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

Abstract

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.

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

“…2017 ). The other class, Karyorelictea, can be of similar sizes yet often have numerous clusters of somatic nuclei with relatively low DNA content (∼1.1–12 times more DNA in their somatic nuclei; reviewed in Yan et al. 2017 ).…”

Further analyses on the evolutionary “key‐protist”Halteria(Protista, Ciliophora) based on transcriptomic data

“…2017; Wang, Chen, Sheng, Liu, & Gao, 2017;Wang, Zhang, et al, 2017;Xiong et al, 2016;Yan et al, 2018;Yan, Rogers, Gao, & Katz, 2017;Zhang, Wang, Katz, & Gao, 2018;Zhao, Wang, Wang, Liu, & Gao, 2017;Zhao, Yi, Warren, & Song, 2018). Although these topics have been studied for hundreds of years, there are still many unresolved issues, such as the considerable discordance between morphologies and molecules, which can be caused by convergent morphologies, cryptic species, plastic phenotypes or life-cycle stage variation (reviewed in Lahr, Laughinghouse, Oliverio, Gao, & Katz, 2014).…”

Morphology and Molecular Phylogeny of Two Freshwater Oligotrich Ciliates (Protozoa, Ciliophora, Oligotrichia), Pelagostrombidium fallax (Zacharias, 1895) Krainer, 1991 and Limnostrombidium viride (Stein, 1867) Krainer, 1995, with Brief Notes on Stomatogenesis

“…, ; Yan et al. ; Zhao et al. ), whereas species from the family Pelagostrombidiidae Agatha, 2004a all live in freshwater habitats (Foissner et al.…”