Probing Interactions between CLIP-170, EB1, and Microtubules

Cytoplasmic linker protein 170 (CLIP-170) is a microtubule (MT) plus-end tracking protein (+ TIP) that dynamically localizes to the MT plus end and regulates MT dynamics. The mechanisms of these activities remain unclear because the CLIP-170-MT interaction is poorly understood, and even less is known about how CLIP-170 and other + TIPs act together as a network. CLIP-170 binds to the acidic C-terminal tail of α-tubulin. However, the observation that CLIP-170 has two CAP-Gly (cytoskeleton-associated protein glycine-rich) motifs and multiple serine-rich regions suggests that a single CLIP-170 molecule has multiple tubulin binding sites, and that these sites might bind to multiple parts of the tubulin dimer. Using a combination of chemical cross-linking and mass spectrometry, we find that CLIP-170 binds to both α-tubulin and β-tubulin, and that binding is not limited to the acidic C-terminal tails. We provide evidence that these additional binding sites include the H12 helices of both α-tubulin and β-tubulin and are significant for CLIP-170 activity. Previous work has shown that CLIP-170 binds to end-binding protein 1 (EB1) via the EB1 C-terminus, which mimics the acidic C-terminal tail of tubulin. We find that CLIP-170 can utilize its multiple tubulin binding sites to bind to EB1 and MT simultaneously. These observations help to explain how CLIP-170 can nucleate MTs and alter MT dynamics, and they contribute to understanding the significance and properties of the + TIP network.     

Defining Elastic Fiber Interactions by Molecular Fishing: AN AFFINITY PURIFICATION AND MASS SPECTROMETRY APPROACH*

