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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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Btd likely does not function in mature INPs.(A) A wild-type INP clone with 4 post-mitotic cells. (B) A btd mutant INP clone with 6 post-mitotic cells. INP clones labeled with mCD8-GFP are outlined by dashed circles. INP clones are identified as clones that have more than two cells but no NBs.DOI:http://dx.doi.org/10.7554/eLife.03596.010
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fig4s1: Btd likely does not function in mature INPs.(A) A wild-type INP clone with 4 post-mitotic cells. (B) A btd mutant INP clone with 6 post-mitotic cells. INP clones labeled with mCD8-GFP are outlined by dashed circles. INP clones are identified as clones that have more than two cells but no NBs.DOI:http://dx.doi.org/10.7554/eLife.03596.010

Mentions: Our results showed that Btd is required to suppress Pros in Ase− immature INPs. We next asked if Btd is also required to partially suppress Pros at later stages of INP development. In normal type II NB lineages, Pros is absent in Ase− immature INPs but is expressed at low levels in the cytoplasm of Ase+ immature INPs and mature INPs (Bello et al., 2008; Boone and Doe, 2008; Bowman et al., 2008). Maintaining the expression of Pros at low levels is essential for the self-renewal of INPs (Bayraktar et al., 2010). However, the complete elimination of mature INPs makes it difficult to assess the role of Btd in mature INPs. Therefore, we used erm-GAL4 (III) and erm-GAL4 (II) to knock down Btd. Both erm-GAL4 (III) and erm-GAL4 (II) are expressed in Ase+ immature INPs and mature INPs, whereas erm-GAL4 (II) is also expressed in Ase− immature INPs except for the newly born Ase− immature INPs (Xiao et al., 2012). However, knockdown of Btd using either erm-GAL4 (III) (Figure 4A–B′′,E) or erm-GAL4 (II) (Figure 4C–D′′,F) did not result in any obvious loss of mature INPs in type II NB lineages. In line with these RNAi knockdown results, we were able to recover multicellular btd mutant INP clones that were comparable to wild-type INP clones (Figure 4—figure supplement 1) while we generated btd mutant type II NB clones, indicating that btd mutant INPs were still able to divide multiple rounds like wild-type INPs and did not prematurely differentiate into GMCs. These data suggest that Btd likely suppresses Pros expression only in newly born Ase− immature INPs but not in immature INPs at later developmental stages or mature INPs.10.7554/eLife.03596.009Figure 4.Knockdown of Btd in immature or mature INPs by erm-GAL4 lines does not lead to the loss of mature INPs.


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)

Btd likely does not function in mature INPs.(A) A wild-type INP clone with 4 post-mitotic cells. (B) A btd mutant INP clone with 6 post-mitotic cells. INP clones labeled with mCD8-GFP are outlined by dashed circles. INP clones are identified as clones that have more than two cells but no NBs.DOI:http://dx.doi.org/10.7554/eLife.03596.010
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig4s1: Btd likely does not function in mature INPs.(A) A wild-type INP clone with 4 post-mitotic cells. (B) A btd mutant INP clone with 6 post-mitotic cells. INP clones labeled with mCD8-GFP are outlined by dashed circles. INP clones are identified as clones that have more than two cells but no NBs.DOI:http://dx.doi.org/10.7554/eLife.03596.010
Mentions: Our results showed that Btd is required to suppress Pros in Ase− immature INPs. We next asked if Btd is also required to partially suppress Pros at later stages of INP development. In normal type II NB lineages, Pros is absent in Ase− immature INPs but is expressed at low levels in the cytoplasm of Ase+ immature INPs and mature INPs (Bello et al., 2008; Boone and Doe, 2008; Bowman et al., 2008). Maintaining the expression of Pros at low levels is essential for the self-renewal of INPs (Bayraktar et al., 2010). However, the complete elimination of mature INPs makes it difficult to assess the role of Btd in mature INPs. Therefore, we used erm-GAL4 (III) and erm-GAL4 (II) to knock down Btd. Both erm-GAL4 (III) and erm-GAL4 (II) are expressed in Ase+ immature INPs and mature INPs, whereas erm-GAL4 (II) is also expressed in Ase− immature INPs except for the newly born Ase− immature INPs (Xiao et al., 2012). However, knockdown of Btd using either erm-GAL4 (III) (Figure 4A–B′′,E) or erm-GAL4 (II) (Figure 4C–D′′,F) did not result in any obvious loss of mature INPs in type II NB lineages. In line with these RNAi knockdown results, we were able to recover multicellular btd mutant INP clones that were comparable to wild-type INP clones (Figure 4—figure supplement 1) while we generated btd mutant type II NB clones, indicating that btd mutant INPs were still able to divide multiple rounds like wild-type INPs and did not prematurely differentiate into GMCs. These data suggest that Btd likely suppresses Pros expression only in newly born Ase− immature INPs but not in immature INPs at later developmental stages or mature INPs.10.7554/eLife.03596.009Figure 4.Knockdown of Btd in immature or mature INPs by erm-GAL4 lines does not lead to the loss of mature INPs.

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