What makes a eukaryote a eukaryote? What makes a eukaryote a eukaryote? http://phylogeny.arizona.edu/tree/eukaryotes/eukaryotes.html

eukaryoteseukaryotes are distinguished from prokaryotesprokaryotes by the structural complexity of the cells. - characterized by having many functions segregated into semi-autonomous regions (organellesorganelles), and by the cytoskeletoncytoskeleton.

The most evident organelle in most cells is the nucleusnucleus, and it is from … this organelle that the eukaryotes get their name.

NucleiNuclei contain most of the genetic material of a cell - with other elements of the genome located in mitchondria and plastids (if those organelles are also present). The nucleus is bounded by a membranous envelope. The nuclear envelope is part of the endomembrane system that extends to include the endoplasmic reticulum, dictyosomes (Golgi apparatus) and the plasma membrane that encloses the cell.

Within the nucleus, the genes are located on a number of chromosomeschromosomes. The total amount of DNA in a nucleus measuring less than one hundredth of a millimetre across may stretch to over a metre.

- enzyme myosin

- enzyme dynein

http://phylogeny.arizona.edu/tree/eukaryotes/eukaryotes.htmlThe cytoskeletoncytoskeleton is comprised of a rich array of proteins. The major ones are tubulintubulin (which forms microtubules) and actinactin (forming microfilaments) and a myriad of interacting proteins which effect movement or create the skeletal architecture of cells.

C&R Fig 7.24

Some antimitotic alkaloids are useful as cancer chemotherapy agents. Taxol {from yew} increases the formation of microtubules and stabilizes them so that there is no free tubulin for the formation of mitotic spindlesmitotic spindles. Vinblastine {from periwinkel} causes the disassembly of formed microtubules and causes the aggregation of crystaline tubulin. Because tumor cells multiply faster than normal cells they are more susceptible to antimitotic drugs.

The Endosymbiotic TheoryThe Endosymbiotic Theory of of Eukaryote EvolutionEukaryote Evolution

This idea was promulgated at the turn of the 20th century (Mereschkowsky, 1910) and promoted later by Lynn Margulis (Margulis, 1970).

Lynn Margulis

Right: Spirochetes are masters of movement, corkscrewing about with neither head nor tail.

(Photograpgh by Lyn Margulis)

Bottom: This contemporary protist, Trichonympha, is pushed through its viscous termite hindgut habitat by thousands of symbiotic spirochete bacteria attaching at the rear. (Photography by David Chase)

http://www.earthwise.org/walk/walk_photos/2700.htm

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Diplomonadida and ParabasalaDiplomonadida and Parabasala: lack mitochondriaAccording to what is called the "archaezoa hypothesis," these protists are the modern forms of ancient eukaryotic lineages that evolved before the acquisition of the endosymbiotic bacteria that gave rise to mitochondria. Most protistan systematists have recently rejected that hypothesis based on the discovery of mitochondrial genes in the nuclear genomes …the evidence now supports the hypothesis that these protists lost their mitochondriathese protists lost their mitochondria during their evolution from ancestors in which mitochondria were present.

the DiplomonadsDiplomonads (two nuclei):

http://www.nih.gov/news/pr/aug2001/nichd-15.htmTrichomoniasis is caused by infection with … Trichomonas vaginalisTrichomonas vaginalis. Pregnant women infected with T. vaginalis are more likely to … give birth prematurely to children of low birth weight, … children … are more than twice as likely to be stillborn or to die as newborns…

the TrichomonadsTrichomonads (3 flagella)

http://usa.biologists.com/JCS/gallery.html

Immunofluorescence of the trypanosome mutant snl-1 staining the nucleus and the kinetoplast

(a large mitochondrion),

Trypanosoma gambiense in a blood smear.