Deciphering interacting networks of the extracellular matrix is a major challenge. We describe an affinity purification and mass spectrometry strategy that has provided new insights into the molecular interactions of elastic fibers, essential extracellular assemblies that provide elastic recoil in dynamic tissues. Using cell culture models, we defined primary and secondary elastic fiber interaction networks by identifying molecular interactions with the elastic fiber molecules fibrillin-1, MAGP-1, fibulin-5, and lysyl oxidase. The sensitivity and validity of our method was confirmed by identification of known interactions with the bait proteins. Our study revealed novel extracellular protein interactions with elastic fiber molecules and delineated secondary interacting networks with fibronectin and heparan sulfate-associated molecules. This strategy is a novel approach to define the macromolecular interactions that sustain complex extracellular matrix assemblies and to gain insights into how they are integrated into their surrounding matrix.Mass spectrometry is emerging as a powerful approach to identify protein interaction partners in molecular complexes. We have developed an affinity purification and mass spectrometry strategy that is applicable to the analysis of molecular interactions of extracellular matrix complexes. The extracellular matrix provides structural support to tissues and profoundly influences cell survival, proliferation, migration, and phenotypic state. It is a complex multimolecular and three-dimensional milieu that comprises assembled networks of tissue-specific combinations of structural and cell-adhesive glycoproteins, proteoglycans, and cross-linking enzymes. The matrix also sequesters numerous growth factors and cytokines, thereby controlling their bioavailability. Delineating the molecular nature of the fundamental interacting networks within complex extracellular matrices is a challenging task. Here, mass spectrometry has given new insights into elastic fiber interactions.Elastic fibers are essential structural elements of the extracellular matrix of dynamic connective tissues such as blood vessels, lungs, skin, and ligaments, endowing these tissues with elastic recoil (1, 2). Their importance is emphasized by elastic fiber defects that cause severe acquired diseases such as aortic aneurysms and pulmonary emphysema and life-threatening heritable disorders such as Marfan syndrome, supravalvular stenosis, and cutis laxa. These fibers are extensive multimolecular assemblies that adopt intricate tissue-specific architectural arrangements. At the morphological level, the fibers comprise a cross-linked elastin core and an outer mantle of fibrillin microfibrils. It has proved challenging to define the composition of tissue elastic fibers biochemically. Cross-linked elastin is highly insoluble and its isolation from tissues requires extreme conditions of hot alkali, which destroys other proteins (2). The efficient extraction of tissue microfibrils requires collagenase and other proteolytic activities that may destroy associated molecules (3). Despite these difficulties, a number of associated proteins, including MAGP-1,1 βigH3, fibulins, and lysyl oxidases (LOX and LOXL (also known as LOXL1)), as well as latent TGFβ-binding proteins (LTBPs), collagen VIII, and emilin-1 have been identified in biochemical and/or colocalization studies (1).Fibrillins are very large glycoproteins (350 kDa) containing 43 calcium-binding epidermal growth factor-like domains and seven TGFβ-binding protein-like (8-cysteine) domains (4). Fibrillin-1 is the more abundant isoform; fibrillin-2 is mainly expressed during development (5, 6). Tropoelastin, the secreted soluble form of elastin, comprises alternating hydrophobic and lysine-rich cross-linking domains. LOX and LOXL are copper-dependent amine oxidases that cross-link elastin through the oxidative deamination of specific lysines (7–9). Elastin is mainly expressed and deposited early in life and undergoes very little turnover in healthy tissues (2). MAGP-1 is a microfibril-associated glycoprotein that binds fibrillin-1 and elastin (10, 11) but is not essential for elastic fiber formation (12). βigH3 was originally identified as a matrix protein, MP78/70, in tissue extracts that solubilized elastin-associated microfibrils (13, 14). Fibulin-4 and -5 play essential roles in elastic fiber formation (15, 16), most likely by regulating elastin deposition onto microfibrils (17, 18). Fibulin-2 interacts with fibrillin-1 (19) but is not essential for elastic fiber formation (20). Fibulin-1-null mice, among other symptoms, display anomalies of aortic arch arteries and hemorrhagic blood vessels, suggesting some involvement in elastic fiber biology (21). Fibulin-3 (also known as Efemp1)-deficient mice exhibit early aging and herniation associated with reduced elastic fiber integrity (22). Collagen VIII and emilin-1 also colocalize to elastic fibers (23, 24).The assembly of microfibrils and elastic fibers remains incompletely understood. We and others recently showed that assembly of the microfibril component is orchestrated by the cell surface through interactions with fibronectin and integrin receptors (25, 26). Heparan sulfate, an abundant pericellular glycosaminoglycan chain attached to syndecan and glypican proteoglycan receptors, also critically influences microfibril formation (27–29). Elastin deposition and stabilization on microfibrils require fibulins and the cross-linking enzymes LOX and/or LOXL.To obtain new insights into the molecular interactions of elastic fibers and how they are integrated into their surrounding matrix, we conducted a detailed affinity capture LC-MS/MS analysis of molecules that interact in culture specifically with four His₆-tagged recombinant human elastic fiber molecules (fibrillin-1, MAGP-1, fibulin-5, and LOX). Tropoelastin was not used as bait because of its highly adhesive nature. Our protocol proved to be an effective strategy for defining specific interactions of elastic fiber molecules in the extracellular matrix. Efficacy was demonstrated through confirmation of known interactions and validation of novel extracellular matrix protein-protein interactions. This approach further allowed us to predict secondary elastic fiber interactions, giving powerful insights into the molecular networks that sustain elastic fibers within higher order extracellular matrices.     

HISTORICAL EVIDENCE FOR POPULATION DYNAMICS OF TIBETAN MIGRATORY LOCUST AND THE FORECAST OF ITS OUTBREAK*

Abstract The Tibetan migratory locust (Locusta migratoria tibetensis Chen) is the highest altitude distributed subspecies among the 10 subspecies of migratory locusts. It was discovered and described as new subspecies in 1963. It is mostly distributed above an elevation of 3 000 m, with the highest up to 4 600 m, on the “Roof of the World,” viz. the Qinghai-Xizang Plateau in southwestern China. Recent study on the historic literature revealed ancient records of locust plagues caused by Locusta migratoria tibetensis Chen in many regions of Xizang (Tibet). These disasters took place during 124 years stretching from 1828 to 1952. Forty-five places were infested by locust swarms, and from 1846 to 1857 locust disasters occurred sucessively in 12 years, and affected 18 places of Xizang. At the severe disaster regions crops were damaged by locusts in such a degree that there was no harvest at all. At the same time, locust plagues due to another subspecies also occurred in the plains between the Yellow River and Huaihe and Haihe Rivers in East China. The disasters in Xizang were caused by the Tibetan migratory locust, while in Huang-Huai-Hai Plain disasters were due to the Oriental migratory locust Locusta migratoria manilensis (Meyen). This study not only provides the evidence that the Tibetan migratory locust has been existing as a separate subspecies with a long history, but also reveals the relevant years of locust plagues, their regional distribution and intermittent rules of locust plagues. It also offers a scientific basis for forecasting Tibetan migratory locust disasters and related monitoring strategies; as well as understanding the close relationship between the outbreak of the migratory locust and drought.     

