Host plant growth characteristics as determinants of abundance and phenology in jumping plant-lice on downy willow

1. Salix lapponum host plants at an upper altitudinal site differed significantly in size, structural density, phenology, growth performance, and spatial isolation from those growing at a lower site. 2. Plant differences were paralleled by significant differences in psyllid population density and phenology parameters, with psyllid population density, percentage of catkins occupied, and phenological development relatively lower or retarded at the upper site. Population densities at the upper site, nevertheless, remained high. 3. Plant measurements were good predictors of insect density, often explaining up to 73% of the variance in abundance among plants at a given site. 4. Sets of four plant characters identified by best subsets regression were better predictors of psyllid density and development than single factors, although differences were often not great and the combinations of characters selected by multiple regression sometimes differed from the best single predictors. 5. Best single predictors of psyllid density on catkins were measurements of plant size, particularly height, length, and basal stem diameter. Shoot density and catkin phenology were occasionally important but plant isolation and prior growth performance were less important. 6. By contrast with density, age structure of the psyllid population was predicted best from plant phenological measurements, notably catkin phenology.     

A cDNA from grapevine (Vitis vinifera L.), which shows homology to AGAMOUS and SHATTERPROOF,is not only expressed in flowers but also throughout berry development

An AGAMOUS/SHATTERPROOF homologue (Vvmads1) was isolated from grapevine by differential display between berry and leaf mRNA. The predicted protein sequence of the full-length clone shows a high degree of homology to PLENA (77% identity) and to SHP1 and SHP2 (75% and 74% identity respectively), and is grouped with AGAMOUS/PLENA homologues when the conserved MADS and K domains are compared. Vvmads1 is expressed only in the later stages of flower development and throughout berry development, although expression is reduced after ripening commenced. When Vvmads1 was over-expressed in tobacco, the resulting plants display altered morphologies in the outer two floral whorls. In the most extreme cases, the inner whorls were surrounded by a carpelloid structure created by the modified sepals. Within these sepals were petals which had been split into sections and which were attached at the base of the flower by structures with the appearance of filaments. The results of this study suggest that Vvmads1 has a regulatory role in flower development before fertilisation and a role in fruit development after fertilisation.     

Chlorophyll reduction in the seed of Brassica napus with a glutamate 1-semialdehyde aminotransferase antisense gene*

Chlorophyll reduction in the seed of Brassica can be achieved by downregulating its synthesis. To reduce chlorophyll synthesis, we have used a cDNA clone of Brassica napus encoding glutamate 1-semialdehyde aminotransferase (GSA-AT) to make an antisense construct for gene manipulation. Antisense glutamate 1-semialdehyde aminotransferase gene (Gsa) expression, directed by a Brassica napin promoter, was targeted specifically to the embryo of the developing seed. Transformants expressing antisense Gsa showed varying degrees of inhibition resulting in a range of chlorophyll reduction in the seeds. Seed growth and development were not affected by reduction of chlorophyll. Seeds from selfed transgenic plants germinated with high efficiency and growth of seedlings was vigorous. Seedlings from T₂ transgenic lines segregated into three distinctive phenotypes: dark green, light green and yellow, indicating the dominant inheritance of Gsa antisense gene. These transgenic lines have provided useful materials for the development of a low chlorophyll seed variety of B. napus.     

Costs of jasmonate-induced responses in plants competing for limited resources

We present a design to quantify fitness consequences of jasmonate-induced responses in plants that are competing for limited resources with a conspecific. Under both high and low nitrogen supply rates, uninduced (control) Nicotiana attenuata plants growing next to a plant induced with 250 μg methyl jasmonate (MJ) yielded more seed capsules than control plants competing with another control plant. We conclude that there is a opportunity benefit for control plants growing next to an induced plant. Initially, MJ-induced plants grew more slowly, but by senescence they had produced the same number of seed capsules as control plants that had competed with another control plant. Replacement series showed that the fitness of MJ-induced plants is not influenced by the competitive status of their neighbour plant. We argue that competitive designs are useful tools for evaluating the phenotypic costs of ecologically important traits.     

