Quantifying crater production and regolith overturn on the Moon with temporal imaging

Random bombardment by comets, asteroids and associated fragments form and alter the lunar regolith and other rocky surfaces. The accumulation of impact craters over time is of fundamental use in evaluating the relative ages of geologic units. Crater counts and radiometric ages from returned samples provide constraints with which to derive absolute model ages for unsampled units on the Moon and other Solar System objects. However, although studies of existing craters and returned samples offer insight into the process of crater formation and the past cratering rate, questions still remain about the present rate of crater production, the effect of early-stage jetting during impacts and the influence that distal ejecta have on the regolith. Here we use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) temporal ('before and after') image pairs to quantify the contemporary rate of crater production on the Moon, to reveal previously unknown details of impact-induced jetting, and to identify a secondary impact process that is rapidly churning the regolith. From this temporal dataset, we detected 222 new impact craters and found 33 per cent more craters (with diameters of at least ten metres) than predicted by the standard Neukum production and chronology functions for the Moon. We identified broad reflectance zones associated with the new craters that we interpret as evidence of a surface-bound jetting process. We also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81,000 years-more than a hundred times faster than previous models estimated from meteoritic impacts (ten million years).

Torsional power study using CENTURION phacoemulsification technology

BACKGROUND

To evaluate the effect of varying levels of power on phacoemulsification efficiency using the CENTURION Vision System.

METHODS

Formalin-soaked porcine lenses were divided into 2-mm cubes; 0.9-mm, balanced tips were used. Torsional power levels were tested from 10% to 100% at 10% intervals. Vacuum was set to 550 mmHg, aspiration to 50 ml/min, and intraocular pressure at 50 mmHg. Efficiency (time to lens removal) and chatter (number of lens fragment repulsions from the tip) were determined.

RESULTS

Increasing torsional power up to 60% increased efficiency. This effect was linear from 30 to 60% power (R²  = .90; P < 0.05). There were no significant differences in efficiency past 60%. Chatter was highest at 10% power and decreased linearly (R²  = .87; P = 0.007) as power was increased up to 60% power, and chatter did not improve above this power level.

CONCLUSIONS

Power improved efficiency only up to a 60% power level, and then was negligible. Chatter correlated well with power up to the 60% level, so that as power was increased, chatter decreased. Because there are no additional benefits in efficiency past 60% power, and because chatter is minimal at 60% power, we recommend torsional ultrasound at 60% as the optimal power setting for using the CENTURION System for phacoemulsification.l.

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.

Evolution of the Rembrandt impact basin on Mercury

MESSENGER's second Mercury flyby revealed a ~715-kilometer-diameter impact basin, the second-largest well-preserved basin-scale impact structure known on the planet. The Rembrandt basin is comparable in age to the Caloris basin, is partially flooded by volcanic plains, and displays a unique wheel-and-spoke-like pattern of basin-radial and basin-concentric wrinkle ridges and graben. Stratigraphic relations indicate a multistaged infilling and deformational history involving successive or overlapping phases of contractional and extensional deformation. The youngest deformation of the basin involved the formation of a approximately 1000-kilometer-long lobate scarp, a product of the global cooling and contraction of Mercury.

Reticulated platelets

Young or reticulated platelets contain some residual mRNA, which is rapidly degraded after platelet release into the circulation. They can be easily detected either with supravital dye staining (e.g. new methylene blue) on blood films, or more commonly with fluorescent dyes (e.g thiazole orange) and flow cytometry. Using the latter technique many different groups have demonstrated that the measurement of reticulated platelets has much clinical potential. It is apparent that the level of reticulated platelets gives a relatively simple and non-invasive measurement of the rate of thrombopoiesis in an analogous fashion to the red cell reticulocyte count. Many research groups are currently measuring reticulated platelets but with wide variation in data and methods. An international platelet panel has begun to develop protocols and between laboratory comparisons, which will result in the standardization of the procedure. Platelet reticulocyte analysis should thus become part of accepted haematological practice and provide useful clinical information for the investigation and monitoring of platelet production in various thrombocytopenic conditions. In particular, measurement of reticulated platelets will provide an excellent and simple means for monitoring the response of chemotherapy and transplant patients to growth factors (e.g. thrombopoietin) resulting in a decrease in the demand for platelet transfusion.