The kinetoplastidskinetoplastids have a single large mitochondrion associated with a unique organelle, the kinetoplast, that houses extranuclear DNA. Trypanosoma cause African sleeping sickness, a human disease that is spread by the bite of the tsetse fly

The euglenoidseuglenoids (such as Euglena) are characterized by an anterior pocket from which one or two flagella emerge. Paramylon, a glucose polymer that functions as a storage molecule, is also characteristic of euglenoids.

A few species of TrypanosomaTrypanosoma are found in the New World. From the standpoint of human health, the most important is Trypanosoma cruziTrypanosoma cruzi, causing American trypanosomiasis or Chagas' disease. 

http://www.biosci.ohio-state.edu/~parasite/chagas.html

The vector for Chagas' disease is a "true bug" (Hemiptera) {‘kissing bug’} In the human host, Chagas' disease affects primarily the nervous system and heart.  Chronic infections result in various neurological disorders, including dementia, megacolon, and megaesophagus, and damage to the heart muscle. Left untreated, Chagas' disease is often fatal.

Protist: EuglenozoaEuglenozoa: KinetoplastsKinetoplasts: TrypanosomaTrypanosoma

Small animals such as dogs, cats, guinea pigs, rats and opossums can serve as reservoirs for the parasite. T. cruzi generally does not cause the significant disease in animals as it does in people. …There is no known cure for T. cruzi infection in dogs and cats. Because of this and the extreme danger to people, it is generally recommended that infected animals be euthanized. The most effective means of control is the elimination of the kissing bugs.

AlveolataAlveolata draws together a group of flagellates (the dinoflagellates), a group of parasites (apicomplexans), and a distinctive group of eukaryotes that move by means of cilia (the ciliates). Alveolates have small membrane-bounded cavities (alveoli) under their cell surfaces. The function of the alveoli is unknown;

the DinoflagellatesDinoflagellates: phytoplankton - Red Tides

Pfiesteria piscicidaPfiesteria piscicida (‘the Cell from Hell!’)

the CilliatesCilliates - ParameciumParamecium - Fig 28.14macronucleus (approx 50n) controls ‘everyday functions’& micronuclei - swapped in sexual conjugation - Fig 28.15

the ApicomplexansApicomplexans (sporozoan parasites)PlasmodiumPlasmodium - malaria- Fig 28.7At present, at least 300,000,000 people are affected by malaria globally, and there are between 1,000,000 and 1,500,000 malaria deaths per year.

Haplotype diversity and linkage disequilibrium at human G6PD: Recent origin of alleles that confer malarial resistance.Tishkoff et al SCIENCE 293 (5529): 455-462 JUL 20 2001Abstract:The frequencies of Low-activity alleles of glucose-6-phosphate dehydrogenase in humans are highly correlated with the prevalence of malaria. These "deficiency" alleles are thought to provide reduced risk from infection by the Plasmodium parasite and are maintained at high frequency despite the hemopathologies that they cause. Haplotype analysis of "A-" and "Med" mutations at this Locus indicates that they have evolved independently and have increased in frequency at a rate that is too rapid to be explained by random genetic drift. Statistical modeling indicates that the A- allele arose within the past 3840 to 11,760 years and the Med allele arose within the past 1600 to 6640 years. These results support the hypothesis that malaria has had a major impact on humans only since the introduction of agriculture within the past 10,000 years and provide a striking example of the signature of selection the signature of selection on the human genome.on the human genome.

PhD - MSU 1986

AlveolataAlveolata: DinoflagellatesDinoflagellates:

http://www.epa.gov/owow/estuaries/pfiesteria/fact.htmlWhat is Pfiesteria ?

Pfiesteria piscicidaPfiesteria piscicida (fee-STEER-ee-uh pis-kuh-SEED-uh) is a toxic dinoflagellate that has been associated with fish lesions and fish kills in coastal waters from Delaware to North Carolina.

… dinoflagellates are microscopic, free-swimming, single-celled organisms, usually classified as a type of alga.

Although many dinoflagellates are plant-like and obtain energy by photosynthesis, others, including PfiesteriaPfiesteria, are more animal-like and acquire some or all of their energy by eating other organisms.

