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PubMed2002

Theoretical clues to the mechanism of dioxygen formation at the oxygen-evolving complex of photosystem II.

The mechanism of the generation of dioxygen at the oxygen-evolving complex (OEC) of photosystem II (PSII), a crucial step in photosynthesis, is still under debate. The simplest unit present in the OEC that can produce O2 is a dinuclear oxo-bridge manganese complex within the tetranuclear Mn4 cluster. In this paper we report a theoretical study of the model complexes [Mn2(mu-O)2(NH3)6(H2O)2]n+ (n = 2-5), for which density functional calculations have been carried out for several electronic configurations. The molecular orbital picture deduced from the calculations indicates that one-electron oxidation of the Mn2IV,IV/(O2-)2 complex (n = 4) mostly affects the oxygen atoms, thus ruling out the existence of a MnV oxidation state in this context, while the incipient formation of an O-O bond in the O2(3-) transient species evolves exothermally toward the dissociation of dioxygen and a Mn2II,III couple. These results identify the electronic features that could be needed to enable an intramolecular mechanism of oxygen-oxygen bond formation to exist at the OEC during photosynthesis.

Electron Transport↗
PubMedDate not supplied

Child abuse and the balance of power in parental relationships: an evolved domain-independent mental mechanism that accounts for behavioral variation.

Previous studies use zero-order analyses to show a link between child abuse and exposure to "stepfathers." These studies rest on a proposed evolved, domain-specific cognitive mechanism that induces adult males to abuse or kill offspring not their own and, so, contribute directly to reproductive success. However, child abuse may reflect an evolved neurological mechanism that creates behavioral plasticity and adaptability by assigning emotional weights (which in consciousness appear rationalized as costs and benefits) to choice alternatives in all behavioral domains. This mechanism should act as a selective mechanism to create enhanced ability to avoid predation (social exploitation) and to obtain access to resources, given the properties of specific ecosystems, and should control behavioral responses to variation in the balance of power in social relationships. Power equalities should elicit good treatment for both parties; power inequalities, by contrast, should elicit exploitative and coercive behavior on the part of those who hold the balance of power. This paper reports a test of both hypotheses simultaneously, controlling for a standard social science risk factor (growing up in poverty). Once we control for the balance of power in parental relationships, exposure to a stepfather and growing up in poverty show no effect on the intensity of child abuse. Powerful women negotiated affectionate behavior from their partners for both themselves and their children; powerless women's negotiations with partners usually left both themselves and their children open to violence.

Adult↗
PubMed1994

Rapidly evolving myopathy with myosin-deficient muscle fibers.

Five patients with rapidly evolving, severe weakness had an unusual myopathy with virtually complete loss of myosin in 5 to 40% of muscle fibers. Three of the 5 patients began to develop weakness 1 to 2 weeks after lung transplantation. The fourth became weak after a febrile illness. The fifth presented with diabetic ketoacidosis and weakness. All patients had received corticosteroid therapy. In all cases the weakness was progressive and led to severe disability, with respiratory failure in 4 patients. Initial diagnostic testing did not localize an underlying cause for the weakness. Creatine kinase was normal or minimally elevated. Electromyography generally showed mildly myopathic or nondiagnostic changes. However, muscle biopsy revealed numerous small angular fibers with no myosin ATPase staining at any pH. Immunocytochemical staining and ultrastructural studies confirmed a severe loss of myosin in many fibers. This rapidly evolving myopathy with myosin-deficient muscle fibers appears to be different clinically and pathologically from previously described syndromes involving rapidly progressive weakness. Slow recovery over a period of months is the most common outcome.

Adult↗
PubMed2002

Increase in expression of receptor activator of nuclear factor kappaB at sites of bone erosion correlates with progression of inflammation in evolving collagen-induced arthritis.

