Olfactory selection of Plantago lanceolata by snails declines with seedling age.

BACKGROUND AND AIMS: Despite recent recognition that (1) plant-herbivore interactions during the establishment phase, (2) ontogenetic shifts in resource allocation and (3) herbivore response to plant volatile release are each pivotal to a comprehensive understanding of plant defence, no study has examined how herbivore olfactory response varies during seedling ontogeny. METHODS: Using a Y-tube olfactometer we examined snail (Helix aspersa) olfactory response to pellets derived from macerated Plantago lanceolata plants harvested at 1, 2, 3, 4, 5, 6 and 8 weeks of age to test the hypothesis that olfactory selection of plants by a generalist herbivore varies with plant age. Plant volatiles were collected for 10 min using solid-phase microextraction technique on 1- and 8-week-old P. lanceolata pellets and analysed by gas chromatography coupled with a mass spectrometer. KEY RESULTS: Selection of P. lanceolata was strongly negatively correlated with increasing age; pellets derived from 1-week-old seedlings were three times more likely to be selected as those from 8-week-old plants. Comparison of plant selection experiments with plant volatile profiles from GC/MS suggests that patterns of olfactory selection may be linked to ontogenetic shifts in concentrations of green leaf volatiles and ethanol (and its hydrolysis derivatives). CONCLUSIONS: Although confirmatory of predictions made by contemporary plant defence theory, this is the first study to elucidate a link between seedling age and olfactory selection by herbivores. As a consequence, this study provides a new perspective on the ontogenetic expression of seedling defence, and the role of seedling herbivores, particularly terrestrial molluscs, as selective agents in temperate plant communities.

The lethal and sub-lethal consequences of entomopathogenic nematode infestation and exposure for adult pine weevils, Hylobius abietis (Coleoptera: Curculionidae).

Entomopathogenic nematodes (EPN) frequently kill their host within 1-2 days, and interest in EPN focuses mainly on their lethality. However, insects may take longer to die, or may fail to die despite being infected, but little is known about the effects of EPN infection on insects, other than death. Here we investigate both lethal and sub-lethal effects of infection by two EPN species, Steinernema carpocapsae and Heterorhabditis downesi, on adults of the large pine weevil, Hylobius abietis. Following 12h nematode-weevil contact in peat, S. carpocapsae killed a significantly higher proportion of weevils (87-93%) than H. downesi (43-57%) at all concentrations tested. Less than 10% of weevils were dead within 2 days, and weevils continued to die for up to 10 days after exposure (LT(50) of 3 days or more). In a separate experiment, live weevils dissected 6 days after a 24h exposure to nematodes on filter paper harbored encapsulated and dead nematodes, showing that weevils could defend themselves against infection. Some live weevils also harbored live nematodes 6 days after they had been removed from the nematode infested medium. Feeding by weevils was not affected by infection with, or exposure to, either species of EPN. We discuss these results in relation to the use of EPN in biological control against H. abietis.

Apoptosis induced in mammalian cells by small peptides that functionally antagonize the Rb-regulated E2F transcription factor.

A variety of studies implicate the E2F transcription factor as a critical regulator of the mammalian cell cycle. The E2F pathway is aberrant in most, if not all, human tumor cells; therefore, therapeutic regimes that modulate E2F activity may provide an approach for reinstating growth control in situations where normal physiological control is lost. To elucidate the role of E2F in the cell cycle and assess its value as a therapeutic target, we have introduced peptides that functionally antagonize E2F DNA binding activity into mammalian cells. Introduction of these peptides into mammalian tumor cells caused the rapid onset of apoptosis, an outcome that correlates with the inactivation of physiological E2F.

Functional interaction between DP-1 and p53.

