Download Overview of Lecture: Eukaryotes: Protists. Read: Text Ch 24 (review

Overview of Lecture: Eukaryotes: Protists.
Read: Text Ch 24 (review Ch 4) Bullet Points: • eukaryotes
• some properties of eukaryotic cells • endosymbiont theory of origins
• protists: a paraphyletic “junk drawer”
• a couple if interesting protists:
• Trypanosoma – sleeping sickness & Chagas’ disease
• Toxoplasma gondii
How Your Cat Is Making You Crazy The lecturer doth
• cellular slime molds
protist too much,
genetic conflict & cooperation
methinks.
~Hamlet Act 3, scene 2
• FYI -­ a News & Views example
Learning Goals:
1. Understand and be able to explain …
The endosymbiotic theory for the evolutionary origin of eukaryotes. Give a very general overview of the genetic and metabolic roles of the remaining mitrochondrial
genes in modern animals, including humans. How does this division of genes and metabolic labor set the stage for both (a) sexual selection for males with nuclear genes that are compatible with a female’s mitochondrial genes, and (2) the ‘three parent’ genetic engineering technique recently employed in humans?
2. Understand and be able to …
Describe two important diseases caused by Trypanosoma species. Explain why (a) penicillin won’t work on trypanosomes, and (b) it is so difficult to find antibiotics that target these diseases and are also safe for human use. How do trypanosomes evade the adaptive immune system?
3. Give a brief description of the life cycle of the slime mold Dictostelium and explain why it is used of a simple model of the evolution of sociality and social cooperation and cheating.
Important features likely present in the common ancestor of eukaryotes.
{ shared derived homologous traits }
Some of these features have been lost in some lineages, {mitochondria}
• Cytoskeleton consisting of tubulin-­based microtubules and actin-­based microfilaments
• Motile cell extensions called ‘flagella’ or ‘cilia’ that contain 9 peripheral microtubular doublets and 2 central microtubules. • An endomembrane system that consists of endoplasmic reticulum, Golgi bodies, vacuoles, lysosomes, peroxisomes, and the nuclear envelope. • Primary genome of each cell consisting of multiple linear chromosomes
contained within a membrane-­bound nucleus. {the “eukaryote”}
• Following replication, the chromosomes are segregated by mitosis.
• Mitochondria -­ organelles with diverse functions, usually including aerobic respiration and synthesis and breakdown of lipids, amino acids etc. Mitochondria are bounded by two membranes, and usually contain a small genome. They are the descendents of an alpha-­proteobacterial endosymbiont. • Translation machinery in the form of 80S ribosomes, {prokaryotes have 70s}
The Endosymbiotic Theory of Eukaryote Evolution
This idea was promulgated at the turn of the 20th century (Mereschkowsky, 1910) and championed later by Lynn Margulis. Lynn Margulis
Mitochondria & plastids replicate by a process ~ binary fission in prokaryotes. Each organelle contains a single, circular DNA molecule that, like the chromosomes of bacteria, is not associated with histones or other proteins. In terms of size, nucleotide sequence, and sensitivity to certain antibiotics, the ribosomes of mitochondria & plastids are more similar to prokaryotic ribosomes than they are to eukaryotic ribosomes.
Comparisons of rRNA from mitochondria, plastids, & various prokaryotes indicate that alpha proteobacteria are the closest relatives of mitochondria, & cyanobacteria are the closest relatives of plastids.
Over time, some of the genes originally present in mitochondria and plastids were transferred to the host cell nucleus. [making the organelles dependent on ‘host’]
EVOLUTION: Growing Closer Together
Laura M. Zahn, PLOS ONE 5, E11486 (2010)
The conversion of a free-­living organism into a domesticated organelle is a remarkable event, The fern (left) and the and mitochondria and chloroplasts have become bacterium (right).
virtually indispensable components of eukaryotic life. CREDIT: RAN ET AL.
