In recent years, membrane contact sites (MCS), which mediate interactions between virtually all subcellular organelles, have been extensively characterized and shown to be essential for intracellular communication. In this review essay, we focus on an emerging topic: the regulation of MCS. Focusing on the tether proteins themselves, we discuss some of the known mechanisms which can control organelle tethering events and identify apparent common regulatory hubs, such as the VAP interface at the endoplasmic reticulum (ER). We also highlight several (...) currently hypothetical concepts, including the idea of tether oligomerization and redox regulation playing a role in MCS formation. We identify gaps in our current understanding, such as the identity of the majority of kinases/phosphatases involved in tether modification and conclude that a holistic approach—incorporating the formation of multiple MCS, regulated by interconnected regulatory modulators—may be required to fully appreciate the true complexity of these fascinating intracellular communication systems. (shrink)

Joining an antagonistic phosphoinositide (PtdInsP) kinase and phosphatase into a single protein complex may regulate rapid and local PtdInsP changes. This may be important for processes such as membrane fission that require a specific PtdInsP and that are innately local and rapid. Such a complex could couple vesicle formation, with erasing of the identity of the donor organelle from the vesicle prior to its fusion with target organelles, thus preventing organelle identity intermixing. Coordinating signals are postulated (...) to switch the relative activities of the kinase and phosphatase in a spatio‐temporal manner that matches membrane fission events. The discovery of two such complexes supports this hypothesis. One regulates the interconversion of phosphatidylinositol and PtdIns(3)P by joining the Vps34 PtdIns 3‐kinase and the myotubularin 3‐phosphatases. The other regulates the interconversion between PtdIns(3)P and PtdIns(3,5)P2 through the Fab1/PIKfyve kinase and the Fig4/mFig4 phosphatase. These lipids are essential components of the endosomal identity code. (shrink)

In the mouse, at least 16 genes regulate vesicle trafficking to specialized lysosome‐related organelles, including platelet dense granules and melanosomes. Fourteen of these genes have been identified by positional cloning. All 16 mouse mutants are models for the genetically heterogeneous human disease, Hermansky–Pudlak Syndrome (HPS). Five HPS genes encode known vesicle trafficking proteins. Nine genes are novel, are found only in higher eukaryotes and encode members of three protein complexes termed BLOCs (Biogenesis of Lysosome‐related Organelles Complexes). Mutations in murine HPS (...) genes, which encode protein co‐members of BLOCs, produce essentially identical phenotypes. In addition to their well‐known effects on pigmentation, platelet function and lysosome secretion, HPS genes control a wide range of physiological processes including immune recognition, neuronal functions and lung surfactant trafficking. Studies of the molecular functions of HPS proteins will reveal important details of vesicle trafficking and may lead to therapies for HPS. BioEssays 26:616–628, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

The biological membranes of eukaryotic cells harbor sensitive surveillance systems to establish, sense, and maintain characteristic physicochemical properties that ultimately define organelle identity. They are fundamentally important for membrane homeostasis and play active roles in cellular signaling, protein sorting, and the formation of vesicular carriers. Here, we compare the molecular mechanisms of Mga2 and Ire1, two sensors involved in the regulation of fatty acid desaturation and the response to unfolded proteins and lipid bilayer stress in order to identify (...) their commonalities and specializations. We will speculate on the cellular significance of membrane property sensors in other organelles and discuss their putative mechanisms. Based on these findings, we propose membrane property sensors as an emerging class of proteins with wide implications for organelle communication and function. (shrink)

The organism is one of the fundamental concepts of biology and has been at the center of many discussions about biological individuality, yet what exactly it is can be confusing. The definition that we find generally useful is that an organism is a unit in which all the subunits have evolved to be highly cooperative, with very little conflict. We focus on how often organisms evolve from two or more formerly independent organisms. Two canonical transitions of this type—replicators clustered in (...) cells and endosymbiotic organelles within host cells—demonstrate the reality of this kind of evolutionary transition and suggest conditions that can favor it. These conditions include co-transmission of the partners across generations and rules that strongly regulate and limit conflict, such as a fair meiosis. Recently, much attention has been given to associations of animals with microbes involved in their nutrition. These range from tight endosymbiotic associations like those between aphids and Buchnera bacteria, to the complex communities in animal intestines. Here, starting with a reflection about identity through time, we consider the distinctions between these kinds of animal–bacteria interactions and describe the criteria by which a few can be considered jointly organismal but most cannot. (shrink)

are synthetic a priori judgements possible?" In both cases, i~thas usually been t'aken for granted in fife one case by Kant that synthetic a priori judgements were possible, and in the other case in contemporary,'d-". philosophical literature that contingent statements of identity are ppss. ible. I do not intend to deal with the Kantian question except to mention:ssj~".

