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A cytoplasm-specific activity encoded by the Trithorax-like ATX1 gene.

Ndamukong I, Lapko H, Cerny RL, Avramova Z - Nucleic Acids Res. (2011)

Bottom Line: It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET).It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A).Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA.

ABSTRACT
Eukaryotes produce multiple products from a single gene locus by alternative splicing, translation or promoter usage as mechanisms expanding the complexity of their proteome. Trithorax proteins, including the Arabidopsis Trithorax-like protein ATX1, are histone modifiers regulating gene activity. Here, we report that a novel member of the Trithorax family has a role unrelated to chromatin. It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET). It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A). Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

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The actin cytoskeleton and RNAi-SET. Actin filaments stained with phalloidin in wild-type leaf cells exhibiting actin bundles of various thicknesses (a–c). A contrast image (d) of the cells shown in (c) illustrating the TVS (arrows). Bars are 20 µM. Actin filaments in RNAi-SET expressing cells in (e–j). Granular particles on the vacuolar periphery are indicated by arrows in e. (g) Bars are 20 µM. Closer look at vacuolar-associated actin (h–j). Arrows indicate the cell wall. Bar is 10 µM. Actin bundles in atx1 mutant cells (k–m). Bars are 20 µM.
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Figure 6: The actin cytoskeleton and RNAi-SET. Actin filaments stained with phalloidin in wild-type leaf cells exhibiting actin bundles of various thicknesses (a–c). A contrast image (d) of the cells shown in (c) illustrating the TVS (arrows). Bars are 20 µM. Actin filaments in RNAi-SET expressing cells in (e–j). Granular particles on the vacuolar periphery are indicated by arrows in e. (g) Bars are 20 µM. Closer look at vacuolar-associated actin (h–j). Arrows indicate the cell wall. Bar is 10 µM. Actin bundles in atx1 mutant cells (k–m). Bars are 20 µM.

Mentions: Consistent with available data, actin in wild-type leaf cells was observed at the plasma membrane (cortical actin) and as fine and thick bundled actin networks (Figure 6a–c). Longitudinal, transverse, and randomly oriented actin bundles, considered general features of interphase plant cells (19), are clearly displayed. The transvacuolar cytoplasmic strands (TVSs) providing direct connections between different regions in the cytoplasm are also prominent in wild-type cells. In contrast, RNAi-SET expressing cells displayed a dramatically different pattern of reduced actin bundles and absent TVSs (Figure 6e–j). The fluorescent signal is associated mostly with particulate structures at the vacuolar periphery suggesting a collapse of the bundled structures. These changes were displayed by all RNAi-SET expressing cells implicating SET-domain activity in the actin bundling in Arabidopsis cells. In sharp contrast, actin bundles and TVSs similar to the wild type were prominently displayed in atx1 mutant cells (Figure 6k–m).Figure 6.


A cytoplasm-specific activity encoded by the Trithorax-like ATX1 gene.

Ndamukong I, Lapko H, Cerny RL, Avramova Z - Nucleic Acids Res. (2011)

The actin cytoskeleton and RNAi-SET. Actin filaments stained with phalloidin in wild-type leaf cells exhibiting actin bundles of various thicknesses (a–c). A contrast image (d) of the cells shown in (c) illustrating the TVS (arrows). Bars are 20 µM. Actin filaments in RNAi-SET expressing cells in (e–j). Granular particles on the vacuolar periphery are indicated by arrows in e. (g) Bars are 20 µM. Closer look at vacuolar-associated actin (h–j). Arrows indicate the cell wall. Bar is 10 µM. Actin bundles in atx1 mutant cells (k–m). Bars are 20 µM.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 6: The actin cytoskeleton and RNAi-SET. Actin filaments stained with phalloidin in wild-type leaf cells exhibiting actin bundles of various thicknesses (a–c). A contrast image (d) of the cells shown in (c) illustrating the TVS (arrows). Bars are 20 µM. Actin filaments in RNAi-SET expressing cells in (e–j). Granular particles on the vacuolar periphery are indicated by arrows in e. (g) Bars are 20 µM. Closer look at vacuolar-associated actin (h–j). Arrows indicate the cell wall. Bar is 10 µM. Actin bundles in atx1 mutant cells (k–m). Bars are 20 µM.
Mentions: Consistent with available data, actin in wild-type leaf cells was observed at the plasma membrane (cortical actin) and as fine and thick bundled actin networks (Figure 6a–c). Longitudinal, transverse, and randomly oriented actin bundles, considered general features of interphase plant cells (19), are clearly displayed. The transvacuolar cytoplasmic strands (TVSs) providing direct connections between different regions in the cytoplasm are also prominent in wild-type cells. In contrast, RNAi-SET expressing cells displayed a dramatically different pattern of reduced actin bundles and absent TVSs (Figure 6e–j). The fluorescent signal is associated mostly with particulate structures at the vacuolar periphery suggesting a collapse of the bundled structures. These changes were displayed by all RNAi-SET expressing cells implicating SET-domain activity in the actin bundling in Arabidopsis cells. In sharp contrast, actin bundles and TVSs similar to the wild type were prominently displayed in atx1 mutant cells (Figure 6k–m).Figure 6.

Bottom Line: It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET).It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A).Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA.

ABSTRACT
Eukaryotes produce multiple products from a single gene locus by alternative splicing, translation or promoter usage as mechanisms expanding the complexity of their proteome. Trithorax proteins, including the Arabidopsis Trithorax-like protein ATX1, are histone modifiers regulating gene activity. Here, we report that a novel member of the Trithorax family has a role unrelated to chromatin. It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET). It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A). Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

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