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Dynamic rewiring of the Drosophila retinal determination network switches its function from selector to differentiation.

Atkins M, Jiang Y, Sansores-Garcia L, Jusiak B, Halder G, Mardon G - PLoS Genet. (2013)

Bottom Line: Organ development is directed by selector gene networks.We found that central to the transition is a switch from positive regulation of ey transcription to negative regulation and that both types of regulation require so.We conclude that changes in the regulatory relationships among members of the retinal determination gene network are a driving force for key transitions in retinal development.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America.

ABSTRACT
Organ development is directed by selector gene networks. Eye development in the fruit fly Drosophila melanogaster is driven by the highly conserved selector gene network referred to as the "retinal determination gene network," composed of approximately 20 factors, whose core comprises twin of eyeless (toy), eyeless (ey), sine oculis (so), dachshund (dac), and eyes absent (eya). These genes encode transcriptional regulators that are each necessary for normal eye development, and sufficient to direct ectopic eye development when misexpressed. While it is well documented that the downstream genes so, eya, and dac are necessary not only during early growth and determination stages but also during the differentiation phase of retinal development, it remains unknown how the retinal determination gene network terminates its functions in determination and begins to promote differentiation. Here, we identify a switch in the regulation of ey by the downstream retinal determination genes, which is essential for the transition from determination to differentiation. We found that central to the transition is a switch from positive regulation of ey transcription to negative regulation and that both types of regulation require so. Our results suggest a model in which the retinal determination gene network is rewired to end the growth and determination stage of eye development and trigger terminal differentiation. We conclude that changes in the regulatory relationships among members of the retinal determination gene network are a driving force for key transitions in retinal development.

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Related in: MedlinePlus

Eya and So can cooperate to negatively regulate Ey expression in vivo.(A) Expression patterns of Ey, Eya, and So in a w1118 third instar eye imaginal disc. The yellow dashed line indicates the approximate location of the orthogonal section in B–B′″. (B) Orthogonal section of A. (B′) Grayscale image of Ey expression, red in B, apical Ey expression is detected in the peripodium, sections excluded in normal Z projection. (B″) Grayscale image of Eya expression, green in B. (B′″) Grayscale image of So expression, magenta in B. (C–G) Expression of UAS-GFP marks the clone(C, D, F, G); lack of GFP marks the clone in E. Crosses were raised at 25°C, except D, raised at 18°C. (C) UAS-so and UAS-eya were co-overexpressed anterior to the furrow. (C′) Grayscale image of GFP expression in C. (C″) Grayscale image of Ey expression in C. (D) Flipout-Gal4 was used to co-express UAS-so, UAS-eya, and UAS-GFP. (D′) Grayscale image of GFP expression, green in D. (D″) Grayscale image of Ey expression, red in D. (E) Double loss of function clones for smod16  allele and mad1–2 hypomorphic allele were generated by inducing hs-flp expression at 48 hrs AEL. (E′) Grayscale image of GFP expression, green in E. (E″) Grayscale image of Ey expression, red in E. (E′″) Grayscale image of ELAV expression, magenta in E, shows differentiating photoreceptors. (F) MARCM clones that are mutant for smod16 and mad1–2 while overexpressing so and eya. (F′) Grayscale image of GFP expression in F; the ELAV-like pattern is due to non-specific antibody interaction. (F″) Grayscale image of Ey expression in F. (F′″) Grayscale image of ELAV expression in F shows differentiating photoreceptors. (G–G′″) Same as F showing a clone extending anterior to the furrow.
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pgen-1003731-g005: Eya and So can cooperate to negatively regulate Ey expression in vivo.(A) Expression patterns of Ey, Eya, and So in a w1118 third instar eye imaginal disc. The yellow dashed line indicates the approximate location of the orthogonal section in B–B′″. (B) Orthogonal section of A. (B′) Grayscale image of Ey expression, red in B, apical Ey expression is detected in the peripodium, sections excluded in normal Z projection. (B″) Grayscale image of Eya expression, green in B. (B′″) Grayscale image of So expression, magenta in B. (C–G) Expression of UAS-GFP marks the clone(C, D, F, G); lack of GFP marks the clone in E. Crosses were raised at 25°C, except D, raised at 18°C. (C) UAS-so and UAS-eya were co-overexpressed anterior to the furrow. (C′) Grayscale image of GFP expression in C. (C″) Grayscale image of Ey expression in C. (D) Flipout-Gal4 was used to co-express UAS-so, UAS-eya, and UAS-GFP. (D′) Grayscale image of GFP expression, green in D. (D″) Grayscale image of Ey expression, red in D. (E) Double loss of function clones for smod16 allele and mad1–2 hypomorphic allele were generated by inducing hs-flp expression at 48 hrs AEL. (E′) Grayscale image of GFP expression, green in E. (E″) Grayscale image of Ey expression, red in E. (E′″) Grayscale image of ELAV expression, magenta in E, shows differentiating photoreceptors. (F) MARCM clones that are mutant for smod16 and mad1–2 while overexpressing so and eya. (F′) Grayscale image of GFP expression in F; the ELAV-like pattern is due to non-specific antibody interaction. (F″) Grayscale image of Ey expression in F. (F′″) Grayscale image of ELAV expression in F shows differentiating photoreceptors. (G–G′″) Same as F showing a clone extending anterior to the furrow.