Seismic resurfacing by a single impact on the asteroid 433 Eros

Impact cratering creates a wide range of topography on small satellites and asteroids. The population of visible craters evolves with impacts, and because there are no competing endogenic processes to modify the surface, determining the various ways younger craters add to or subtract from the population is a fundamental aspect of small-body geology. Asteroid 433 Eros, the most closely studied small body, has regions of substantially different crater densities that remain unexplained. Here we show that the formation of a relatively young crater (7.6 km in diameter) resulted in the removal of other craters as large as 0.5 km over nearly 40 percent of the asteroid. Burial by ejecta cannot explain the observed pattern of crater removal. The limitation of reduced crater density to a zone within a particular straight-line distance through the asteroid from the centre of the large crater suggests degradation of the topography by seismic energy released during the impact. Our observations indicate that the interior of Eros is sufficiently cohesive to transmit seismic energy over many kilometres, and the outer several tens of metres of the asteroid must be composed of relatively non-cohesive material.

Constant illumination at the lunar north pole

Images returned by the spacecraft Clementine have been used to produce a quantitative illumination map of the north pole of the Moon, revealing the percentage of time that points on the surface are illuminated during the lunar day. We have used this map to identify areas that are constantly illuminated during a lunar day in summer and which may therefore be in permanent sunlight. All are located on the northern rim of Peary crater, close to the north pole. Permanently sunlit areas represent prime locations for lunar outpost sites as they have abundant solar energy, are relatively benign thermally (when compared with equatorial regions), and are close to permanently shadowed regions that may contain water ice.

Adaptins

Clathrin has long been known to provide the structural basis for vesicle budding from the plasma membrane during endocytosis, but how is clathrin targeted specifically to some cellular membranes and not others? The answer seems to lie in the adaptors--protein complexes whose shape resembles the head of Mickey Mouse--which seem to be required both for clathrin-coat assembly and for sequestering specific receptors by interacting with their cytoplasmic domains. In this article, Margaret Robinson describes what is currently known about these versatile proteins.

GGAs: roles of the different domains and comparison with AP-1 and clathrin

We have previously identified a novel family of proteins called the GGAs (Golgi-localized, gamma-ear-containing, ADP-ribosylation factor-binding proteins). These proteins consist of an NH(2)-terminal VHS domain, followed by a GAT domain, a variable domain, and a gamma-adaptin ear homology domain. Studies from our own laboratory and others, making use of both yeast and mammals cells, indicate that the GGAs facilitate trafficking from the trans-Golgi network to endosomes. Here we have further investigated the function of the GGAs. We find that GGA-deficient yeast are not only defective in vacuolar protein sorting but they are also impaired in their ability to process alpha-factor. Using deletion mutants and chimeras, we show that the VHS domain is required for GGA function and that the VHS domain from Vps27p will not substitute for the GGA VHS domain. In contrast, the gamma-adaptin ear homology domain contributes to GGA function but is not absolutely required, and full function can be restored by replacing the GGA ear domain with the gamma-adaptin ear domain. Deleting the gamma-adaptin gene together with the two GGA genes exacerbates the phenotype in yeast, suggesting that they function on parallel pathways. In mammalian cells, the association of GGAs with the membrane is extremely unstable, which may account for their absence from purified clathrin-coated vesicles. Double- and triple-labeling immunofluorescence experiments indicate that the GGAs and AP-1 are associated with distinct populations of clathrin-coated vesicles budding from the trans-Golgi network. Together with results from other studies, our findings suggest that the GGAs act as monomeric adaptors, with the four domains involved in cargo selection, membrane localization, clathrin binding, and accessory protein recruitment.

The nature of ponded deposits on Eros

One of the surprises of the NEAR-Shoemaker mission was that Eros's surface exhibits a wide variety of landforms, which are indicative of a global covering of loose fragmental debris. At one extreme in roughness is the Shoemaker Regio area, which is characterized by a high density of boulders up to 100 m across, slumps, slides, and finer blanketing material. At the other extreme are distinctive, flat deposits that appear smooth down to a resolution of 1.2 cm per pixel. Here we report the results of global mapping and colour analysis of these smooth deposits. They have formed most efficiently in restricted areas, and appear to be the result of deposition of finer material sorted from the upper portion of the asteroid's regolith. The smooth deposits constitute a family of features with a range of morphologies, but all appear to be the result of sedimentation. The geography of the deposits is consistent with some predicted aspects of photoelectric sorting, but these exotic transport and depositional mechanisms are not well understood. Deposits with the properties seen on Eros have no obvious analogues in previous lunar or asteroid data.

Shoemaker crater as the source of most ejecta blocks on the asteroid 433 Eros

The loose material--regolith--on the surfaces of asteroids is thought to represent ballistically emplaced ejecta from impacts but the identification of source craters and the detailed study of the regolith modification have been hampered by the limited spatial resolution and area coverage of the few asteroids imaged by spacecraft. Here we report the results of global mapping of the asteroid 433 Eros from high-resolution images obtained by the NEAR-Shoemaker spacecraft. Based on the images and ejecta-emplacement models, we suggest that most large ejecta blocks on Eros originate from a relatively young 7.6-km-diameter crater. A large fraction of the ejecta from impacts pre-dating that crater has apparently been buried or eroded. The images also show evidence for the action of a variety of sorting environments for regolith particles after they are deposited on the surface.