Process for the isolation of preparative quantities of

A number of proteins that play key roles in biological regulatory events undergo a process of post-translational modifications termed prenylation. The prenylation pathway consists of three enzymatic steps; the final processed protein is isoprenoid-modified and methylated on the C-terminal cysteine. This protein modification pathway plays a significant role in cancer biology because many oncogenic proteins undergo prenylation. Methylation of the C terminus by isoprenylcysteine carboxylmethyltransferase (Icmt) is the final step in the prenylation pathway. Cysmethynil, a specific Icmt inhibitor discovered in our laboratory, is able to inhibit Ras-mediated signaling, cell growth, and oncogenesis. We sought to examine the role of Icmt-mediated methylation on the behaviors of cancer cells associated with metastatic potential. Our results indicate that inhibition of methylation reduces migration of the highly metastatic MDA-MB-231 breast cancer cell line. In addition, cell adhesion and cell spreading are also significantly impacted by cysmethynil. To examine the mechanism of Icmt-dependent migration we focused on RhoA and Rac1, prenylated proteins that are important mediators of cell migration through their control of the actin cytoskeleton. Inhibition of Icmt significantly decreases the activation of both RhoA and Rac1; an increase in Rho GDP-dissociation inhibitor (RhoGDI) binding in the absence of methylation appears to contribute to this effect. Furthermore, in the absence of Icmt activity the addition of exogenous RhoA or Rac1 is able to partially rescue directed and random migration, respectively. These findings establish a role for Icmt-mediated methylation in cell migration and advance our understanding of the biological consequences of Rho methylation.Post-translational modifications of proteins play vital roles in many aspects of cell biology. Hence, identifying and understanding the biological impact of these processes is crucial to furthering our basic understanding of how cells function. Numerous proteins that control important biological regulatory events undergo a complex series of post-translational modifications that are directed by the presence of a so-called CaaX motif at their C terminus. This post-translational pathway, termed protein prenylation, is initiated by the attachment of an isoprenoid lipid to an invariant cysteine residue, the C of the CaaX motif (1, 2). Either a 15-carbon farnesyl or 20-carbon geranylgeranyl isoprenoid is covalently attached to this cysteine by protein farnesyltransferase (FTase)² or protein geranylgeranyltransferase-I (GGTase-I), respectively (3). The prenylation step is followed by cleavage of the three C-terminal amino acids (the -AAX) by an endoplasmic reticulum (ER)-bound protease termed Rce1. Finally, the prenylated cysteine, which is now located at the C terminus, is methylated by isoprenylcysteine carboxylmethyltransferase (Icmt), another integral ER membrane protein (4, 5). The final result of these modifications is a protein that contains a prenylated and methylated cysteine at its C terminus. Numerous studies have demonstrated that this post-translational processing not only facilitates protein association with cellular membranes, but also can play important roles in protein-protein interactions and protein stability (1, 6, 7). Thus, it is clear that CaaX processing is necessary for the biological activities of these proteins.The prenylation pathway has been targeted for potential anticancer therapy because most members of the Ras superfamily, which contains many known oncogenes, undergo CAAX processing. The Ras superfamily consists of five large subfamilies; the two most well-characterized are the Ras and Rho subfamilies (8). Both Ras and Rho proteins are processed by the CaaX pathway; Ras family members are farnesylated, while most Rho family members are geranylgeranylated. These monomeric GTPases cycle between a GDP-bound inactive state and a GTP-bound active state. In their active states, Ras and Rho subfamily members control numerous cell signaling pathways that are involved in cell proliferation, differentiation, migration, polarity, and morphology (9).Abnormally high activity of Ras and Rho signaling pathways contribute to initiation and progression of many types of cancer (10, 11). For example, many breast cancers that are highly metastatic express abnormally high levels of Rho proteins (12). Rho proteins control migration and invasion of cells by tightly coordinating changes in the actin and microtubule cytoskeletons. Acting through their effectors, Rho proteins rearrange the actin cytoskeleton to respond to chemo-attractant gradients, polarize cells, and control migration and invasion. While cell migration is necessary for development, leukocyte function, and other normal cell biologies, dysregulation of migration and invasion results in cancer metastasis (13). Metastasis is an important and deadly progression of cancer and understanding the biology of migrating cancer cells is crucial for therapeutic targeting of this aspect of cancer.Pharmacologic targeting of the enzymes involved in the CaaX-processing pathway has emerged as a promising anticancer strategy. In particular, there has been much effort in designing inhibitors against the protein prenyltransferases, most notably FTase (14, 15). There is also recent evidence that inhibition of geranygeranylation of Rho proteins also impacts oncogenesis and metastasis (16–18). However, the overall success of the FTase inhibitors (FTIs) in the clinical setting has been somewhat disappointing. One possible reason is a phenomenon termed “alternate prenylation” in which some FTase substrates, most notably K- and N- Ras, are modified by GGTase and escape inhibition by FTIs (19–21). Because the Rce1 protease and Icmt methyltransferase act on all CaaX proteins, problems such as alternate prenylation would not arise if these enzymes were targeted. Hence, while protein prenyltransferase inhibitors still show some promise as anticancer agents, the emerging view that global attenuation of CaaX protein function may be advantageous in blocking cancer cell growth has increased interest in studying the two downstream enzymes involved in CaaX processing.While the biological consequences of prenylation are fairly well understood, the precise roles of C-terminal methylation in CaaX protein function are still elusive. Depending on the CaaX protein, methylation has been ascribed to roles in localization, protein-protein interactions and protein stability (11). The development of an Icmt knock-out mouse model has furthered our understanding of Icmt function (22, 23). Localization studies conducted in cells with genetically deleted Icmt have shown that methylation is important for proper membrane association of Ras proteins. However, the localization of Rho proteins in the absence of Icmt activity appears to be more complicated and may vary depending on family member and activation status (24–26). Importantly, inhibition of CaaX protein methylation via either genetic or pharmacologic targeting has shown a clear impact on oncogenic transformation and tumor growth (23, 27, 28).Defining the role of Icmt-mediated methylation in complex cellular behaviors such as migration and invasion is crucial for furthering our understanding of the impact of CaaX protein methylation on the biology of normal and cancer cells. In the current study, we have assessed the impact of Icmt inhibition on cell biological processes associated with the function of Rho proteins, specifically cell adhesion, morphology, and migration. We found that inhibition of Icmt results in a disruption of the actin cytoskeleton and impairs ligand-mediated activation of RhoA and Rac1, a potential consequence of increased RhoGDI binding to both RhoA and Rac1 when their methylation is impaired. Further, we show that the impact of Icmt inhibition on cell migration is due at least in part to impairment of RhoA and Rac1function. These findings establish a role for Icmt-mediated methylation in cell migration and further elucidate the role that methylation plays in the function of Rho GTPases.     