OBJECTIVE: The receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL) pathway is critical in osteoclastogenesis and bone resorption and has been implicated in the process of focal bone erosion in arthritis. This study was undertaken to identify in vivo the hitherto-unknown origin and localization of RANK-expressing osteoclast precursor cells at sites of bone erosion in arthritis. METHODS: DBA-1 mice were immunized with bovine type II collagen/Freund's complete adjuvant and were given an intraperitoneal booster injection of type II collagen on day 21. Arthritis was monitored visually, and joint pathology was examined histologically. RANK and RANKL expression were analyzed using specific immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining was performed. In addition, TRAP and cathepsin K messenger RNA expression were analyzed by in situ hybridization. RESULTS: A marked increase in the number of cells expressing RANK correlated with the progression of synovial inflammation and clinical disease severity in evolving collagen-induced arthritis (CIA). Interestingly, RANK expression demonstrated a gradient pattern with increased numbers of RANK-positive cells within the synovial infiltrate in areas closer to periosteum and cortical bone. Cells expressing RANK included cells in synovial tissue, bone lining cells on the surface of trabecular bone at sites of erosion, and cells in periosteal areas adjacent to synovial inflammation. In areas where RANK-positive cells were abundant, TRAP-positive, multinucleated osteoclast-like cells were also present at sites of focal bone erosion, suggesting differentiation of synovially derived RANK-positive osteoclast precursor cells into osteoclasts. In addition, TRAP- and cathepsin K-double-positive osteoclast-like cells were detected on the synovial side of cortical bone at sites of early and advanced cortical bone erosion. Sites of RANK expression also correlated well with sites of RANKL expression, and there was a close correlation of the temporal expression of the receptor-ligand pair. CONCLUSION: Cells expressing RANK increased in abundance with the progression of arthritis in evolving CIA, and sites of RANK-expressing cells correlated with sites of TRAP-positive, multinucleated osteoclast-like cells as well as with sites of RANKL expression. These data support the hypothesis that the RANK/RANKL pathway plays an important role in the process of bone erosion in CIA.

Animals↗
PubMed2004

Hepatitis C infection and injection drug use: the role of hepatologists in evolving treatment efforts.

Treatment regimens for both substance abuse and hepatitis C infection are complex and evolving. New pharmacotherapy for opioid addiction allows for office-based treatment and, thus, an opportunity for expanded treatment in the context of hepatitis C infection. The current article addresses the newly evolving, complex issues in the medical management of hepatitis C and injection drug use.

Hepatitis C↗
PubMed1994

An infectious viroid RNA replicon evolved from an in vitro-generated non-infectious viroid deletion mutant via a complementary deletion in vivo.

The 359 nucleotides (nt) long potato spindle tuber prototype viroid (PSTVd) is sensitive to experimentally introduced mutations as the substitution or deletion of a single nucleotide usually abolishes its infectivity, although certain sequence alterations are tolerated. This is illustrated by the fact that viroid progeny can evolve in planta upon inoculation with substitution mutants generated in vitro, and by the existence of genetically stable 356-360 nt long PSTVd field isolates. However, to date, no viable in vitro-generated deletion mutant of PSTVd has been reported. We have now found a 341 nt long infectious PSTVd RNA replicon that evolved in agrotransformed plants transformed with the dimeric form of an in vitro-deleted, non-infectious 350 bp long PSTVd cDNA unit by an additional complementary deletion of 9 nt in vivo. This is the first report that the deletion-abolished infectivity of a viroid is restored by an additional deletion that concurrently restabilized its perturbed secondary structure by abandoning an internal segment of the rod-like molecule. The fact that approximately 5% of the total PSTVd RNA genome was deleted demonstrates that the maintenance of this viroid-specific rod-like structure is not only essential for nuclease protection but also for the infectivity, i.e. transmissibility, replicability, processibility and pathogenicity of these minimal infectious agents.

Base Sequence↗
PubMed2025

Recently Evolved, Stage-Specific Genes Are Enriched at Life-Stage Transitions in Flies.