Adaptor-related proteins

Two new adaptor-related protein complexes, AP-3 and AP-4, have recently been identified, and both have been implicated in protein sorting at the trans-Golgi network (TGN) and/or endosomes. In addition, two families of monomeric proteins with adaptor-related domains, the GGAs and the stoned B family, have also been identified and shown to act at the TGN and plasma membrane, respectively. Together with the two conventional adaptors, AP-1 and AP-2, these proteins may act to direct different types of cargo proteins to different post-Golgi membrane compartments.

Platelet reactivity in acute coronary syndromes: evidence for differences in platelet behaviour between unstable angina and myocardial infarction

Previous work has shown that P-selectin and mean platelet volume, two markers associated with platelet reactivity, are elevated in acute coronary syndromes. This study investigated the possibility that these markers may define unstable angina (UA) and acute myocardial infarction (MI) as two separate conditions based on platelet behaviour. Mean platelet volume (MPV) was higher in UA patients (n = 15) than in those diagnosed with MI (n = 15) (10.7 +/- 0.25 fL, vs. 9.8 +/- 0.27 fL, P = 0.005). Platelet count was lower in UA than in MI (215 +/- 13 x 10(9)/L vs. 271 +/- 20 x 10(9)/L, P = 0.03). The percentage of platelets expressing P-selectin was higher in MI than in UA (9.1 +/- 1.9% vs. 4.2 +/- 0.85%, P = 0.03). This parameter was positively correlated with MPV in UA (r = 0.5, P = 0.04) but negatively correlated in MI (r = -0.6, P = 0.01), with no correlation for ACS as a whole (r = -0.32, P = 0.1). Our results suggest that in MI there is an acute process of generalised platelet activation that is unrelated to changes in MPV, whereas in UA there is an ongoing process of platelet consumption that leads to an increase in platelet size to compensate for a persistent decrease in platelet count. This study suggests that there is a fundamental difference in platelet biology between these two diseases.

The Temple-Wisconsin Cognitive Vulnerability to Depression Project: lifetime history of axis I psychopathology in individuals at high and low cognitive risk for depression

The authors tested the cognitive vulnerability hypotheses of depression with a retrospective behavioral high-risk design. Individuals without current Axis I diagnoses who exhibited either negative or positive cognitive styles were compared on lifetime prevalence of depressive and other disorders and the clinical parameters of depressive episodes. Consistent with predictions, cognitively high-risk participants had higher lifetime prevalence than low-risk participants of major and hopelessness depression and marginally higher prevalence of minor depression. These group differences were specific to depressive disorders. The high-risk group also had more severe depressions than the low-risk group, but not longer duration or earlier onset depressions. The risk group differences in prevalence of depressive disorders were not mediated by current depressive symptoms.

Interconnection of a two-dimensional array of vertical-cavity surface-emitting lasers to a receiver array by means of a fiber image guide

The implementation of a 10-channel parallel optical interconnect consisting of a two-dimensional array of vertical-cavity surface-emitting lasers, a 1.35-m fiber image guide, and a metal-semiconductor-metal receiver array is described. Transmission rates of 250 Mbits/s per channel are demonstrated with an optical cross talk of less than -27 dB and a loss of -3 dB. Coupling issues associated with image guides are analyzed and discussed.

Characterization of a fourth adaptor-related protein complex

Adaptor protein complexes (APs) function as vesicle coat components in different membrane traffic pathways; however, there are a number of pathways for which there is still no candidate coat. To find novel coat components related to AP complexes, we have searched the expressed sequence tag database and have identified, cloned, and sequenced a new member of each of the four AP subunit families. We have shown by a combination of coimmunoprecipitation and yeast two-hybrid analysis that these four proteins (epsilon, beta4, mu4, and sigma4) are components of a novel adaptor-like heterotetrameric complex, which we are calling AP-4. Immunofluorescence reveals that AP-4 is localized to approximately 10-20 discrete dots in the perinuclear region of the cell. This pattern is disrupted by treating the cells with brefeldin A, indicating that, like other coat proteins, the association of AP-4 with membranes is regulated by the small GTPase ARF. Immunogold electron microscopy indicates that AP-4 is associated with nonclathrin-coated vesicles in the region of the trans-Golgi network. The mu4 subunit of the complex specifically interacts with a tyrosine-based sorting signal, indicating that, like the other three AP complexes, AP-4 is involved in the recognition and sorting of cargo proteins with tyrosine-based motifs. AP-4 is of relatively low abundance, but it is expressed ubiquitously, suggesting that it participates in a specialized trafficking pathway but one that is required in all cell types.

