Cadherin Sequences That Inhibit β-Catenin Signaling: A Study in Yeast and Mammalian Cells

Drosophila Armadillo and its mammalian homologue β-catenin are scaffolding proteins involved in the assembly of multiprotein complexes with diverse biological roles. They mediate adherens junction assembly, thus determining tissue architecture, and also transduce Wnt/Wingless intercellular signals, which regulate embryonic cell fates and, if inappropriately activated, contribute to tumorigenesis. To learn more about Armadillo/β-catenin's scaffolding function, we examined in detail its interaction with one of its protein targets, cadherin. We utilized two assay systems: the yeast two-hybrid system to study cadherin binding in the absence of Armadillo/β-catenin's other protein partners, and mammalian cells where interactions were assessed in their presence. We found that segments of the cadherin cytoplasmic tail as small as 23 amino acids bind Armadillo or β-catenin in yeast, whereas a slightly longer region is required for binding in mammalian cells. We used mutagenesis to identify critical amino acids required for cadherin interaction with Armadillo/β-catenin. Expression of such short cadherin sequences in mammalian cells did not affect adherens junctions but effectively inhibited β-catenin–mediated signaling. This suggests that the interaction between β-catenin and T cell factor family transcription factors is a sensitive target for disruption, making the use of analogues of these cadherin derivatives a potentially useful means to suppress tumor progression.

Finite-size scaling analysis of the distributions of pseudo-critical temperatures in spin glasses

Using the results of large scale numerical simulations we study the probability distribution of the pseudo critical temperature for the three dimensional Edwards Anderson Ising spin glass and for the fully connected Sherrington-Kirkpatrick model. We find that the behaviour of our data is nicely described by straightforward finitesize scaling relations.

Chemical composition of plagioclase from DSDP Legs 45 and 46, Atlantic Ocean

Phyric basalts recovered from DSDP Legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains (megacrysts) or aggregates (glomerocrysts) and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition. Almost all the plagioclase crystals are complexly zoned. In most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts: core, mantle and rim. The cores exhibit two major types of morphology: tabular, with a euhedral to slightly rounded outline; or a skeletal inner core wrapped by a slightly rounded homogeneous outer core. The mantle region is characterized by a zoning pattern composed of one to several spikes/plateaus superimposed on a gently zoned base line, with one large plateau always at the outside of the mantle, and by, in most cases, a rounded internal morphology. The inner rim is typically oscillatory zoned. The width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow. The presence of a skeletal inner core and the concentration of glass inclusions in low-An zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount. The resorption features at the outer margins of low-An zones indicate superheating of the liquid with respect to the crystal. It is proposed that the plagioclase cores formed during injection of primitive magma into a previously existing magma chamber, that the mantle formed during mixing of a partially mixed magma and the remaining magma already in the chamber, and that the inner rim formed when the mixed magma was in a sheeted dike system. The large plateau at the outside of the mantle may have formed during the injection of the next batch of primitive magma into the main chamber, which may trigger an eruption. This model is consistent with fluid dynamic calculations and geochemically based magma mixing models, and is suggested to be the major mechanism for generating the disequilibrium conditions in the magma.

Selected major elements and trace elements of ferrar dolerite clasts from sediment core CRP-1 (Table 1,2)

One of the objectives of the Cape Roberts Project is to study the tectonic history of the western Ross Sea region. Timing of the uplift of the Transantarctic Mountains, which are adjacent to the drillsite, will be a component of the tectonic studies (International Steering Committee, 1994; Cale Roberts Science Team, 1998a). The study of the clast samples from the core will be an important means of providing insight into the timing of uplift of the Transantarctic Mountains. Tholeiitic igneous rocks of the Jurassic (180 Ma) Ferrar large igneous province (FLIP) are widespreaded along the Transantarctic Mountains and have the potential to provide distinct indicators of erosion during uplift of the mountains. In the Transantarctic Mountains adjacent to the Cape Roberts drill site the FLIP is represented by lavas and pyroclastic of the Kirkpatrick basalts and by thick Ferrar dolerite sills which intrude the Beacon Supergroup sediments and, occasionally, the granitic basement rocks. In the Prince Albert Mountains, the youngest Kirkpatrick basalt lava is over 150 m thick, and has a very distinct high TiO2 chemical composition which is unique in the FLIP. If such rocks can be identified in the core they may provide precise timing of the initiation of uplift and denudation of the Transantarctic Mountains. Here we report on an examination of 20 Ferrar dolerite clasts. This brief report is intended as a pilot study to the examination of FLIP clasts from older drillcore.

(Table 1) Detrital modes for sand grains in sediment core CRP-3

Detrital modes determined on 68 sandstone samples from CRP-3 drillcore indicate a continuation of the dynamic history of uplift-related erosion and unroofing previously documented in CRP-1 and CRP-2/2A. The source area is identified very strongly with the Transantarctic Mountains (TAM) Dry Valleys block in southern Victoria Land. Initial unroofing of the TAM comprised removal of much of a former capping sequence of Jurassic Kirkpatrick basalts, which preceded the formation of the Victoria Land Basin. Erosion of Beacon Supergroup outcrops took place during progressive uplift of the TAM in the Oligocene. Earliest CRP-3 Oligocene samples above 788 metres below the sea floor (mbsf) were sourced overwhelmingly in Beacon Supergroup strata, including a recognisable contribution from Triassic volcanogenic Lashly Formation sandstones (uppermost Victoria Group). Moving up-section, by 500 mbsf, the CRP-3 samples are depauperate quartz arenites dominantly derived from the quartzose Devonian Taylor Group. Between c. 500 and 450 mbsf, the modal parameters show a distinctive change indicating that small outcrops of basement granitoids and metamorphic rocks were also being eroded along with the remaining Beacon (mainly Taylor Group) sequence. Apart from enigmatic fluctuations in modal indices above 450 mbsf, similar to those displayed by samples in CRP-2/2A, the CRP-3 modes are essentially constant (within a broad data scatter) to the top of CRP-3. The proportion of exposed basement outcrop remained at < 20 %, indicating negligible uplift (i.e. relative stability) throughout that period.

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