Ran et al. have sequenced the genome of a nitrogen-­fixing symbiont of the water fern Azolla filiculoides and suggest that
this cyanobacterium may have been partly domesticated by its host. They note that there appears to have been co-­evolution between the two organisms, as revealed in the intricate means by which Azolla maintains cyanobacterial colonies through successive generations. {vertical trans.}
Furthermore, hallmarks of genome reduction in the symbiont, such as excessive pseudogenization {loss of function}, were identified,
and the pattern of gene losses … {symbiont becoming ’genetically dependent’}
Several basic metabolic processes {that the fern can do}
such as glycolysis, replication, and nutrient import had suffered losses, yet nitrogen-­fixing pathways {that the fern lacks} had remained intact. This apparent streamlining of the genome indicates that progress toward a full mutualism between the plant and the cyanobacterium may be well under way. Mitonuclear Ecology
Geoffrey E. Hill Mol Biol Evol (2015) doi: 10.1093/molbev/msv104
Eukaryotes were born of a chimeric union between two prokaryotes
-­ the progenitors of the mitochondrial and nuclear genomes. Early in eukaryote evolution, most mitochondrial genes were lost or transferred to the nucleus, but a core set of genes remained in the mitochondrion. The products of these mitochondrial genes [passed from mother to offspring in egg]
work in intimate association with the products of nuclear genes to enable oxidative phosphorylation and core energy production. The need for coadaptation [a good match between mitochondial and nuclear genes], … and the possibility of genomic conflict between mitochondrial and nuclear genes have profound consequences for the ecology and evolution of eukaryotic life. An emerging interdisciplinary field that I call “mitonuclear ecology” is reassessing core concepts in evolutionary ecology including sexual reproduction, two sexes, sexual selection, adaptation, and speciation in light of the interactions of mitochondrial and nuclear genomes.
The mitonuclear compatibility hypothesis of sexual selection
Geoffrey E. Hill, James D. Johnson 2013 Proceedings of the Royal Society 280
See: https://www.youtube.com/watch?v=uQZ2TR8NgpU [50 min]
Why females assess ornaments when choosing mates remains a central question in evolutionary biology. We hypothesize that the imperative for a choosing female to find a mate with nuclear oxidative phosphorylation (OXPHOS) genes that are compatible with her mitochondrial OXPHOS genes drives the evolution of ornaments. …
https://www.washingtonpost.com/news/speaking-­of-­science/wp/2016/09/27/first-­ever-­baby-­born-­using-­three-­parent-­genetic-­engineering/
First-­ever baby born using ‘three parent’ genetic engineering technique
By Rachel Feltman September 27 2016
… a Jordanian couple conceived and gave birth to a child with [three] genetic parents.
These techniques involve the transfer of mitochondrial DNA or mtDNA. … the mitochondria convert energy from food into energy that can power a cell. When someone's mitochondria don't function properly, it's bad news indeed for cells. Mitochondrial diseases can cause a whole host of life-­threatening problems, … ~4,000 children are born with such conditions in the United States each year. Mitochondrial DNA, which contains just 37 genes compared to the staggering 20,000 or so carried by DNA in a cell's nucleus, comes entirely from the egg cell -­ the sperm cell contributes no mitochondria to the fertilized embryo, [maternal inheritance – “mitochondrial Eve” https://en.wikipedia.org/wiki/Mitochondrial_Eve ]
Replacing the mother's faulty mitochondria with donor mitochondria in the newly conceived embryonic cells can produce a healthy baby while preserving the vast majority of its mother's [nuclear] DNA.
in a ”state of flux”
The protists
are the ‘junk drawer’ of eukaryotes that traditionally were not considered to be animals, fungi or plants. Advances in systematics have caused the kingdom Protista to crumble. the former kingdom is paraphyletic: some protists are more closely related to plants, fungi, or animals than to other protists.
{& plants are a problem: sister clade to “green algae”
– but not included in “protists”}
As a result, the kingdom Protista has been abandoned ... Biologists still use ‘protist’ informally, {like ‘reptile’ or ‘dog’}
as a convenient way to refer to eukaryotes that are neither plants, animals, nor fungi.
Euglenozoa: Kinetoplasts: Trypanosoma
African Trypanosomiasis (African Sleeping Sickness)
Trypanosomiasis is caused by the parasite Trypanosoma brucei. ... transmitted by the bite of the tsetse fly ... confined to tropical Africa ...
According to WHO, 25,000-­45,000 cases of trypanosomiasis are reported annually;; however, the actual prevalence of cases is estimated to be 300,000 to 500,000. Trypanosomes evade immune detection with a “bait–and–switch” defense. The surface of a trypanosome is coated with millions of copies of a single protein. However, before the host′s [adaptive] immune system can mount an attack, new generations of the parasite switch to another surface protein. {antigenic shift}
~ 1/3 of Trypanosoma′s genome is dedicated to these surface proteins.