Abnormal expression and subcellular distribution of subunit proteins of the AP-3 adaptor complex lead to platelet storage pool deficiency in the pearl mouse

The pearl mouse is a model for Hermansky Pudlak Syndrome (HPS), whose symptoms include hypopigmentation, lysosomal abnormalities, and prolonged bleeding due to platelet storage pool deficiency (SPD). The gene for pearl has recently been identified as the beta3A subunit of the AP-3 adaptor complex. The objective of these experiments was to determine if the expression and subcellular distribution of the AP-3 complex were altered in pearl platelets and other tissues. The beta3A subunit was undetectable in all pearl cells and tissues. Also, expression of other subunit proteins of the AP-3 complex was decreased. The subcellular distribution of the remaining AP-3 subunits in platelets, macrophages, and a melanocyte-derived cell line of pearl mice was changed from the normal punctate, probably endosomal, pattern to a diffuse cytoplasmic pattern. Ultrastructural abnormalities in mutant lysosomes were likewise apparent in mutant kidney and a cultured mutant cell line. Genetically distinct mouse HPS models had normal expression of AP-3 subunits. These and related experiments strongly suggest that the AP-3 complex regulates the biogenesis/function of organelles of platelets and other cells and that abrogation of expression of the AP-3 complex leads to platelet SPD.

The beta3A subunit gene (Ap3b1) of the AP-3 adaptor complex is altered in the mouse hypopigmentation mutant pearl, a model for Hermansky-Pudlak syndrome and night blindness

Lysosomes, melanosomes and platelet-dense granules are abnormal in the mouse hypopigmentation mutant pearl. The beta3A subunit of the AP-3 adaptor complex, which likely regulates protein trafficking in the trans - Golgi network/endosomal compartments, was identified as a candidate for the pearl gene by a positional/candidate cloning approach. Mutations, including a large internal tandem duplication and a deletion, were identified in two respective pearl alleles and are predicted to abrogate function of the beta3A protein. Significantly lowered expression of altered beta3A transcripts occurred in kidney of both mutant alleles. The several distinct pearl phenotypes suggest novel functions for the AP-3 complex in mammals. These experiments also suggest mutations in AP-3 subunits as a basis for unique forms of human Hermansky-Pudlak syndrome and congenital night blindness, for which the pearl mouse is an appropriate animal model.

Performance of the platelet function analyser PFA-100 in testing abnormalities of primary haemostasis

The PFA-100 device is a new instrument for the in-vitro testing of platelet function. Primary haemostasis is stimulated by recording the closure time taken for platelets to seal a 150 microm aperture in the centre of a membrane coated with collagen and either epinephrine or ADP. Patients with type 3 von Willebrand's disease (n = 4) all had infinitely prolonged closure times (> 200 s) with both types of cartridge. A patient with afibrinogenemia exhibited only slightly prolonged closure times of 111 and 166 s for the ADP and epinephrine membranes, respectively. Patients with Glanzmann's thrombasthenia (n = 6) and Bernard Soulier syndrome (n = 2) had grossly prolonged closure times (> 200 s) with both types of cartridges. These results confirmed that the PFA-100 system was highly dependent on normal von Willebrand factor, glycoprotein Ib and glycoprotein IIb/IIIa levels but not on plasma fibrinogen. Patients with storage pool disease (n = 6) and Hermansky Pudlak syndrome (n = 7) had prolonged closure times with the epinephrine cartridge. There was no evidence of enhanced platelet function in patients with antiphospholipid syndrome, in sickle-cell disease or thalassemia. However, ingestion of aspirin resulted in a near consistent and significant prolongation of the closure time for the epinephrine cartridge but not for the ADP cartridge in both normal subjects and patients. The test offers a reliable, reproducible, rapid and simple means of assessing high-shear platelet function in vitro.

Polarization-dependent interference effects in grazing-angle Fourier transform infrared reflection-absorption spectroscopy to determine the thickness of water-ice films

Interference fringes appeared between 6000 and 4095 cm(-1) in the infrared spectra of thin water-ice films vapor deposited on an aluminum substrate and probed with grazing-angle Fourier transform infrared reflection-absorption spectroscopy. At grazing incidence the position of the fringe under perpendicularly polarized light (E(sigma)) is 180 degrees out of phase with the position of the fringe under parallel polarized light (E(pi)). This shift in fringe position with polarization offers a convenient way to estimate the thickness (+/-5%) of water-ice films between 0.5 and 1.4 microm.