THE EFFECT OF TEMPERATURE ON BODY SIZE AND FECUNDITY IN FEMALE DROSOPHILA MELANOGASTER: EVIDENCE FOR ADAPTIVE PLASTICITY

The reaction norm linking rearing temperature and size in Drosophila melanogaster results in progressively larger flies as the temperature is lowered from 30°C to 18°C, but it has remained unclear whether this phenotypic plasticity is part of an adaptive response to temperature. We found that female D. melanogaster reared to adulthood at 18°C versus 25°C showed a 12% increase in dry weight. Measurements of the fecundity of these two types of fly showed that the size change had no effect on lifetime fecundity, regardless of the adult test temperature. Thus the phenotypic plasticity breaks the usual positive correlation between body size and fecundity. However, at a given temperature, early fecundity (defined as productivity for days 5 through 12 after eclosion at 25°C and days 7 through 17 at 18°C) was highest when the rearing and test temperatures were the same. The early fecundity advantage due to rearing at the test temperature was 25% at 18°C and 16% at 25°C, a result consistent with the overall phenotypic response to temperature being adaptive. This conclusion is further supported by the finding that the temperature treatments resulted in a trade-off between early fecundity and longevity, a trade-off that parallels the known genetic correlation. Another parallel is that both the temperature-induced and genetic effects are independent of total fecundity. By contrast, within the temperature treatments, the phenotypic correlation between early fecundity and longevity was positive, illustrating the danger of assuming that phenotypic and genetic correlations are similar, or even of the same sign.     

Endoplasmic Reticulum-associated Degradation of Niemann-Pick C1: EVIDENCE FOR THE ROLE OF HEAT SHOCK PROTEINS AND IDENTIFICATION OF LYSINE RESIDUES THAT ACCEPT UBIQUITIN*

Most cases with Niemann-Pick disease type C carry mutations in NPC1. Some of the mutations, including the most frequent I1061T, give rise to unstable proteins selected for endoplasmic reticulum-associated degradation. The purpose of the current study was to shed mechanistic insights into the degradation process. A proteasome inhibitor MG132 prolonged the life span of the wild-type NPC1 expressed in COS cells. The expressed protein associated with multiple chaperones including heat shock protein 90 (Hsp90), Hsp70, heat shock cognate protein 70 (Hsc70), and calnexin. Accordingly, expression of an E3 ligase CHIP (carboxyl terminus of Hsp70-interacting protein) enhanced MG132-induced accumulation of ubiquitylated NPC1. Co-expression and RNAi knockdown experiments in HEK cells indicated that Hsp70/Hsp90 stabilized NPC1, whereas Hsc70 destabilized it. In human fibroblasts carrying the I1061T mutation, adenovirus-mediated expression of Hsp70 or treatment with an HSP-inducer geranylgeranylacetone (GGA) increased the level of the mutant protein. In GGA-treated cells, the rescued protein was localized in the late endosome and ameliorated cholesterol accumulation. MALDI-TOF mass spectrometry revealed three lysine residues at amino acids 318, 792, and 1180 as potential ubiquitin-conjugation sites. Substitutions of the three residues with alanine yielded a mutant protein with a steady-state level more than three times higher than that of the wild-type. Introduction of the same substitutions to the I1061T mutant resulted in an increase in its protein level and functional restoration. These findings indicated the role of HSPs in quality control of NPC1 and revealed the role of three lysine residues as ubiquitin-conjugation sites.     

EFFECT OF FEEDING STIMULANT ON THE FEEDING BEHAVIOR AND MORTALITY OF HELICOVERPA ARMIGERA ON DIETS WITH BACILLUS THURINGIENSIS*

Abstract Bacillus thuringiensis (Bt) was noticed to be highly deterrent to the feeding of Helicoverpa armigera larva when incorporated into diets, even at the non‐lethal dosage. As the dosage of Bt increased, the deterrence showed a tendency of elevation. Feeding stimulant, FS‐1 could attract larvae for feeding, and increase larval feeding time and consumption. Addition of 1% (vlv) FS1 could alleviate the deterrent effect of Bt, especialy in low concentration. In no‐choice test, it was observed that while 1% (v/v) FS1 was added, LC₅₀, of Bt underwent a 41% decrease, but in the choice test, the mortality of larvae was not significantly enhanced.     

