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Genome-wide analysis reveals a major role in cell fate maintenance and an unexpected role in endoreduplication for the Drosophila FoxA gene Fork head.

Maruyama R, Grevengoed E, Stempniewicz P, Andrew DJ - PLoS ONE (2011)

Bottom Line: Transcription factors drive organogenesis, from the initiation of cell fate decisions to the maintenance and implementation of these decisions.Thus, unlike the worm FoxA protein PHA-4, Fkh does not function to specify cell fate.Overall, this study demonstrates an important role for Fkh in determining how an organ preserves its identity throughout development and provides an alternative paradigm for how FoxA proteins function in organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACT
Transcription factors drive organogenesis, from the initiation of cell fate decisions to the maintenance and implementation of these decisions. The Drosophila embryonic salivary gland provides an excellent platform for unraveling the underlying transcriptional networks of organ development because Drosophila is relatively unencumbered by significant genetic redundancy. The highly conserved FoxA family transcription factors are essential for various aspects of organogenesis in all animals that have been studied. Here, we explore the role of the single Drosophila FoxA protein Fork head (Fkh) in salivary gland organogenesis using two genome-wide strategies. A large-scale in situ hybridization analysis reveals a major role for Fkh in maintaining the salivary gland fate decision and controlling salivary gland physiological activity, in addition to its previously known roles in morphogenesis and survival. The majority of salivary gland genes (59%) are affected by fkh loss, mainly at later stages of salivary gland development. We show that global expression of Fkh cannot drive ectopic salivary gland formation. Thus, unlike the worm FoxA protein PHA-4, Fkh does not function to specify cell fate. In addition, Fkh only indirectly regulates many salivary gland genes, which is also distinct from the role of PHA-4 in organogenesis. Our microarray analyses reveal unexpected roles for Fkh in blocking terminal differentiation and in endoreduplication in the salivary gland and in other Fkh-expressing embryonic tissues. Overall, this study demonstrates an important role for Fkh in determining how an organ preserves its identity throughout development and provides an alternative paradigm for how FoxA proteins function in organogenesis.

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Fkh regulates some SG genes indirectly through maintaining CrebA expression.(A) In situ hybridization of the baiser gene in WT, fkh H99, CrebA mutants. As shown here with baiser, many genes whose SG expression disappears only in late fkh mutants require CrebA for their SG expression at all times. Red arrowheads: SGs. (B) Fkh and CrebA bind different sites on SG polytene chromosomes, suggesting that regulation of target genes does not involve cooperative regulation by Fkh and CrebA. Red: αFkh, green: αCrebA, blue: DAPI.
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pone-0020901-g004: Fkh regulates some SG genes indirectly through maintaining CrebA expression.(A) In situ hybridization of the baiser gene in WT, fkh H99, CrebA mutants. As shown here with baiser, many genes whose SG expression disappears only in late fkh mutants require CrebA for their SG expression at all times. Red arrowheads: SGs. (B) Fkh and CrebA bind different sites on SG polytene chromosomes, suggesting that regulation of target genes does not involve cooperative regulation by Fkh and CrebA. Red: αFkh, green: αCrebA, blue: DAPI.

Mentions: Salivary gland expression of the 19 continuously expressed genes in the ‘decreased’ group was either significantly decreased or gone at all stages in fkh mutants (Figure 2D and 3F). These genes are also good candidates for direct regulation by Fkh. Among this group of targets is PH4αSG2, which encodes an ER enzyme whose expression has been shown to be directly activated by Fkh [28]. The ‘only late expression lost’ group of continuously expressed genes (27 genes) is likely to include both direct and indirect Fkh targets (Figure 2D and 3G). An example of a direct target in this group is CrebA, which encodes a bZip transcription factor required for increased secretory capacity [29], [37]. CrebA expression is initially activated by the same transcription factors that activate fkh expression in the SG - Scr, Exd and Hth. Both CrebA and Fkh subsequently become directly dependent on Fkh for their maintained expression, since expression of Scr, Exd and Hth disappears early as the SG cells begin to invaginate [25], [29], [30]. Examples of likely indirect targets in the ‘only late expression lost’ group are 18 genes whose expression is also downregulated in CrebA mutants, based on in situ and/or microarray analysis [29], [37]. Twelve CrebA target genes in the ‘only late expression lost’ group have been categorized as being involved in secretion and endocytosis based on Gene Ontology assignments, including baiser (bai) (Figure 4A), which encodes a p24 protein family member involved in ER-Golgi transport [38]( Table S1). Given previous findings that Fkh directly maintains CrebA expression in the SG [29] and that CrebA has been shown to directly regulate expression of most secretory genes [37], Fkh may affect expression of these genes only indirectly by maintaining CrebA expression. Importantly, the secretory pathway genes that are also regulated by CrebA represent a large proportion of the ‘only late expression lost’ group.