Role of Isoprenylcysteine Carboxylmethyltransferase-catalyzed Methylation in Rho Function and Migration

A number of proteins that play key roles in biological regulatory events undergo a process of post-translational modifications termed prenylation. The prenylation pathway consists of three enzymatic steps; the final processed protein is isoprenoid-modified and methylated on the C-terminal cysteine. This protein modification pathway plays a significant role in cancer biology because many oncogenic proteins undergo prenylation. Methylation of the C terminus by isoprenylcysteine carboxylmethyltransferase (Icmt) is the final step in the prenylation pathway. Cysmethynil, a specific Icmt inhibitor discovered in our laboratory, is able to inhibit Ras-mediated signaling, cell growth, and oncogenesis. We sought to examine the role of Icmt-mediated methylation on the behaviors of cancer cells associated with metastatic potential. Our results indicate that inhibition of methylation reduces migration of the highly metastatic MDA-MB-231 breast cancer cell line. In addition, cell adhesion and cell spreading are also significantly impacted by cysmethynil. To examine the mechanism of Icmt-dependent migration we focused on RhoA and Rac1, prenylated proteins that are important mediators of cell migration through their control of the actin cytoskeleton. Inhibition of Icmt significantly decreases the activation of both RhoA and Rac1; an increase in Rho GDP-dissociation inhibitor (RhoGDI) binding in the absence of methylation appears to contribute to this effect. Furthermore, in the absence of Icmt activity the addition of exogenous RhoA or Rac1 is able to partially rescue directed and random migration, respectively. These findings establish a role for Icmt-mediated methylation in cell migration and advance our understanding of the biological consequences of Rho methylation.Post-translational modifications of proteins play vital roles in many aspects of cell biology. Hence, identifying and understanding the biological impact of these processes is crucial to furthering our basic understanding of how cells function. Numerous proteins that control important biological regulatory events undergo a complex series of post-translational modifications that are directed by the presence of a so-called CaaX motif at their C terminus. This post-translational pathway, termed protein prenylation, is initiated by the attachment of an isoprenoid lipid to an invariant cysteine residue, the C of the CaaX motif (1, 2). Either a 15-carbon farnesyl or 20-carbon geranylgeranyl isoprenoid is covalently attached to this cysteine by protein farnesyltransferase (FTase)² or protein geranylgeranyltransferase-I (GGTase-I), respectively (3). The prenylation step is followed by cleavage of the three C-terminal amino acids (the -AAX) by an endoplasmic reticulum (ER)-bound protease termed Rce1. Finally, the prenylated cysteine, which is now located at the C terminus, is methylated by isoprenylcysteine carboxylmethyltransferase (Icmt), another integral ER membrane protein (4, 5). The final result of these modifications is a protein that contains a prenylated and methylated cysteine at its C terminus. Numerous studies have demonstrated that this post-translational processing not only facilitates protein association with cellular membranes, but also can play important roles in protein-protein interactions and protein stability (1, 6, 7). Thus, it is clear that CaaX processing is necessary for the biological activities of these proteins.The prenylation pathway has been targeted for potential anticancer therapy because most members of the Ras superfamily, which contains many known oncogenes, undergo CAAX processing. The Ras superfamily consists of five large subfamilies; the two most well-characterized are the Ras and Rho subfamilies (8). Both Ras and Rho proteins are processed by the CaaX pathway; Ras family members are farnesylated, while most Rho family members are geranylgeranylated. These monomeric GTPases cycle between a GDP-bound inactive state and a GTP-bound active state. In their active states, Ras and Rho subfamily