Graphical AbstractOrganelles are reaction vessels containing metabolic pathways. As in a chemical factory, the size of the reaction vessels limits the rate of product formation. Organelle size is tuned to metabolic needs, hence reprogramming organelle size could be a novel therapeutic strategy as well as a new tool for metabolic engineering.

Many philosophers hypothesize that our concept of personal identity is partly constituted by the one-person-one-place rule, which states that a person can only be in one place at a time. This hypothesis has been assumed by the most influential contemporary work on personal identity. In this paper, we report a series of studies testing whether the hypothesis is true. In these studies, people consistently judged that the same person existed in two different places at the same time. This (...) result undermines some widely held philosophical assumptions, supports others, and fits well with recent discoveries on identity judgments about inanimate objects and non-human animals. (shrink)

When talking about personal identity in the context of medical ethics, ethicists tend to borrow haphazardly from different philosophical notions of personal identity, or to abjure these abstract metaphysical concerns as having nothing to do with practical questions in medical ethics. In fact, however, part of the moral authority for respecting a patient’s self-regarding decisions can only be made sense of if we make certain assumptions that are central to a particular, psychological picture of personal identity, namely, (...) that patients will remain psychologically connected to a certain degree with their future selves. I draw this out, show problems with approaches in medical ethics based on alternate theories of personal identity that do not recognise this, and explore some important implications. Namely, I show how this recognition can better explain the circumstances under which we should respect advance directives and why, and how it can better make sense of patient fears that they will not "survive" personality-altering deep brain stimulation procedures, and provide guidance on approaching patient decisions concerning this type of procedure in a manner that captures and addresses such concerns. (shrink)

The recent development of RNA replicating protocells and capsules that enclose complex biosynthetic cascade reactions are encouraging signs that we are gradually getting better at mastering the complexity of biological systems. The road to truly cellular compartments is still very long, but concrete progress is being made. Compartmentalization is a crucial natural methodology to enable control over biological processes occurring within the living cell. In fact, compartmentalization has been considered by some theories to be instrumental in the creation of life. (...) With the advancement of chemical biology, artificial compartments that can mimic the cell as a whole, or that can be regarded as cell organelles, have recently received much attention. The membrane between the inner and outer environment of the compartment has to meet specific requirements, such as semi‐permeability, to allow communication and molecular transport over the border. The membrane can either be built from natural constituents or from synthetic polymers, introducing robustness to the capsule. (shrink)

In the organelles of plants and mammals, recent evidence suggests that genomic instability stems in large part from template switching events taking place during DNA replication. Although more than one mechanism may be responsible for this, some similarities exist between the different proposed models. These can be separated into two main categories, depending on whether they involve a single‐strand‐switching or a reciprocal‐strand‐switching event. Single‐strand‐switching events lead to intermediates containing Y junctions, whereas reciprocal‐strand‐switching creates Holliday junctions. Common features in all the (...) described models include replication stress, fork stalling and the presence of inverted repeats, but no single element appears to be required in all cases. We review the field, and examine the ideas that several mechanisms may take place in any given genome, and that the presence of palindromes or inverted repeats in certain regions may favor specific rearrangements. (shrink)

Why the DNA‐containing organelles, chloroplasts, and mitochondria, are inherited maternally is a long standing and unsolved question. However, recent years have seen a paradigm shift, in that the absoluteness of uniparental inheritance is increasingly questioned. Here, we review the field and propose a unifying model for organelle inheritance. We argue that the predominance of the maternal mode is a result of higher mutational load in the paternal gamete. Uniparental inheritance evolved from relaxed organelle inheritance patterns because it avoids (...) the spread of selfish cytoplasmic elements. However, on evolutionary timescales, uniparentally inherited organelles are susceptible to mutational meltdown (Muller's ratchet). To prevent this, fall‐back to relaxed inheritance patterns occurs, allowing low levels of sexual organelle recombination. Since sexual organelle recombination is insufficient to mitigate the effects of selfish cytoplasmic elements, various mechanisms for uniparental inheritance then evolve again independently. Organelle inheritance must therefore be seen as an evolutionary unstable trait, with a strong general bias to the uniparental, maternal, mode. (shrink)

