Developmental progression of Tetrahymena through the cell cycle and conjugation

Cole, Elliot; Sugai, Toshiro

doi:10.1016/b978-0-12-385967-9.00007-4

Cited by 50 publications

(92 citation statements)

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“…3b), ruling out a direct role in meiotic chromatin dynamics. Meiosis of the micronucleus produces gametes that cross-fertilize, and after fertilization, two successive mitotic divisions of the zygote produce four equivalent nuclei by h 6 (27). Two of these nuclei differentiate into transcriptionally silent, heterochromatinized micronuclei, and the other two differentiate into new transcriptionally active macronuclei, a process that involves genome amplifications and establishment of condensed and decondensed chromatin domains (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Cell conjugation was initiated, and synchrony of the developmental events was monitored by determining the fraction of conjugating pairs in a particular morphological stage through a series of measurements at 1-h intervals (Fig. 3a) (27). Whole-cell protein extracts made from the samples at each time point were resolved by size and charge through acid urea-polyacrylamide gel electrophoresis (AU-PAGE), and resolved Hhp1 isoforms were detected by immunoblotting with anti-Hhp1 antiserum.…”

Section: Resultsmentioning

confidence: 99%

“…Growing and conjugating cells were fixed in 2% paraformaldehyde and processed for immunofluorescence assay as previously described (27). Fixed cells were incubated overnight at 4°C with anti-H3K27Me 3 antiserum (1:500; Active Motif catalog number 39155) in 1% bovine serum albumin (BSA)–phosphate-buffered saline (PBS)–0.1% Tween 20 (PBST).…”

Section: Methodsmentioning

confidence: 99%

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Phosphorylation-Dependent Targeting of Tetrahymena HP1 to Condensed Chromatin

Yale

Tackett

Neuman

et al. 2016

mSphere

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Compacting the genome to various degrees influences processes that use DNA as a template, such as gene transcription and replication. This project was aimed at learning more about the cellular mechanisms that control genome compaction. Posttranslational modifications of proteins involved in genome condensation are emerging as potentially important points of regulation. To help elucidate protein modifications and how they affect the function of condensation proteins, we investigated the phosphorylation of the chromatin protein called Hhp1 in the ciliated protozoan Tetrahymena thermophila. This is one of the first functional investigations of these modifications of a nonhistone chromatin condensation protein that acts on the ciliate genome, and discoveries will aid in identifying common, evolutionarily conserved strategies that control the dynamic compaction of genomes.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Phosphorylation-Dependent Targeting of Tetrahymena HP1 to Condensed Chromatin

Yale

Tackett

Neuman

et al. 2016

mSphere

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“…Although sex is very well documented in many protist groups, and members of some taxa, such as ciliates (Alveolata), diatoms (Stramenopiles), or green algae (Chloroplastida), even serve as models to study various aspects of sexuality (3)(4)(5), direct observation of sexual processes is lacking for a majority of protist species (6,7), and entire protist lineages cannot be considered sexual with any certainty yet. However, information about the life history of many protists is rudimentary, and a strong bias, especially toward parasitic lineages, is also found in the selection of current genome sequencing projects (8).…”

Section: Sex In Eukaryotic Microorganisms: More Voyeurs Neededmentioning

confidence: 99%

Sex is a ubiquitous, ancient, and inherent attribute of eukaryotic life

Speijer

Lukeš

Eliáš

2015

Proc. Natl. Acad. Sci. U.S.A.