Functional Interactions between Cytochromes P450 1A2 and 2B4 Require Both Enzymes to Reside in the Same Phospholipid Vesicle: EVIDENCE FOR PHYSICAL COMPLEX FORMATION*

Previous studies have shown that the combined presence of two cytochrome P450 enzymes (P450s) can affect the function of both enzymes, results that are consistent with the formation of heteromeric P450·P450 complexes. The goal of this study was to provide direct evidence for a physical interaction between P450 1A2 (CYP1A2) and P450 2B4 (CYP2B4), by determining if the interactions required both enzymes to reside in the same lipid vesicles. When NADPH-cytochrome P450 reductase (CPR) and a single P450 were incorporated into separate vesicles, extremely slow reduction rates were observed, demonstrating that the enzymes were anchored in the vesicles. Next, several reconstituted systems were prepared: 1) CPR·CYP1A2, 2) CPR·CYP2B4, 3) a mixture of CPR·CYP1A2 vesicles with CPR·CYP2B4 vesicles, and 4) CPR·CYP1A2·CYP2B4 in the same vesicles (ternary system). When in the ternary system, CYP2B4-mediated metabolism was significantly inhibited, and CYP1A2 activities were stimulated by the presence of the alternate P450. In contrast, P450s in separate vesicles were unable to interact. These data demonstrate that P450s must be in the same vesicles to alter metabolism. Additional evidence for a physical interaction among CPR, CYP1A2, and CYP2B4 was provided by cross-linking with bis(sulfosuccinimidyl) suberate. The results showed that after cross-linking, antibody to CYP1A2 was able to co-immunoprecipitate CYP2B4 but only when both proteins were in the same phospholipid vesicles. These results clearly demonstrate that the alterations in P450 function require both P450s to be present in the same vesicles and support a mechanism whereby P450s form a physical complex in the membrane.     

PIGMENT AND CYTOLOGICAL EVIDENCE FOR RECLASSIFICATION OF NANNOCHLORIS OCULATA AND MONALIANTUS SALINA IN THE EUSTIGMATOPHYCEAE1

Nannochloris oculata Droop and Monallantus salina Bourrelly produce similar chloroplast pigments and show alike ultrastructural features separating them from the Chlorophyceae and Xanthophyceae, respectively, and linking them to the Eustigmatophyceae. It is proposed that N. oculata should be removed from the chlorophyceaen genus Nannochloris and transferred to a new taxon of coccoid eustigmatophytes containing the closely related M. salina: nomenclatural revisions are required for both strains.     

The TRPM8 Protein Is a Testosterone Receptor: II. FUNCTIONAL EVIDENCE FOR AN IONOTROPIC EFFECT OF TESTOSTERONE ON TRPM8*

Testosterone is a key steroid hormone in the development of male reproductive tissues and the regulation of the central nervous system. The rapid signaling mechanism induced by testosterone affects numerous behavioral traits, including sexual drive, aggressiveness, and fear conditioning. However, the currently identified testosterone receptor(s) is not believed to underlie the fast signaling, suggesting an orphan pathway. Here we report that an ion channel from the transient receptor potential family, TRPM8, commonly known as the cold and menthol receptor is the major component of testosterone-induced rapid actions. Using cultured and primary cell lines along with the purified TRPM8 protein, we demonstrate that testosterone directly activates TRPM8 channel at low picomolar range. Specifically, testosterone induced TRPM8 responses in primary human prostate cells, PC3 prostate cancer cells, dorsal root ganglion neurons, and hippocampal neurons. Picomolar concentrations of testosterone resulted in full openings of the purified TRPM8 channel in planar lipid bilayers. Furthermore, acute applications of testosterone on human skin elicited a cooling sensation. Our data conclusively demonstrate that testosterone is an endogenous and highly potent agonist of TRPM8, suggesting a role of TRPM8 channels well beyond their well established function in somatosensory neurons. This discovery may further imply TRPM8 channel function in testosterone-dependent behavioral traits.     