The cellular transcription factor DRTF1/E2F and the tumor suppressor protein p53 play important roles in controlling early cell cycle events. DRTF1/E2F is believed to coordinate and integrate the transcription of cell cycle-regulating genes, for example, those involved in DNA synthesis, with the activity of regulatory proteins, such as the retinoblastoma tumor suppressor gene product (pRb), which modulate its transcriptional activity. In contrast, p53 is thought to monitor the integrity of chromosomal DNA and when appropriate interfere with cell cycle progression, for example, in response to DNA damage. Generic DRTF1/E2F DNA binding activity and transcriptional activation arise when members of two distinct families of proteins, such as DP-1 and E2F-1, interact as DP/E2F heterodimers. In many cell types, DP-1 is a widespread component of DRTF1/E2F DNA binding activity which when expressed at high levels oncogenically transforms embryonic fibroblasts. Here, we document an association between DP-1 and p53 and demonstrate its presence in mammalian cell extracts. In vitro p53 interacts with an immunochemically distinct form of DP-1 and in vivo can regulate transcription driven by the DP-1/E2F-1 heterodimer. At the biochemical level, p53 competes with E2F-1 for DP-1, with a consequent reduction in DNA binding activity. Mutational analysis defines within DP-1 a C-terminal region required for the interaction with p53 and within p53 an N-terminal region distinct from that required to bind to MDM2. Our results establish DRTF1/E2F as a common cellular target in growth control mediated through the activities of pRb and p53 and suggest an alternative mechanism through which p53 may regulate cellular proliferation.

Proto-oncogenic properties of the DP family of proteins.

The cellular transcription factor DRTF1/E2F is implicated in the control of cellular proliferation due to its interaction with key regulators of cell cycle progression, such as the retinoblastoma tumour suppressor gene product, cyclins and cyclin-dependent kinases. DRTF1/E2F is a heterodimeric DNA binding activity which arises when a member of two distinct families of proteins, DP and E2F, interact as DP/E2F heterodimers, for example, DP-1 and E2F-1. In DRTF1/E2F the activity of DP-1 is under cell cycle control, possibly by phosphorylation, and in many types of cells it is a frequent, if not general DNA binding component of DRTF1/E2F. The expression of other DP proteins, such as DP-2, is tissue-restricted. Here, we show that DP-1 and DP-2 are integrated with another growth regulating pathway which involves signal transduction emanating from activated Ras protein. Thus, activated Ha-ras can co-operate with DP-1 or DP-2 in the transformation of rat embryo fibroblasts, establishing for the first time that DP proteins are endowed with proto-oncogenic activity. Moreover, an analysis of a dominant-negative and mutant DP-1 proteins suggests that the primary target through which DP-1 mediates its oncogenic activity is unlikely to be due to the regulation of E2F site-transcription, suggesting an E2F-independent effector function for DP-1. These results therefore establish DP genes as proto-oncogenes and thus argue that deregulating the normal control of DP protein activity will be important in promoting aberrant cellular proliferation.

Molecular characterization of Xenopus laevis DP proteins.

It is widely believed that in mammalian cells the cellular transcription factor (DRTF1/E2F integrates cell-cycle events with the transcription apparatus by interacting with important regulators of the cell cycle, such as the retinoblastoma gene product (pRb) and related proteins, cyclins, and cyclin-dependent kinases. Here, we have defined DRTF1/E2F in Xenopus laevis that, like its mammalian counterpart, specifically binds to the E2F site, is regulated during development, and interacts with pRb and related proteins. We have isolated cDNAs that encode the functional homologue of mammalian DP-1, X1 DP-1, together with a close relative, X1 DP-2. X1 DP-1, which is highly conserved with murine DP-1, is a major DNA binding component of X1 DRTF1/E2F. Both DP-1 and DP-2 synergistically interact with members of the E2F family of proteins, E2F-1, E2F-2, and E2F-3, to generate DNA binding complexes that specifically recognize the E2F site and functionally interact with E2F-1 in E2F site-dependent transcriptional activation of cellular genes. DP-1 and DP-2 encode maternally stored transcripts that are expressed during early development. In the adult however, the expression of DP-1 and DP-2 is tissue restricted. This study therefore defines a new family of transcription factors, the DP proteins, members of which can interact combinatorially with E2F proteins to generate an array of DNA binding complexes that integrate cell-cycle progression with the transcription apparatus through the E2F binding site. The tissue-specific expression of DP family members suggests that the combination of DP/E2F heterodimers that constitute DRTF1/E2F is influenced by the phenotype of the cell.