members control numerous cell signaling pathways that are involved in cell proliferation, differentiation, migration, polarity, and morphology (9).Abnormally high activity of Ras and Rho signaling pathways contribute to initiation and progression of many types of cancer (10, 11). For example, many breast cancers that are highly metastatic express abnormally high levels of Rho proteins (12). Rho proteins control migration and invasion of cells by tightly coordinating changes in the actin and microtubule cytoskeletons. Acting through their effectors, Rho proteins rearrange the actin cytoskeleton to respond to chemo-attractant gradients, polarize cells, and control migration and invasion. While cell migration is necessary for development, leukocyte function, and other normal cell biologies, dysregulation of migration and invasion results in cancer metastasis (13). Metastasis is an important and deadly progression of cancer and understanding the biology of migrating cancer cells is crucial for therapeutic targeting of this aspect of cancer.Pharmacologic targeting of the enzymes involved in the CaaX-processing pathway has emerged as a promising anticancer strategy. In particular, there has been much effort in designing inhibitors against the protein prenyltransferases, most notably FTase (14, 15). There is also recent evidence that inhibition of geranygeranylation of Rho proteins also impacts oncogenesis and metastasis (16–18). However, the overall success of the FTase inhibitors (FTIs) in the clinical setting has been somewhat disappointing. One possible reason is a phenomenon termed “alternate prenylation” in which some FTase substrates, most notably K- and N- Ras, are modified by GGTase and escape inhibition by FTIs (19–21). Because the Rce1 protease and Icmt methyltransferase act on all CaaX proteins, problems such as alternate prenylation would not arise if these enzymes were targeted. Hence, while protein prenyltransferase inhibitors still show some promise as anticancer agents, the emerging view that global attenuation of CaaX protein function may be advantageous in blocking cancer cell growth has increased interest in studying the two downstream enzymes involved in CaaX processing.While the biological consequences of prenylation are fairly well understood, the precise roles of C-terminal methylation in CaaX protein function are still elusive. Depending on the CaaX protein, methylation has been ascribed to roles in localization, protein-protein interactions and protein stability (11). The development of an Icmt knock-out mouse model has furthered our understanding of Icmt function (22, 23). Localization studies conducted in cells with genetically deleted Icmt have shown that methylation is important for proper membrane association of Ras proteins. However, the localization of Rho proteins in the absence of Icmt activity appears to be more complicated and may vary depending on family member and activation status (24–26). Importantly, inhibition of CaaX protein methylation via either genetic or pharmacologic targeting has shown a clear impact on oncogenic transformation and tumor growth (23, 27, 28).Defining the role of Icmt-mediated methylation in complex cellular behaviors such as migration and invasion is crucial for furthering our understanding of the impact of CaaX protein methylation on the biology of normal and cancer cells. In the current study, we have assessed the impact of Icmt inhibition on cell biological processes associated with the function of Rho proteins, specifically cell adhesion, morphology, and migration. We found that inhibition of Icmt results in a disruption of the actin cytoskeleton and impairs ligand-mediated activation of RhoA and Rac1, a potential consequence of increased RhoGDI binding to both RhoA and Rac1 when their methylation is impaired. Further, we show that the impact of Icmt inhibition on cell migration is due at least in part to impairment of RhoA and Rac1function. These findings establish a role for Icmt-mediated methylation in cell migration and further elucidate the role that methylation plays in the function of Rho GTPases.     