Genome-wide analysis reveals a major role in cell fate maintenance and an unexpected role in endoreduplication for the Drosophila FoxA gene Fork head.

Maruyama R, Grevengoed E, Stempniewicz P, Andrew DJ - PLoS ONE (2011)

Fkh regulates some SG genes indirectly through maintaining CrebA expression.(A) In situ hybridization of the baiser gene in WT, fkh H99, CrebA mutants. As shown here with baiser, many genes whose SG expression disappears only in late fkh mutants require CrebA for their SG expression at all times. Red arrowheads: SGs. (B) Fkh and CrebA bind different sites on SG polytene chromosomes, suggesting that regulation of target genes does not involve cooperative regulation by Fkh and CrebA. Red: αFkh, green: αCrebA, blue: DAPI.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3116861&req=5

pone-0020901-g004: Fkh regulates some SG genes indirectly through maintaining CrebA expression.(A) In situ hybridization of the baiser gene in WT, fkh H99, CrebA mutants. As shown here with baiser, many genes whose SG expression disappears only in late fkh mutants require CrebA for their SG expression at all times. Red arrowheads: SGs. (B) Fkh and CrebA bind different sites on SG polytene chromosomes, suggesting that regulation of target genes does not involve cooperative regulation by Fkh and CrebA. Red: αFkh, green: αCrebA, blue: DAPI.
Mentions: Salivary gland expression of the 19 continuously expressed genes in the ‘decreased’ group was either significantly decreased or gone at all stages in fkh mutants (Figure 2D and 3F). These genes are also good candidates for direct regulation by Fkh. Among this group of targets is PH4αSG2, which encodes an ER enzyme whose expression has been shown to be directly activated by Fkh [28]. The ‘only late expression lost’ group of continuously expressed genes (27 genes) is likely to include both direct and indirect Fkh targets (Figure 2D and 3G). An example of a direct target in this group is CrebA, which encodes a bZip transcription factor required for increased secretory capacity [29], [37]. CrebA expression is initially activated by the same transcription factors that activate fkh expression in the SG - Scr, Exd and Hth. Both CrebA and Fkh subsequently become directly dependent on Fkh for their maintained expression, since expression of Scr, Exd and Hth disappears early as the SG cells begin to invaginate [25], [29], [30]. Examples of likely indirect targets in the ‘only late expression lost’ group are 18 genes whose expression is also downregulated in CrebA mutants, based on in situ and/or microarray analysis [29], [37]. Twelve CrebA target genes in the ‘only late expression lost’ group have been categorized as being involved in secretion and endocytosis based on Gene Ontology assignments, including baiser (bai) (Figure 4A), which encodes a p24 protein family member involved in ER-Golgi transport [38]( Table S1). Given previous findings that Fkh directly maintains CrebA expression in the SG [29] and that CrebA has been shown to directly regulate expression of most secretory genes [37], Fkh may affect expression of these genes only indirectly by maintaining CrebA expression. Importantly, the secretory pathway genes that are also regulated by CrebA represent a large proportion of the ‘only late expression lost’ group.

Bottom Line: Transcription factors drive organogenesis, from the initiation of cell fate decisions to the maintenance and implementation of these decisions.Thus, unlike the worm FoxA protein PHA-4, Fkh does not function to specify cell fate.Overall, this study demonstrates an important role for Fkh in determining how an organ preserves its identity throughout development and provides an alternative paradigm for how FoxA proteins function in organogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Johns Hopkins University, School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACT
Transcription factors drive organogenesis, from the initiation of cell fate decisions to the maintenance and implementation of these decisions. The Drosophila embryonic salivary gland provides an excellent platform for unraveling the underlying transcriptional networks of organ development because Drosophila is relatively unencumbered by significant genetic redundancy. The highly conserved FoxA family transcription factors are essential for various aspects of organogenesis in all animals that have been studied. Here, we explore the role of the single Drosophila FoxA protein Fork head (Fkh) in salivary gland organogenesis using two genome-wide strategies. A large-scale in situ hybridization analysis reveals a major role for Fkh in maintaining the salivary gland fate decision and controlling salivary gland physiological activity, in addition to its previously known roles in morphogenesis and survival. The majority of salivary gland genes (59%) are affected by fkh loss, mainly at later stages of salivary gland development. We show that global expression of Fkh cannot drive ectopic salivary gland formation. Thus, unlike the worm FoxA protein PHA-4, Fkh does not function to specify cell fate. In addition, Fkh only indirectly regulates many salivary gland genes, which is also distinct from the role of PHA-4 in organogenesis. Our microarray analyses reveal unexpected roles for Fkh in blocking terminal differentiation and in endoreduplication in the salivary gland and in other Fkh-expressing embryonic tissues. Overall, this study demonstrates an important role for Fkh in determining how an organ preserves its identity throughout development and provides an alternative paradigm for how FoxA proteins function in organogenesis.

Show MeSH
Related in: MedlinePlus