Understanding how genomic information is selectively utilized across different life stages is essential for deciphering the developmental and evolutionary strategies of metazoans. In holometabolous insects, the dynamic expression of genes enables distinct functional adaptations at embryonic, larval, pupal, and adult stages, likely contributing to their evolutionary success. While Drosophila melanogaster (D. melanogaster) has been extensively studied, less is known about the evolutionary dynamics that could govern stage-specific gene expression. To address this question, we compared the distribution of stage-specific genes, that is, genes expressed in temporally restricted developmental stages, across the development of D. melanogaster and Aedes aegypti (A. aegypti). Using tau-scoring, a computational method to determine gene expression specificity, we found that, on average, a large proportion of genes (20%-30% of all protein-coding genes) in both species exhibit restricted expression to specific developmental stages. Phylostratigraphy analysis, a method to date the age of genes, further revealed that stage-specific genes fall into two major categories: highly conserved and recently evolved. Notably, many of the recently evolved and stage-specific genes identified in A. aegypti and D. melanogaster are restricted to Diptera order (20%-35% of all stage-specific genes), highlighting ongoing evolutionary processes that continue to shape life-stage transitions. Overall, our findings underscore the complex interplay between gene evolutionary age, expression specificity, and morphological transformations in development. These results suggest that the attraction of genes to critical life-stage transitions is an ongoing process that may not be constant across evolutionary time or uniform between different lineages, offering new insights into the adaptability and diversification of dipteran genomes.

Animals↗
PubMed1999

Gregarious development in alysiine parasitoids evolved through a reduction in larval aggression.

Population genetic models have suggested that siblicide between the larvae of parasitoid wasps, once gained, can be lost only under stringent conditions, making transitions from solitary to gregarious development rare. However, phylogenetic studies suggest that gregarious development has evolved on numerous occasions, although the mechanisms are largely unknown. We report experiments, on two morphologically similar species of alysiine braconids, directed at an understanding of how gregarious development evolved in one subfamily. We compared the oviposition behaviour and development of Aphaereta genevensis and A. pallipes in the laboratory, on the host Drosophila virilis. Aphaereta genevensis usually lays a single egg in each host, and only a single wasp usually develops successfully even when several eggs are laid. However, A. pallipes often lays more than one egg in each host, and several offspring often complete development. Dissections of superparasitized hosts showed that this difference is accompanied by differences in larval behaviour: first-instar A. genevensis use their sharp mandibles to kill other parasitoid eggs or larvae in the same host. First-instar A. pallipes also have sharp mandibles, but do not attack conspecific larvae, suggesting that siblicide might have been lost by a simple change in larval behaviour. Aphaereta genevensis shows some features that may have helped select for reduction in larval aggression in the subfamily: a longer development time, multiple egg clutches and incomplete brood reduction. Aphaereta spp. show great promise as model systems for studying the evolution of siblicide. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Nest desertion and cowbird parasitism: evidence for evolved responses and evolutionary lag.

Nest desertion with subsequent renesting is a frequently cited response to parasitism by the brown-headed cowbird, Molothrus ater, yet the role of desertion as an antiparasite defence is widely debated. To determine whether desertion represents an evolutionary response to brown-headed cowbird parasitism, we searched the primary literature, yielding data on the desertion frequencies of 60 host populations from 35 species. Species were categorized according to three habitat types (forest, intermediate and nonforest). Because cowbirds prefer open habitat and rarely penetrate deeply into forests, nonforest species have long been exposed to widespread cowbird parasitism, whereas forest species have not. However, due to increased forest fragmentation, forest species are being increasingly exposed to extensive parasitism. The frequency of desertion of parasitized nests was significantly higher in nonforest than forest species, suggesting that the latter experience evolutionary lag. We also considered whether desertion is affected by predation frequency, degree of current or recent sympatry with cowbirds, parasitism frequency, length of host laying season, phylogenetic relationships, and potential cost of cowbird parasitism. None of these variables created biases that could account for the observed difference in desertion frequencies of nonforest and forest species. However, species that incur large costs when parasitized had higher desertion rates among nonforest species but not among forest species. These results indicate that increased nest desertion is an evolved response to cowbird parasitism, as one would otherwise expect no relationship between desertion frequency and thezx costs and length of exposure to cowbird parasitism. Although nearly all hosts have eggs easily distinguished from cowbird eggs, few or none desert in response to cowbird eggs. Instead, desertion may be a response to adult cowbirds. The scarcity of species that desert in response to cowbird eggs suggests that egg recognition is more difficult to evolve than heightened desertion tendencies and that egg recognition quickly leads to ejection behaviour once it does develop. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1993