266

267

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Sexual reproduction and clonality in eukaryotes are mostly seen as exclusive, the latter being rather exceptional. This view might be biased by focusing almost exclusively on metazoans. We analyze and discuss reproduction in the context of extant eukaryotic diversity, paying special attention to protists. We present results of phylogenetically extended searches for homologs of two proteins functioning in cell and nuclear fusion, respectively (HAP2 and GEX1), providing indirect evidence for these processes in several eukaryotic lineages where sex has not been observed yet. We argue that (i) the debate on the relative significance of sex and clonality in eukaryotes is confounded by not appropriately distinguishing multicellular and unicellular organisms; (ii) eukaryotic sex is extremely widespread and already present in the last eukaryotic common ancestor; and (iii) the general mode of existence of eukaryotes is best described by clonally propagating cell lines with episodic sex triggered by external or internal clues. However, important questions concern the relative longevity of true clonal species (i.e., species not able to return to sexual procreation anymore). Long-lived clonal species seem strikingly rare. We analyze their properties in the light of meiotic sex development from existing prokaryotic repair mechanisms. Based on these considerations, we speculate that eukaryotic sex likely developed as a cellular survival strategy, possibly in the context of internal reactive oxygen species stress generated by a (proto) mitochondrion. Thus, in the context of the symbiogenic model of eukaryotic origin, sex might directly result from the very evolutionary mode by which eukaryotic cells arose.reactive oxygen species | evolution | protists | eukaryotes | sex

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“…Indeed, it is well documented that micronuclei age and eventually lose the ability to transmit genes [8-10]. As in other systems, meiosis effects repair of genetic damage [11], up to a limit. Ciliates also likely benefit by replacing the macronucleus, as there is an old and extensive literature on macronuclear failure and death of clones prevented from having sex [8].…”

Section: Introductionmentioning

confidence: 99%

Abandoning sex: multiple origins of asexuality in the ciliate Tetrahymena

Doerder

2014

BMC Evol Biol

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BackgroundBy segregating somatic and germinal functions into large, compound macronuclei and small diploid micronuclei, respectively, ciliates can explore sexuality in ways other eukaryotes cannot. Sex, for instance, is not for reproduction but for nuclear replacement in the two cells temporarily joined in conjugation. With equal contributions from both conjugants, there is no cost of sex which theory predicts should favor asexuality. Yet ciliate asexuality is rare. The exceptional Tetrahymena has abandoned sex through loss of the micronucleus; its amicronucleates are abundant in nature where they reproduce by binary fission but never form conjugating pairs. A possible reason for their abundance is that the Tetrahymena macronucleus does not accumulate mutations as proposed by Muller’s ratchet. As such, Tetrahymena amicronucleates have the potential to be very old. This study used cytochrome oxidase-1 barcodes to determine the phylogenetic origin and relative age of amicronucleates isolated from nature.ResultsAmicronucleates constituted 25% of Tetrahymena-like wild isolates. Of the 244 amicronucleates examined for cox1 barcodes, 237 belonged to Tetrahymena, seven to other genera. Sixty percent originated from 12 named species or barcoded strains, including the model Tetrahymena thermophila, while the remaining 40% represent 19 putative new species, eight of which have micronucleate counterparts and 11 of which are known only as amicronucleates. In some instances, cox1 haplotypes were shared among micronucleate and amicronucleates collected from the same source. Phylogenetic analysis showed that most amicronucleates belong to the “borealis” clade in which mating type is determined by gene rearrangement. Some amicronucleate species were clustered on the SSU phylogenetic tree and had longer branch lengths, indicating more ancient origin.ConclusionsNaturally occurring Tetrahymena amicronucleates have multiple origins, arising from numerous species. Likely many more new species remain to be discovered. Shared haplotypes indicate that some are of contemporary origin, while phylogeny indicates that others may be millions of years old. The apparent success of amicronucleate Tetrahymena may be because macronuclear assortment and recombination allow them to avoid Muller’s ratchet, incorporate beneficial mutations, and evolve independently of sex. The inability of amicronucleates to mate may be the result of error(s) in mating type gene rearrangement.

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Developmental progression of Tetrahymena through the cell cycle and conjugation

Cited by 50 publications

References 149 publications

Phosphorylation-Dependent Targeting of Tetrahymena HP1 to Condensed Chromatin

Phosphorylation-Dependent Targeting of Tetrahymena HP1 to Condensed Chromatin

Sex is a ubiquitous, ancient, and inherent attribute of eukaryotic life

Abandoning sex: multiple origins of asexuality in the ciliate Tetrahymena

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