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The Drosophila Sp8 transcription factor Buttonhead prevents premature differentiation of intermediate neural progenitors.

Xie Y, Li X, Zhang X, Mei S, Li H, Urso A, Zhu S - Elife (2014)

Bottom Line: We provide evidence to demonstrate that Btd prevents the premature differentiation by suppressing the expression of the homeodomain protein Prospero in immature INPs.We further show that Btd functions cooperatively with the Ets transcription factor Pointed P1 to promote the generation of INPs.Thus, our work reveals a critical mechanism that prevents premature differentiation and cell cycle exit of Drosophila INPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, United States.

ABSTRACT
Intermediate neural progenitor cells (INPs) need to avoid differentiation and cell cycle exit while maintaining restricted developmental potential, but mechanisms preventing differentiation and cell cycle exit of INPs are not well understood. In this study, we report that the Drosophila homolog of mammalian Sp8 transcription factor Buttonhead (Btd) prevents premature differentiation and cell cycle exit of INPs in Drosophila larval type II neuroblast (NB) lineages. We show that the loss of Btd leads to elimination of mature INPs due to premature differentiation of INPs into terminally dividing ganglion mother cells. We provide evidence to demonstrate that Btd prevents the premature differentiation by suppressing the expression of the homeodomain protein Prospero in immature INPs. We further show that Btd functions cooperatively with the Ets transcription factor Pointed P1 to promote the generation of INPs. Thus, our work reveals a critical mechanism that prevents premature differentiation and cell cycle exit of Drosophila INPs.

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Overexpression of Btd promotes the generation of INP-like cells.(A–A′′) INP specific marker R9D11-CD4-tdTomato is not expressed in any type I NB lineages (e.g. arrows) on the ventral side of a larval brain. (B–B′′) Overexpression of Btd induces the generation of INP-like cells in a subset of type I NB lineages on the ventral side of a larval brain as indicated by the expression of R9D11-CD4-tdTomato (e.g. arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.018
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fig7s2: Overexpression of Btd promotes the generation of INP-like cells.(A–A′′) INP specific marker R9D11-CD4-tdTomato is not expressed in any type I NB lineages (e.g. arrows) on the ventral side of a larval brain. (B–B′′) Overexpression of Btd induces the generation of INP-like cells in a subset of type I NB lineages on the ventral side of a larval brain as indicated by the expression of R9D11-CD4-tdTomato (e.g. arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.018

Mentions: To coexpress PntP1 and Btd in type I NB lineages, we used either btd-GAL4 to drive the expression of UAS-pntP1 in Btd-positive type I NB lineages or insc-GAL4 to drive the expression of UAS-pntP1 and UAS-btd simultaneously in all type I NB lineages. INP-like cells were identified by their expression of Ase and Dpn as well as INP-specific marker R9D11-CD4-tdTomato. Since the GAL4 insertion in the btd-GAL4 line causes a lethal mutation in btd (Estella et al., 2003), we examined the phenotype of the expression of UAS-pntP1 driven by btd-GAL4 only in btd-GAL4 heterozygous female larvae. As shown in Figure 6A–A′, type II NB lineages in btd-GAL4 heterozygous mutant larvae are indistinguishable from those in wild-type animals (e.g. Figure 1A–A′). Furthermore, as mentioned above, btd-GAL4 homozygous mutant type II NB clones develop normally (Figure 6—figure supplement 1). Therefore, the generation of INPs is not affected in the btd-GAL4 line. Interestingly, ectopic expression of PntP1 using btd-GAL4 as a driver induced the generation of INP-like cells in about 90% Btd-positive type I NB lineages in both larval brains (Figure 7A–C′,J) and VNCs (Figure 7—figure supplement 1). Consistently, the co-expression of UAS-pntP1 and UAS-btd driven by insc-GAL4 induced INP-like cells in about 95% of type I NB lineages in both larval brains and VNCs (Figure 7F–F′,I–I′,J, Figure 7—figure supplement 1). In contrast, the expression of UAS-pntP1 alone driven by insc-GAL4 only induced INP-like cells in about 10% and 46% of type I NB lineages in larval brains (Figure 7H–H′,J) and VNCs (Figure 7—figure supplement 1), respectively, although ectopic PntP1 expression suppressed Ase in nearly all type I NBs (Figure 7H, Figure 7—figure supplement 1). The expression of UAS-btd alone neither suppressed Ase nor induced the generation of INP-like cells in VNCs (Figure 7—figure supplement 1), whereas in larval brains, the expression of UAS-btd driven by insc-GAL4 suppressed/reduced the expression of Ase in the NB and promoted the generation of INP-like cells in about 20% of type I NB lineages (Figure 7G–G′,J). These ectopic INP-like cells induced by the expression of UAS-btd also expressed INP-specific marker R9D11-CD4-tdTomato (Figure 7—figure supplement 2). These results indicate that the generation of INP-like cells induced by the ectopic PntP1 expression requires Btd activity, whereas the expression of either PntP1 or Btd alone has limited ability to induce the generation of INP-like cells in type I NB lineages.


