Time-course analysis of nuclear events during conjugation in the marine ciliate Euplotes vannus and comparison with other ciliates (Protozoa, Ciliophora)

Abstract

Ciliates represent a morphologically and genetically distinct group of single-celled eukaryotes that segregate germline and somatic functions into two types of nuclei and exhibit complex cytogenetic events during the sexual process of conjugation, which is under the control of the so-called "mating type systems". Studying conjugation in ciliates may provide insight into our understanding of the origins and evolution of sex and fertilization. In the present work, we studied in detail the sexual process of conjugation using the model species Euplotes vannus, and compared these nuclear events with those occurring in other ciliates. Our results indicate that in E. vannus: 1) conjugation requires about 75 hours to complete: the longest step is the development of the new macronucleus (ca. 64h), followed by the nuclear division of meiosis I (5h); the mitotic divisions usually take only 2h; 2) there are three prezygotic divisions (mitosis and meiosis I and II), and two of the eight resulting nuclei become pronuclei; 3) after the exchange and fusion of the pronuclei, two postzygotic divisions occur; two of the four products differentiate into the new micronucleus and macronucleus, respectively, and the parental macronucleus degenerates completely; 4) comparison of the nuclear events during conjugation in different ciliates reveals that there are generally three prezygotic divisions while the number of postzygotic divisions is highly variable. These results can serve as reference to investigate the mating type system operating in this species and to analyze genes involved in the different steps of the sexual process.

New contributions to two ciliate genera (Ciliophora, Heterotrichea) based on morphological and molecular analyses, with description of a new Gruberia species

“…The invertible function in Photoshop was used to adjust the photomicrographs of the infraciliature to show the structure more clearly. Hoechst 33342 solution was used to reveal the nuclear apparatus [45]. Counts, measurements, and drawings of stained specimens were made from photomicrographs (Nikon Y-IDT).…”

“…Although the description provided by Gelei [37] was brief, the somatic kinety number is an important character in ciliate species circumscription, so we posit that this population may represent a different species of Linostomella. Dragesco [38] described an isolate collected from a freshwater pond in Mokolo, Cameroon, which has fewer adoral membranelles (19)(20)(21)(22) than L. vorticella (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51) (Table 3). We agree with Foissner et al…”

Genome analyses of the new model protist Euplotes vannus focusing on genome rearrangement and resistance to environmental stressors

“…One of the most diverse and highly differentiated group among single‐celled microorganisms are ciliates, which emerged approximately one billion years ago (Parfrey, Lahr, Knoll, & Katz, ) and are abundant in diverse habitats across the globe, where they are among the most important components of food webs in aquatic ecosystems (Gao et al, ; Lynn, ). Ciliate diversity, physiology and abundance have been linked to studies of environmental change (Gong, Song, & Warren, ; Xu, Zhang, Jiang, & Yang, ), pollution monitoring (Gutiérrez, Martín‐González, Díaz, & Ortega, ; Jiang et al, ; Stoeck, Kochems, Forster, Lejzerowicz, & Pawlowski, ), biogeography (Foissner, Chao, & Katz, ; Liu et al, ; Petz, Valbonesi, Schiftner, Quesada, & Cynan Ellis‐Evans, ), adaptive evolution (Clark & Peck, ; He et al, ), cell biology (Jiang, Zhang, Vallesi, Yang, & Gao, ; Wang, Zhang, et al, ; Zheng et al, ) and epigenetics (Wang, Chen, Sheng, Liu, & Gao, ; Xiong et al, ; Zhao, Wang, Wang, Liu, & Gao, ).…”

Conjugation in Euplotes raikovi (Protista, Ciliophora): New Insights into Nuclear Events and Macronuclear Development from Micronucleate and Amicronucleate Cells

“…Conjugation has been widely studied since it was discovered in Paramecium [18] and has been described in many ciliates, such as Tetrahymena, Chilodonella, Oxytricha, and Euplotes [19][20][21][22][23][24]. During the sexual process for most species, two cells unite in a mating pair, fuse their cell membranes to form a cytoplasmic bridge, and exchange gametic pronuclei derived from MIC meiotic divisions before separating.…”