Discovered in 1988 by researchers at North Carolina State University, Pfiesteria piscicidaPfiesteria piscicida is now known to have a highly complex life-cycle with 24 reported forms, a few of which can produce toxins.

… Pfiesteria only becomes toxic in the presence of fish, triggered by their secretions or excrement in the water. At that point, Pfiesteria cells shift forms and begin emitting a powerful toxina powerful toxin that stuns the fish … Other toxins are believed to break down fish skin tissue, …As fish are incapacitated, the Pfiesteria cells feed on their tissues …

PhD - MSU 1986

HEADLINE: The 'Cell From Hell''Cell From Hell' Newsweek August 25, 1997 … what triggers the proliferation of Pfiesteria. In Maryland, environmentalists are blaming the manure runoff from the region's 600 million chickens. In North Carolina, environmentalists say the culprit is mostly runoff from hog farms. … Burkholder's struggles to get North Carolina to recognize Pfiesteria are legion.A new book, "And the Waters Turned to Blood," recounts how corporations and state officials attacked Burkholder's credibility

HEADLINE: Scary monsters super creeps   New Scientist June 3, 2000 She calls it the career from hell - and she's only half joking. She's been hounded by powerful industries …and watched her funding disappear. North Carolina had tried for years to deny there was a problem, in Maryland action was swift. The governor … asked for medical tests on about 15 people who had been exposed to the toxins. Some of them were diagnosed in the bottom 2 per cent of the US population in their ability to learn and remember. North Carolina was, I think, embarrassed and the state legislature provided generous funding for a new biohazard level 3 lab. With that we are now making good progress …

Pfiesteria piscicida and P. shumwayae reportedly secrete potent exotoxinsreportedly secrete potent exotoxins thought to cause fish lesion events, acute fish kills and human disease…Pfiesteria toxins have never been isolated or characterized8. We investigated mechanisms by which P. shumwayae kills fish …Here we show that larval fish bioassays conducted in tissue culture plates fitted with polycarbonate membrane inserts exhibited mortality (100%) only in treatments where fish and dinospores were in physical contact. No mortalities occurred in treatments where the membrane prevented contact between dinospores and fish. …Videomicrography and electron microscopy show dinospores swarming toward and attaching to skin, actively feeding, and rapidly denuding fish of epidermis. We show here that our cultures of actively fish-killing P. shumwayae do not secrete potent exotoxinsdo not secrete potent exotoxins; rather, fish mortality results from micropredatory feeding. …

A ‘target article’

Certain episodes of mass fish mortality in coastal waters off the eastern United States have been ascribed to a planktonic organism called Pfiesteria. There are now fresh clues to how these fish are killed.

In James Powlik's novel Sea Change1, a colony of mutant cells called Pfiesteria grows into a carpet-like monster stretching over several square miles of the Strait of Juan de Fuca, a body of water separating the west coast of the United States and Canada. Its slow movement south threatens the residents of Seattle with a nightmarish fate — death following inhalation or ingestion of a toxin produced by the microbes. The good news is that the Sea Change story is fiction; the bad news is that Pfiesteria is fact. But what is the truth about this 'phantom of the ocean'? It is thought that Pfiesteria, which belongs to a group of planktonic organisms called dinoflagellates, releases a toxin that ultimately kills fish2. But using simple methods, Vogelbein and his colleagues (page 967 of this issue3) conclude that the toxin is not released into the environment and that the organism kills by direct methods.

continued …

A cute, catchy title

Luring in the readerwith a question (below)& a teaser (above)

Establishing a problem

The ‘established wisdom’’

The ‘bottom line’’ on how the target article is goingto change the ‘established wisdom’’

A digression on your News & Views assignment

In reality, the presence of Pfiesteria has not been documented along the US west coast but rather along the eastern seaboard, with a range from Delaware to Alabama4. It has been associated with massive fish kills, especially off North Carolina2. Because of the harm that results when Pfiesteria multiplies to high numbers, it is categorized with other plankton known to cause harmful 'blooms'. Many of these bloom-forming organisms produce potent toxins, so the assumption that Pfiesteria releases a toxin is not unfounded. Moreover, the population explosions of various single-celled plankton, including diatoms and dinoflagellates, are frequently associated with the production of nerve toxins — saxitoxin, brevetoxin, maitotoxin and the like5 — that are damaging when ingested by higher organisms.

