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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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So regulates ey expression through a binding site in an ey eye enhancer.(A–F) reporter expression in third instar discs; columns of Sens positive cells were counted to compare furrow progression at different times. (A–C) expression of ey-dGFP (green) and Sens (red) in early (one column of photoreceptors) (A), mid (12 columns of photoreceptors) (B) and late (20 columns of photoreceptors) (C) third instar eye imaginal discs; individual channels shown in Figure S3. (D–F) expression of eymut-dGFP (green) and Sens (red) in third instar eye imaginal discs; individual channels shown in Figure S3. (D) one column of photoreceptors, (E) 11 columns of photoreceptors, (F) 18 columns of photoreceptors. (G) ey-dGFP expression in so3  clone anterior (yellow arrow) and posterior (yellow arrowhead) to the morphogenetic furrow. (G′) Grayscale image of β-Galactosidase expression, magenta in G; loss of β-Galactosidase marks the clone (G″) Grayscale image of ey-dGFP expression, green in G (H–H″) Maximum projection of orthogonal sections through the posterior clone indicated by a yellow arrowhead in G–G″. (I) eymut-dGFP (green) expression in so3  clone marked by loss of β-Galactosidase expression (magenta) in a disc aged between panels D and E. The yellow arrowhead marks the furrow; the orange arrow indicates non-clone tissue, blue arrow indicates anterior clone; similar expression detected in and out of clone (I′) Grayscale image of β-Galactosidase expression, magenta in I. (I″) Grayscale image of ey-dGFP expression, green in I.
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pgen-1003731-g003: So regulates ey expression through a binding site in an ey eye enhancer.(A–F) reporter expression in third instar discs; columns of Sens positive cells were counted to compare furrow progression at different times. (A–C) expression of ey-dGFP (green) and Sens (red) in early (one column of photoreceptors) (A), mid (12 columns of photoreceptors) (B) and late (20 columns of photoreceptors) (C) third instar eye imaginal discs; individual channels shown in Figure S3. (D–F) expression of eymut-dGFP (green) and Sens (red) in third instar eye imaginal discs; individual channels shown in Figure S3. (D) one column of photoreceptors, (E) 11 columns of photoreceptors, (F) 18 columns of photoreceptors. (G) ey-dGFP expression in so3 clone anterior (yellow arrow) and posterior (yellow arrowhead) to the morphogenetic furrow. (G′) Grayscale image of β-Galactosidase expression, magenta in G; loss of β-Galactosidase marks the clone (G″) Grayscale image of ey-dGFP expression, green in G (H–H″) Maximum projection of orthogonal sections through the posterior clone indicated by a yellow arrowhead in G–G″. (I) eymut-dGFP (green) expression in so3 clone marked by loss of β-Galactosidase expression (magenta) in a disc aged between panels D and E. The yellow arrowhead marks the furrow; the orange arrow indicates non-clone tissue, blue arrow indicates anterior clone; similar expression detected in and out of clone (I′) Grayscale image of β-Galactosidase expression, magenta in I. (I″) Grayscale image of ey-dGFP expression, green in I.

Mentions: So is a homeodomain transcription factor, leading us to ask if So suppresses ey expression at the transcriptional level. To test this, we required a reporter that recapitulates ey regulation anterior and posterior to the morphogenetic furrow. Published ey enhancer reporters [22], [38], unlike Ey expression, persist posterior to the morphogenetic furrow, possibly due to perdurance of beta-galactosidase. We therefore constructed a new destabilized GFP (dGFP) reporter. To compare wild-type and mutant constructs while avoiding position effects, we utilized a vector that could integrate only at specific sites in our analysis [39]–[41]. We cloned a previously characterized full-length eye enhancer from the ey locus into this new dGFP vector, “ey-dGFP”[38], [39]. We detected robust expression with ey-dGFP throughout larval development (Figure 3A–C, Figure S3A–C). Similar to ey expression, ey-dGFP is expressed throughout the eye disc in first instar (not shown) and is maintained throughout the eye disc until furrow initiation (Figure 3A). During the third instar ey-dGFP is maintained anterior to the morphogenetic furrow and suppressed at the morphogenetic furrow, similar to Ey expression (Figure 3B). This expression pattern is maintained throughout the third instar (Figure 3C). Therefore, this enhancer recapitulates the Ey expression pattern in the eye field.