From stem cells to oocyte, Drosophila germ cells undergo a short, defined lineage. Molecular genetic analyses of a collection of female sterile mutations have indicated that a germ cell‐specific organelle called the fusome has a central role at several steps in this lineage. The fusome grows from a prominent spherical organelle to an elongated and branched structure that connects all mitotic sisters in a germ cell syncytium. The organelle is assembled from proteins normally found in the membrane (...) skeleton and, additionally, contains an extensive membranous reticulum, the probable product of differentiation‐dependent vesicle trafficking. This review briefly summarizes a current view of the processes that drive germ cell differentiation, particularly the various roles that the fusome might play in regulating the developmental events. Future efforts will consider to what extent an organelle assembly‐dependent model for differentiation is heuristic and whether the Drosophila fusome represents a homolog of a similar organelle in vertebrate lymphocytes. (shrink)

When philosophers address personal identity, they usually explore numerical identity: what are the criteria for a person's continuing existence? When non-philosophers address personal identity, they often have in mind narrative identity: Which characteristics of a particular person are salient to her self-conception? This book develops accounts of both senses of identity, arguing that both are normatively important, and is unique in its exploration of a range of issues in bioethics through the lens of identity. (...) Defending a biological view of our numerical identity and a framework for understanding narrative identity, DeGrazia investigates various issues for which considerations of identity prove critical: the definition of death; the authority of advance directives in cases of severe dementia; the use of enhancement technologies; prenatal genetic interventions; and certain types of reproductive choices. He demonstrates the power of personal identity theory to illuminate issues in bioethics as they bring philosophical theory to life. (shrink)

There is a widespread notion, both within the sciences and among the general public, that mental deterioration can rob individuals of their identity. Yet there have been no systematic investigations of what types of cognitive damage lead people to appear to no longer be themselves. We measured perceived identity change in patients with three kinds of neurodegenerative disease: frontotemporal dementia, Alzheimer’s disease, and amyotrophic lateral sclerosis. Structural equation models revealed that injury to the moral faculty plays the primary (...) role in identity discontinuity. Other cognitive deficits, including amnesia, have no measurable impact on identity persistence. Accordingly, frontotemporal dementia has the greatest effect on perceived identity, and amyotrophic lateral sclerosis has the least. We further demonstrated that perceived identity change fully mediates the impact of neurodegenerative disease on relationship deterioration between patient and caregiver. Our results mark a departure from theories that ground personal identity in memory, distinctiveness, dispositional emotion, or global mental function. (shrink)

Most metazoan organisms have evolved a mildly acidified and calcium diminished sorting hub in the early secretory pathway commonly referred to as the Endoplasmic Reticulum‐Golgi intermediate compartment (ERGIC). These membranous vesicular‐tubular clusters are found tightly juxtaposed to ER subdomains that are competent for the production of COPII‐coated transport carriers. In contrast to many unicellular systems, metazoan COPII carriers largely transit just a few hundred nanometers to the ERGIC, prior to COPI‐dependent transport on to the cis‐Golgi. The mechanisms underlying formation and (...) maintenance of ERGIC membranes are poorly defined. However, recent evidence suggests an important role for Trk‐fused gene (TFG) in regulating the integrity of the ER/ERGIC interface. Moreover, in the absence of cytoskeletal elements to scaffold tracks on which COPII carriers might move, TFG appears to promote anterograde cargo transport by locally tethering COPII carriers adjacent to ERGIC membranes. This action, regulated in part by the intrinsically disordered domain of TFG, provides sufficient time for COPII coat disassembly prior to heterotypic membrane fusion and cargo delivery to the ERGIC. -/- . (shrink)

