Meiosis in protists. Some structural and physiological aspects of meiosis in algae, fungi, and protozoa.

Heywood, Peter; Magee, P T

doi:10.1128/mmbr.40.1.190-240.1976

Cited by 28 publications

(7 citation statements)

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“…The regular establishment of diploid–haploid cycles probably happened later, mostly in multicellular eukaryotes. The diversity of meiosis variants in protists supports the hypothesis of a stepwise establishment process with many experimentations [ 77 ]. Meiotic recombination with its typical extant features (e.g.…”

Section: Evolution Of Meiosis As a Response To Oxidative Damagementioning

confidence: 53%

How oxygen gave rise to eukaryotic sex

Hörandl

Speijer

2018

Proc. R. Soc. B.

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How did full meiotic eukaryotic sex evolve and what was the immediate advantage allowing it to develop? We propose that the crucial determinant can be found in internal reactive oxygen species (ROS) formation at the start of eukaryotic evolution approximately 2 × 109 years ago. The large amount of ROS coming from a bacterial endosymbiont gave rise to DNA damage and vast increases in host genome mutation rates. Eukaryogenesis and chromosome evolution represent adaptations to oxidative stress. The host, an archaeon, most probably already had repair mechanisms based on DNA pairing and recombination, and possibly some kind of primitive cell fusion mechanism. The detrimental effects of internal ROS formation on host genome integrity set the stage allowing evolution of meiotic sex from these humble beginnings. Basic meiotic mechanisms thus probably evolved in response to endogenous ROS production by the ‘pre-mitochondrion’. This alternative to mitosis is crucial under novel, ROS-producing stress situations, like extensive motility or phagotrophy in heterotrophs and endosymbiontic photosynthesis in autotrophs. In multicellular eukaryotes with a germline–soma differentiation, meiotic sex with diploid–haploid cycles improved efficient purging of deleterious mutations. Constant pressure of endogenous ROS explains the ubiquitous maintenance of meiotic sex in practically all eukaryotic kingdoms. Here, we discuss the relevant observations underpinning this model.

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Section: Evolution Of Meiosis As a Response To Oxidative Damagementioning

confidence: 53%

How oxygen gave rise to eukaryotic sex

Hörandl

Speijer

2018

Proc. R. Soc. B.

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“…Homologs of meiosis-specific genes were detected in the genomes of each of these organisms, indicating that they are derived from sexual lineages and may be sexual themselves (Figure 5.1). Consistent with this inference, meiosis has been observed in relatives of each of these organisms, except in other diplomonads (reviewed by [130,157,295,308,309]).…”

Section: Meiotic Genes In Presumed Asexualsmentioning

confidence: 65%

“…The presence of homologs of meiosis-specific genes is indicated by red dots, the presence of general-function genes indicated by green dots, black dots indicate the absence of genes from completely sequenced genome projects and yellow circles represent "missing data", from incompletely annotated genomes. The presence of the synaptonemal complex is indicated by blue circles and its absence by "-", summarized from references [160,[294][295][296][297][298][299][300][301][302][303][304][305][306]. Though it is not directly involved in mediating crossover resolution, Msh2 is included as an example of a ubiquitous gene found in completely annotated genome projects.…”

Section: Phylogenetic Analysismentioning

confidence: 99%

“…Protists reveal evidence of both evolutionary conservation and variation in the meiotic machinery; both unconventional meiosis and no meiosis have been reported among protists [157]. Indeed, sexuality is variant-even deviant-among the protists [130,295]; whether they possess meiotic machinery homologous to that in AFP is unknown since underlying molecular mechanisms have generally not been determined due to the lack of genetic tools. Recent protist genome sequencing projects have allowed access to such genetic data, making comparative genomic studies feasible.…”

Section: Future Directionsmentioning

confidence: 99%

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The early evolution of meiotic genes

