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Correlated Levels of mRNA and Soma Size in Single Identified Neurons: Evidence for Compartment-specific Regulation of Gene Expression.

Ransdell JL, Faust TB, Schulz DJ - Front Mol Neurosci (2010)

Bottom Line: Levels of mRNA for the K+ channel shal, which is localized exclusively to the soma, are negatively correlated with soma size, suggesting that gene expression does not simply track positively with compartment size.Conversely, levels of beta-actin and beta-tubulin mRNA, which are major cytoskeletal proteins of neuronal processes, do not correlate with soma size, but are strongly correlated with one another.These results suggest that steady-state transcript levels are differentially regulated based on the subcellular compartment within which a given gene product primarily acts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Missouri Columbia Columbia, MO, USA.

ABSTRACT
In addition to the overall complexity of transcriptional regulation, cells also must take into account the subcellular distribution of these gene products. This is particularly challenging for morphologically complex cells such as neurons. Yet the interaction between cellular morphology and gene expression is poorly understood. Here we provide some of the first evidence for a relationship between neuronal compartment size and maintenance of mRNA levels in neurons. We find that single-cell transcript levels of 18S rRNA, GAPDH, and EF1-alpha, all gene products with primary functions in the cell soma, are strongly correlated to soma size in multiple distinct neuronal types. Levels of mRNA for the K+ channel shal, which is localized exclusively to the soma, are negatively correlated with soma size, suggesting that gene expression does not simply track positively with compartment size. Conversely, levels of beta-actin and beta-tubulin mRNA, which are major cytoskeletal proteins of neuronal processes, do not correlate with soma size, but are strongly correlated with one another. Additionally, actin/tubulin expression levels correlate with voltage-gated ion channels that are uniquely localized to axons. These results suggest that steady-state transcript levels are differentially regulated based on the subcellular compartment within which a given gene product primarily acts.

No MeSH data available.


Related in: MedlinePlus

Correlations between the voltage-gated ion channels shal (A–C), CbNav (D–F), and shaker (G–I) and soma size, actin, and tubulin expression. Points represent mean ± SEM. Individual neuron types as labeled, sample sizes listed in Figure 1. Relative measurements are made with PD neurons as the reference population. Dashed lines represent regression fits for the second analysis that omits the LG neuron (see text). R2 values are results of Pearson's correlation analyses.
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Figure 5: Correlations between the voltage-gated ion channels shal (A–C), CbNav (D–F), and shaker (G–I) and soma size, actin, and tubulin expression. Points represent mean ± SEM. Individual neuron types as labeled, sample sizes listed in Figure 1. Relative measurements are made with PD neurons as the reference population. Dashed lines represent regression fits for the second analysis that omits the LG neuron (see text). R2 values are results of Pearson's correlation analyses.

Mentions: Because there was a far weaker relationship between actin, tubulin, and soma size, we hypothesized that the complex architecture of neurons and their extensive processes (and thus cytoskeletal infrastructure) may require differences in mRNA levels for these gene products that are strongly related to their subcellular localization (i.e., soma vs. processes). To explore this hypothesis, we analyzed the mRNA levels of three different voltage-gated ion channels (Table 1), as the subcellular distribution of these channel proteins is documented. shal is a K+ channel localized to the soma of pyloric neurons (Baro et al., 2000), shaker is a K+ channel localized to the axon of pyloric cells (Baro et al., 2000), and CbNav is a Na+ channel that is likely localized to the axons of STG neurons (Graubard and Hartline, 1991; Golowasch and Marder, 1992). Overall, there were no significant correlations between shal and soma size. However, after inspecting the data we saw a possible correlation for shal expression among pyloric neurons [all neuron types except LG in this study are pyloric] (see Figure 5A). Therefore, we performed a second analysis that included only the pyloric cells. When LG (the only non-pyloric neuron in this study) is omitted in the second analysis, levels of shal mRNA were significantly negatively correlated with cell soma size (p < 0.005; R2 = 0.93; Figure 5A). The subcellular localization of shal channels has not been directly investigated in the LG cell (Baro et al., 2000), and therefore may not be localized to the soma as in the pyloric cells. In this second analysis, there was a weaker and not statistically significant relationship between expression of shal and actin (p = 0.08; R2 = 0.71; Figure 5B) and tubulin (p = 0.07; R2 = 0.73; Figure 5C). Conversely, levels of shaker and CbNav expression, both of which are localized to the axon, had the opposite relationships to soma size and actin/tubulin expression. Shaker and CbNav expression were not significantly correlated to soma size (p = 0.08; R2 = 0.69 for both; Figures 5D,G), but both shaker and CbNav were strongly correlated with actin (p < 0.001; R2 > 0.98; Figures 5E,H) and tubulin (p < 0.001; R2 > 0.95; Figures 5F,I).