The expression of the transthyretin gene in liver evolved during the radiation of diprotodont marsupials in Australia.

Thyroid hormone-binding proteins in blood plasma were identified in 28 different marsupial species by their capacity to bind radioactive thyroxine. All species contained albumin. Transthyretin was not found in the blood from any of 12 polyprotodont marsupial species, but was abundant in the blood from all of 16 diprotodont marsupial species investigated. Transthyretin mRNA was absent from the liver of the stripe-faced dunnart, a polyprotodont marsupial, but abundant in the liver of the diprotodont grey kangaroo. Diprotodont marsupials probably evolved in Australia from polyprotodont marsupials after their transantarctic migration from South America, about 40 million years ago. It is suggested that hepatic transthyretin expression evolved in marsupials during the radiation of herbivorous, diprotodont species in Australia. The earlier appearance of transthyretin gene expression in the choroid plexus of the stem reptiles, about 300 million years ago, contrasts with hepatic transthyretin synthesis, a relatively late evolutionary event, occurring independently in at least three lineages.

Animals↗
PubMed2002

Sequence analysis of the ly49 cluster in C57BL/6 mice: a rapidly evolving multigene family in the immune system.

The cytotoxic activity of murine natural killer cells is controlled in part through the action of genes belonging to the Ly49 family. Members of this multigene family are found in a region on mouse chromosome 6 termed the natural killer gene complex. Using data available through public databases, we performed sequence analysis of a 620-kb region in C57Bl/6 (B6) mice that contains the Ly49 genes. The contiguous genomic sequence has allowed us to describe the complete B6 Ly49 gene repertoire, which includes two recently described genes as well as three partial genes. We have shown that the genes in the cluster have evolved through a series of large duplication events involving units of one or more genes and we have attempted to characterize the nature of the duplication end points. Finally, we have used information regarding gene sequence relationships and insertion of repetitive elements to construct a model for the evolution of the gene cluster. Our study illustrates that the Ly49 cluster represents an example of a rapidly evolving gene family, and continued analysis of this region in other strains will undoubtedly provide further insight into mechanisms for generating genomic diversity.

Animals↗
PubMed1999

Did knuckle walking evolve twice?

Although African great apes share a similar quadrupedal locomotor behaviour, there are marked differences in hand morphology and size between the species. Hence, whilst all three species (two genera) of African ape frequently knuckle walk as adults, debate remains as to whether this behaviour is derived from a common ancestor or whether it evolved in parallel in chimpanzees and gorillas. This exploratory morphometric study of the sub-adult and adult wrist of these two genera aims to contribute to this debate. A total of twenty-seven dimensions of the lunate, triquetral, hamate and capitate of sub-adult and adult Pan troglodytes and Gorilla gorilla were analysed in order to determine whether carpal dimensions are generally ontogenetically scaled, and whether differences in growth trajectories, or length of growth, and adult morphologies can be explained by behavioural differences between the two species. Only 56% of all dimensions studied were ontogenetically scaled in sub-adults and some of these dimensions exhibit differing adult proportions between the two species. In general, the dimensions analysed fell into two categories: Pan and Gorilla either follow the same growth trajectories (Pattern A) or the Pan reduced major axis (RMA) regressions were significantly transposed above those of Gorilla (Pattern B). Additionally, it was found that Gorilla carpals appear to cease growing relatively earlier than those of Pan. While a small number of differences, notably those of the lunate, can be accounted for by differences in behaviour between the species, the majority of differences indicate heterochronic modifications of development during evolution, which correspond to kinematic differences in knuckle walking between the African great apes. In light of morphological, behavioural and ecological data currently available it is parsimonious to suggest that knuckle walking has evolved in parallel in the two lineages.