Protein Tyrosine Phosphatase PTP1B Is Involved in Hippocampal Synapse Formation and Learning

ER-bound PTP1B is expressed in hippocampal neurons, and accumulates among neurite contacts. PTP1B dephosphorylates ß-catenin in N-cadherin complexes ensuring cell-cell adhesion. Here we show that endogenous PTP1B, as well as expressed GFP-PTP1B, are present in dendritic spines of hippocampal neurons in culture. GFP-PTP1B overexpression does not affect filopodial density or length. In contrast, impairment of PTP1B function or genetic PTP1B-deficiency leads to increased filopodia-like dendritic spines and a reduction in mushroom-like spines, while spine density is unaffected. These morphological alterations are accompanied by a disorganization of pre- and post-synapses, as judged by decreased clustering of synapsin-1 and PSD-95, and suggest a dynamic synaptic phenotype. Notably, levels of ß-catenin-Tyr-654 phosphorylation increased ∼5-fold in the hippocampus of adult PTP1B^−/− (KO) mice compared to wild type (WT) mice and this was accompanied by a reduction in the amount of ß-catenin associated with N-cadherin. To determine whether PTP1B-deficiency alters learning and memory, we generated mice lacking PTP1B in the hippocampus and cortex (PTP1B^fl/fl–Emx1-Cre). PTP1B^fl/fl–Emx1-Cre mice displayed improved performance in the Barnes maze (decreased time to find and enter target hole), utilized a more efficient strategy (cued), and had better recall compared to WT controls. Our results implicate PTP1B in structural plasticity within the hippocampus, likely through modulation of N-cadherin function by ensuring dephosphorylation of ß-catenin on Tyr-654. Disruption of hippocampal PTP1B function or expression leads to elongation of dendritic filopodia and improved learning and memory, demonstrating an exciting novel role for this phosphatase.     

How Could Language Have Evolved?

The evolution of the faculty of language largely remains an enigma. In this essay, we ask why. Language''s evolutionary analysis is complicated because it has no equivalent in any nonhuman species. There is also no consensus regarding the essential nature of the language “phenotype.” According to the “Strong Minimalist Thesis,” the key distinguishing feature of language (and what evolutionary theory must explain) is hierarchical syntactic structure. The faculty of language is likely to have emerged quite recently in evolutionary terms, some 70,000–100,000 years ago, and does not seem to have undergone modification since then, though individual languages do of course change over time, operating within this basic framework. The recent emergence of language and its stability are both consistent with the Strong Minimalist Thesis, which has at its core a single repeatable operation that takes exactly two syntactic elements a and b and assembles them to form the set {a, b}.It is uncontroversial that language has evolved, just like any other trait of living organisms. That is, once—not so long ago in evolutionary terms—there was no language at all, and now there is, at least in Homo sapiens. There is considerably less agreement as to how language evolved. There are a number of reasons for this lack of agreement. First, “language” is not always clearly defined, and this lack of clarity regarding the language phenotype leads to a corresponding lack of clarity regarding its evolutionary origins. Second, there is often confusion as to the nature of the evolutionary process and what it can tell us about the mechanisms of language. Here we argue that the basic principle that underlies language''s hierarchical syntactic structure is consistent with a relatively recent evolutionary emergence.