Cells are the fundamental building blocks of organisms and their organization holds the key to our understanding of the processes that control Development and Physiology as well as the mechanisms that underlie disease. Traditional methods of analysis of subcellular structure have relied on the purification of organelles and the painstaking biochemical description of their components. The arrival of high‐throughput genomic and, more significantly, proteomic technologies has opened hereto unforeseen possibilities for this task. Recently two reports(1,2) show how much can be (...) gleaned from the combination of analytical centrifugation, mass spectrometry and advanced statistical techniques focused on a high‐throughput analysis of the content and organization of plant and animal cells. The results reveal intriguing possibilities for the future and the possibility of mapping much of the known proteome onto our current map of the cell. BioEssays 28: 780–784, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

In this essay, I develop the concept of episodic value, which describes a form of value connected to a particular object or individual expressed and delivered through a narrative. Narrative can bestow special kinds of value on objects, as exemplified by auction articles or museum collections. To clarify the nature of episodic value, I show how the notion of episodic value fundamentally differs from the traditional axiological picture. I extend my discussion of episodic value to argue that the notion of (...) episodic value readily incorporates the role of narratives into the construction of identity in personal and social contexts. My main contentions are twofold. First, events or experiences from our personal narratives are episodically valuable insofar as they contribute to shaping our narrative identities. Second, when engaged in a collective action, we write a joint narrative with other participants that confers special meanings on the actions of each participant. (shrink)

Awareness of, and respect for differences of gender, race, religion, language, and culture have liberated many oppressed groups from the hegemony of white, Western males. However, respect for previously denigrated collective identities should not be allowed to confine individuals to identities constructed around one main component used for political mobilisation, or to identities that depend on a priority of properties that are not optional, like race, gender, and language. In this article I want to sketch an approach for accommodating different (...) kinds of identity within a multicultural constitutional democracy. From a vantage point provided by a definition and explanation of personal identity, I want to show how people define, construct and change their personal identities to make themselves into unique individuals. Next I show how democratic political institutions and the personal identities of individuals reciprocally influence one another. In the final section I sketch ways in which diverse personal identities ought to be accommodated in multicultural constitutional democracies. The conclusion is that a society which gives its members the liberty, space, and opportunity to freely construct their own identities might avoid the formation of closed groups committed exclusively to their own sectional interests. (shrink)

Like '&', '=' is no term; it represents no extrasentential property. It marks an atomic, nonpredicative, declarative structure, sentences true solely by codesignation. Identity (its necessity and total reflexivity, its substitution rule, its metaphysical vacuity) is the objectual face of codesignation. The syntax demands pure reference, without predicative import for the asserted fact. 'Twain is Clemens' is about Twain, but nothing is predicated of him. Its informational value is in its 'metailed' semantic content: the fact of codesignation (that 'Twain' (...) names Clemens) that explains what fact it asserts and why it is necessary. Critiques of concepts of rigidity and elimination of singular terms result. (shrink)

Our aim in this entry is to articulate the state of the art in the moral psychology of personal identity. We begin by discussing the major philosophical theories of personal identity, including their shortcomings. We then turn to recent psychological work on personal identity and the self, investigations that often illuminate our person-related normative concerns. We conclude by discussing the implications of this psychological work for some contemporary philosophical theories and suggesting fruitful areas for future work on (...) personal identity. (shrink)

Background: Recent literature on addiction and judgments about the characteristics of agents has focused on the implications of adopting a ‘brain disease’ versus ‘moral weakness’ model of addiction. Typically, such judgments have to do with what capacities an agent has (e.g., the ability to abstain from substance use). Much less work, however, has been conducted on the relationship between addiction and judgments about an agent’s identity, including whether or to what extent an individual is seen as the same person (...) after becoming addicted. Methods: We conducted a series of vignette-based experiments (total N = 3,620) to assess lay attitudes concerning addiction and identity persistence, systematically manipulating key characteristics of agents and their drug of addiction. Conclusions: In Study 1, we found that US participants judged an agent who became addicted to drugs as being closer to ‘a completely different person’ than ‘completely the same person’ as the agent who existed prior to the addiction. In Studies 2-6, we investigated the intuitive basis for this result, finding that lay judgments of altered identity as a consequence of drug use and addiction are driven primarily by perceived negative changes in the moral character of drug users, who are seen as having deviated from their good true selves. (shrink)