These toxins are the key for researchers wishing to unlock the secrets of harmful algal blooms. By knowing the chemical identity of the toxins, highly specific detection methods can be developed to track the location of blooms and to discover where they originate, how they spread and when they are most toxic. The impact of harmful algae on living creatures, such as seabirds, marine mammals and even humans, can be assessed by determining the levels of toxin in their tissues and body fluids. But first the toxins must be isolated from the clusters of cells that release them into the environment.

This is typically done by picking a single suspect cell from the mixture of microbes in a water sample from an estuary or ocean during a harmful event, and allowing it to multiply in the laboratory. Chemical constituents are then extracted from several litres of the cells, and toxic components are identified using a bioassay, a test that assesses whether a particular fraction is poisonous, usually to a fish or mouse. For almost a decade, researchers have tried unsuccessfully to identify, from many litres of isolated Pfiesteria cells, a toxin that could explain the mass mortalities observed in the wild6. continued …

The basic story before the

target article

Vogelbein et al.3 and — in a related study, with some authors in common — Berry et al.7 have taken a different approach to the quest for a toxin released by Pfiesteria. First, they grew Pfiesteria in the lab and determined that the cultures could kill fish through direct contact. Then they separated the cells from the rest of the material using several methods, including filtration, centrifugation and dialysis (Fig. 1). They theorized that, if Pfiesteria cells release a toxin into sea water, this should be present in the cell-free fractions. But the experiments showed that the cell-free fractions do not cause fish death, and that Pfiesteria is lethal only when cells are in direct contact with the fish. The researchers therefore concluded that a toxin is not released into the surrounding sea water.

Figure 1 The dialysis technique used by Vogelbein et al.3

If they are not killed by a toxin, how do fish exposed to Pfiesteria die? It has been known for many years that Pfiesteria cells extend a suction-cup-like appendage called a peduncle to digest fish tissue2. Vogelbein et al. go a step further and propose that fish die because Pfiesteria literally sucks the life out of them. It attaches to fish skin using the peduncle, extending finger-like protrusions called filopodia, then ingests cell matter from the fish. This parasitic feeding behaviour by Pfiesteria is detailed in high-magnification microscope images in Vogelbein et al.3, and in a video clip available in their Supplementary Information.

continued …

A nice, simplesummary of

what the authorsdid & found

The new work promises to bring us closer to unveiling the true nature of this phantom of the ocean. Many loose ends remain, however, and it is possible nonetheless that a toxin is involved. Humans have suffered from memory impairment thought to stem from exposure to Pfiesteria8. Are these memory problems caused by a toxin, in aerosol form, produced by another organism that often coexists with Pfiesteria, as Berry et al.7 suggest? Do the rod-shaped granules that Vogelbein and colleagues identified in Pfiesteria (see Fig. 4 on page 969) contain toxins that are released only after the peduncle becomes attached? Do only certain Pfiesteria isolates produce toxins, as Burkholder et al.9 have proposed, indicating that the Pfiesteria studied by Vogelbein, Berry and their colleagues were simply non-toxic strains? Can contamination by a fungus or other microbe explain why Pfiesteria cultures routinely grown in the presence of fish do indeed appear to produce a toxin10?

Assembling these pieces of the complex puzzle posed by Pfiesteria will require exceptional cooperation among researchers of differing expertise. The opportunity to discuss the outstanding questions and to establish new collaborations will engage scientists at the Tenth International Conference on Harmful Algal Blooms, to be held in St Petersburg, Florida, this October.