CHEMICAL COMPOSITION AND PHOTOSYNTHETIC CHARACTERISTICS OF ETHMODISCUS REX (BACILLARIOPHYCEAE): EVIDENCE FOR VERTICAL MIGRATION1

Ethmodiscus rex (Rattray) Wiseman and Hendey cells from near surface net tows in the Southwest Atlantic Ocean and Caribbean Sea were examined for chemical composition, internal nutrient pool concentrations, and oxygen evolution characteristics. Elemental ratios indicated nitrogen limitation with C:N:P ratios of 125:9:1 (atoms), and carbon: chlorophyll (chl) ratios of 129:1 (weight). However, internal nitrate pools (1.4–27.1 mM) suggested that cells were not N-limited. Intracellular NO₃^? accounted for up to 54% (range = 3–54%) of the total N quota in some samples. Photosynthetic parameters were consistent with a high-light-adapted population and suggested an instantaneous maximum chl-specific photosynthetic rate (P^B_max) of 4.8–12.4 nmol O₂·μg chl^?1· h^?1. Respiration rates varied ten-fold and were inversely related to P^B_max Ethmodiscus chemical composition and buoyancy characteristics are similar to vertically migrating Rhizosolenia mats and the non-motile dinoflagellate Pyrocystis noctiluca Murray (Schuett). The presence of internal NO₃^? pools in Ethmodiscus suggests that this genus is also vertically migrating to exploit sub-surface nitrogen pools. Such behavior may be widespread in large, non-motile oceanic phytoplankton. Based on ascent rate data, chemical composition, and photosynthetic rates, we estimate that the entire division–migration cycle for Ethmodiscus requires at least 7–12 days.     

动物单种群动态的ALLEE效应的数学模型及其解的性态

本文根据单种群动态ALLEE效应的特点,引入一个适当的数学模型,并对其解的振动性、有界性和渐近稳定性进行了研究。     

THE ZYGOSPORE WALL OF CHLAMYDOMONAS MONOICA (CHLOROPHYCEAE): MORPHOGENESIS AND EVIDENCE FOR THE PRESENCE OF SPOROPOLLENIN1

Chlamydomonas monoica Strehlow is being developed as a model for genetic analysis of zygospore morphogenesis, and many relevant mutant strains are available. To provide the basis for interpreting the ultrastructural phenotypes of zygospore mutants, an analysis of wall morphogenesis in wildtype zygospores of C. monoica was undertaken. Following synthesis of a thick, fibrous, primary zygote wall, granular material accumulated between the plasma membrane and the primary zygote wall and aggregated into a repetitive array of electron-opaque fibrous stripes. A new wall layer, the outer layer of the secondary zygospore wall, first appeared as segments with a fibrous outer surface overlying a well-defined band of electron-translucent material. These segments gave rise to an intact sheath adjacent to the plasma membrane. Beneath this sheath, electron-opaque material (forming the inner layer of the secondary zygospore wall) accumulated unevenly and forced the surface sheath to undulate, creating a pattern of peaks and valleys that was exposed to the external environment 4 rupture and release of the primary zygote wall. The zygospore wall included material resistant to degradation by potassium hydroxide, 2-aminoethanol, and acetolysis, but it was destroyed by exposure to chromic acid. These characteristics, in combination with the autofluorescence of untreated zygospore walls and their failure to stain with phloroglucinol, suggest that sporopollenin may be responsible for many of the resistant properties associated with the mature zygospore of Chlamydomonas.     

Nonsynonymous Mutations within APOB in Human Familial Hypobetalipoproteinemia: EVIDENCE FOR FEEDBACK INHIBITION OF LIPOGENESIS AND POSTENDOPLASMIC RETICULUM DEGRADATION OF APOLIPOPROTEIN B*

Five nontruncating missense APOB mutations, namely A31P, G275S, L324M, G912D, and G945S, were identified in heterozygous carriers of familial hypobetalipoproteinemia (FHBL) in the Italian population. To test that the FHBL phenotype was a result of impaired hepatic secretion of mutant apoB proteins, we performed transfection studies using McA-RH7777 cells stably expressing wild type or mutant forms of human apolipoprotein B-48 (apoB-48). All mutant proteins displayed varied impairment in secretion, with G912D the least affected and A31P barely secreted. Although some A31P was degraded by proteasomes, a significant proportion of it (although inappropriately glycosylated) escaped endoplasmic reticulum (ER) quality control and presented in the Golgi compartment. Degradation of the post-ER A31P was achieved by autophagy. Expression of A31P also decreased secretion of endogenous apoB and triglycerides, yet the impaired lipoprotein secretion did not lead to lipid accumulation in the cells or ER stress. Rather, expression of genes involved in lipogenesis was down-regulated, including liver X receptor α, sterol regulator element-binding protein 1c, fatty acid synthase, acetyl-CoA carboxylase 1, stearoyl-CoA desaturase 1, and lipin-1. These results suggest that feedback inhibition of hepatic lipogenesis in conjunction with post-ER degradation of misfolded apoB proteins can contribute to reduce fat accumulation in the FHBL liver.     