Malik¹

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Thesis Supervisor: Associate Professor John M. Logsdon Jr.Meiosis is a hallmark of eukaryotes. However, to demonstrate that homologous sexual processes are pan-eukaryotic, it is necessary to compare the molecular machinery of meiotic recombination across diverse eukaryotic groups, especially protists. The homologs of 34 meiotic genes encoding components of the meiotic recombination machinery, sister chromatid cohesion and synaptonemal complexes were identified in the genomes of diverse eukaryotes and verified by phylogenetic analyses. Twelve of these genes function only in meiosis in model organisms Hop1, Hop2, Mnd1, Dmc1, Msh4, Msh5, Mer3, Zip1, Zip4 and Rec8). Homologs of meiosis-specific genes were identified in several organisms previously considered to be asexual, indicating that they are derived from sexual lineages, and may have as-yet-unobserved meiosis. The putatively early-diverged protists Trichomonas and Giardia have orthologs of eight and six of the meiosis-specific genes, respectively. Using degenerate PCR, additional meiosis-specific genes were identified in Naegleria, Acanthamoeba, Amphidinium and other protists. All of the meiotic genes are conserved in animals, fungi and plants; most of the meiotic genes (including the meiosis-specific genes) are also broadly conserved among protist lineages. These data indicate that the molecular machinery for meiotic recombination evolved once, early during eukaryotic evolution, prior to the divergence of major eukaryotic lineages. Thus, the eukaryotic cenancestor likely had each component of this "meiosis detection toolkit". Many of the 34 meiotic genes -including ten meiosis-specific genes -evolved by gene duplications early during eukaryotic evolution, revealing that gene duplication has been a pervasive evolutionary force in the evolution of the meiotic machinery. Abstract Approved: ____________________________________ Thesis Supervisor ____________________________________ ii To my grandmothers, Bano-bai Mazher Master binte Imran-bhai Shamsi and the late Zainab-bai Gulamali Malik binte Noman-bhai Rangwala, and to my mother, Nafisa Hatim Malik binte Mazher-bhai Master. iii ACKNOWLEDGMENTS I would like to express my gratitude towards the many people who contributed towards my growth as a scientist while I have pursued this degree, from Emory University to the University of Iowa. First and foremost, I would like to thank my thesis advisor, John Logsdon, for his time, advice, many discussions, and for giving me the opportunity to work with him on the projects culminating in this thesis. I also feel fortunate that John has sent me to present my work at a conference almost every year, and really helped me to network with other scientists. I am grateful to my other thesis advisory committee members, Bryant McAllister, Bob Malone, Debashish Bhattacharya and Chris Brochu, for their time, constructive criticism and helpful advice. I am indebted to Mark Farmer and David Patterson for illustrative discussions about protists. I am thankful to Chris Beck, Sonia Altiz...

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“…The fate of the nucleolus during trypanosoine mitosis is highly variable-it niay remain intact ( 1 4 ) , it may fragment (17,19), or it may dispcmr (1.). Although this range of behavior is known from other protists ( 7 ) , it is of interest to note its occurrence ivithin a single genus. Material of presuniptive nuclcolar origin can often lie recognized in the vicinity of the spindle microtulirilrs.…”

Section: Discussionmentioning

confidence: 98%

Mitosis in the Hemoflagellate *Trypanosoma cyclops**

Heywood

Weinman

1978

The Journal of Protozoology

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The ultrastructure of interphase and mitotic nuclei of the epimastigote form of Trypanosoma cyclops Weinman is described. In the interphase nucleus the nucleolus is located centrally while at the periphery of the nucleus condensed chromatin is in contact with the nuclear envelope. The nucleolus fragments at the onset of mitosis, but granular material of presumptive nucleolar origin is often recognizable in the mitotic nucleus. Peripheral chromatin is in contact with the nuclear envelope throughout mitosis, and it seems reasonable to assume that the nuclear envelope is involved in its segregation to the daughter nuclei. Spindle microtubules extend between the poles of the dividing nucleus and terminate close to the nuclear envelope. The basal body and kinetoplast divide before the onset of mitosis and do not appear to have any morphologic involvement in that process. Spindle pole bodies, kinetochores, and chromosomal microtubules have not been observed.

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Meiosis in protists. Some structural and physiological aspects of meiosis in algae, fungi, and protozoa.

Cited by 28 publications

References 164 publications

How oxygen gave rise to eukaryotic sex

How oxygen gave rise to eukaryotic sex

The early evolution of meiotic genes

Mitosis in the Hemoflagellate *Trypanosoma cyclops**

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Meiosis in protists. Some structural and physiological aspects of meiosis in algae, fungi, and protozoa.

Cited by 28 publications

References 164 publications

How oxygen gave rise to eukaryotic sex

How oxygen gave rise to eukaryotic sex

The early evolution of meiotic genes

Mitosis in the Hemoflagellate Trypanosoma cyclops*

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Product

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Mitosis in the Hemoflagellate *Trypanosoma cyclops**