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Caudal regulates the spatiotemporal dynamics of pair-rule waves in Tribolium.

El-Sherif E, Zhu X, Fu J, Brown SJ - PLoS Genet. (2014)

Bottom Line: However, neither a molecular candidate nor a functional role has been identified to date for such a frequency gradient, either in vertebrates or elsewhere.Further, we show that besides its absolute importance for stripe generation in the static phase of the Tribolium blastoderm, a frequency gradient might serve as a buffer against noise during axis elongation phase in Tribolium as well as vertebrates.Our results highlight the role of frequency gradients in pattern formation.

View Article: PubMed Central - PubMed

Affiliation: Genetics Program, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
In the short-germ beetle Tribolium castaneum, waves of pair-rule gene expression propagate from the posterior end of the embryo towards the anterior and eventually freeze into stable stripes, partitioning the anterior-posterior axis into segments. Similar waves in vertebrates are assumed to arise due to the modulation of a molecular clock by a posterior-to-anterior frequency gradient. However, neither a molecular candidate nor a functional role has been identified to date for such a frequency gradient, either in vertebrates or elsewhere. Here we provide evidence that the posterior gradient of Tc-caudal expression regulates the oscillation frequency of pair-rule gene expression in Tribolium. We show this by analyzing the spatiotemporal dynamics of Tc-even-skipped expression in strong and mild knockdown of Tc-caudal, and by correlating the extension, level and slope of the Tc-caudal expression gradient to the spatiotemporal dynamics of Tc-even-skipped expression in wild type as well as in different RNAi knockdowns of Tc-caudal regulators. Further, we show that besides its absolute importance for stripe generation in the static phase of the Tribolium blastoderm, a frequency gradient might serve as a buffer against noise during axis elongation phase in Tribolium as well as vertebrates. Our results highlight the role of frequency gradients in pattern formation.

No MeSH data available.


Tc-cad expression in Tribolium.(A–D) Concurrent Tc-cad in situ hybridization (red; first column) and Tc-EVE antibody staining (green; second column) were merged (third column) to show that Tc-cad expression overlaps with the emerging first two stripes of Tc-Eve in the blastoderm (A, B), and retreats to the posterior while the third stripe emerges (C). Tc-cad expression is confined in the growth zone during the germband stage to overlap with emerging stripes (fourth stripe in D). (E, F) Measuring Tc-cad expression across AP axis of the blastoderm (E, Text S3) and fitting raw measurements (thin blue line in F) to a linear-with-plateau curve (thick blue line in F) and calculating its three descriptors (F, Text S3). (G, H) As revealed by the change in the three descriptors of Tc-cad gradient over time (G), Tc-cad expression gradient builds up during 14–17 hours AEL but does not shift. Tc-cad dynamics are summarized in H; dashed curve: early, solid curve: late expression. Anterior to left. Error bars represent 95% confidence intervals.
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pgen-1004677-g001: Tc-cad expression in Tribolium.(A–D) Concurrent Tc-cad in situ hybridization (red; first column) and Tc-EVE antibody staining (green; second column) were merged (third column) to show that Tc-cad expression overlaps with the emerging first two stripes of Tc-Eve in the blastoderm (A, B), and retreats to the posterior while the third stripe emerges (C). Tc-cad expression is confined in the growth zone during the germband stage to overlap with emerging stripes (fourth stripe in D). (E, F) Measuring Tc-cad expression across AP axis of the blastoderm (E, Text S3) and fitting raw measurements (thin blue line in F) to a linear-with-plateau curve (thick blue line in F) and calculating its three descriptors (F, Text S3). (G, H) As revealed by the change in the three descriptors of Tc-cad gradient over time (G), Tc-cad expression gradient builds up during 14–17 hours AEL but does not shift. Tc-cad dynamics are summarized in H; dashed curve: early, solid curve: late expression. Anterior to left. Error bars represent 95% confidence intervals.