Clathrin and adaptors

Clathrin and adaptors are components of clathrin-coated pits and vesicles. The AP-1 adaptor complex is associated with clathrin-coated vesicles budding from the TGN, while the AP-2 adaptor complex is associated with clathrin-coated vesicles budding from the plasma membrane. The clathrin forms a polyhedral lattice and is believed to be the driving force behind membrane invagination leading to vesicle budding. The adaptors attach the clathrin to the membrane and also interact with the cytoplasmic domains of selected transmembrane proteins, causing these proteins to become concentrated in clathrin-coated vesicles. Clathrin-coated vesicles budding from the TGN have been implicated in the sorting of newly synthesised lysosomal enzymes, while clathrin-coated vesicles budding from the plasma membrane facilitate the receptor-mediated endocytosis of ligands, such as low density lipoproteins and transferrin. A novel adaptor-related complex, AP-3, has recently been identified, which is recruited onto membranes of the TGN and a more peripheral compartment but does not appear to be associated with clathrin. Genetic studies indicate that AP-3 plays a role in the sorting of proteins to lysosomes and lysosome-related organelles.

Mutation in AP-3 delta in the mocha mouse links endosomal transport to storage deficiency in platelets, melanosomes, and synaptic vesicles

The mouse mutant mocha, a model for the Hermansky-Pudlak storage pool deficiency syndrome, is characterized by defective platelets, coat and eye color dilution, lysosomal abnormalities, inner ear degeneration, and neurological deficits. Here, we show that mocha is a null allele of the delta subunit of the adaptor-like protein complex AP-3, which is associated with coated vesicles budding from the trans-Golgi network, and that AP-3 is missing in mocha tissues. In mocha brain, the ZnT-3 transporter is reduced, resulting in a lack of zinc-associated Timm historeactivity in hippocampal mossy fibers. Our results demonstrate that the AP-3 complex is responsible for cargo selection to lysosome-related organelles such as melanosomes and platelet dense granules as well as to neurotransmitter vesicles.

Flow cytometric analysis of reticulated platelets: evidence for a large proportion of non-specific labelling of dense granules by fluorescent dyes

The labelling of platelets with thiazole orange (TO) has been utilized by various laboratories to determine the percentage of reticulated platelets within whole blood or platelet-rich plasma (PRP). A proportion of TO labelling, however, is not entirely mRNA specific and remains to be fully defined. Almost half of the total TO-positive signal within normal platelets (n = 5) was shown to be abrogated upon degranulation with 80 microM thrombin receptor activating peptide (TRAP) (P = 0.006), strongly suggesting that platelet granules are non-specifically labelling with dye. We have confirmed this hypothesis by studying TO labelling of platelets within whole blood from dense granule deficient patients, e.g. Hermansky-Pudlak syndrome (HPS) (n = 5) and storage pool disease (SPD) (n = 4). The levels of TO-positive platelets were found to be significantly lower than normal (P = 0.0003 and P = 0.0002 respectively), but not significantly different from TRAP degranulated platelets. Upon degranulation of HPS and SPD platelets there was very little further reduction in the TO signal. Incubation of normals and SPD whole blood with different concentrations of either TO or coriphosphine-O confirmed that dense granules were non-specifically labelling even at high concentrations of both dyes. These findings suggest that although TO labelling is in part RNA specific, the dense granular pool of nucleotides appears to cause a substantial amount (approximately 50%) of non-specific labelling observed under these conditions of assay. This can easily be controlled for by a degranulation step with a non-enzymatic platelet agonist such as TRAP, and may have important consequences for the eventual standardization. clinical utilization and automation of reticulated platelet assays.

Experimental indication of a naphthalene-base molecular aggregate for the carrier of the 2175 angstroms interstellar extinction feature

Experiments where the simple polycyclic aromatic hydrocarbon (PAH) naphthalene (C10H8) is subjected to the energetic environment of a plasma have resulted in the synthesis of a molecular aggregate that has ultraviolet spectral characteristics that suggest it provides insight into the nature of the carrier of the 2175 angstroms interstellar extinction feature and may be a laboratory analog. Ultraviolet, visible, infrared, and mass spectroscopy, along with gas chromatography, indicate that it is a molecular aggregate in which an aromatic double ring ("naphthalene") structural base serves as the electron "box" chromophore that gives rise to the envelope of the 2175 angstroms feature. This chromophore can also provide the peak of the feature or function as a mantle in concert with another peak provider such as graphite. The molecular base/chromophore manifests itself both as a structural component of an alkyl-aromatic polymer and as a substructure of hydrogenated PAH species. Its spectral and molecular characteristics are consistent with what is generally expected for a complex molecular aggregate that has a role as an interstellar constituent.