The Drosophila Sp8 transcription factor Buttonhead prevents premature differentiation of intermediate neural progenitors.

Xie Y, Li X, Zhang X, Mei S, Li H, Urso A, Zhu S - Elife (2014)

Overexpression of Btd promotes the generation of INP-like cells.(A–A′′) INP specific marker R9D11-CD4-tdTomato is not expressed in any type I NB lineages (e.g. arrows) on the ventral side of a larval brain. (B–B′′) Overexpression of Btd induces the generation of INP-like cells in a subset of type I NB lineages on the ventral side of a larval brain as indicated by the expression of R9D11-CD4-tdTomato (e.g. arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.018
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4221738&req=5

fig7s2: Overexpression of Btd promotes the generation of INP-like cells.(A–A′′) INP specific marker R9D11-CD4-tdTomato is not expressed in any type I NB lineages (e.g. arrows) on the ventral side of a larval brain. (B–B′′) Overexpression of Btd induces the generation of INP-like cells in a subset of type I NB lineages on the ventral side of a larval brain as indicated by the expression of R9D11-CD4-tdTomato (e.g. arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.018
Mentions: To coexpress PntP1 and Btd in type I NB lineages, we used either btd-GAL4 to drive the expression of UAS-pntP1 in Btd-positive type I NB lineages or insc-GAL4 to drive the expression of UAS-pntP1 and UAS-btd simultaneously in all type I NB lineages. INP-like cells were identified by their expression of Ase and Dpn as well as INP-specific marker R9D11-CD4-tdTomato. Since the GAL4 insertion in the btd-GAL4 line causes a lethal mutation in btd (Estella et al., 2003), we examined the phenotype of the expression of UAS-pntP1 driven by btd-GAL4 only in btd-GAL4 heterozygous female larvae. As shown in Figure 6A–A′, type II NB lineages in btd-GAL4 heterozygous mutant larvae are indistinguishable from those in wild-type animals (e.g. Figure 1A–A′). Furthermore, as mentioned above, btd-GAL4 homozygous mutant type II NB clones develop normally (Figure 6—figure supplement 1). Therefore, the generation of INPs is not affected in the btd-GAL4 line. Interestingly, ectopic expression of PntP1 using btd-GAL4 as a driver induced the generation of INP-like cells in about 90% Btd-positive type I NB lineages in both larval brains (Figure 7A–C′,J) and VNCs (Figure 7—figure supplement 1). Consistently, the co-expression of UAS-pntP1 and UAS-btd driven by insc-GAL4 induced INP-like cells in about 95% of type I NB lineages in both larval brains and VNCs (Figure 7F–F′,I–I′,J, Figure 7—figure supplement 1). In contrast, the expression of UAS-pntP1 alone driven by insc-GAL4 only induced INP-like cells in about 10% and 46% of type I NB lineages in larval brains (Figure 7H–H′,J) and VNCs (Figure 7—figure supplement 1), respectively, although ectopic PntP1 expression suppressed Ase in nearly all type I NBs (Figure 7H, Figure 7—figure supplement 1). The expression of UAS-btd alone neither suppressed Ase nor induced the generation of INP-like cells in VNCs (Figure 7—figure supplement 1), whereas in larval brains, the expression of UAS-btd driven by insc-GAL4 suppressed/reduced the expression of Ase in the NB and promoted the generation of INP-like cells in about 20% of type I NB lineages (Figure 7G–G′,J). These ectopic INP-like cells induced by the expression of UAS-btd also expressed INP-specific marker R9D11-CD4-tdTomato (Figure 7—figure supplement 2). These results indicate that the generation of INP-like cells induced by the ectopic PntP1 expression requires Btd activity, whereas the expression of either PntP1 or Btd alone has limited ability to induce the generation of INP-like cells in type I NB lineages.

Bottom Line: We provide evidence to demonstrate that Btd prevents the premature differentiation by suppressing the expression of the homeodomain protein Prospero in immature INPs.We further show that Btd functions cooperatively with the Ets transcription factor Pointed P1 to promote the generation of INPs.Thus, our work reveals a critical mechanism that prevents premature differentiation and cell cycle exit of Drosophila INPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, United States.

ABSTRACT
Intermediate neural progenitor cells (INPs) need to avoid differentiation and cell cycle exit while maintaining restricted developmental potential, but mechanisms preventing differentiation and cell cycle exit of INPs are not well understood. In this study, we report that the Drosophila homolog of mammalian Sp8 transcription factor Buttonhead (Btd) prevents premature differentiation and cell cycle exit of INPs in Drosophila larval type II neuroblast (NB) lineages. We show that the loss of Btd leads to elimination of mature INPs due to premature differentiation of INPs into terminally dividing ganglion mother cells. We provide evidence to demonstrate that Btd prevents the premature differentiation by suppressing the expression of the homeodomain protein Prospero in immature INPs. We further show that Btd functions cooperatively with the Ets transcription factor Pointed P1 to promote the generation of INPs. Thus, our work reveals a critical mechanism that prevents premature differentiation and cell cycle exit of Drosophila INPs.

Show MeSH
Related in: MedlinePlus