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The presence of nuclear cactus in the early Drosophila embryo may extend the dynamic range of the dorsal gradient.

O'Connell MD, Reeves GT - PLoS Comput. Biol. (2015)

Bottom Line: We found that two assumptions are required for the model to match experimental data in both Dorsal distribution and gene expression patterns.And second, we assume that fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal.Our results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

View Article: PubMed Central - PubMed

Affiliation: North Carolina State University Department of Chemical and Biomolecular Engineering, Raleigh, North Carolina, United States of America.

ABSTRACT
In a developing embryo, the spatial distribution of a signaling molecule, or a morphogen gradient, has been hypothesized to carry positional information to pattern tissues. Recent measurements of morphogen distribution have allowed us to subject this hypothesis to rigorous physical testing. In the early Drosophila embryo, measurements of the morphogen Dorsal, which is a transcription factor responsible for initiating the earliest zygotic patterns along the dorsal-ventral axis, have revealed a gradient that is too narrow to pattern the entire axis. In this study, we use a mathematical model of Dorsal dynamics, fit to experimental data, to determine the ability of the Dorsal gradient to regulate gene expression across the entire dorsal-ventral axis. We found that two assumptions are required for the model to match experimental data in both Dorsal distribution and gene expression patterns. First, we assume that Cactus, an inhibitor that binds to Dorsal and prevents it from entering the nuclei, must itself be present in the nuclei. And second, we assume that fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal. Our model explains the dynamic behavior of the Dorsal gradient at lateral and dorsal positions of the embryo, the ability of Dorsal to regulate gene expression across the entire dorsal-ventral axis, and the robustness of gene expression to stochastic effects. Our results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

No MeSH data available.


Related in: MedlinePlus

Summary.(a) In the classical model of dl/Cact dynamics, the import of dl is of primary concern. (b) In our extended model, the coexistence of dl, Cact and dl/Cact complex due to nuclear porosity must be taken into account to interpret the results of fluorescence studies. (c) Our modeling results predict the export of dl/Cact complex from dorsal nuclei contributes to a decrease in nuclear fluorescence, and the import of cytoplasmic dl contributes to the increase in nuclear fluorescence in ventral nuclei. (d) In all nuclei, free dl and dl/Cact complex are both fluorescently tagged but only free dl contributes to gene expression.
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pcbi.1004159.g008: Summary.(a) In the classical model of dl/Cact dynamics, the import of dl is of primary concern. (b) In our extended model, the coexistence of dl, Cact and dl/Cact complex due to nuclear porosity must be taken into account to interpret the results of fluorescence studies. (c) Our modeling results predict the export of dl/Cact complex from dorsal nuclei contributes to a decrease in nuclear fluorescence, and the import of cytoplasmic dl contributes to the increase in nuclear fluorescence in ventral nuclei. (d) In all nuclei, free dl and dl/Cact complex are both fluorescently tagged but only free dl contributes to gene expression.

Mentions: Recently, detailed measurements of morphogen gradients have led to rapid advances in our understanding of morphogen dynamics. However, questions remain as to how the spatial information carried by a morphogen gradient results in gene expression boundaries. In this study, we attempt to address this question by analyzing a mechanistic model of dl/Cact dynamics in the early embryo in light of recent live imaging measurements of nuclear dl-Venus fluorescence [10]. In comparing our modeling results against the experimental data, we found that only when our model includes nuclear Cact and nuclear dl/Cact complex can it account for experimental observations such as the declining basal levels of dl-Venus fluorescence (Fig. 8a-c). In such a model, the most straightforward assumption is that fluorescence measurements are a combination of both free nuclear dl and dl/Cact complex (Fig. 8d). This assumption implies that the dl nuclear concentration gradient, as measured by fluorescence, represents total nuclear dl, and not necessarily the gradient of dl activity. This is especially true on the lateral and dorsal side of the embryo, where dl/Cact complex becomes the dominant dl-containing species.