The role of ADP-ribosylation factor and phospholipase D in adaptor recruitment

AP-1 and AP-2 adaptors are recruited onto the TGN and plasma membrane, respectively. GTPgammaS stimulates the recruitment of AP-1 onto the TGN but causes AP-2 to bind to an endosomal compartment (Seaman, M.N.J., C.L. Ball, and M.S. Robinson. 1993. J. Cell Biol. 123:1093-1105). We have used subcellular fractionation followed by Western blotting, as well as immunofluorescence and immunogold electron microscopy, to investigate both the recruitment of AP-2 adaptors onto the plasma membrane and their targeting to endosomes, and we have also examined the recruitment of AP-1 under the same conditions. Two lines of evidence indicate that the GTPgammaS-induced targeting of AP-2 to endosomes is mediated by ADP-ribosylation factor-1 (ARF1). First, GTPgammaS loses its effect when added to ARF-depleted cytosol, but this effect is restored by the addition of recombinant myristoylated ARF1. Second, adding constitutively active Q71L ARF1 to the cytosol has the same effect as adding GTPgammaS. The endosomal membranes that recruit AP-2 adaptors have little ARF1 or any of the other ARFs associated with them, suggesting that ARF may be acting catalytically. The ARFs have been shown to activate phospholipase D (PLD), and we find that addition of exogenous PLD has the same effect as GTPgammaS or Q71L ARF1. Neomycin, which inhibits endogenous PLD by binding to its cofactor phosphatidylinositol 4,5-bisphosphate, prevents the recruitment of AP-2 not only onto endosomes but also onto the plasma membrane, suggesting that both events are mediated by PLD. Surprisingly, however, neither PLD nor neomycin has any effect on the recruitment of AP-1 adaptors onto the TGN, even though AP-1 recruitment is ARF mediated. These results indicate that different mechanisms are used for the recruitment of AP-1 and AP-2.

Characterization of the adaptor-related protein complex, AP-3

We have recently shown that two proteins related to two of the adaptor subunits of clathrincoated vesicles, p47 (mu3) and beta-NAP (beta3B), are part of an adaptor-like complex not associated with clathrin (Simpson, F., N.A. Bright, M.A. West, L.S. Newman, R.B. Darnell, and M.S. Robinson, 1996. J. Cell Biol. 133:749-760). In the present study we have searched the EST database and have identified, cloned, and sequenced a ubiquitously expressed homologue of beta-NAP, beta3A, as well as homologues of the alpha/gamma and sigma adaptor subunits, delta and sigma3, which are also ubiquitously expressed. Antibodies raised against recombinant delta and sigma3 show that they are the other two subunits of the adaptor-like complex. We are calling this complex AP-3, a name that has also been used for the neuronalspecific phosphoprotein AP180, but we feel that it is a more appropriate designation for an adaptor-related heterotetramer. Immunofluorescence using anti-delta antibodies reveals that the AP-3 complex is associated with the Golgi region of the cell as well as with more peripheral structures. These peripheral structures show only limited colocalization with endosomal markers and may correspond to a postTGN biosynthetic compartment. The delta subunit is closely related to the protein product of the Drosophila garnet gene, which when mutated results in reduced pigmentation of the eyes and other tissues. Because pigment granules are believed to be similar to lysosomes, this suggests either that the AP-3 complex may be directly involved in trafficking to lysosomes or alternatively that it may be involved in another pathway, but that missorting in that pathway may indirectly lead to defects in pigment granules.

Heterogeneous distribution of technetium-99m-labeled microspheres in rat lungs: microautoradiographic evidence and dosimetric consequences

The heterogeneity of 99mTc-labeled microspheres distribution within rat lung was visualized and quantified using a microautoradiographic "track" method (MAR).

METHODS

MAR was used to study the uptake of radioactivity by individual microspheres, thereby enabling calculation of the range of particle activity. MAR was also used to visualize in rat lung sections the intrapulmonary distribution of the microspheres within the lungs after intravenous administration. The mean doses delivered to the cells in close contact with the labeled microspheres were calculated taking only the 99mTc electron emissions into account.

RESULTS

All the microspheres were labeled. Nevertheless, the spectrum of visible tracks varied by a factor of 10, inducing a variable activity per microsphere from < 36 Bq to 325 Bq (mean activity-94 Bq/microsphere). No correlation existed between the radioactivity uptake and the size of microspheres. A very heterogeneous tridimensional distribution of the microspheres within the lungs were demonstrated with interparticle distances ranging from 57-4400 microns. On the other hand, only 1 of 2000 rat lung capillaries was obstructed. Using the mean activity, calculated delivered doses were found to reach approximately 6 Gy for the closest endothelial cells and 2 Gy for epithelial cells. However, such high doses were delivered to only a few cells.

CONCLUSION

The number of obstructed capillaries in human lungs is lower than in rat lungs; the distances between microspheres should be larger. Nevertheless, the individual doses absorbed by the pulmonary cells closest to the microspheres should be very important.