References 3.Vogelbein, W. K. et al. Nature 418, 967-970 (2002);

What questionsare left

unanswered& what needs to be done next?

You only need to citethe target article

StramenopilaStramenopila includes several heterotrophic groups as well as a variety of photosynthetic protists (algae). The term stramenopila refers to the numerous fine, hairlike projections on the flagella that are characteristic of these organisms

the Water MoldsWater Molds (not fungi because cell walls cellulose, not chitin) ‘ick’ on fish - Fig 28.16 downy mildews on plants: potato blight, vine root rot

the DiatomsDiatoms: - Fig 28.17 have unique glasslike walls consisting of hydrated silica embedded in an organic matrix. Each wall is in two parts that overlap like a shoe box and lid –most of the year, diatoms reproduce asexually by mitotic cell divisions, with each daughter cell receiving half of the cell wall of its parent and regenerating a new second half.

Most golden algaegolden algae are unicellular, their cells biflagellated.Some species are mixotrophic, absorbing dissolved organic compounds or ingesting food particles and bacteria by phagocytosis,

Many of the ‘seaweeds’ are brown algae (ex: kelp).brown algae (ex: kelp).

Unlike other eukaryotic algae, red algaered algae have no flagellated stages in their life cycle. They are reddish because of an accessory pigment called phycoerythrin also found in cyanobacteria.

Molecular systematics and cellular morphology leave little doubt that green algaegreen algae and land plants are closely related. Some systematists advocate an expanded kingdom, the Viridiplantae.

Fig 28.24

Amoeboid thingsAmoeboid things‘A diversity of protists that use pseudopodia for movement and feedingLittle is known about their phylogeny, although it is clear that they represent several distinct eukaryotic lineages. Because of taxonomic uncertainties, we have not included these protists on the phylogenetic tree

?

the RhizopodsRhizopods (amoebas) ‘a polyphyletic group’The cytoskeleton of microtubules and microfilaments functions in amoeboid movement.Entamoeba histolytica causes amoebic dysentery.

ActinopodActinopod means "ray foot," a reference to the slender pseudopodia that radiate from these protists. Each axopodium is reinforced by a bundle of microtubules covered by a thin layer of cytoplasm. Most actinopods are planktonic, and their projections place an extensive area of cellular surface in contact with the surrounding water,

ForaminiferansForaminiferans, or forams, are named for their porous shells. Almost all are marine, most species live in the sand or on rocks and algae, but some are also abundant in plankton, deriving nourishment from the photosynthesis of symbiotic algae that live within the shells.

MycetozoaMycetozoa translates as "fungus animals," though these protists are neither fungi nor animals.

http://www.ucmp.berkeley.edu/protista/slimemolds.html

Plasmodial slime molds, like Physarum shown here, are formed when individual flagellated cells swarm together and fuse into one large bag of cytoplasm with many diploid nuclei.

Acellular PlasmodialAcellular Plasmodial slime molds - diploid - Fig 28.29

Dictyostelida (Cellular Slime Molds) Dictyostelida (Cellular Slime Molds) – haploid Fig 28.30Although the feeding stage of the life cycle consists of solitary cells that function individually, when food is depleted the cells form an aggregate that functions as a unit. Poses questions about what it means to be an individual organism.

Serves as a model for evolution of multicellularity & cooperation

C&R Fig 28.30

http://www.ucmp.berkeley.edu/protista/slimemolds.html

the cellular slime moldscellular slime molds, spend most of their lives as separate single-celled amoeboid protists, but upon the release of a chemical signal {cAMP}, the individual cells aggregate … they provide a comparatively simple and easily manipulated system for understanding how cells interact to generate a multicellular organism.how cells interact to generate a multicellular organism.

