Topographic-compositional units on the moon and the early evolution of the lunar crust

The distribution of elevations on the moon determined by Clementine deviates strongly from a normal distribution, suggesting that several geologic processes have influenced the topography. The hypsograms for the near side and far side of the moon are distinctly different, and these differences correlate with differences in composition as determined by Apollo orbital geochemistry, Clementine global multispectral imaging, and ground-based spectroscopy. The hypsograms and compositional data indicate the presence of at least five compositional-altimetric units. The lack of fill of the South Pole-Aitken Basin by mare basalts suggests poor production efficiency of mare basalt in the mantle of this area of the moon.     

Structures of SAS-6 suggest its organization in centrioles

Centrioles are cylindrical, ninefold symmetrical structures with peripheral triplet microtubules strictly required to template cilia and flagella. The highly conserved protein SAS-6 constitutes the center of the cartwheel assembly that scaffolds centrioles early in their biogenesis. We determined the x-ray structure of the amino-terminal domain of SAS-6 from zebrafish, and we show that recombinant SAS-6 self-associates in vitro into assemblies that resemble cartwheel centers. Point mutations are consistent with the notion that centriole formation in vivo depends on the interactions that define the self-assemblies observed here. Thus, these interactions are probably essential to the structural organization of cartwheel centers.     

Expression of bovine 17 alpha-hydroxylase cytochrome P-450 cDNA in nonsteroidogenic (COS 1) cells

Cortisol production requires the activity of only 17 alpha-hydroxylase, whereas the formation of sex steroids requires both 17 alpha-hydroxylase and 17,20-lyase activities. Studies in reconstituted enzyme systems have suggested that a single steroid hydroxylase, 17 alpha-hydroxylase cytochrome P-450 (P-450(17) alpha), catalyzes both activities. By expression of bovine adrenocortical P-450(17 alpha) in COS 1 (transformed monkey kidney) cells, which normally contain no detectable P-450(17) alpha, it has now been established in situ that a single polypeptide chain does catalyze both the 17 alpha-hydroxylase and the 17,20-lyase reactions. This heterologous system supports 17 alpha-hydroxylation of pregnenolone and progesterone with equal efficiency, but catalyzes about five times as much 17,20-lyase activity when 17 alpha-hydroxypregnenolone is the substrate than when 17 alpha-hydroxyprogesterone is the substrate. For these activities to be observed in COS 1 cells, newly synthesized apocytochrome P-450(17) alpha must bind heme and insert into the endoplasmic reticulum such that endogenous cytochrome P-450 reductase can support hydroxylation. Thus, COS 1 cells are a useful system for expression and study of various forms of cytochrome P-450.     

Ancient geodynamics and global-scale hydrology on Mars

Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.     

The clementine mission to the moon: scientific overview

In the course of 71 days in lunar orbit, from 19 February to 3 May 1994, the Clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths. These data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side. In addition, laser-ranging measurements provided the first view of the global topographic figure of the moon. The topography of many ancient impact basins has been measured, and a global map of the thickness of the lunar crust has been derived from the topography and gravity.     

Bilateral Testicular Mixed Germ Cell-sex Cord-stromal Tumours in a Stallion

An 18-year-old Friesian stallion was examined approximately one week after reportedly presenting scrotal swelling due to torsion of the spermatic cords. Upon presentation no scrotal swelling was noted, the testes were normally oriented, and no abnormalities of the spermatic cords were noted. However, both testes were smaller than expected for a mature stallion and deep palpation revealed that the consistency of the testes was nodular. Ultrasonographic evaluation of the testes revealed diffuse heterogeneous parenchyma with multiple hypoechoic nodular areas. Grossly, the testicular parenchyma was effaced by multiple gray-tan nodules of varying consistency interspersed with gray-white bands of tissue. Microscopic analysis revealed multiple pleomorphic neoplastic foci disseminated throughout both testes. Histological and immunohistochemical features were atypical and consistent with the diagnosis of bilateral testicular mixed germ cell-sex cord stromal tumours. Bilateral testicular tumours and testicular mixed cell tumours are extremely rare in stallions and this is the first report of bilateral testicular mixed germ cell-sex cord-stromal tumours in a stallion. Our findings indicate that certain ultrasonographic characteristics are suggestive of testicular tumour and that immunohistochemistry markers can be used to better characterize testicular neoplasms in stallions.