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Expression of Groucho/TLE proteins during pancreas development.

Hoffman BG, Zavaglia B, Beach M, Helgason CD - BMC Dev. Biol. (2008)

Bottom Line: Of note, Tle2 and Tle3 are co-expressed with Gro/TLE interaction domain containing transcription factors that are essential for endocrine pancreas development.We further demonstrate that Tle2 can interact with several of these factors and that Tle2 modulate Arx's repressive activity.Taken together our studies suggest that Gro/TLE proteins play a role in the repression of target genes during endocrine cell specification.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cancer Endocrinology, BC Cancer Research Center, 675 West 10th Avenue, Vancouver, BC, V5Z 1L3, Canada. bhoffman@bccrc.ca

ABSTRACT

Background: The full-length mammalian homologs of groucho, Tle1, 2, 3, and 4, act as transcriptional corepressors and are recruited by transcription factors containing an eh1 or WRPW/Y domain. Many transcription factors critical to pancreas development contain a Gro/TLE interaction domain and several have been shown to require Gro/TLE interactions for proper function during neuronal development. However, a detailed analysis of the expression patterns of the Gro/TLE proteins in pancreas development has not been performed. Moreover, little is known about the ability of Gro/TLE proteins to interact with transcription factors in the pancreas.

Results: We describe the expression of Gro/TLE family members, and of 34 different transcription factors that contain a Gro/TLE interaction motif, in the pancreas utilizing nine SAGE libraries created from the developing and adult pancreas, as well as the GenePaint database. Next, we show the dynamic expression of Tle1, 2, 3, 4, 5 and 6 during pancreas development by qRT-PCR. To further define the cell-type specificity of the expression of these proteins we use immunofluorescence to co-localize them with Pdx1 at embryonic day 12.5 (E12.5), Ngn3 at E14.5, Pdx1, Nkx2-2, Insulin, Glucagon, Pancreatic polypeptide and Somatostatin at E18.5, as well as Insulin and Glucagon in the adult. We then show that Tle2 can interact with Nkx2-2, Hes1, Arx, and Nkx6-1 which are all critical factors in pancreas development. Finally, we demonstrate that Tle2 modulates the repressive abilities of Arx in a beta-cell line.

Conclusion: Although Tle1, 2, 3, and 4 show overlapping expression in pancreatic progenitors and in the adult islet, the expression of these factors is restricted to different cell types during endocrine cell maturation. Of note, Tle2 and Tle3 are co-expressed with Gro/TLE interaction domain containing transcription factors that are essential for endocrine pancreas development. We further demonstrate that Tle2 can interact with several of these factors and that Tle2 modulate Arx's repressive activity. Taken together our studies suggest that Gro/TLE proteins play a role in the repression of target genes during endocrine cell specification.

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A model of the proposed role of the Gro/TLE factors in cell fate choices during endocrine pancreas development. A schematic depicting a cross-repressive model of the genetic network regulating α-, β-, and ε-cell fate is shown based on our experimental data, as well as evidence from the literature on pancreas development [3,47] and on models of neuronal cell specification.
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Figure 10: A model of the proposed role of the Gro/TLE factors in cell fate choices during endocrine pancreas development. A schematic depicting a cross-repressive model of the genetic network regulating α-, β-, and ε-cell fate is shown based on our experimental data, as well as evidence from the literature on pancreas development [3,47] and on models of neuronal cell specification.

Mentions: Our results agree with studies on neuronal development that have defined a dual role for Gro/TLE factors in first controlling the differentiation of progenitor cell types and then later in the specification and maturation of specific cell types [46]. Our co-immunoprecipitation data demonstrates that Tle2 is able to interact with Nkx2-2, Nkx6-1, Hes1 and Arx, which are key controllers of endocrine cell specification and maturation. Further our IHC data indicates that Tle2 and Tle3, in particular, co-localize with these factors in pancreas development suggesting these interactions occur in vivo. Based on our results we propose a model for Gro/TLE action in the developing pancreas (Figure 10). In this model Tle1, 2, and 3 initially play a redundant role in enacting the repression of Hes1 target genes, such as Ngn3, thereby maintaining the cells in a progenitor state. In cells that begin to express higher Ngn3 levels, Hes1 expression is lost and cells differentiate into multipotent endocrine progenitors. Subsequently tripotent α/β/ε precursors develop into an ε (ghrelin producing) precursor or an α/β bipotent precursor based on repression of the ε cell fate by Nkx2-2 [3]. Experimental evidence has demonstrated that Gro/TLE interactions are critical to this process and both Tle2 and 3 are co-expressed with Nkx2-2 and can interact with it [3]. Subsequently, α/β-cell precursors undergo α or β cell specification wherein we hypothesize that pro-β-cell eh1 motif containing factors repress α-cell activating factors while pro-α-cell eh1 motif containing factors repress α-cell activating factors, several of which do so in a putatively Gro/TLE dependent fashion. The specific targets of these genes, in general, are not known.