FLEXURAL STIFFNESS ALLOMETRIES OF ANGIOSPERM AND FERN PETIOLES AND RACHISES: EVIDENCE FOR BIOMECHANICAL CONVERGENCE

Evidence for convergence in biomechanical and anatomical features of leaves (elastic modulus E, second moment of area I, taper of petioles, the longitudinal distribution of petiolar and laminar weight, and volumes of tissues) is presented based on a survey of 22 species (distributed among dicots, monocots, and ferns). In general, regardless of taxonomic affinity, petioles were found to be mechanically constructed in one of two ways: Type I petioles—as cantilevered, end-loaded beams with relatively uniform flexural stiffness (EI) (simple and palmate leaves); and Type II petioles—as tapered cantilevered beams whose static loadings (biomass) and EI increase basipetally (pinnate leaves). In general, collenchyma and sclerenchyma were found to be peripherally located in transections through Type I and II petioles, respectively. Statistical analyses within each species and among species with either type of petiole indicated that EI ≈ k₁Lp^2.98 and EI ≈ k₂Lp^2.05 for Type I and II petioles, respectively, where k₁ and k₂ are dimensional constants and Lp is petiolar length. The data are interpreted to indicate that Type I and II petioles mechanically operate to deal with static loadings in two distinct ways, such that Type II petioles function in an analogous manner to branches supporting separate leaves (leaflets). The convergence in mechanical “designs” among taxonomically distinct lineages (angiosperms and ferns) is interpreted as evidence for selection on mechanical attributes of load supporting structures (petioles).     

VARIATION IN SEED CHARACTERS IN NEMOPHILA MENZIESII: EVIDENCE OF A GENETIC BASIS FOR MATERNAL EFFECT

A growing body of evidence indicates that phenotypic selection on juvenile traits of both plants and animals may be considerable. Because juvenile traits are typically subject to maternal effects and often have low heritabilities, adaptive responses to natural selection on these traits may seem unlikely. To determine the potential for evolutionary response to selection on juvenile traits of Nemophila menziesii (Hydrophyllaceae), we conducted two quantitative genetic studies. A reciprocal factorial cross, involving 16 parents and 1960 progeny, demonstrated a significant maternal component of variance in seed mass and additive genetic component of variance in germination time. This experiment also suggested that interaction between parents, though small, provides highly significant contributions to the variance of both traits. Such a parental interaction could arise by diverse mechanisms, including dependence of nuclear gene expression on cytoplasmic genotype, but the design of this experiment could not distinguish this from other possible causes, such as effects on progeny phenotype of interaction between the environmental conditions of both parents. The second experiment, spanning three generations with over 11,000 observations, was designed for investigation of the additive genetic variance in maternal effect, assessment of paternal effects, as well as further partitioning of the parental interaction identified in the reciprocal factorial experiment. It yielded no consistent evidence of paternal effects on seed mass, nor of parental interactions. Our inference of such interaction effects from the first experiment was evidently an artifact of failing to account for the substantial variance among fruits within crosses. The maternal effect was found to have a large additive genetic component, accounting for at least 20% of the variation in individual seed mass. This result suggests that there is appreciable potential for response to selection on seed mass through evolution of the maternal effect. We discuss aspects that may nevertheless limit response to individual selection on seed mass, including trade-offs between the size of individual seeds and germination time and between the number of seeds a maternal plant can mature and their mean size.     

PHENOTYPIC PLASTICITY AND EPIGENETIC MARKING: AN ASSESSMENT OF EVIDENCE FOR GENETIC ACCOMMODATION

The relationship between genotype (which is inherited) and phenotype (the target of selection) is mediated by environmental inputs on gene expression, trait development, and phenotypic integration. Phenotypic plasticity or epigenetic modification might influence evolution in two general ways: (1) by stimulating evolutionary responses to environmental change via population persistence or by revealing cryptic genetic variation to selection, and (2) through the process of genetic accommodation, whereby natural selection acts to improve the form, regulation, and phenotypic integration of novel phenotypic variants. We provide an overview of models and mechanisms for how such evolutionary influences may be manifested both for plasticity and epigenetic marking. We point to promising avenues of research, identifying systems that can best be used to address the role of plasticity in evolution, as well as the need to apply our expanding knowledge of genetic and epigenetic mechanisms to our understanding of how genetic accommodation occurs in nature. Our review of a wide variety of studies finds widespread evidence for evolution by genetic accommodation.     