Vaccination is impossible due to antigenic variation of the parasites. In untreated patients ... progressive neurologic dysfunction and death. { It is difficult to find metabolic targets for drugs against eukaryotic diseases that don’t have severe side effects for our eukaryotic selves! }
Trypanosomosis, is arguably the main constraint to livestock production on the continent, preventing full use of the land
to feed the rapidly increasing human population.
{by replacing wildlife w/ cattle} http://www.biosci.ohio-­state.edu/~parasite/chagas.html
Euglenozoa: Kinetoplasts: Trypanosoma
A few species of Trypanosoma are found in the New World.
From the standpoint of human health, the most important is Trypanosoma cruzi, causing American trypanosomiasis or Chagas' disease.
The vector for Chagas' disease
is a "true bug" (Hemiptera)
In the human host, Chagas' disease affects primarily the nervous system and heart.
Chronic infections result in various neurological disorders, including dementia, and damage to the heart muscle. Left untreated, Chagas' disease is often fatal.
http://www.cdc.gov/parasites/chagas/ The two drugs used to treat infection are nifurtimox and benznidazole. These drugs are not FDA approved !!!!
Small animals such as dogs, cats, guinea pigs, rats and opossums can serve as reservoirs for the parasite. T. cruzi.
There is no known cure for T. cruzi infection in dogs and cats. {nor humans?} 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. the ranges of T. cruzi & vectors are spreading north w/ global warming, into USA
A Tropical Disease Hits the Road. M. Leslie. Science 19 August 2011
Toxoplasma gondii
The Model Apicomplexan: Perspectives and Methods Edited by Louis Weiss & Kami Kim
Toxoplasmosis is caused by a one-­celled protozoan {protist} parasite known as Toxoplasma gondii. The parasite increases likelihood of entering cat host by altering mouse and rat behavior – and potentially alters human behavior as well?
Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors.
Vyas et al. 2007. Proc Natl Acad Sci U S A. 104(15): 6442–6447. I love c at urine!
In the US … ~30% of cats, the primary carriers, have been infected …
By the age of 50, 40% of people test positive for the parasite.
Most humans contract toxoplasmosis by eating cyst-­contaminated raw or undercooked meat, vegetables, or milk or when they come into contact with the T. gondii eggs from cat feaces while cleaning a cat's litterbox, gardening, or playing in a sandbox. The predilection of this parasite is for the central nervous system (CNS), causing behavioral and personality alterations as well as fatal necrotizing encephalitis, …
http://www.theatlantic.com/magazine/archive/2012/03/how-­your-­cat-­is-­making-­you-­crazy/308873/
How Your Cat Is Making You Crazy MARCH 2012 ATLANTIC MAGAZINE
… a woman who becomes infected during pregnancy can transmit the disease to the fetus, in some cases resulting in severe brain damage or death. … in the early days of the AIDS epidemic … it was to blame for the dementia that afflicted many patients at the disease’s end stage. Healthy children and adults, however, usually experience
nothing worse than brief flu-­like symptoms before quickly fighting off the {protists}, which thereafter lies dormant inside brain cells -­ or at least that’s the standard medical wisdom.
Published: Aug. 16, 2012
COMMON PARASITE MAY TRIGGER SUICIDE ATTEMPTS
New research … adds to the growing work linking infection by the Toxoplasma gondii parasite
to suicide attempts. MSU’s Lena Brundin …
About 10-­20 percent of people in the United States have T. gondii, in their bodies, … it appears the parasite can cause inflammation over time, which produces harmful metabolites that can damage brain cells.
Previous research has found signs of inflammation
in the brains of suicide victims and people battling depression, In our study we found that if you are positive for the parasite, you are seven times more likely to attempt suicide.
[correlation – yes;; cause – maybe]
… the Relationship between Cat Bites and Human Depression …
Hanauer et al 2013 PLOS One. Depression affected 41% of 750 patients with cat bites,
9% of the total 1.3 million patients Watch: https://www.youtube.com/watch?v=vjRPla0BONA Watch: https://www.youtube.com/watch?v=duLTekqtkmk
include slime molds
http://www.ucmp.berkeley.edu/protista/slimemolds.html
the cellular slime molds, spend most of their lives as separate single-­celled amoeboid protists, but {when food is depleted}
the release of a chemical signal {cAMP},
causes the cells to aggregate … they provide a simple system for understanding how cells interact to generate a multicellular organism.