Coats and vesicle budding

Transport vesicles need coat proteins in order to form. The coat proteins are recruited from the cytosol onto a particular membrane, where they drive vesicle budding and select the vesicle cargo. So far, three types of coated transport vesicles have been purified and characterized, and candidates for components of other types of coats have been identified. This review gives a brief overview of what is known about the various coats and their role in transport vesicle formation.

Recalibrated Mariner 10 Color Mosaics: Implications for Mercurian Volcanism

Recalibration of Mariner 10 color image data allows the identification of distinct color units on the mercurian surface. We analyze these data in terms of opaque mineral abundance, iron content, and soil maturity and find color units consistent with the presence of volcanic deposits on Mercury's surface. Additionally, materials associated with some impact craters have been excavated from a layer interpreted to be deficient in opaque minerals within the crust, possibly analogous to the lunar anorthosite crust. These observations suggest that Mercury has undergone complex differentiation like the other terrestrial planets and the Earth's moon.

Inference of a 7.75 eV lower limit in the ultraviolet pumping of interstellar polycyclic aromatic hydrocarbon cations with resulting unidentified infrared emissions

The discrete infrared features known as the unidentified infrared (UIR) bands originating in starburst regions of other galaxies, and in H II regions and planetary nebulae within the Milky Way, are widely thought to be the result of ultraviolet pumped infrared fluorescence of polycyclic aromatic hydrocarbon (PAH) molecules and ions. These UIR emissions are estimated to account for 10%-30% of the total energy emitted by galaxies. Laboratory absorption spectra including the vacuum ultraviolet region, as described in this paper, show a weakening of the intensity of absorption features as the population of cations increases, suggesting that strong pi* <-- pi transitions are absent in the spectra of PAH cations. This implies a lower energy bound for ultraviolet photons that pump infrared emissions from such ions at 7.75 eV, an amount greater than previously thought. The implications include size and structure limitations on the PAH molecules and ions which are apparent constituents of the interstellar medium. Also, this might affect estimations of the population of early-type stars in regions of rapid star formation.

Cytosolic and membrane-associated proteins involved in the recruitment of AP-1 adaptors onto the trans-Golgi network

The AP-1 adaptor complex is recruited from the cytosol onto the trans-Golgi network membrane, where it co-assembles with clathrin into a coat that drives vesicle budding. The GTPase ARF1 has been shown to be required for AP-1 recruitment, and here we demonstrate that we can reconstitute full GTPgammaS-dependent recruitment of adaptors onto an enriched trans-Golgi network membrane fraction by adding purified AP-1 and recombinant myristylated ARF1, indicating that these are the only soluble proteins required for binding. To identify some of the membrane proteins involved in recruitment, we have incubated permeabilized metabolically labeled cells with cytosol under conditions that promote adaptor binding, then cross-linked the samples with 3,3'dithiobis(sulfosuccinimidylproprionate), denatured by boiling in SDS, and immunoprecipitated with antibodies against the various subunits. Under these conditions, the adaptor subunits co-precipitate not only with each other and with clathrin, but also with three novel proteins: p75, which is specifically cross-linked to gamma-adaptin; p80, which is specifically cross-linked to beta'-adaptin; and p60, which is specifically cross-linked to AP47. These proteins are all candidates for components of the adaptor docking site on the trans-Golgi network membrane.

A novel adaptor-related protein complex

Coat proteins are required for the budding of the transport vesicles that mediate membrane traffic pathways, but for many pathways such proteins pathways, but for many pathways such proteins have not yet been identified. We have raised antibodies against p47, a homologue of the medium chains of the adaptor complexes of clathrin-coated vesicles (Pevsner, J., W. Volknandt, B.R. Wong, and R.H. Scheller. 1994. Gene (Amst.). 146:279-283), to determine whether this protein might be a component of a new type of coat. p47 coimmunoprecipitates with three other proteins: two unknown proteins of 160 and 25 kD, and beta-NAP, a homologue of the beta/beta'-adaptins, indicating that it is a subunit of an adaptor-like heterotetrameric complex. However, p47 is not enriched in preparations of clathrin-coated vesicles. Recruitment of the p47-containing complex onto cell membranes is stimulated by GTP gamma S and blocked by brefeldin A, indicating that, like other coat proteins, its membrane association is regulated by an ARF. The newly recruited complex is localized to non-clathrin-coated buds and vesicles associated with the TGN. Endogenous complex in primary cultures of neuronal cells is also localized to the TGN, and in addition, some complex is associated with the plasma membrane. These results indicate that the complex is a component of a novel type of coat that facilitates the budding of vesicles from the TGN, possibly for transporting newly synthesized proteins to the plasma membrane.