In eukaryotes, RNA trans‐splicing is an important RNA‐processing form for the end‐to‐end ligation of primary transcripts that are derived from separately transcribed exons. So far, three different categories of RNA trans‐splicing have been found in organisms as diverse as algae to man. Here, we review one of these categories: the trans‐splicing of discontinuous group II introns, which occurs in chloroplasts and mitochondria of lower eukaryotes and plants. Trans‐spliced exons can be predicted from DNA sequences derived from a large number of (...) sequenced organelle genomes. Further molecular genetic analysis of mutants has unravelled proteins, some of which being part of high‐molecular‐weight complexes that promote the splicing process. Based on data derived from the alga Chlamydomonas reinhardtii, a model is provided which defines the composition of an organelle spliceosome. This will have a general relevance for understanding the function of RNA‐processing machineries in eukaryotic organelles. (shrink)

Steven French and Decio Krause examine the metaphysical foundations of quantum physics. They draw together historical, logical, and philosophical perspectives on the fundamental nature of quantum particles and offer new insights on a range of important issues. Focusing on the concepts of identity and individuality, the authors explore two alternative metaphysical views; according to one, quantum particles are no different from books, tables, and people in this respect; according to the other, they most certainly are. Each view comes with (...) certain costs attached and after describing their origins in the history of quantum theory, the authors carefully consider whether these costs are worth bearing. Recent contributions to these discussions are analyzed in detail and the authors present their own original perspective on the issues. The final chapter suggests how this perspective can be taken forward in the context of quantum field theory. (shrink)

_Identity and Discrimination_, originally published in 1990 and the first book by respected philosopher Timothy Williamson, is now reissued and updated with the inclusion of significant new material. Williamson here proposes an original and rigorous theory linking identity, a relation central to metaphysics, and indiscriminability, a relation central to epistemology.__ Updated and reissued edition of Williamson’s first publication, with the inclusion of significant new material Argues for an original cognitive account of the relation between identity and discrimination that (...) has been influential in the philosophy of perception Pioneers the use of epistemic logic to solve puzzles about indiscriminability Develops the application of techniques from mathematical logic to understand issues about identity over time and across possible worlds. (shrink)

Some claim that Composition as Identity (CI) entails Mereological Essentialism (ME). If this is right, then we have an effective modus tollens against CI: ME is clearly false, so CI is, too. Rather than deny the conditional, I will argue that a CI theorist should embrace ME. I endorse a theory of modal parts such that ordinary objects are spatially, temporally, and modally extended. Accepting modal parts is certainly beneficial to CI theorists, but it also provides elegant solutions to (...) the traditional puzzles of constitution, making it a competitive move in its own right. (shrink)

A collection of 14 essays honoring the life and work of Oxford philosopher Wiggins touching on topics from ancient philosophy to ethics, metaphysics and the theory of meaning. The contributing scholars debate many of the seminal issues of Wiggins' work, including the determinancy of distinctness, relative identity, naturalism in ethics, logic and truth in moral judgments, and the practical wisdom of Aristotle. The collection uniquely features replies by Wiggins to each of the papers. Annotation copyright by Book News, Inc., (...) Portland, OR. (shrink)

Reorganization of cell organelle‐deprived host red blood cells by the apicomplexan malaria parasite Plasmodium falciparum enables their cytoadherence to endothelial cells that line the microvasculature. This increases the time red blood cells infected with mature developmental stages remain within selected organs such as the brain to avoid the spleen passage, which can lead to severe complications and cumulate in patient death. The Maurer's clefts are a novel secretory organelle of parasite origin established by the parasite in the cytoplasm (...) of the host red blood cell in order to facilitate the establishment of cytoadherence by conducting the trafficking of immunovariant adhesins to the host cell surface. Another important function of the organelle is the sorting of other proteins the parasite traffics into its host cell. Although the organelle is of high importance for the pathology of malaria, additional putative functions, structure, and genesis remain shrouded in mystery more than a century after its discovery. In this review, we highlight our current knowledge about the Maurer's clefts and other novel secretory organelles established within the host cell cytoplasm by human‐pathogenic malaria parasites and other parasites that reside within human red blood cells. (shrink)

Identity and Difference consists of English translations and the original German versions of two little-known lectures given in 1957 by Martin Heidegger, "The Principle of Identity" and "The Onto-theo-logical Constitution of Metaphysics.

What does it mean to say that this person at this time is 'the same' as that person at an earlier time? If the brain is damaged or the memory lost, how far does a person's identity continue? In this book two eminent philosophers develop very different approaches to the problem.