DictyosteliumDictyostelium amoebae amoebae feed on bacteria during growth, but when the food supply is exhausted, they aggregate to form a … cylindrical slug … about 80% of the amoebae form spore cells, whereas 20% form stalk cells. Spore cells germinate to give rise to the next generation, but stalk cells die. The stalk cells haveThe stalk cells have been described as altruistic, been described as altruistic, sacrificing themselvessacrificing themselves for the improvedfor the improved dispersal of spores. dispersal of spores.

Ennis et al 2000. PNAS 97:3292-3297.

One of the problems … is that in the wild, parasiticparasitic forms of forms of DictyosteliumDictyostelium should arise that should arise that form only spore cells.form only spore cells. Such parasites, not having to tithe 20% to the stalk cells, would increase in the population and eventually impede the cooperativeness that leads to fruiting body formation.impede the cooperativeness that leads to fruiting body formation.

Altruism and social cheating in the social amoeba Dictyostelium discoideumStrassmann JE, Zhu Y, Queller DCNATURE 408 (6815): 965-967 DEC 21 2000Abstract:The social amoeba, Dictyostelium discoideum, is widely used as a simple model organism for multicellular development(1,2), but its multicellular fruiting stage is really a society. its multicellular fruiting stage is really a society. Most of the time, D. discoideum lives as haploid, free-living, amoeboid cells that divide asexually. When starved, 10(4)-10(5) of these cells aggregate into a slug. The anterior 20% of the slug altruistically differentiates into a non-viable stalk, supporting the remaining cells, most of which become viable spores(3-5). If aggregating cells come from multiple clones, there should be selection for clones to exploit other clones by contributing less than their proportional share to the sterile stalk. Here we use microsatellite markers to show that different clones collected from a field population readily mix to form chimaeras. Half of the chimaeric mixtures show a clear cheater and victim. Thus, unlike the clonal and highly cooperative development of most multicellular organisms, the development of D. discoideum is partly competitive, with conflicts of interests among cells. These conflicts complicate the use of D. discoideum as a model for some aspects of development, but they make it highly attractive as a model system for social evolutiona model system for social evolution. Continued …

In social situations, opportunities arise for some individuals to take advantage of others. This happens in wild populations of the social amoeba Dictyostelium discoideum. Most of the organisms studied by developmental biologists — the fruitfly Drosophila, for instance — arise from a fertilized egg. So, apart from the mature reproductive cells, the cells from which these organisms are made are genetically identical. No cell has a genetic advantage over the others, and any variants that do arise are excluded from the germ line. Because of the lack of genetic diversity among their cells and the presence of a germ line, cheating by individual cells is restricted in most multicellular organisms. But there is another route to multicellularity, taken by organisms such as Dictyostelium and Myxococcus, a group of social bacteria. As they describe on page 965 of this issue1, Strassmann and colleagues have studied the curious cooperative behaviour of Dictyostelium, and find that some genetic variants cheat on their partners during the process of spore formation (Fig. 1). continued …

replicatingDNA molecule

Vol. 96, Issue 16, 8801-8803, August 3, 1999CommentarySlime moldsSlime molds, ascidians, and the utility of evolutionary theory Leo W. Buss

Consider a social insect colony. The colony as a unit reproduces. The ants within a colony reproduce. The cells within each ant reproduce. The mitochondria with each cell reproduce, as doesthe chromosome of the mitochondria and those of the nucleus. And within those chromosomes are likely transposable elements …

ChimerasChimeras that pit one unit of selection against anotherpit one unit of selection against another arise in specific ecological contexts, as exemplified by … slime molds …

They also can arise by mutationThey also can arise by mutation during the life of an individual, during the life of an individual, as any oncologist knows well.as any oncologist knows well.

Any modern organism is a Russian doll Any modern organism is a Russian doll ofof actually or potentially reproducing units.actually or potentially reproducing units.

Selection can, in principle,Selection can, in principle, act on each such unit. act on each such unit. We will, of course, not see its operation in most modern contexts, because conflict between units of selection are evident only when a chimera is formed.

{on Ennis et al 2000. PNAS 97:3292-3297.}