Dictyostelida (Cellular Slime Molds)
Raise questions about what it means to be an individual organism. Serves as a model for the evolution of multicellularity & cooperation & cheating
Altruism and social cheating in the social amoeba Dictyostelium discoideum
Strassmann et al. 2000. NATURE 408 (6815): 965-­967 Most of the time, D. discoideum lives as haploid, free-­living, amoeboid cells... When starved, 104-­105 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. If aggregating cells come from multiple clones, {different genotypes – unrelated}
there should be selection for clones to exploit other clones by contributing less than their proportional share to the sterile stalk. ...
High relatedness maintains multicellular cooperation in a social amoeba by controlling cheater mutants. Gilbert, OM et al. 2007. Proc. Natl. Acad. Sci. USA. 104:8913-­8917. Cooperative groups are vulnerable to exploitation by cheaters, ... high relatedness is thought to aid in selection against cheaters. ... cheaters and cooperators will tend to be in different groups, which both limits opportunities for cheaters to exploit cooperators and exposes any group-­level defects of cheaters to selection.
We show that relatedness in cooperative groups of D. discoideum
is very high, higher even than in most eusocial insect colonies. It is not clear what maintains high relatedness in D. discoideum. As in most eusocial insects, kin discrimination might be important. Kin preference in a social microbe. Mehdiabadiet al. 2006. Nature. 442: 881-­882.
... Dictyostelium purpureum preferentially associates with kin ...
http://www.cell.com/current-­biology/pdf/S0960-­9822(02)01344-­1.pdf
What is kin selection? Kin selection is a part of natural selection. Selection normally favors a gene if it increases reproduction, because the offspring share copies of that gene,
but a gene can also be favored if it aids other relatives,
who also share copies.
It is this selection via relatives that is referred to as kin selection.
Does kin selection matter to cell and molecular biology? Yes, if for no other reason than the fact that multicellular organisms
evolved because of the high relatedness among cells (usually single clones, though multicellular Dictyostelium
can be mixtures of clones). Kin selection should affect any interactions among related pathogens,
including many that determine virulence. Finally, the leading theory of the function of genomic imprinting is based on the fact that genes inherited from the mother or from the father may have different optimal
kin selection strategies.
Learning Goals:
1. Understand and be able to explain …
The endosymbiotic theory for the evolutionary origin of eukaryotes. Give a very general overview of the genetic and metabolic roles of the remaining mitrochondrial
genes in modern animals, including humans. How does this division of genes and metabolic labor set the stage for both (a) sexual selection for males with nuclear genes that are compatible with a female’s mitochondrial genes, and (2) the ‘three parent’ genetic engineering technique recently employed in humans?
2. Understand and be able to …
Describe two important diseases caused by Trypanosoma species. Explain why (a) penicillin won’t work on trypanosomes, and (b) it is so difficult to find antibiotics that target these diseases and are also safe for human use. How do trypanosomes evade the adaptive immune system?
3. Give a brief description of the life cycle of the slime mold Dictostelium and explain why it is used of a simple model of the evolution of sociality and social cooperation and cheating.
http://www.epa.gov/owow/estuaries/pfiesteria/fact.html
What is Pfiesteria ? Alveolata: Dinoflagellates: Pfiesteria 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 Pfiesteria, are more animal-­like and acquire some or all of their energy by eating other organisms. Pfiesteria 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 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 …
A digression on your News & Views assignment
A ‘target article’: an original research report with data in a scientific journal Pfiesteria piscicida and P. shumwayae reportedly 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 exotoxins;; rather, fish mortality results from micropredatory feeding. …
A digression on your News & Views assignment
A cute, catchy title
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 …
Establishing a problem
Luring in the reader
with a teaser (above)
& a question (below)
The ‘established wisdom’’
The ‘bottom line’’ on how
the target article is going
to change the ‘established wisdom’’
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
{you can get this from the TA Intro.
& the text}
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, simple
summary of
what the authors
did & found
-­ you need to craft
this with your
own brain!
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 questions
are left unanswered
& what needs to be done next?
-­more critical creativity from
your own brain! You only need to cite
the target article
The grading rubric: http://www.msu.edu/course/bs/182h/fall2016/News&Viewsrubric.pdf
Example student papers: http://www.msu.edu/course/bs/182h/fall2016/N&Vexamples.pdf