Organelles transported along microtubules are normally moved to precise locations within cells. For example, synaptic vesiceles are transported to the neruronal synapse, the Golgi apparatus is generally found in a perinuclear location, and the membranes of the endoplasmic reticulum are actively extended to the cell periphery. The correct positioning of these organelles depends on microtubules and microtubule motors. Melanophores provide an extreme example of organized organelle transport. These cells are specialized to transport pigment granules, which are coordinately moved towards (...) or away from the cell center, and result in the cell appearing alternately light or dark. Melanophores have proved to be an ideal system for studying the mechanisms by which the cell controls the direction of its organelle transport. Pigment granule dispersion (the movement away from the cell center) requires protein phosphorylation, while pigment aggregation (the movement towards the cell center) requires protein dephosphorylation. The target of this phosphorylation and dephosphorylation event is a protein that interacts with the microtubule motor protein, kinesin. Thus, the direction of organelle transport along microtubules may be regulated by controlling the activity of a microtubule motor. (shrink)

The conundrum of the unconstitutional constitution -- The quest for a compelling unity -- The permeability of constitutional borders -- The sounds of silence : militant and acquiescent constitutionalism -- "The first page of the constitution" : family, state, and identity.

The author attacks the view that identity, Like largeness, Is a relative relation. The primary advocate of the view that identity is relative is p.T. Geach. It is argued that geach has not shown that the failure of the identity of indiscernibles principle, As a truth of logic, Forces us to stop taking indiscernibility within particular formal theories or languages as a sufficient condition for identity. The author also argues that the whole notion of relative (...) class='Hi'>identity, As explicated by geach, Is very probably incoherent. (shrink)

Identity Economics provides an important and compelling new way to understand human behavior, revealing how our identities--and not just economic incentives--influence our decisions. In 1995, economist Rachel Kranton wrote future Nobel Prize-winner George Akerlof a letter insisting that his most recent paper was wrong. Identity, she argued, was the missing element that would help to explain why people--facing the same economic circumstances--would make different choices. This was the beginning of a fourteen-year collaboration--and of Identity Economics. The authors (...) explain how our conception of who we are and who we want to be may shape our economic lives more than any other factor, affecting how hard we work, and how we learn, spend, and save. Identity economics is a new way to understand people's decisions--at work, at school, and at home. With it, we can better appreciate why incentives like stock options work or don't; why some schools succeed and others don't; why some cities and towns don't invest in their futures--and much, much more. Identity Economics bridges a critical gap in the social sciences. It brings identity and norms to economics. People's notions of what is proper, and what is forbidden, and for whom, are fundamental to how hard they work, and how they learn, spend, and save. Thus people's identity--their conception of who they are, and of who they choose to be--may be the most important factor affecting their economic lives. And the limits placed by society on people's identity can also be crucial determinants of their economic well-being. (shrink)

Objections to uploading may be parsed into substrate issues, dealing with the computer platform of upload and personal identity. This paper argues that the personal identity issues of uploading are no more or less challenging than those of bodily transfer often discussed in the philosophical literature. It is argued that what is important in personal identity involves both token and type identity. While uploading does not preserve token identity, it does save type identity; and (...) even qua token, one may have good reason to think that the preservation of the type is worth the cost. (shrink)

What factors drove the transformation of the cyanobacterial progenitor of plastids (e.g. chloroplasts) from endosymbiont to bona fide organelle? This question lies at the heart of organelle genesis because, whereas intracellular endosymbionts are widespread in both unicellular and multicellular eukaryotes (e.g. rhizobial bacteria, Chlorella cells in ciliates, Buchnera in aphids), only two canonical eukaryotic organelles of endosymbiotic origin are recognized, the plastids of algae and plants and the mitochondrion. Emerging data on (1) the discovery of non‐canonical plastid protein (...) targeting, (2) the recent origin of a cyanobacterial‐derived organelle in the filose amoeba Paulinella chromatophora, and (3) the extraordinarily reduced genomes of psyllid bacterial endosymbionts begin to blur the distinction between endosymbiont and organelle. Here we discuss the use of these terms in light of new data in order to highlight the unique aspects of plastids and mitochondria and underscore their central role in eukaryotic evolution. BioEssays 29:1239–1246, 2007. © 2007 Wiley Periodicals, Inc. (shrink)