Animals↗
PubMed1998

Solving the complementarity dilemma: evolving strategies for simultaneous hermaphroditism.

We introduce a complementarity dilemma, a two-player, binary response game in which the playoffs are highest when the two players respond differently. Using the classifier EvA, we determine the evolutionary dynamics and structure of strategies that evolve to play an iterated version of this game, and we relate the results to the evolution of major types of sexual reproduction, particularly simultaneous hermaphroditism. We find that complementarity strategies consistently evolve under a broad range of conditions, but that those most consistent with the simultaneous hermaphroditism can predominate only when a substantial cost of repeatedly adopting the female role is imposed. The cost is analogous to the fecundity reduction to be expected when a single partner must repeatedly produce the eggs in sexual reproduction.

Animals↗
PubMed2000

Evolving populations with overlapping generations.

In this paper, we extend a previously published model of an evolving finite population of multi-locus organisms, where the dynamics of the evolving system are described by the cumulants of the population efficacy distribution. We consider the case of overlapping generations and compare it to the previously studied case where generations are discrete. In the weak selection limit, we can solve the dynamics analytically and show that the changes in population genetic variance due to stochastic effects-genetic drift-is twice as great when generations overlap. The comparison of the dynamics of the two models shows many of the features seen in the comparison, performed by Moran, of simple one-locus genetic models with overlapping and non-overlapping generations. Studying the dynamics of the two models gives some insights into these comparisons.

Animals↗
PubMed1987

Why should senescence evolve? An answer based on a simple demographic model.

The demographic model of senescence described here provides an answer to the question, "Why should senescence evolve?" Most generally stated, the answer is that senescence should be expected to evolve if its negative effect on the rate of natural increase of a nonsenescent population is sufficiently offset by the early appearance of an advantageous characteristic. This is a nonadaptive point of view in the sense discussed by Kirkwood (1985) and by Kirkwood and Cremer (1982). It corresponds more closely to Medawar's (1952) position than to Weisman's (1889). The demographically based model in which senescence is represented by sudden death supplies an explanation which is simple and credible for the evolution of senescence. It supports the following specific conclusions: 1. The introduction of sudden death (case 2) in a nonsenescent population otherwise subject only to randomly occurring death (case 1) is, by itself, disadvantageous from the standpoint of natural selection. 2. However the population may enjoy a net selective advantage if the disadvantage of sudden-death senescence is compensated by an appropriate improvement early in its life history, e.g., by a reduction in its presenescent death rate. 3. In the most extreme example possible, in which the presenescent death rate is zero and the survival curve is rectangular (case 3), the early improvement is associated with an increase in the degree of sensescence of the population, in its mean longevity, and in its average age at death. Thus natural selection can simultaneously favor both senescence and longevity. 4. Among populations in which the age of sudden death is balanced against the presenescent death rate in such a way that mean longevity is held constant (case 4), sudden-death senescence provides selective advantage relative to a nonsenescent population (case 1). Up to the point at which the survival curve becomes rectangular, the earlier the age at which sudden-death occurs, the greater the selective advantage. Similar conclusions were reached earlier with respect to forms of senescence which take effect more gradually than the sudden-death mechanism postulated here. 5. Populations in which the age of sudden death is balanced against the presenescent death rate in such a way that the average age at death is held constant (case 5) are selectively neutral with respect to a nonsenescent population (case 1). Thus a reduction in mortality at a nearly age can compensate for the sudden death of the whole population at an advanced age because so few individuals in the nonsenescent population survive to reproduce when old.

