans and eumetazoans. The disparate evolutionary outcomes of these two ancient metazoan lineages may be reflected in the composition, architecture, and regulation of genomes of modern representatives. As a case study, we compare the sizes of upstream intergenic regions of genes found within the NK homeobox cluster of the demosponge Amphimedon queenslandica with eumetazoan orthologs. This analysis includes NK genes as well as five structural genes interspersed in the cluster. The upstream intergenic regions of the homeobox genes are significantly smaller in Amphimedon than in eumetazoan orthologs, suggesting that the sponge genes house less cis-regulatory information. In contrast, the upstream intergenic regions of the structural genes are not significantly different. The simple developmental expression patterns of representative NK genes in Amphimedon lends support to the proposition that their regulatory apparatuses, unlike those of bilaterians, do not encode the information for dynamic, pleiotropic gene expression. On the basis of this example, we suggest that the size of the intergenic regions upstream of the transcription start site may act as a proxy for estimating regulatory complexity and reflect the limitations of the sponge genome to direct complex and varied morphogenetic processes

Porifera. In: Invertebrate Histology

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