THE EFFECT OF INTESTINAL RESECTION ON THIRY-VELLA FISTULAE OF JEJUNAL AND ILEAL ORIGIN IN THE RAT: EVIDENCE FOR A SYSTEMIC CONTROL MECHANISM OF CELL RENEWAL

Local and systemic control mechanisms have been postulated to explain the maintenance of steady state cell renewal in intestinal epithelium. Permanent alterations of cell renewal resulting in a new steady state imply alterations in control. Intestinal resection appears to cause such alterations resulting in hyper-plasia of the residual intestine. To test the hypothesis of a systemic control, the effect of 60% mid-intestinal resection on Thiry-Vella fistulae of both jejunal and ileal origin was observed in rats. Results showed that hypoplasia occurred in fistulae without resection of the remaining intestine in continuity. Cell counts of crypt and villus columns and tritiated thymidine uptake in isolated whole crypts were reduced. Scanning electron microscopy showed marked hypoplastic alterations in villi. However, when 60% of the intestine in continuity was resected, hyperplasia occurred not only in the residual intestine but in the fistulae of both jejunal and ileal origin. Cell counts of villus and crypt columns were increased along with increased tritiated thymidine uptake per crypt. Neutral cc-glucosidase and non-specific esterase activities did not change as a result of resection but the activities of both enzymes were greater in ileal fistulae than in ileum in situ. Observations on the different resection response of the jejunal versus ileal fistulae lead to a distinction between inherent and induced differences within the small intestine. This study suggests a systemic control of cell renewal. A possible mechanism involving intestinal vascular physiology is discussed.     

VA MYCORRHIZAE IN STRAND VEGETATION OF HAWAII: EVIDENCE FOR LONG-DISTANCE CODISPERSAL OF PLANTS AND FUNGI

Vesicular-arbuscular mycorrhizal fungi (VAMF) were a nearly constant component of the coastal strand of the Hawaiian Islands, occurring in beach sand, driftline debris, in roots of 23 of 31 species of vascular plants examined, and in association with rhizomes of two native species, Sporobolus virginicus and Jacquemontia sandwicensis. Mycorrhizae were most frequent and intensity of VAM development was greatest in endemic plants, less in indigenous species, and least in alien species. Spores of VAMF were produced in abundance between the rhizome and the leaf sheaths of Sporobolus. Roots of two strand species, including roots of Sporobolus that were immersed in seawater for 7 days, functioned as inocula of VAMF in pot-culture studies. The close association between propagules of VAMF and vegetative fragments of indigenous plants found in the present study suggests a mechanism of codispersal that appears to ensure the maintenance of the symbiosis in nutrient-deficient sites where it is most beneficial. The codispersal of fungus and plant may explain the high frequency of mycotrophy in strand species in the tropical Pacific.     

VEGETATIVE GROWTH OF ACETABULARIA ACETABULUM (CHLOROPHYTA): STRUCTURAL EVIDENCE FOR JUVENILE AND ADULT PHASES IN DEVELOPMENT1

We characterized vegetative development in two inbred cell lines of Acetabularia acetabulum (L.) Silva. Cell growth occurred at the apex and by elongation of older interwhorls throughout vegetative development. Although cell length and hairs per whorl increased regularly during development, interwhorl length, hair persistence on the stalk, and complexity of each whorl (degree of branching of whorl hairs) showed sharp discontinuities during development in both cell lines. The first (earliest) discontinuity, formation of a short interwhorl, was the sixth interwhorl made in all cells. Even though cell line Aa1055 was twice the height ofAa4010 when mature, cells in both lines were 0.8–1.0 cm tall after formation of the short interwhorl. The second discontinuity, increases in hair persistence on the stalk and complexity of each whorl of hairs, began shortly before cap initiation. We propose the following nomenclature: 1) that slower growth before formation of the short interwhorl be called “juvenile”; 2) that more rapid growth after formation of the short interwhorl be called “adult”; and 3) that adult growth be separated into “early” and “late” phases by the discontinuities in whorl hair characteristics. The proposed developmental phases (juvenile, early adult, and late adult) are temporally sequential and spatially stacked.