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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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Mira expression in Btd RNAi knockdown type II NB clone.(A–A′) Mira is expressed in INPs (yellow arrows) in a wild-type type II NB lineage and forms a basal crescent (white arrows) at metaphase. (B–B′) In a Btd RNAi knockdown type II NB lineage without mature INPs, Mira is expressed in Ase+ daughter cells (yellow arrows) next to the Ase− immature INP (open arrows) but does not form a basal crescent at metaphase in the dividing Ase+ cell (white arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.006
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fig2s1: Mira expression in Btd RNAi knockdown type II NB clone.(A–A′) Mira is expressed in INPs (yellow arrows) in a wild-type type II NB lineage and forms a basal crescent (white arrows) at metaphase. (B–B′) In a Btd RNAi knockdown type II NB lineage without mature INPs, Mira is expressed in Ase+ daughter cells (yellow arrows) next to the Ase− immature INP (open arrows) but does not form a basal crescent at metaphase in the dividing Ase+ cell (white arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.006

Mentions: Why does the loss of Btd lead to the elimination of mature INPs? When mature INPs are eliminated in the absence of Btd, the type II NBs without the ectopic Ase expression still produce Ase− immature INPs and a few Ase+ Dpn− daughter cells. In normal type II NB lineages, Ase+ Dpn− cells can be either Ase+ immature INPs or GMCs. Therefore, three possible scenarios could happen when mature INPs are eliminated in the absence of Btd: 1) Ase− immature INPs differentiate into GMCs instead of Ase+ immature INPs; 2) Ase− immature INPs differentiate into Ase+ immature INPs, which then directly differentiate into neurons/glia without further dividing; 3) Ase− immature INPs differentiate into Ase+ immature INPs, which in turn differentiate into terminally dividing GMCs. To distinguish these possibilities, we first wanted to determine if Ase− immature INPs still differentiate into Ase+ immature INP in the absence of Btd by examining the expression of INP specific marker R9D11-CD4-tdTomato and progenitor marker Miranda (Mira) in the Ase+ cells next to the Ase− immature INPs. R9D11-CD4-tdTomato utilizes a DNA fragment R9D11 from the erm promoter to drive the expression of CD4-tdTomato (Han et al., 2011). In normal type II NB lineages, R9D11-CD4-tdTomato is first turned on in Ase+ immature INPs and becomes stronger as INPs mature (Figure 2A–A′), which is similar to R9D11-mCD8-GFP (Zhu et al., 2011). Mira is expressed in all NBs as well as INPs but not (or very weakly) in GMCs (Figure 2—–figure supplement 1). In Btd RNAi knockdown type II NB lineages without mature INPs, we found that R9D11-CD4-tdTomato was expressed in Ase+ daughter cells next to the Ase− immature INPs but its overall expression was much weaker than that in normal type II NB lineages (Figure 2B–B′,I). Consistently, Mira is also expressed in those Ase+ cells next to the Ase− immature INPs in the Btd RNAi knockdown type II NB lineages (Figure 2—figure supplement 1). The expression of R9D11-CD4-tdTomato and Mira suggests that Ase− immature INPs still differentiate into Ase+ immature INP in the absence of Btd as in wild-type type II NB lineages (Figure 2J).10.7554/eLife.03596.005Figure 2.Loss of Btd results in ectopic nuclear Pros in immature INPs and premature differentiation of Ase+ immature INPs into GMCs.


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)

Mira expression in Btd RNAi knockdown type II NB clone.(A–A′) Mira is expressed in INPs (yellow arrows) in a wild-type type II NB lineage and forms a basal crescent (white arrows) at metaphase. (B–B′) In a Btd RNAi knockdown type II NB lineage without mature INPs, Mira is expressed in Ase+ daughter cells (yellow arrows) next to the Ase− immature INP (open arrows) but does not form a basal crescent at metaphase in the dividing Ase+ cell (white arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.006
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2s1: Mira expression in Btd RNAi knockdown type II NB clone.(A–A′) Mira is expressed in INPs (yellow arrows) in a wild-type type II NB lineage and forms a basal crescent (white arrows) at metaphase. (B–B′) In a Btd RNAi knockdown type II NB lineage without mature INPs, Mira is expressed in Ase+ daughter cells (yellow arrows) next to the Ase− immature INP (open arrows) but does not form a basal crescent at metaphase in the dividing Ase+ cell (white arrows).DOI:http://dx.doi.org/10.7554/eLife.03596.006
Mentions: Why does the loss of Btd lead to the elimination of mature INPs? When mature INPs are eliminated in the absence of Btd, the type II NBs without the ectopic Ase expression still produce Ase− immature INPs and a few Ase+ Dpn− daughter cells. In normal type II NB lineages, Ase+ Dpn− cells can be either Ase+ immature INPs or GMCs. Therefore, three possible scenarios could happen when mature INPs are eliminated in the absence of Btd: 1) Ase− immature INPs differentiate into GMCs instead of Ase+ immature INPs; 2) Ase− immature INPs differentiate into Ase+ immature INPs, which then directly differentiate into neurons/glia without further dividing; 3) Ase− immature INPs differentiate into Ase+ immature INPs, which in turn differentiate into terminally dividing GMCs. To distinguish these possibilities, we first wanted to determine if Ase− immature INPs still differentiate into Ase+ immature INP in the absence of Btd by examining the expression of INP specific marker R9D11-CD4-tdTomato and progenitor marker Miranda (Mira) in the Ase+ cells next to the Ase− immature INPs. R9D11-CD4-tdTomato utilizes a DNA fragment R9D11 from the erm promoter to drive the expression of CD4-tdTomato (Han et al., 2011). In normal type II NB lineages, R9D11-CD4-tdTomato is first turned on in Ase+ immature INPs and becomes stronger as INPs mature (Figure 2A–A′), which is similar to R9D11-mCD8-GFP (Zhu et al., 2011). Mira is expressed in all NBs as well as INPs but not (or very weakly) in GMCs (Figure 2—–figure supplement 1). In Btd RNAi knockdown type II NB lineages without mature INPs, we found that R9D11-CD4-tdTomato was expressed in Ase+ daughter cells next to the Ase− immature INPs but its overall expression was much weaker than that in normal type II NB lineages (Figure 2B–B′,I). Consistently, Mira is also expressed in those Ase+ cells next to the Ase− immature INPs in the Btd RNAi knockdown type II NB lineages (Figure 2—figure supplement 1). The expression of R9D11-CD4-tdTomato and Mira suggests that Ase− immature INPs still differentiate into Ase+ immature INP in the absence of Btd as in wild-type type II NB lineages (Figure 2J).10.7554/eLife.03596.005Figure 2.Loss of Btd results in ectopic nuclear Pros in immature INPs and premature differentiation of Ase+ immature INPs into GMCs.

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