Mentions: Eya and So each overlap Ey expression just anterior to the morphogenetic furrow, but do not negatively regulate Ey expression in this zone. Therefore, we re-examined the expression of Eya and So in the eye imaginal disc to determine if their expression patterns could suggest how Eya and So could be required to suppress ey expression posterior to the furrow. Quantification of Eya and So expression in orthogonal sections revealed that expression of both factors is increased posterior to the morphogenetic furrow (Figure 5A,B). To test if the increased level is sufficient to repress Ey, we overexpressed both eya and so within the Ey domain using the Flipout-Gal4 strategy. Co-misexpression of eya and so was sufficient to repress Ey expression to background levels within the eye field, while ectopic Ey expression was detected in clones in other discs (Figure 5C, and data not shown). These data suggest that, within the developing retinal field, increased so and eya expression is sufficient to repress Ey expression anterior to the morphogenetic furrow. When we utilized the temperature sensitivity of the Gal4-UAS system to overexpress eya+so at 18°C, which results in lower expression of eya+so than at 25°C, they failed to repress Ey expression in the eye field, but were still sufficient to ectopically activate Ey expression in the antennal disc (Figure 5D, Figure S6A, white arrow).


Dynamic rewiring of the Drosophila retinal determination network switches its function from selector to differentiation.

Atkins M, Jiang Y, Sansores-Garcia L, Jusiak B, Halder G, Mardon G - PLoS Genet. (2013)

Eya and So can cooperate to negatively regulate Ey expression in vivo.(A) Expression patterns of Ey, Eya, and So in a w1118 third instar eye imaginal disc. The yellow dashed line indicates the approximate location of the orthogonal section in B–B′″. (B) Orthogonal section of A. (B′) Grayscale image of Ey expression, red in B, apical Ey expression is detected in the peripodium, sections excluded in normal Z projection. (B″) Grayscale image of Eya expression, green in B. (B′″) Grayscale image of So expression, magenta in B. (C–G) Expression of UAS-GFP marks the clone(C, D, F, G); lack of GFP marks the clone in E. Crosses were raised at 25°C, except D, raised at 18°C. (C) UAS-so and UAS-eya were co-overexpressed anterior to the furrow. (C′) Grayscale image of GFP expression in C. (C″) Grayscale image of Ey expression in C. (D) Flipout-Gal4 was used to co-express UAS-so, UAS-eya, and UAS-GFP. (D′) Grayscale image of GFP expression, green in D. (D″) Grayscale image of Ey expression, red in D. (E) Double loss of function clones for smod16  allele and mad1–2 hypomorphic allele were generated by inducing hs-flp expression at 48 hrs AEL. (E′) Grayscale image of GFP expression, green in E. (E″) Grayscale image of Ey expression, red in E. (E′″) Grayscale image of ELAV expression, magenta in E, shows differentiating photoreceptors. (F) MARCM clones that are mutant for smod16 and mad1–2 while overexpressing so and eya. (F′) Grayscale image of GFP expression in F; the ELAV-like pattern is due to non-specific antibody interaction. (F″) Grayscale image of Ey expression in F. (F′″) Grayscale image of ELAV expression in F shows differentiating photoreceptors. (G–G′″) Same as F showing a clone extending anterior to the furrow.
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Related In: Results  -  Collection