DP-1: a cell cycle-regulated and phosphorylated component of transcription factor DRTF1/E2F which is functionally important for recognition by pRb and the adenovirus E4 orf 6/7 protein.

The cellular transcription factor DRTF1/E2F integrates cell cycle events with the transcription apparatus through its cyclical interactions with important regulators of cellular proliferation. Two sequence-specific DNA binding proteins, DP-1 and E2F-1, are components of DRTF1/E2F which synergistically interact in a DP-1/E2F-1 heterodimer. Here, we show that DP-1 is a very frequent, possibly universal, component of DRTF1/E2F in 3T3 cells since it is present in all forms of the DNA binding activity that occur during cell cycle progression. Furthermore, the DP-1 polypeptide, which is phosphorylated, undergoes a phosphorylation-dependent mobility shift during the cell cycle suggesting that its level of phosphorylation is regulated during cell cycle progression. A C-terminal region in DP-1 can interact with pRb which, in the context of the DP-1/E2F-1 heterodimer, contributes to the efficiency of pRb binding. The DP-1/E2F-1 heterodimer specifically interacts with the adenovirus type 5 E4 orf 6/7 protein, to produce a DNA binding activity which binds co-operatively to, and transcriptionally activates through, two appropriately positioned E2F sites in a manner which resembles the regulation of DRTF1/E2F by E4 orf 6/7 during adenovirus infection. We conclude that DP-1 is a frequent and cell cycle-regulated component of DRTF1/E2F, and that in the DP-1/E2F-1 heterodimer it is functionally important for recognition by pRb and the E4 orf 6/7 protein.

A new component of the transcription factor DRTF1/E2F.

Transcription factor DRTF1/E2F coordinates events in the cell cycle with transcription by its cyclical interactions with important regulators of cellular proliferation like the retinoblastoma tumour-suppressor gene product (Rb) and the Rb-related protein, p107 (refs 1-8). DRTF1/E2F binding sites occur in the control regions of genes involved in proliferation, and both Rb and p107 repress the capacity of DRTF1/E2F to activate transcription (refs 11, 12; M. Zamanian and N.B.L.T., manuscript submitted). Mutant Rb proteins isolated from tumour cells are unable to bind DRTF1/E2F (refs 11-13), and certain viral oncoproteins, such as adenovirus E1A, sequester Rb and p107 in order to free active DRTF1/E2F (refs 5, 11, 12, 14, 15). Here we report the isolation of a complementary DNA encoding DRTF1-polypeptide-1 (DP-1), a major sequence-specific binding protein that is present in DRTF1/E2F, including Rb- and p107-associated DRTF1/E2F. The DNA-binding domain of DP-1 contains a region that resembles that of E2F-1 (refs 16, 17), and recognizes the same sequence. DRTF1/E2F thus appears to contain at least two sequence-specific DNA-binding proteins.

Structure of human hemoglobin C: a disease with intraerythrocytic crystals.

Crystals of human cyanomethemoglobin C (beta 6A3 glu leads to Lys) crystallized in the orthorhombic space group P212121, A = 158(1), B = 65.5(4), C = 54.9(5) A with Z =4. Single crystal electron micrographs show filaments parallel to the b direction. The molecules are unusually densely packed compared to other hemoglobin crystals, and this may be related to the ease of intraerythrocytic crystallization.

Crystallography and oriented single crystal electron microscopy of hemoglobin deer II, a hemoglobin that exhibits matchstick-shaped erythrocytes.

Deer hemoglobin beta chain type II has been crystallized and preliminary diffraction data and oriented single crystal transmission electron micrographs have been obtained. The crystals are monoclinic P21 with Z = 4. The electron micrographs show a herringbonelike structure in the ab plane with open rectangular solvent channels and a fiber-like arrangement of molecules perpendicular to this plane.