Matrix Metalloproteinase Inhibitors Disrupt Spicule Formation by Primary Mesenchyme Cells in the Sea Urchin Embryo

AbstractThe primary mesenchyme cells of the sea urchin embryo construct an elaborate calcareous endoskeletal spicule beginning at gastrulation. This process begins by ingression of prospective primary mesenchyme cells into the blastocoel, after which they migrate and then fuse to form a syncytium. Skeleton deposition occurs in spaces enclosed by the cytoplasmic cables between the cell bodies. Experiments are described which probe the role of proteases in these early events of spicule formation and their role in the continued elaboration of the spicule during later stages of embryogenesis. We find that several inhibitors of metalloproteinases inhibit the continuation of spiculogenesis, an effect first reported by Roeet al.(Exp. Cell Res.181, 542–550, 1989). A detailed study of one of these inhibitors, BB-94, shows that fusion of primary mesenchyme cells still occurs in the presence of the inhibitor and the formation of the first calcite granule is not impeded. Continued elaboration of the spicule, however, is completely stopped; addition of the inhibitor during the active elongation of the spicule stops further elongation immediately. Removal of the inhibitor allows resumption of spicule growth. The inhibition is accompanied by almost complete cessation of massive Ca ion transport via the primary mesenchyme cells to the spicule. The inhibitor does not prevent the continued synthesis of several spicule matrix proteins. Electron microscopic examination of inhibited primary mesenchyme cells shows an accumulation of characteristic vesicles in the cytoplasm. Gel zymography demonstrates that although most proteases in homogenates of primary mesenchyme cells are not sensitive to the inhibitorin vitro,a protease of low abundance detectable in the medium of cultured primary mesenchyme cells is inhibited by BB-94. We propose that the inhibitor is interfering with the delivery of precipitated calcium carbonate and matrix proteins to the site(s) of spicule growth

Hubble Space Telescope Observations of the 1990 Equatorial Disturbance on Saturn: Images, Albedos, and Limb Darkening

In September 1990 a major equatorial eruption on Saturn produced a disturbance that spread in longitude until it completely girdled the planet. We report here on 150 images recorded in six passbands with the Wide Field/Planetary Camera (WF/PC) aboard the Hubble Space Telescope (HST) on 17 and 18 November 1990. For comparison, we used HST-WF/PC observations of Saturn obtained in three colors on 26 August 1990 before the onset of the disturbance, and in six colors on 5 and 6 June 1991 when almost no evidence of the disturbance remained. At both of those times, the equatorial belt was “normal” in appearance. Four of the passbands (with mean wavelengths of 336, 435, 546, and 716 nm) were selected for photometric analysis, and a patch of the B ring near the central meridian was used for photometric calibration. Using deconvolved images from all three epochs of observation, we measured reflectivities (I/F) of the disk along parallels of latitude as a function of longitudinal distance from the central meridian and also along the central meridian as a function of latitude from 0° to 90°. The longitudinal measurements cover essentially the whole visible disk; they were made at 1° intervals of planetographic latitude from 0° to 80°, and the results are expressed in terms of Minnaert coefficients k and Minnaert albedos (I/F)_0. We find that the cloud particles associated with the disturbance must differ in character from those that normally make up the visible cloud deck on Saturn. They were brighter and bluer, they had greater limb darkening, and their limb darkening was spectrally more neutral. The mutual relationship of those properties is such that features which stand out strongly near the meridian fade to invisibility when near the limb

Galileo Imaging of Jupiter’s Atmosphere: The Great Red Spot, Equatorial Region, and White Ovals

During the first six orbits of the Galileo spacecraft's prime mission, the Solid State Imaging (SSI) system acquired multispectral image mosaics of Jupiter's Great Red Spot, an equatorial belt/zone boundary, a “5-μm hot spot” similar to the Galileo Probe entry site, and two of the classic White Ovals. We present mosaics of each region, approximating their appearance at visible wavelengths and showing cloud height and opacity variations. The local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly 1 and 10 hr. Vertical cloud structure is derived in a companion paper by Banfieldet al. (Icarus135, 230–250). Galileo's brief, high-resolution observations complement Earth-based and Voyager studies and offer local meteorological context for the Galileo Probe results. Our results show that the dynamics of the zonal jets and large vortices have changed little since Voyager, with a few exceptions. We detect a cyclonic current within the center of the predominantly anticyclonic Great Red Spot. The zonal velocity difference between 0° S and 6° S has increased by 20 m sec^(−1). We measure a strong northeast flow approaching the hot spot. This flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hot spot. The current compact arrangement of two White Ovals and a cyclonic structure greatly perturbs the zonal jets in that region