Expression of Groucho/TLE proteins during pancreas development.

Hoffman BG, Zavaglia B, Beach M, Helgason CD - BMC Dev. Biol. (2008)

A model of the proposed role of the Gro/TLE factors in cell fate choices during endocrine pancreas development. A schematic depicting a cross-repressive model of the genetic network regulating α-, β-, and ε-cell fate is shown based on our experimental data, as well as evidence from the literature on pancreas development [3,47] and on models of neuronal cell specification.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2551604&req=5

Figure 10: A model of the proposed role of the Gro/TLE factors in cell fate choices during endocrine pancreas development. A schematic depicting a cross-repressive model of the genetic network regulating α-, β-, and ε-cell fate is shown based on our experimental data, as well as evidence from the literature on pancreas development [3,47] and on models of neuronal cell specification.
Mentions: Our results agree with studies on neuronal development that have defined a dual role for Gro/TLE factors in first controlling the differentiation of progenitor cell types and then later in the specification and maturation of specific cell types [46]. Our co-immunoprecipitation data demonstrates that Tle2 is able to interact with Nkx2-2, Nkx6-1, Hes1 and Arx, which are key controllers of endocrine cell specification and maturation. Further our IHC data indicates that Tle2 and Tle3, in particular, co-localize with these factors in pancreas development suggesting these interactions occur in vivo. Based on our results we propose a model for Gro/TLE action in the developing pancreas (Figure 10). In this model Tle1, 2, and 3 initially play a redundant role in enacting the repression of Hes1 target genes, such as Ngn3, thereby maintaining the cells in a progenitor state. In cells that begin to express higher Ngn3 levels, Hes1 expression is lost and cells differentiate into multipotent endocrine progenitors. Subsequently tripotent α/β/ε precursors develop into an ε (ghrelin producing) precursor or an α/β bipotent precursor based on repression of the ε cell fate by Nkx2-2 [3]. Experimental evidence has demonstrated that Gro/TLE interactions are critical to this process and both Tle2 and 3 are co-expressed with Nkx2-2 and can interact with it [3]. Subsequently, α/β-cell precursors undergo α or β cell specification wherein we hypothesize that pro-β-cell eh1 motif containing factors repress α-cell activating factors while pro-α-cell eh1 motif containing factors repress α-cell activating factors, several of which do so in a putatively Gro/TLE dependent fashion. The specific targets of these genes, in general, are not known.

Bottom Line: Of note, Tle2 and Tle3 are co-expressed with Gro/TLE interaction domain containing transcription factors that are essential for endocrine pancreas development.We further demonstrate that Tle2 can interact with several of these factors and that Tle2 modulate Arx's repressive activity.Taken together our studies suggest that Gro/TLE proteins play a role in the repression of target genes during endocrine cell specification.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cancer Endocrinology, BC Cancer Research Center, 675 West 10th Avenue, Vancouver, BC, V5Z 1L3, Canada. bhoffman@bccrc.ca

ABSTRACT

Background: The full-length mammalian homologs of groucho, Tle1, 2, 3, and 4, act as transcriptional corepressors and are recruited by transcription factors containing an eh1 or WRPW/Y domain. Many transcription factors critical to pancreas development contain a Gro/TLE interaction domain and several have been shown to require Gro/TLE interactions for proper function during neuronal development. However, a detailed analysis of the expression patterns of the Gro/TLE proteins in pancreas development has not been performed. Moreover, little is known about the ability of Gro/TLE proteins to interact with transcription factors in the pancreas.

Results: We describe the expression of Gro/TLE family members, and of 34 different transcription factors that contain a Gro/TLE interaction motif, in the pancreas utilizing nine SAGE libraries created from the developing and adult pancreas, as well as the GenePaint database. Next, we show the dynamic expression of Tle1, 2, 3, 4, 5 and 6 during pancreas development by qRT-PCR. To further define the cell-type specificity of the expression of these proteins we use immunofluorescence to co-localize them with Pdx1 at embryonic day 12.5 (E12.5), Ngn3 at E14.5, Pdx1, Nkx2-2, Insulin, Glucagon, Pancreatic polypeptide and Somatostatin at E18.5, as well as Insulin and Glucagon in the adult. We then show that Tle2 can interact with Nkx2-2, Hes1, Arx, and Nkx6-1 which are all critical factors in pancreas development. Finally, we demonstrate that Tle2 modulates the repressive abilities of Arx in a beta-cell line.

Conclusion: Although Tle1, 2, 3, and 4 show overlapping expression in pancreatic progenitors and in the adult islet, the expression of these factors is restricted to different cell types during endocrine cell maturation. Of note, Tle2 and Tle3 are co-expressed with Gro/TLE interaction domain containing transcription factors that are essential for endocrine pancreas development. We further demonstrate that Tle2 can interact with several of these factors and that Tle2 modulate Arx's repressive activity. Taken together our studies suggest that Gro/TLE proteins play a role in the repression of target genes during endocrine cell specification.

Show MeSH