Mentions: The wave dynamics of Tc-eve in Tribolium can be explained by assuming a posterior-to-anterior gradient that positively regulates the frequency of Tc-eve oscillations [13]. Tc-cad is an obvious candidate to encode such a frequency gradient because its mRNA expression forms a posterior-to-anterior gradient that overlaps the Tc-eve expression waves arising at the posterior throughout Tribolium segmentation (Figure 1 A–D). Since studying segmentation in the germband phase of Tribolium development is hindered by the truncation phenotype generated by most segmentation gene knock-downs, we largely restricted our analysis to the stripes that form during the blastoderm stage. The expression of Tc-cad in the blastoderm (Figure 1 E) is approximated with reasonable accuracy by a posterior-to-anterior linear gradient that plateaus at the posterior end (Figure 1 F; Text S3). We used three descriptors to characterize this gradient: maximum posterior (plateau) value, position of anterior border, and slope (Figure 1 F). We analyzed the temporal dynamics of the Tc-cad gradient by calculating its three descriptors at 14–17 and 17–20 hours after egg lay (AEL) (Figure 1 G), spanning the formation of the first and second Tc-eve expression stripes in wild type (WT) [13] (analysis of later times was precluded by primitive pit formation, asterisk in Figure 1 C). As shown in Figure 1 G, the anterior border of Tc-cad expression gradient did not experience a significant shift during the formation of the first and second Tc-eve stripes, (which is also evident in Figure 1 A, B). However, both the maximum posterior value and the slope of the Tc-cad gradient increased over time. This indicates that the Tc-cad gradient was building up during the formation of the first and second Tc-eve stripes, but did not undergo a substantial shift along the AP axis (Figure 1 H). Characterizing Tc-cad gradient dynamics with higher temporal resolution (Figure S1) indicates that this buildup phase occurred between 14 to 16 hours AEL (i.e. before completion of the first Tc-eve stripe), after which the gradient was more or less static. This argues against a substantial influence of Tc-cad temporal dynamics on the wave dynamics of Tc-eve expression in the blastoderm. By the time the third stripe formed in the germ rudiment, the Tc-cad gradient had retreated toward posterior (Figure 1 C).


Caudal regulates the spatiotemporal dynamics of pair-rule waves in Tribolium.

El-Sherif E, Zhu X, Fu J, Brown SJ - PLoS Genet. (2014)