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)

So regulates ey expression through a binding site in an ey eye enhancer.(A–F) reporter expression in third instar discs; columns of Sens positive cells were counted to compare furrow progression at different times. (A–C) expression of ey-dGFP (green) and Sens (red) in early (one column of photoreceptors) (A), mid (12 columns of photoreceptors) (B) and late (20 columns of photoreceptors) (C) third instar eye imaginal discs; individual channels shown in Figure S3. (D–F) expression of eymut-dGFP (green) and Sens (red) in third instar eye imaginal discs; individual channels shown in Figure S3. (D) one column of photoreceptors, (E) 11 columns of photoreceptors, (F) 18 columns of photoreceptors. (G) ey-dGFP expression in so3  clone anterior (yellow arrow) and posterior (yellow arrowhead) to the morphogenetic furrow. (G′) Grayscale image of β-Galactosidase expression, magenta in G; loss of β-Galactosidase marks the clone (G″) Grayscale image of ey-dGFP expression, green in G (H–H″) Maximum projection of orthogonal sections through the posterior clone indicated by a yellow arrowhead in G–G″. (I) eymut-dGFP (green) expression in so3  clone marked by loss of β-Galactosidase expression (magenta) in a disc aged between panels D and E. The yellow arrowhead marks the furrow; the orange arrow indicates non-clone tissue, blue arrow indicates anterior clone; similar expression detected in and out of clone (I′) Grayscale image of β-Galactosidase expression, magenta in I. (I″) Grayscale image of ey-dGFP expression, green in I.
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Related In: Results  -  Collection

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pgen-1003731-g003: So regulates ey expression through a binding site in an ey eye enhancer.(A–F) reporter expression in third instar discs; columns of Sens positive cells were counted to compare furrow progression at different times. (A–C) expression of ey-dGFP (green) and Sens (red) in early (one column of photoreceptors) (A), mid (12 columns of photoreceptors) (B) and late (20 columns of photoreceptors) (C) third instar eye imaginal discs; individual channels shown in Figure S3. (D–F) expression of eymut-dGFP (green) and Sens (red) in third instar eye imaginal discs; individual channels shown in Figure S3. (D) one column of photoreceptors, (E) 11 columns of photoreceptors, (F) 18 columns of photoreceptors. (G) ey-dGFP expression in so3 clone anterior (yellow arrow) and posterior (yellow arrowhead) to the morphogenetic furrow. (G′) Grayscale image of β-Galactosidase expression, magenta in G; loss of β-Galactosidase marks the clone (G″) Grayscale image of ey-dGFP expression, green in G (H–H″) Maximum projection of orthogonal sections through the posterior clone indicated by a yellow arrowhead in G–G″. (I) eymut-dGFP (green) expression in so3 clone marked by loss of β-Galactosidase expression (magenta) in a disc aged between panels D and E. The yellow arrowhead marks the furrow; the orange arrow indicates non-clone tissue, blue arrow indicates anterior clone; similar expression detected in and out of clone (I′) Grayscale image of β-Galactosidase expression, magenta in I. (I″) Grayscale image of ey-dGFP expression, green in I.
Mentions: So is a homeodomain transcription factor, leading us to ask if So suppresses ey expression at the transcriptional level. To test this, we required a reporter that recapitulates ey regulation anterior and posterior to the morphogenetic furrow. Published ey enhancer reporters [22], [38], unlike Ey expression, persist posterior to the morphogenetic furrow, possibly due to perdurance of beta-galactosidase. We therefore constructed a new destabilized GFP (dGFP) reporter. To compare wild-type and mutant constructs while avoiding position effects, we utilized a vector that could integrate only at specific sites in our analysis [39]–[41]. We cloned a previously characterized full-length eye enhancer from the ey locus into this new dGFP vector, “ey-dGFP”[38], [39]. We detected robust expression with ey-dGFP throughout larval development (Figure 3A–C, Figure S3A–C). Similar to ey expression, ey-dGFP is expressed throughout the eye disc in first instar (not shown) and is maintained throughout the eye disc until furrow initiation (Figure 3A). During the third instar ey-dGFP is maintained anterior to the morphogenetic furrow and suppressed at the morphogenetic furrow, similar to Ey expression (Figure 3B). This expression pattern is maintained throughout the third instar (Figure 3C). Therefore, this enhancer recapitulates the Ey expression pattern in the eye field.

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