Computed three-dimensional structures for theras-binding domain of theraf-p74 protein complexed withras-p21 and with its suppressor protein, rap-1A

The three-dimensional structures of theras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to theras-binding domain, RBD (residues 55–131), of theraf-p74 protein, a critical target protein ofras-p21 in theras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of bothras- p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of theras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains ofras-p21 and rap-1a, including residues 32–47, a domain that directly interacts with RBD, 60–66, 96–110, involved in the interaction ofras-p21 withjun kinase (JNK) andjun protein, and 115–126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its-2 binding loop (residues 63–71) and residues 89–91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK andjun.     

Association of specific leaf weight, an estimate of chlorophyll, and chlorophyll concentration with apparent photosynthesis in soybean

Increasing specific leaf weight (SLW) may improve leaf apparent photosynthesis (AP) in soybean [Glycine max (L.) Merr.] but screening for SLW and AP is laborious. The Objectives of this study were (i) to determine the time course of SLW and chlorophyll concentration in experimental lines selected for differences in SLW and (ii) to evaluate the potential use of the Minolta 502 SPAD meter as a rapid estimator of SLW, AP and chlorophyll concentration in leaves of soybean. In 1991 and 1992, sixteen experimental lines representing extremes in SLW were grown at Urbana, IL, and West Lafayette, IN, with three replications at each location. SPAD values, SLW and AP were measured at the R2 (full flower), R4 (full pod) and R5 (beginning seed) growth stages. In 1992 SLW, SPAD values and chlorophyll concentration were measured weekly. Seasonal patterns of SPAD values, SLW, and chlorophyll concentration were very similar through R5. After R5, SLW continued to increase but SPAD values and chlorophyll concentration declined. SPAD values and SLW were highly correlated at the R2, R4 and R5 stages at both locations and in both years. Environmental conditions during this research were not suitable for maximum AP expression, which is likely why AP and SPAD values were correlated only at the R4 growth stage at Urbana in 1992. SPAD measurements were consistent across diverse environments and effectively separated the high SLW lines from the low SLW lines. Measuring with the Minolta 502 SPAD meter is rapid, simple and non-destructive and could be an alternative method for direct selection for SLW.Abbreviations AP- leaf apparent photosynthesis - CV- coefficient of variation - Rug- leaf rugosity - SLW- specific leaf weight - SPAD-L- SPAD value of the most recently expanded terminal leaflet - SPAD-P- SPAD value of leaflet used to measure AP - SPAD-S- SPAD value of leaflets used to measure SLW - SPAD-U- SPAD value of the terminal leaflet one node above the most recently expanded terminal leaflet The US Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged     

Effects of light,moisture, temperature,and litter on the regeneration of five tree species in the tropical montane wet forest of Puerto Rico

Field experiments were conducted to investigate the effects of light, moisture, temperature, and litter on the regeneration of two early-, one mid-, and two late-successional tropical tree species. High light and litter seem to be universally good cues for regeneration, increasing seed/seedling survival for all species except for Cecropia (an early-successional species) whose small seeds may not be able to penetrate the litter layer. In addition, the high temperature environment in both artificially shaded and nonshaded areas of a natural gap exhibits less seed loss, an increase in the percent and rate of germination, and an increase in seedling survival for Dacryodes (a late-successional species), than the lower temperature environment under an intact canopy. Low soil water is also a good cue for Dacryodes germination as it is for Prestoea and Cecropia. Finally, the lower temperature environment found under the forest canopy (compared to the natural gap) leads to less seed loss and more germination for Guarea (a mid-successional species). Our results suggest that a good patch for regeneration of many species in this forest, early- as well as late-successional species, would have high light and a litter layer that moderates temperature and moisture extremes. The substantial variation in suitability among regeneration filters and species could: (1) contribute to low establishment success, i.e., most dispersed propagules do not become trees, (2) make it difficult to group species into germination strategies, and (3) make it hard to generalize about a net effect of any specific environmental variable on establishment. We suggest that tropical disturbances should be viewed in terms of their impact on a variety of environmental cues, which may signal germination and impact subsequent growth and survival.     

MORBILLIVIRUS INFECTION IN BOTTLENOSE DOLPHINS: EVIDENCE FOR RECURRENT EPIZOOTICS IN THE WESTERN ATLANTIC AND GULF OF MEXICO

Morbillivirus infection is widespread among odontocetes of the western Atlantic and Gulf of Mexico. Serologic evidence of infection in bottlenose dolphins, Tursiops truncatus , was first detected during an epizootic along the mid-Atlantic coast in 1987. Here, we report recurrent epizootics in the coastal dolphin population since at least the early 1980s based on serological surveys and regional stranding frequencies. The first observed epizootic of this series occurred in the Indian and Banana Rivers in 1982 and was followed by others on the mid-Atlantic coast in 1987–1988 and in the Gulf of Mexico between 1992 and 1994. This temporal pattern of infection is likely facilitated by the population size and its fragmentation into relatively discrete coastal communities. Introduction of morbillivirus into a community with a sufficient number of naive hosts may precipitate an epizootic, depending on the potential for transmission within the group. Propagation of an epizootic along the coast is probably determined by frequency of contact between adjacent communities and seasonal migrations.
Morbillivirus antibodies were also detected in serum from offshore bottlenose dolphins. The sero-prevalence in the latter may be higher than in coastal dolphins because of their close association with enzootically infected pilot whales ( Globicephala spp.). Occasional contact between offshore and coastal dolphins may provide an epizootiologic link between pilot whales and coastal dolphin communities.     