Targeting signals and subunit interactions in coated vesicle adaptor complexes

There are two clathrin-coated vesicle adaptor complexes in the cell, one associated with the plasma membrane and one associated with the TGN. The subunit composition of the plasma membrane adaptor complex is alpha-adaptin, beta-adaptin, AP50, and AP17; while that of the TGN adaptor complex is gamma-adaptin, beta'-adaptin, AP47, and AP19. To search for adaptor targeting signals, we have constructed chimeras between alpha-adaptin and gamma-adaptin within their NH2-terminal domains. We have identified stretches of sequence in the two proteins between amino acids approximately 130 and 330-350 that are essential for targeting. Immunoprecipitation reveals that this region determines whether a construct coassemblies with AP50 and AP17, or with AP47 and AP19. These observations suggest that these other subunits may play an important role in targeting. In contrast, beta- and beta'-adaptins are clearly not involved in this event. Chimeras between the alpha- and gamma-adaptin COOH-terminal domains reveal the presence of a second targeting signal. We have further investigated the interactions between the adaptor subunits using the yeast two-hybrid system. Interactions can be detected between the beta/beta'-adaptins and the alpha/gamma-adaptins, between the beta/beta'-adaptins and the AP50/AP47 subunits, between alpha-adaptin and AP17, and between gamma-adaptin and AP19. These results indicate that the adaptor subunits act in concert to target the complex to the appropriate membrane.

Expression and localization of alpha-adaptin isoforms

There are two alpha-adaptin genes, alpha A and alpha C, which in brain encode proteins of of M(r) 108 × 10(3) and 104 × 10(3), respectively. Although both mRNAs can be detected on northern blots of brain and liver, the higher molecular mass polypeptide can only be detected on western blots of brain. Here we explain these observations by showing that alpha A is alternatively spliced and that the protein product in most tissues is different from the one expressed in brain in that it is missing 21 amino acids within the hinge region, giving it a similar mobility to that of alpha C. Monospecific antibodies were raised against the various alpha-adaptin isoforms and used to compare their distribution in cells and tissues. Both alpha A and alpha c are co-assembled into the same coated pits, and the larger isoform of alpha A is co-assembled with the smaller isoforms of alpha-adaptin, both in cells that naturally express it an in transfected cells. Examination of brain and spinal cord sections, labelled either for the larger isoform of alpha A or for alpha C, reveals that that the two are to some extent differentially distributed, consistent with previous in situ hybridisation studies. This finding, combined with the observation that there is considerable variability in the relative expression of the two isoforms in different tissues, indicates that the two genes are switched on in response to different stimuli. Moreover, the larger isoform of alpha A appears to be more efficiently concentrated in the nerve terminals than alpha C, which is found not only at the terminals but also diffusely distributed in the cell bodies and dendrites. This suggests that alpha C may play more of a role in the recycling of membrane components throughout the cell.

Plasma processing of interstellar PAHs into solar system kerogen

Processes resulting in the formation of hydrocarbons of carbonaceous chondrites and the identity of the interstellar molecular precursors involved are an objective of investigations into the origin of the solar system and perhaps even life on earth. We have combined the resources and experience of an astronomer and physicists doing laboratory simulations with those of a chemical expert in the analysis of meteoritic hydrocarbons, in a project that investigated the conversion of polycyclic aromatic hydrocarbons (PAHs) formed in stellar atmospheres into alkanes found in meteorites. Plasma hydrogenation has been found in the University of Alabama at Birmingham Astrophysics Laboratory to produce from the precursor PAH naphthalene, a new material having an IR absorption spectrum (Lee, W. and Wdowiak, T.J., Astrophys. J. 417, L49-L51, 1993) remarkably similar to that obtained at Arizona State University of the benzene-methanol extract of the Murchison meteorite (Cronin, J.R. and Pizzarello, S., Geochim. Cosmochim. Acta 54, 2859-2868, 1990). There are astrophysical and meteoritic arguments for PAH species from extra-solar sources being incorporated into the solar nebula, where plasma hydrogenation is highly plausible. Conversion of PAHs into alkanes could also have occurred in the interstellar medium. The synthesis of laboratory analogs of meteoritic hydrocarbons through plasma hydrogenation of PAH species is underway, as is chemical analysis of those analogs. The objective is to clarify this heretofore uninvestigated process and to understand its role during the origin of the solar system as a mechanism of production of hydrocarbon species now found in meteorites. Results have been obtained in the form of time-of-flight spectroscopy and chemical analysis of the lab analog prepared from naphthalene.

The South pole region of the moon as seen by clementine

The Clementine mission has provided the first comprehensive set of high-resolution images of the south pole region of the moon. Within 5 degrees of latitude of the pole, an area of an estimated 30,000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits. The Schrödinger Basin (320 kilometers in diameter), centered at 75 degrees S, is one of the two youngest, least modified, great multiring impact basins on the moon. A large maar-type volcano localized along a graben within the Schrödinger Basin probably erupted between 1 and 2 billion years ago.