TY - JOUR

T1 - Loss of a fragile chromosome region leads to the Screwy phenotype in Paramecium tetraurelia

AU - Nekrasova, Irina

AU - Nikitashina, Vera

AU - Bhullar, Simran

AU - Arnaiz, Olivier

AU - Singh, Deepankar P.

AU - Meyer, Eric

AU - Potekhin, Alexey

N1 - Publisher Copyright: © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2019/7/6

Y1 - 2019/7/6

N2 - A conspicuous cell-shape phenotype known as “screwy” was reported to result from mutations at two or three uncharacterized loci in the ciliate Paramecium tetraurelia. Here, we describe a new screwy mutation, Spinning Top, which appeared spontaneously in the cross of an unrelated mutant with reference strain 51. The macronuclear (MAC) genome of the Spinning Top mutant is shown to lack a ~28.5-kb segment containing 18 genes at the end of one chromosome, which appears to result from a collinear deletion in the micronuclear (MIC) genome. We tested several candidate genes from the deleted locus by dsRNA-induced silencing in wild-type cells, and identified a single gene responsible for the phenotype. This gene, named Spade, encodes a 566-aa glutamine-rich protein with a C 2 HC zinc finger. Its silencing leads to a fast phenotype switch during vegetative growth, but cells recover a wild-type phenotype only 5–6 divisions after silencing is stopped. We analyzed 5 independently-obtained mutant alleles of the Sc1 locus, and concluded that all of them also lack the Spade gene and a number of neighboring genes in the MAC and MIC genomes. Mapping of the MAC deletion breakpoints revealed two different positions among the 5 alleles, both of which differ from the Spinning Top breakpoint. These results suggest that this MIC chromosome region is intrinsically unstable in strain 51.

AB - A conspicuous cell-shape phenotype known as “screwy” was reported to result from mutations at two or three uncharacterized loci in the ciliate Paramecium tetraurelia. Here, we describe a new screwy mutation, Spinning Top, which appeared spontaneously in the cross of an unrelated mutant with reference strain 51. The macronuclear (MAC) genome of the Spinning Top mutant is shown to lack a ~28.5-kb segment containing 18 genes at the end of one chromosome, which appears to result from a collinear deletion in the micronuclear (MIC) genome. We tested several candidate genes from the deleted locus by dsRNA-induced silencing in wild-type cells, and identified a single gene responsible for the phenotype. This gene, named Spade, encodes a 566-aa glutamine-rich protein with a C 2 HC zinc finger. Its silencing leads to a fast phenotype switch during vegetative growth, but cells recover a wild-type phenotype only 5–6 divisions after silencing is stopped. We analyzed 5 independently-obtained mutant alleles of the Sc1 locus, and concluded that all of them also lack the Spade gene and a number of neighboring genes in the MAC and MIC genomes. Mapping of the MAC deletion breakpoints revealed two different positions among the 5 alleles, both of which differ from the Spinning Top breakpoint. These results suggest that this MIC chromosome region is intrinsically unstable in strain 51.

KW - Chromosome fragile sites

KW - Cortical inheritance

KW - Epimutation

KW - Maternal inheritance

KW - Micronuclear deletion

KW - Paramecium

KW - Trichocysts

KW - Genes, Protozoan

KW - Protozoan Proteins/genetics

KW - Chromosome Fragility

KW - Phenotype

KW - Paramecium tetraurelia/genetics

KW - Mutation

KW - epimutation

KW - trichocysts

KW - cortical inheritance

KW - maternal inheritance

KW - micronuclear deletion

KW - AURELIA

KW - PROTEINS

KW - chromosome fragile sites

KW - MACRONUCLEAR DEVELOPMENT

UR - http://www.scopus.com/inward/record.url?scp=85069433919&partnerID=8YFLogxK

U2 - 10.3390/genes10070513

DO - 10.3390/genes10070513

M3 - Article

C2 - 31284605

VL - 10

JO - Genes

JF - Genes

SN - 2073-4425

IS - 7

M1 - 513

ER -