Tc-cad expression in Tribolium.(A–D) Concurrent Tc-cad in situ hybridization (red; first column) and Tc-EVE antibody staining (green; second column) were merged (third column) to show that Tc-cad expression overlaps with the emerging first two stripes of Tc-Eve in the blastoderm (A, B), and retreats to the posterior while the third stripe emerges (C). Tc-cad expression is confined in the growth zone during the germband stage to overlap with emerging stripes (fourth stripe in D). (E, F) Measuring Tc-cad expression across AP axis of the blastoderm (E, Text S3) and fitting raw measurements (thin blue line in F) to a linear-with-plateau curve (thick blue line in F) and calculating its three descriptors (F, Text S3). (G, H) As revealed by the change in the three descriptors of Tc-cad gradient over time (G), Tc-cad expression gradient builds up during 14–17 hours AEL but does not shift. Tc-cad dynamics are summarized in H; dashed curve: early, solid curve: late expression. Anterior to left. Error bars represent 95% confidence intervals.
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pgen-1004677-g001: Tc-cad expression in Tribolium.(A–D) Concurrent Tc-cad in situ hybridization (red; first column) and Tc-EVE antibody staining (green; second column) were merged (third column) to show that Tc-cad expression overlaps with the emerging first two stripes of Tc-Eve in the blastoderm (A, B), and retreats to the posterior while the third stripe emerges (C). Tc-cad expression is confined in the growth zone during the germband stage to overlap with emerging stripes (fourth stripe in D). (E, F) Measuring Tc-cad expression across AP axis of the blastoderm (E, Text S3) and fitting raw measurements (thin blue line in F) to a linear-with-plateau curve (thick blue line in F) and calculating its three descriptors (F, Text S3). (G, H) As revealed by the change in the three descriptors of Tc-cad gradient over time (G), Tc-cad expression gradient builds up during 14–17 hours AEL but does not shift. Tc-cad dynamics are summarized in H; dashed curve: early, solid curve: late expression. Anterior to left. Error bars represent 95% confidence intervals.
Mentions: The wave dynamics of Tc-eve in Tribolium can be explained by assuming a posterior-to-anterior gradient that positively regulates the frequency of Tc-eve oscillations [13]. Tc-cad is an obvious candidate to encode such a frequency gradient because its mRNA expression forms a posterior-to-anterior gradient that overlaps the Tc-eve expression waves arising at the posterior throughout Tribolium segmentation (Figure 1 A–D). Since studying segmentation in the germband phase of Tribolium development is hindered by the truncation phenotype generated by most segmentation gene knock-downs, we largely restricted our analysis to the stripes that form during the blastoderm stage. The expression of Tc-cad in the blastoderm (Figure 1 E) is approximated with reasonable accuracy by a posterior-to-anterior linear gradient that plateaus at the posterior end (Figure 1 F; Text S3). We used three descriptors to characterize this gradient: maximum posterior (plateau) value, position of anterior border, and slope (Figure 1 F). We analyzed the temporal dynamics of the Tc-cad gradient by calculating its three descriptors at 14–17 and 17–20 hours after egg lay (AEL) (Figure 1 G), spanning the formation of the first and second Tc-eve expression stripes in wild type (WT) [13] (analysis of later times was precluded by primitive pit formation, asterisk in Figure 1 C). As shown in Figure 1 G, the anterior border of Tc-cad expression gradient did not experience a significant shift during the formation of the first and second Tc-eve stripes, (which is also evident in Figure 1 A, B). However, both the maximum posterior value and the slope of the Tc-cad gradient increased over time. This indicates that the Tc-cad gradient was building up during the formation of the first and second Tc-eve stripes, but did not undergo a substantial shift along the AP axis (Figure 1 H). Characterizing Tc-cad gradient dynamics with higher temporal resolution (Figure S1) indicates that this buildup phase occurred between 14 to 16 hours AEL (i.e. before completion of the first Tc-eve stripe), after which the gradient was more or less static. This argues against a substantial influence of Tc-cad temporal dynamics on the wave dynamics of Tc-eve expression in the blastoderm. By the time the third stripe formed in the germ rudiment, the Tc-cad gradient had retreated toward posterior (Figure 1 C).

Bottom Line: However, neither a molecular candidate nor a functional role has been identified to date for such a frequency gradient, either in vertebrates or elsewhere.Further, we show that besides its absolute importance for stripe generation in the static phase of the Tribolium blastoderm, a frequency gradient might serve as a buffer against noise during axis elongation phase in Tribolium as well as vertebrates.Our results highlight the role of frequency gradients in pattern formation.

View Article: PubMed Central - PubMed

Affiliation: Genetics Program, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
In the short-germ beetle Tribolium castaneum, waves of pair-rule gene expression propagate from the posterior end of the embryo towards the anterior and eventually freeze into stable stripes, partitioning the anterior-posterior axis into segments. Similar waves in vertebrates are assumed to arise due to the modulation of a molecular clock by a posterior-to-anterior frequency gradient. However, neither a molecular candidate nor a functional role has been identified to date for such a frequency gradient, either in vertebrates or elsewhere. Here we provide evidence that the posterior gradient of Tc-caudal expression regulates the oscillation frequency of pair-rule gene expression in Tribolium. We show this by analyzing the spatiotemporal dynamics of Tc-even-skipped expression in strong and mild knockdown of Tc-caudal, and by correlating the extension, level and slope of the Tc-caudal expression gradient to the spatiotemporal dynamics of Tc-even-skipped expression in wild type as well as in different RNAi knockdowns of Tc-caudal regulators. Further, we show that besides its absolute importance for stripe generation in the static phase of the Tribolium blastoderm, a frequency gradient might serve as a buffer against noise during axis elongation phase in Tribolium as well as vertebrates. Our results highlight the role of frequency gradients in pattern formation.

No MeSH data available.