The Cretaceous-Tertiary boundary marine extinction and global primary productivity collapse

The extinction of marine phyto-and zoo-plankton across the K-T boundary has been well documented. Such an event may have resulted in decreased photosynthetic fixation of carbon in surface waters and a collapse of the food chain in the marine biosphere. Because the vertical and horizontal distribution of the carbon isotopic composition of total dissolved carton (TDC) in the modern ocean is controlled by the transfer of organic carbon from the surface to deep reservoirs, it follows that a major disruption of the marine biosphere would have had a major effect on the distribution of carbon isotopes in the ocean. Negative carbon isotope excursions have been identified at many marine K-T boundary sequences worldwide and are interpreted as a signal of decreased oceanic primary productivity. However, the magnitude, duration and consequences of this productivity crisis have been poorly constrained. On the basis of planktonic and benthic calcareous microfossil carbon isotope and other geochemical data from DSDP Site 577 located on the Shatsky Rise in the north-central Pacific, as well as other sites, researchers have been able to provide a reasonable estimate of the duration and magnitude of this event

Dual Electron Spectrometer for Magnetospheric Multiscale Mission: Results of the Comprehensive Tests of the Engineering Test Unit

The Magnetospheric Multiscale mission (MMS) is designed to study fundamental phenomena in space plasma physics such as a magnetic reconnection. The mission consists of four spacecraft, equipped with identical scientific payloads, allowing for the first measurements of fast dynamics in the critical electron diffusion region where magnetic reconnection occurs and charged particles are demagnetized. The MMS orbit is optimized to ensure the spacecraft spend extended periods of time in locations where reconnection is known to occur: at the dayside magnetopause and in the magnetotail. In order to resolve fine structures of the three dimensional electron distributions in the diffusion region (reconnection site), the Fast Plasma Investigation's (FPI) Dual Electron Spectrometer (DES) is designed to measure three dimensional electron velocity distributions with an extremely high time resolution of 30 ms. In order to achieve this unprecedented sampling rate, four dual spectrometers, each sampling 180 x 45 degree sections of the sky, are installed on each spacecraft. We present results of the comprehensive tests performed on the DES Engineering & Test Unit (ETU). This includes main parameters of the spectrometer such as energy resolution, angular acceptance, and geometric factor along with their variations over the 16 pixels spanning the 180-degree tophat Electro Static Analyzer (ESA) field of view and over the energy of the test beam. A newly developed method for precisely defining the operational space of the instrument is presented as well. This allows optimization of the trade-off between pixel to pixel crosstalk and uniformity of the main spectrometer parameters

Involvement of the V2 Vasopressin Receptor in Adaptation to Limited Water Supply

Mammals adapted to a great variety of habitats with different accessibility to water. In addition to changes in kidney morphology, e.g. the length of the loops of Henle, several hormone systems are involved in adaptation to limited water supply, among them the renal-neurohypophysial vasopressin/vasopressin receptor system. Comparison of over 80 mammalian V2 vasopressin receptor (V2R) orthologs revealed high structural and functional conservation of this key component involved in renal water reabsorption. Although many mammalian species have unlimited access to water there is no evidence for complete loss of V2R function indicating an essential role of V2R activity for survival even of those species. In contrast, several marsupial V2R orthologs show a significant increase in basal receptor activity. An increased vasopressin-independent V2R activity can be interpreted as a shift in the set point of the renal-neurohypophysial hormone circuit to realize sufficient water reabsorption already at low hormone levels. As found in other desert mammals arid-adapted marsupials show high urine osmolalities. The gain of basal V2R function in several marsupials may contribute to the increased urine concentration abilities and, therefore, provide an advantage to maintain water and electrolyte homeostasis under limited water supply conditions

Molecular identification of the gene responsible for congenital nephrogenic diabetes insipidus

Antidiuretic hormone (arginine vasopressin) binds to and activates V2 receptors in renal collecting tubule cells. Subsequent stimulation of the Gs/adenylyl cyclase system promotes insertion of water pores into the luminal membrane and thereby reabsorption of fluid. In congenital nephrogenic diabetes insipidus (CNDI), an X-linked recessive disorder, the kidney fails to respond to arginine vasopressin. Here we report that an affected male of a family with CNDI has a deletion in the open reading frame of the V2 receptor gene, causing a frame shift and premature termination of translation in the third intracellular loop of the receptor protein. A normal receptor gene was found in the patient's brother. Both the normal and the mutant allele were detected in his mother. A different mutation, causing a codon change in the third transmembrane domain of the V2 receptor, was found in the open reading frame of an affected male but not in the unaffected brother belonging to another family suffering from CNDI

Mutations in the vasopressin V2 receptor gene in families with nephrogenic diabetes insipidus and functional expression of the Q-2 mutant

Nephrogenic diabetes insipidus (NDI) is characterized by a resistance of the kidney towards arginine vasopressin (AVP). Following molecular cloning of the vasopressin V2 receptor, we identified different mutations in the V2 receptor gene in families with X-linked NDI, which segregated with the disease. The Hopewell mutation (W71X) causes the disease in the largest North American NDI pedigree, with most of its members residing on Nova Scotia. Different mutations were found in three families from the Quebec area (Q-2: R137H, Q-3: R113W, Q-5: 804delG) and in the large Cannon kindred residing in Utah (L312X). In an Iranian family (O-1), another mutation was detected (A132D). Three of the six mutations (Hopewell, Cannon, Q-5) are predicted to cause the expression of a truncated V2 receptor and are therefore unlikely to function. The functional consequences of missense mutations (Q-2, Q-3, O-1) are less obvious. We therefore introduced the Q-2 mutation into wild-type cDNA. When expressed in COS.M6 or Ltk cells, the Q-2 mutant bound AVP with normal affinity. However, cells expressing the Q-2 mutant failed to respond to AVP with an increase in adenylyl cyclase activity. Thus the Q-2 mutant is unable to interact with or to activate the stimulatory G-protein Gs. The present data indicate that X-linked NDI is frequently attributable to a mutation in the V2 receptor gene. In addition, the data prove biochemically that the Q-2 mutation is the cause of NDI in the Q-2 family

X-linked nephrogenic diabetes insipidus mutations in North America and the Hopewell hypothesis.

In X-linked nephrogenic diabetes insipidus (NDI) the urine of male patients is not concentrated after the administration of the antidiuretic hormone arginine-vasopressin. This disease is due to mutations in the V2 receptor gene that maps to chromosome region Xq28. In 1969, Bode and Crawford suggested that most NDI patients in North America shared common ancestors of Ulster Scot immigrants who arrived in Halifax in 1761 on the ship Hopewell. A link between this family and a large Utah kindred was also suggested. DNA was obtained from 17 affected male patients from the "Hopewell" kindred and from four additional families from Nova Scotia and New Brunswick who shared the same Xq28 NDI haplotype. The Utah kindred and two families (Q2, Q3) from Quebec were also studied. The "Hopewell" mutation, W71X, is a single base substitution (G-->A) that changes codon 71 from TGG (tryptophan) to TGA (stop). The W71X mutation was found in affected members of the Hopewell and of the four satellite families. The W71X mutation is the cause of X-linked NDI for the largest number of related male patients living in North America. Other families (Utah, Q2 and Q3) that are historically and ethnically unrelated bear other mutations in the V2 receptor gene