Correlated Levels of mRNA and Soma Size in Single Identified Neurons: Evidence for Compartment-specific Regulation of Gene Expression.

Ransdell JL, Faust TB, Schulz DJ - Front Mol Neurosci (2010)

Correlations between the voltage-gated ion channels shal (A–C), CbNav (D–F), and shaker (G–I) and soma size, actin, and tubulin expression. Points represent mean ± SEM. Individual neuron types as labeled, sample sizes listed in Figure 1. Relative measurements are made with PD neurons as the reference population. Dashed lines represent regression fits for the second analysis that omits the LG neuron (see text). R2 values are results of Pearson's correlation analyses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2991126&req=5

Figure 5: Correlations between the voltage-gated ion channels shal (A–C), CbNav (D–F), and shaker (G–I) and soma size, actin, and tubulin expression. Points represent mean ± SEM. Individual neuron types as labeled, sample sizes listed in Figure 1. Relative measurements are made with PD neurons as the reference population. Dashed lines represent regression fits for the second analysis that omits the LG neuron (see text). R2 values are results of Pearson's correlation analyses.
Mentions: Because there was a far weaker relationship between actin, tubulin, and soma size, we hypothesized that the complex architecture of neurons and their extensive processes (and thus cytoskeletal infrastructure) may require differences in mRNA levels for these gene products that are strongly related to their subcellular localization (i.e., soma vs. processes). To explore this hypothesis, we analyzed the mRNA levels of three different voltage-gated ion channels (Table 1), as the subcellular distribution of these channel proteins is documented. shal is a K+ channel localized to the soma of pyloric neurons (Baro et al., 2000), shaker is a K+ channel localized to the axon of pyloric cells (Baro et al., 2000), and CbNav is a Na+ channel that is likely localized to the axons of STG neurons (Graubard and Hartline, 1991; Golowasch and Marder, 1992). Overall, there were no significant correlations between shal and soma size. However, after inspecting the data we saw a possible correlation for shal expression among pyloric neurons [all neuron types except LG in this study are pyloric] (see Figure 5A). Therefore, we performed a second analysis that included only the pyloric cells. When LG (the only non-pyloric neuron in this study) is omitted in the second analysis, levels of shal mRNA were significantly negatively correlated with cell soma size (p < 0.005; R2 = 0.93; Figure 5A). The subcellular localization of shal channels has not been directly investigated in the LG cell (Baro et al., 2000), and therefore may not be localized to the soma as in the pyloric cells. In this second analysis, there was a weaker and not statistically significant relationship between expression of shal and actin (p = 0.08; R2 = 0.71; Figure 5B) and tubulin (p = 0.07; R2 = 0.73; Figure 5C). Conversely, levels of shaker and CbNav expression, both of which are localized to the axon, had the opposite relationships to soma size and actin/tubulin expression. Shaker and CbNav expression were not significantly correlated to soma size (p = 0.08; R2 = 0.69 for both; Figures 5D,G), but both shaker and CbNav were strongly correlated with actin (p < 0.001; R2 > 0.98; Figures 5E,H) and tubulin (p < 0.001; R2 > 0.95; Figures 5F,I).

Bottom Line: Levels of mRNA for the K+ channel shal, which is localized exclusively to the soma, are negatively correlated with soma size, suggesting that gene expression does not simply track positively with compartment size.Conversely, levels of beta-actin and beta-tubulin mRNA, which are major cytoskeletal proteins of neuronal processes, do not correlate with soma size, but are strongly correlated with one another.These results suggest that steady-state transcript levels are differentially regulated based on the subcellular compartment within which a given gene product primarily acts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Missouri Columbia Columbia, MO, USA.

ABSTRACT
In addition to the overall complexity of transcriptional regulation, cells also must take into account the subcellular distribution of these gene products. This is particularly challenging for morphologically complex cells such as neurons. Yet the interaction between cellular morphology and gene expression is poorly understood. Here we provide some of the first evidence for a relationship between neuronal compartment size and maintenance of mRNA levels in neurons. We find that single-cell transcript levels of 18S rRNA, GAPDH, and EF1-alpha, all gene products with primary functions in the cell soma, are strongly correlated to soma size in multiple distinct neuronal types. Levels of mRNA for the K+ channel shal, which is localized exclusively to the soma, are negatively correlated with soma size, suggesting that gene expression does not simply track positively with compartment size. Conversely, levels of beta-actin and beta-tubulin mRNA, which are major cytoskeletal proteins of neuronal processes, do not correlate with soma size, but are strongly correlated with one another. Additionally, actin/tubulin expression levels correlate with voltage-gated ion channels that are uniquely localized to axons. These results suggest that steady-state transcript levels are differentially regulated based on the subcellular compartment within which a given gene product primarily acts.

No MeSH data available.


Related in: MedlinePlus