The presence of nuclear cactus in the early Drosophila embryo may extend the dynamic range of the dorsal gradient.

O'Connell MD, Reeves GT - PLoS Comput. Biol. (2015)

Summary.(a) In the classical model of dl/Cact dynamics, the import of dl is of primary concern. (b) In our extended model, the coexistence of dl, Cact and dl/Cact complex due to nuclear porosity must be taken into account to interpret the results of fluorescence studies. (c) Our modeling results predict the export of dl/Cact complex from dorsal nuclei contributes to a decrease in nuclear fluorescence, and the import of cytoplasmic dl contributes to the increase in nuclear fluorescence in ventral nuclei. (d) In all nuclei, free dl and dl/Cact complex are both fluorescently tagged but only free dl contributes to gene expression.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4400154&req=5

pcbi.1004159.g008: Summary.(a) In the classical model of dl/Cact dynamics, the import of dl is of primary concern. (b) In our extended model, the coexistence of dl, Cact and dl/Cact complex due to nuclear porosity must be taken into account to interpret the results of fluorescence studies. (c) Our modeling results predict the export of dl/Cact complex from dorsal nuclei contributes to a decrease in nuclear fluorescence, and the import of cytoplasmic dl contributes to the increase in nuclear fluorescence in ventral nuclei. (d) In all nuclei, free dl and dl/Cact complex are both fluorescently tagged but only free dl contributes to gene expression.
Mentions: Recently, detailed measurements of morphogen gradients have led to rapid advances in our understanding of morphogen dynamics. However, questions remain as to how the spatial information carried by a morphogen gradient results in gene expression boundaries. In this study, we attempt to address this question by analyzing a mechanistic model of dl/Cact dynamics in the early embryo in light of recent live imaging measurements of nuclear dl-Venus fluorescence [10]. In comparing our modeling results against the experimental data, we found that only when our model includes nuclear Cact and nuclear dl/Cact complex can it account for experimental observations such as the declining basal levels of dl-Venus fluorescence (Fig. 8a-c). In such a model, the most straightforward assumption is that fluorescence measurements are a combination of both free nuclear dl and dl/Cact complex (Fig. 8d). This assumption implies that the dl nuclear concentration gradient, as measured by fluorescence, represents total nuclear dl, and not necessarily the gradient of dl activity. This is especially true on the lateral and dorsal side of the embryo, where dl/Cact complex becomes the dominant dl-containing species.

Bottom Line: We found that two assumptions are required for the model to match experimental data in both Dorsal distribution and gene expression patterns.And second, we assume that fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal.Our results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

View Article: PubMed Central - PubMed

Affiliation: North Carolina State University Department of Chemical and Biomolecular Engineering, Raleigh, North Carolina, United States of America.

ABSTRACT
In a developing embryo, the spatial distribution of a signaling molecule, or a morphogen gradient, has been hypothesized to carry positional information to pattern tissues. Recent measurements of morphogen distribution have allowed us to subject this hypothesis to rigorous physical testing. In the early Drosophila embryo, measurements of the morphogen Dorsal, which is a transcription factor responsible for initiating the earliest zygotic patterns along the dorsal-ventral axis, have revealed a gradient that is too narrow to pattern the entire axis. In this study, we use a mathematical model of Dorsal dynamics, fit to experimental data, to determine the ability of the Dorsal gradient to regulate gene expression across the entire dorsal-ventral axis. We found that two assumptions are required for the model to match experimental data in both Dorsal distribution and gene expression patterns. First, we assume that Cactus, an inhibitor that binds to Dorsal and prevents it from entering the nuclei, must itself be present in the nuclei. And second, we assume that fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal. Our model explains the dynamic behavior of the Dorsal gradient at lateral and dorsal positions of the embryo, the ability of Dorsal to regulate gene expression across the entire dorsal-ventral axis, and the robustness of gene expression to stochastic effects. Our results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

No MeSH data available.


Related in: MedlinePlus