Invertebrate phosphatidylinositol-specific phospholipases C and their role in cell signaling

Phosphatidylinositol-specific phospholipase C (PLC) is a family of enzymes that occupy a pivotal role in one of the largest classes of cellular signaling pathways known. Mammalian PLC enzymes have been divided into four major classes and a variety of subclasses based on their structural characteristics and immunological differences. There have been five invertebrate PLC-encoding genes cloned thus far and these fall within three of the four major classes used in categorizing mammalian PLC. Four of these invertebrate genes have been cloned fromDrosophila melanogaster and one is fromArtemia, a brine shrimp. Structural characteristics of the invertebrate enzymes include the presence of highly conserved Box X and Box Y domains found in major types of mammalian PLC as well as novel features. Two of the invertebrate PLC genes encode multiple splice-variant subtypes which is a newly emerging level of diversity observed in mammalian enzymes. Studies of the invertebrate PLCs have contributed to the identification of the physiological functions of individual isozymes. These identified roles include cellular processes such as phototransduction, olfaction, cell growth and differentiation.     

Neurotrophin-4/5, brain-derived neurotrophic factor,and neurotrophin-3 promote survival of cultured vestibular ganglion neurons and protect them against neurotoxicity of ototoxins

The ability of neurotrophin-4/5 (NT-4/5), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and nerve growth factor (NGF) to promote survival of postnatal rat vestibular ganglion neurons (VGNs) was examined in dissociated cell cultures. Of the four neurotrophins, NT-4/5 and BDNF were equally effective but more potent than NT-3 in promoting the survival of VGNs. In contrast, NGF showed no detectable effects. As expected, TrkB-IgG (a fusion protein of extracellular domain of TrkB and Fc domain of human immunoglobulin G) specifically inhibited the survival-promoting effects by NT-4/5 or BDNF and TrkC-IgG fusion protein completely blocked that of NT-3. Immunohistochemistry with TrkB, TrkA, and p75 antisera revealed that VGNs made TrkB and p75 proteins, but not TrkA protein. Ototoxic therapeutic drugs such as cisplatin and gentamicin often induce degeneration of hair cells and ganglion neurons in both auditory and vestibular systems that leads to impairment of hearing and balance. When cisplatin and gentamicin were added to the dissociated VGN culture in which the hair cells were absent, additional cell death of VGNs was induced, suggesting that the two ototoxins may have a direct neurotoxic effect on ganglion neurons in addition to their known toxicity on hair cells. However, if the cultures were co-treated with neurotrophins, NT-4/5, BDNF, and NT-3, but not NGF, prevented or reduced the neurotoxicity of the two ototoxins. Thus, the three neurotrophins are survival factors for VGNs and are implicated in the therapeutic prevention of VGN loss caused by injury and ototoxins. © 1995 John Wiley & Sons, Inc.     

Pollen tube pathway through the gynoecium of Monotropsis odorata (Monotropaceae)

Monotropsis odorata Elliott. is one of the most cryptic and relatively rare North American endemic species of the Monotropaceae; therefore, information concerning the biology of this achlorophyllous, mycotrophic angiosperm is limited. Bright field and fluorescence microscopic investigations of postpollination gynoecia reveal that pollen tubes follow a continuous pathway from the receptive surface of the stigma to micropyles of the ovules. The pollen tube pathway is characterized by discrete strands of transmitting tissue connecting an exudate-coated stigma to an exudate-filled, stylar canal that leads directly to exudate-coated placentae. Pollen tube growth appears restricted to those areas associated with an exudate. The gynoecial pathway for pollen tube growth in this taxon conforms to those described from other monotropàceous species.     

Genetic variation,breeding system evolution,and conservation of the narrow sand dune endemic Stellaria arenicola and the widespread S. longipes (Caryophyllaceae)

Genetic variation was examined by electrophoresis in 14 populations of Stellaria arenicola, an endemic of the Athabasca sand dunes in northern Saskatchewan, Canada, and seven populations of S. longipes, its progenitor. Three of the 5. longipes populations were sympatric with the endemic. Populations of the endemic were found to have fewer alleles per polymorphic locus (2.21 vs. 2.37), fewer polymorphic loci (29.9 vs. 33.8), and lower genetic diversity (0.087 vs. 0.107) than populations of the progenitor. Genetic identities for all pairs of populations were high (0.932 to 1.000). The endemic had one novel allele and shared ten alleles with progenitor populations from the sand dunes that were not found in other populations of S. longipes. Populations of both species were found to partition most of their genetic variation within populations. An investigation of the multilocus outcrossing rates revealed that S. arenicola had higher rates of selling and biparental inbreeding than S. longipes. This study suggests that partial genetic isolation through a shift in the breeding system, in addition to previously reported strong directional selection, has been important in the sympatric evolution of the endemic S. arenicola. The close genetic relationship between populations of S. arenicola and S. longipes found on the Athabasca sand dunes supports the suggestion that the endemic evolved while sympatric to the gene pool of the progenitor species that is found presently in the region.