Alternative Splicing Events Are a Late Feature of Pathology in a Mouse Model of Spinal Muscular Atrophy

Spinal muscular atrophy is a severe motor neuron disease caused by inactivating mutations in the SMN1 gene leading to reduced levels of full-length functional SMN protein. SMN is a critical mediator of spliceosomal protein assembly, and complete loss or drastic reduction in protein leads to loss of cell viability. However, the reason for selective motor neuron degeneration when SMN is reduced to levels which are tolerated by all other cell types is not currently understood. Widespread splicing abnormalities have recently been reported at end-stage in a mouse model of SMA, leading to the proposition that disruption of efficient splicing is the primary mechanism of motor neuron death. However, it remains unclear whether splicing abnormalities are present during early stages of the disease, which would be a requirement for a direct role in disease pathogenesis. We performed exon-array analysis of RNA from SMN deficient mouse spinal cord at 3 time points, pre-symptomatic (P1), early symptomatic (P7), and late-symptomatic (P13). Compared to littermate control mice, SMA mice showed a time-dependent increase in the number of exons showing differential expression, with minimal differences between genotypes at P1 and P7, but substantial variation in late-symptomatic (P13) mice. Gene ontology analysis revealed differences in pathways associated with neuronal development as well as cellular injury. Validation of selected targets by RT–PCR confirmed the array findings and was in keeping with a shift between physiologically occurring mRNA isoforms. We conclude that the majority of splicing changes occur late in SMA and may represent a secondary effect of cell injury, though we cannot rule out significant early changes in a small number of transcripts crucial to motor neuron survival

Absolute Radiometric Calibration Approach using Different Types of Ground Targets

This paper presents the absolute calibration approach using two types of calibration point targets (passive corner reflector and active transponder), and discusses calibration results on the example of TerraSAR-X

Absolute Radiometric Calibration of TerraSAR-X - Approach and Ground Targets

The German SAR satellite TerraSAR-X was successfully launched in June 2007. During the commissioning phase, the first months after launch, a calibration field campaign was carried out to conduct geometric as well as relative and absolute radiometric calibration. This was necessary to prepare the satellite for scientific and commercial use. This paper addresses results concerning the absolute radiometric accuracy and the reference ground targets involved. The two types of utilized ground targets were trihedral corner reflectors and active transponders. It will be shown that an absolute radiometric accuracy of much better than 1 dB can be achieved using both types of targets

TerraSAR-X Calibration Status - 2 Years in Flight

As TerraSAR-X, launched in June 2007, is an operational scientific mission with commercial potential, product quality is of paramount importance. The success or failure of the mission is essentially dependent on the calibration of the TerraSAR-X system ensuring the product quality and the correct in-orbit operation of the entire SAR system. Based on the excellent calibration results achieved during the commissioning phase after launch, continuing calibration guarantees a stable product quality and monitors the correct operation of the entire SAR system during whole life time of TerraSAR-X. Therefore, one essential task is long term system monitoring (LTSM) performed by periodic measurements over rainforest and permanently deployed reference targets, to ensure stable antenna patterns and constant radiometric accuracy of the instrument. In addition to regular LTSM measurements, an extended re calibration of the TerraSAR-X system was performed in July 2009. In contrast to the nominal LTSM task several beams for a wide range of incidence angles have been measured against a multitude of reference targets. Due to this great amount of different measurements precise results based on reliable statistics have been achieved. The paper describes the different activities performed for LTSM and re calibration of TerraSAR-X and discusses the results

In-Orbit SAR Performance of TerraSAR-X and TanDEM-X Satellites

The paper will show the excellent quality of TerraSAR-X SAR images and the almost identical SAR performance of both satellites

In-Orbit Calibration of both TanDEM-X Satellites

The primary object of the TanDEM-X mission is to generate a highly accurate digital elevation model (DEM) with never achieved accuracy on global scale [1]. But in addition to this DEM acquisition realized by a helix constellation of two satellites, nominal TerraSAR-X operation shall be available anymore, i.e. the bistatic TanDEM-X mission and the monostatic TerraSAR-X mission have to be operated in parallel with both satellites. Consequently the second satellite TDX, successfully launched in June 2010, has to achieve the same accuracy and performance as those of the first satellite TSX, already in-flight since 2007. For this purpose, the commissioning phase (CP) of the TanDEM-X mission was separated into two phases, at first the monostatic phase in order to calibrate the TDX satellite with the same accuracy as achieved for TSX and then the interferometric phase in order to match both satellites for a bistatic constellation and consequently to ensure DEM acquisition during the whole lifetime of the TanDEM-X mission. The main part of all calibration activities, especially of measurements executed against precise reference targets, was concentrated on the monostatic CP for deriving all calibration parameters. The activities executed during the interferometric CP were concentrated on the verification of all these parameters, i.e. whether they are still valid in bistatic constellation and enable consequently a precise synchronization of both systems. Nevertheless, the calibration effort and consequently the duration for commissioning the whole TanDEM-X system could be optimized by the experience and the results which had been achieved for TSX since launch in 2007 [2]. This was the baseline for executing the TanDEM-X commissioning phase as fast as possible. Thus, a maximum overlap of the lifetime of both satellites required for the global DEM acquisition could be achieved. The absolute geometric offset between the TDX and TSX SAR system is smaller than half the wavelength. The radiometric offset is only in the order of one tenth of a dB. Thus, each SAR system could not only be accurately calibrated individually, but also to each other. TDX and TSX are adjusted and calibrated with the accuracy of laboratory equipment. All requirements and/or goals have been achieved improving the predictions in most cases. The measurements and the analyses performed during the interferometric CP were focused on bistatic operation, i.e. one satellite is operated as transmitter and receiver and the other satellite only as a receiver. For this purpose, a bistatic replica, the bistatic geometry, the bistatic elevation patterns and the radiometric characteristics for both bistatic and monostatic operation in close formation were investigated. Based on a short overview of different calibration procedures the paper discusses the calibration results achieved for both monostatic and bistatitc constellation of the whole TanDEM-X system, successfully inflight since June 2010. References [1] G. Krieger, A. Moreira, H. Fiedler, I. Hajnsek, M. Werner, M. Younis, and M. Zink, “TanDEM-X: A Satellite Formation for High Resolution SAR Interferometry,” IEEE Trans. on Geoscience and Remote Sensing, vol. 45, no. 11, pp. 3317-3341, Nov. 2007. [2] M. Schwerdt, B. Bräutigam, M. Bachmann, B. Döring, D. Schrank, and J. H. Gonzalez, “Final TerraSAR-X Calibration Results Based on Novel Efficient Calibration Methods,” IEEE Transaction on Geoscience and Remote Sensing ,Vol. 48, No. 2, February 2010

External Calibration Tool Verification and Validation Plan

Test plan for verification and validation of the External Calibration Too