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pgen-1003731-g005: Eya and So can cooperate to negatively regulate Ey expression in vivo.(A) Expression patterns of Ey, Eya, and So in a w1118 third instar eye imaginal disc. The yellow dashed line indicates the approximate location of the orthogonal section in B–B′″. (B) Orthogonal section of A. (B′) Grayscale image of Ey expression, red in B, apical Ey expression is detected in the peripodium, sections excluded in normal Z projection. (B″) Grayscale image of Eya expression, green in B. (B′″) Grayscale image of So expression, magenta in B. (C–G) Expression of UAS-GFP marks the clone(C, D, F, G); lack of GFP marks the clone in E. Crosses were raised at 25°C, except D, raised at 18°C. (C) UAS-so and UAS-eya were co-overexpressed anterior to the furrow. (C′) Grayscale image of GFP expression in C. (C″) Grayscale image of Ey expression in C. (D) Flipout-Gal4 was used to co-express UAS-so, UAS-eya, and UAS-GFP. (D′) Grayscale image of GFP expression, green in D. (D″) Grayscale image of Ey expression, red in D. (E) Double loss of function clones for smod16 allele and mad1–2 hypomorphic allele were generated by inducing hs-flp expression at 48 hrs AEL. (E′) Grayscale image of GFP expression, green in E. (E″) Grayscale image of Ey expression, red in E. (E′″) Grayscale image of ELAV expression, magenta in E, shows differentiating photoreceptors. (F) MARCM clones that are mutant for smod16 and mad1–2 while overexpressing so and eya. (F′) Grayscale image of GFP expression in F; the ELAV-like pattern is due to non-specific antibody interaction. (F″) Grayscale image of Ey expression in F. (F′″) Grayscale image of ELAV expression in F shows differentiating photoreceptors. (G–G′″) Same as F showing a clone extending anterior to the furrow.
Mentions: Eya and So each overlap Ey expression just anterior to the morphogenetic furrow, but do not negatively regulate Ey expression in this zone. Therefore, we re-examined the expression of Eya and So in the eye imaginal disc to determine if their expression patterns could suggest how Eya and So could be required to suppress ey expression posterior to the furrow. Quantification of Eya and So expression in orthogonal sections revealed that expression of both factors is increased posterior to the morphogenetic furrow (Figure 5A,B). To test if the increased level is sufficient to repress Ey, we overexpressed both eya and so within the Ey domain using the Flipout-Gal4 strategy. Co-misexpression of eya and so was sufficient to repress Ey expression to background levels within the eye field, while ectopic Ey expression was detected in clones in other discs (Figure 5C, and data not shown). These data suggest that, within the developing retinal field, increased so and eya expression is sufficient to repress Ey expression anterior to the morphogenetic furrow. When we utilized the temperature sensitivity of the Gal4-UAS system to overexpress eya+so at 18°C, which results in lower expression of eya+so than at 25°C, they failed to repress Ey expression in the eye field, but were still sufficient to ectopically activate Ey expression in the antennal disc (Figure 5D, Figure S6A, white arrow).

Bottom Line: Organ development is directed by selector gene networks.We found that central to the transition is a switch from positive regulation of ey transcription to negative regulation and that both types of regulation require so.We conclude that changes in the regulatory relationships among members of the retinal determination gene network are a driving force for key transitions in retinal development.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America.

ABSTRACT
Organ development is directed by selector gene networks. Eye development in the fruit fly Drosophila melanogaster is driven by the highly conserved selector gene network referred to as the "retinal determination gene network," composed of approximately 20 factors, whose core comprises twin of eyeless (toy), eyeless (ey), sine oculis (so), dachshund (dac), and eyes absent (eya). These genes encode transcriptional regulators that are each necessary for normal eye development, and sufficient to direct ectopic eye development when misexpressed. While it is well documented that the downstream genes so, eya, and dac are necessary not only during early growth and determination stages but also during the differentiation phase of retinal development, it remains unknown how the retinal determination gene network terminates its functions in determination and begins to promote differentiation. Here, we identify a switch in the regulation of ey by the downstream retinal determination genes, which is essential for the transition from determination to differentiation. We found that central to the transition is a switch from positive regulation of ey transcription to negative regulation and that both types of regulation require so. Our results suggest a model in which the retinal determination gene network is rewired to end the growth and determination stage of eye development and trigger terminal differentiation. We conclude that changes in the regulatory relationships among members of the retinal determination gene network are a driving force for key transitions in retinal development.

Show MeSH
Related in: MedlinePlus