Aging↗
PubMed1991

A protein in the oxygen-evolving complex in the chloroplast is associated with symptom expression on tobacco leaves infected with cucumber mosaic virus strain Y.

To elucidate the molecular basis of symptom expression in virus-infected plants, the changes in proteins between tobacco, Nicotiana tabacum cv. Ky57, leaves inoculated with cucumber mosaic virus strain Y [CMV(Y)] and strain O [CMV(O)], were compared by 2-dimensional (2-D) gel electrophoresis. The appearance of chlorotic spots in CMV(Y)-inoculated tobacco leaves accompanied an increase of 3 polypeptides and a decrease in 6 polypeptides, as compared with those in the CMV(O)-inoculated tobacco which showed no clear symptoms. The decrease in the amounts of two polypeptides of 22 and 23 kDa was particularly significant: these two polypeptides were compared with a 24 kDa polypeptide, which co-migrated with them in 2-D gel electrophoresis but did not clearly decrease at an early stage of infection, as well as major other proteins of CMV(Y)-inoculated tobacco leaves. However, the 22, 23 and 24 kDa polypeptides showed the same peptide mapping pattern. Furthermore, the 12 amino acid residues at N-termini of the three polypeptides match those of the extrinsic 23 kDa polypeptide of an oxygen-evolving complex from spinach. A comparative analysis of the 22, 23 and 24 kDa polypeptides in N. tabacum and its ancestral parents, N. sylvestris and N. tomentosiformis, revealed that the 22 kDa polypeptide derives from N. sylvestris and the 23 kDa polypeptide from N. tomentosiformis; the 24 kDa polypeptide derives from both ancestral Nicotiana species. The results indicate that the polypeptides whose amounts differentially decrease with the progress of symptom expression in N. tabacum inoculated with CMV(Y) are one component of the oxygen-evolving complex in photosystem II.

Amino Acid Sequence↗
PubMed1992

Genetic distance and species formation in evolving populations.

We compare the behavior of the genetic distance between individuals in evolving populations for three stochastic models. In the first model reproduction is asexual and the distribution of genetic distances reflects the genealogical tree of the population. This distribution fluctuates greatly in time, even for very large populations. In the second model reproduction is sexual with random mating allowed between any pair of individuals. In this case, the population becomes homogeneous and the genetic distance between pairs of individuals has small fluctuations which vanish in the limit of an infinitely large population. In the third model reproduction is still sexual but instead of random mating, mating only occurs between individuals which are genetically similar to each other. In that case, the population splits spontaneously into species which are in reproductive isolation from one another and one observes a steady state with a continual appearance and extinction of species in the population. We discuss this model in relation to the biological theory of speciation and isolating mechanisms. We also point out similarities between these three models of evolving populations and the theory of disordered systems in physics.

Biological Evolution↗
PubMed1994

Immunoglobulin-binding FcrA and Enn proteins and M proteins of group A streptococci evolved independently from a common ancestral protein.

Significant sequence homology between M proteins and immunoglobulin (Ig)-binding proteins of group A streptococci suggests that these proteins arose by gene duplication followed by the development of functional diversity due to mutations and intragenic recombinations. The deduced sequence of multiple Ig-binding proteins and M proteins were compared to distinguish between two evolutionary models. Did these functionally distinct genes originate in the distant past from duplication of a common ancestral gene and then functionally evolve independently or did they evolve more recently, one from the other by duplication of a fixed gene? Multiple alignments of conserved sequences of these proteins are consistent with the former hypothesis. Comparison of N termini of Ig-binding proteins revealed less diversity than that of the M proteins' N termini, suggesting that these proteins are under less selective pressure to change.

Amino Acid Sequence↗