Fine structure and cytochemistry of the nuclei of the primitive ciliateTracheloraphis crassus (Karyorelictida)

Genome Biology and Evolution

Pilling

et al. 2018

The emergence of robust single-cell ‘omics techniques enables studies of uncultivable species, allowing for the (re)discovery of diverse genomic features. In this study, we combine single-cell genomics and transcriptomics to explore genome evolution in ciliates (a > 1 Gy old clade). Analysis of the data resulting from these single-cell ‘omics approaches show: 1) the description of the ciliates in the class Karyorelictea as “primitive” is inaccurate because their somatic macronuclei contain loci of varying copy number (i.e., they have been processed by genome rearrangements from the zygotic nucleus); 2) gene-sized somatic chromosomes exist in the class Litostomatea, consistent with Balbiani’s (1890) observation of giant chromosomes in this lineage; and 3) gene scrambling exists in the underexplored Postciliodesmatophora (the classes Heterotrichea and Karyorelictea, abbreviated here as the Po-clade), one of two major clades of ciliates. Together these data highlight the complex evolutionary patterns underlying germline genome architectures in ciliates and provide a basis for further exploration of principles of genome evolution in diverse microbial lineages.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Twisted Tales: Insights into Genome Diversity of Ciliates Using Single-Cell ‘Omics

Maurer‐Alcalá

Genome Biology and Evolution

Pilling

et al. 2018

“…Such high levels of amplification are also documented in the classes Spirotrichea and Phyllopharyngea, two lineages in which extensive fragmentation generates gene-sized chromosomes that are then amplified 1,000 fold or more (Huang and Katz 2014, Xu et al 2012). In contrast, Karyorelictea – the class sister to the Heterotrichea – are described as paradiploid (e.g ~2–2.5N; Raikov and Karadzhan 1985) while other ciliates such as Tetrahymena and Paramecium amplify their somatic genomes ~45 times and ~800 times, respectively (Eisen et al 2006, Duret et al 2008). Hence, ciliates contain a tremendous diversity of nuclear architectures, particularly among somatic macronuclear genomes.…”

Section: Synthesismentioning

confidence: 99%

Nuclear Features of the Heterotrich Ciliate Blepharisma americanum: Genomic Amplification, Life Cycle, and Nuclear Inclusion

Wancura

J Eukaryotic Microbiology

Katz

et al. 2017

Blepharisma americanum, a member of the understudied ciliate class Heterotrichea, has a moniliform somatic macronucleus that resembles beads on a string. Blepharisma americanum is distinguishable by its pink coloration derived from the autofluorescent pigment blepharismin and tends to have a single somatic macronucleus with 3–6 nodes and multiple germline micronuclei. We used fluorescence confocal microscopy to explore the DNA content and amplification between the somatic and germline nuclei of B. americanum through its life cycle. We estimate that the DNA content of the macronucleus and micronucleus are 43 ± 8 Gbp and 83 ± 16 Mbp respectively. This correlates with an approximate DNA content difference of 500‐fold from micronucleus to macronucleus and a macronuclear ploidy of ~1,100 N as compared to the presumably diploid micronucleus. We also investigate a previously reported macronuclear inclusion, which is present sporadically across all life cycle stages; this inclusion looks as if it contains blepharismin based on its fluorescent properties, but its function remains unknown. We also provide additional detail to our understanding of life cycles changes in B. americanum by analyses of fluorescent images. Overall, the data analyzed here contribute to our understanding of the diversity of nuclear architecture in ciliates by providing details on the highly polyploid somatic macronucleus of B. americanum.

“…They persist only through 3–7 cell divisions as estimated from the percentage of degenerating macronuclei per cell in Loxodes magnus , while macronuclei appear to exist longer in Kentrophoros fistulosum (Raikov, 1985, 1994; Raikov and Kovaleva, 1996). In contrast, macronuclei in other ciliates divide by amitosis for many generations until conjugation occurs.…”

Section: Part Ii: Development Of Macronucleimentioning

confidence: 99%

Unusual features of non-dividing somatic macronuclei in the ciliate class Karyorelictea

European Journal of Protistology

Rogers

Gao

et al. 2017

Genome structure and nuclear organization have been intensely studied in model ciliates such as Tetrahymena and Paramecium, yet few studies have focused on nuclear features of other ciliate clades including the class Karyorelictea. In most ciliates, both the somatic macronuclei and germline micronuclei divide during cell division and macronuclear development only occurs after conjugation. However, the macronuclei of Karyorelictea are non-dividing, i.e. division minus (Div−) and develop anew from micronuclei during each asexual division. As macronuclei age within Karyorelictea, they undergo changes in morphology and DNA content until they are eventually degraded and replaced by newly developed macronuclei. No less than two macronuclei and one micronucleus are present in karyorelictid species, which suggests that a mature macronucleus 1) might be needed to sustain the cell while a new macronucleus is developing and 2) likely plays a role in guiding the development of the new macronucleus. Here we use a phylogenetic framework to compile information on the morphology and development of nuclei in Karyorelictea, largely relying on the work of Dr. Igor Raikov (1932–1998). We synthesize data to speculate on the functional implications of key features of Karyorelictea including the presence of at least two macronuclei in each cell and the inability for macronuclei to divide.