Limits...
Putting the model to the test: are APC proteins essential for neuronal polarity, axon outgrowth, and axon targeting?

Rusan NM, Akong K, Peifer M - J. Cell Biol. (2008)

Bottom Line: Experimental data based on dominant-negative approaches suggest that the tumor suppressor adenomatous polyposis coli (APC), a regulator of Wnt signaling and the cytoskeleton, regulates polarity of neuroectodermal precursors and neurons, helping specify one neurite as the axon, promoting its outgrowth, and guiding axon pathfinding.However, such dominant-negative approaches might affect processes in which APC is not essential.Likewise, CB, lobular plug, and mushroom body neurons do not require APCs for polarization, axon outgrowth, or, in the latter two cases, axon targeting.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
The highly polarized architecture of neurons is important for their function. Experimental data based on dominant-negative approaches suggest that the tumor suppressor adenomatous polyposis coli (APC), a regulator of Wnt signaling and the cytoskeleton, regulates polarity of neuroectodermal precursors and neurons, helping specify one neurite as the axon, promoting its outgrowth, and guiding axon pathfinding. However, such dominant-negative approaches might affect processes in which APC is not essential. We completely removed both APCs from Drosophila melanogaster larval neural precursors and neurons, testing whether APCs play universal roles in neuronal polarity. Surprisingly, APCs are not essential for asymmetric cell division or the stereotyped division axis of central brain (CB) neuroblasts, although they do affect cell cycle progression and spindle architecture. Likewise, CB, lobular plug, and mushroom body neurons do not require APCs for polarization, axon outgrowth, or, in the latter two cases, axon targeting. These data suggest that proposed cytoskeletal roles for APCs in mammals should be reassessed using loss of function tools.

Show MeSH

Related in: MedlinePlus

CB NBs do not require APCs for asymmetric cell division. (A) Larval brain. (B) CB NB, GMCs, neurons, and their fasciculated axons and target. (C) Asymmetric APC2 localization in CB NB (arrow). (D–G) Time-lapse images, wild-type, or double mutant NBs from nuclear envelope breakdown through next interphase. In all panels, NB divides asymmetrically (fourth column, brackets). White arrows, contractile ring; yellow arrows, new GMC. (D) Wild-type control clone. CD8∷GFP marks cell membrane, nuclei, and spindle. (inset) Different plane of focus showing nuclear envelope. (E) APC2g10 APC1Q8, CD8∷GFP. (F) Control clone, Tau∷GFP marking MTs. (G) APC2d40 APC1Q8, Tau∷GFP. Time is given in minutes:seconds. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2568018&req=5

fig1: CB NBs do not require APCs for asymmetric cell division. (A) Larval brain. (B) CB NB, GMCs, neurons, and their fasciculated axons and target. (C) Asymmetric APC2 localization in CB NB (arrow). (D–G) Time-lapse images, wild-type, or double mutant NBs from nuclear envelope breakdown through next interphase. In all panels, NB divides asymmetrically (fourth column, brackets). White arrows, contractile ring; yellow arrows, new GMC. (D) Wild-type control clone. CD8∷GFP marks cell membrane, nuclei, and spindle. (inset) Different plane of focus showing nuclear envelope. (E) APC2g10 APC1Q8, CD8∷GFP. (F) Control clone, Tau∷GFP marking MTs. (G) APC2d40 APC1Q8, Tau∷GFP. Time is given in minutes:seconds. Bars, 10 μm.

Mentions: APC2 is asymmetrically localized in larval CB NBs (Fig. 1, A–C; Akong et al., 2002). These neural progenitors undergo a series of asymmetric divisions, giving rise to ganglion mother cells (GMCs) that remain associated with the NB (Fig. 1 B). Progeny of GMCs remain associated as a cluster and differentiate as neurons. CB NB asymmetric divisions occur with a persistent spindle orientation with each new daughter born next to the previous daughter (Akong et al., 2002). This persistent orientation is thought to involve a series of cues, including a fixed centrosome, cortical cues, and cortical interactions of astral MTs (Siller et al., 2005, 2006; Rebollo et al., 2007; Rusan and Peifer, 2007). APC2's striking asymmetric localization suggested it helps orient spindles as it does in the Drosophila male germline (Yamashita et al., 2003).


Putting the model to the test: are APC proteins essential for neuronal polarity, axon outgrowth, and axon targeting?

Rusan NM, Akong K, Peifer M - J. Cell Biol. (2008)

CB NBs do not require APCs for asymmetric cell division. (A) Larval brain. (B) CB NB, GMCs, neurons, and their fasciculated axons and target. (C) Asymmetric APC2 localization in CB NB (arrow). (D–G) Time-lapse images, wild-type, or double mutant NBs from nuclear envelope breakdown through next interphase. In all panels, NB divides asymmetrically (fourth column, brackets). White arrows, contractile ring; yellow arrows, new GMC. (D) Wild-type control clone. CD8∷GFP marks cell membrane, nuclei, and spindle. (inset) Different plane of focus showing nuclear envelope. (E) APC2g10 APC1Q8, CD8∷GFP. (F) Control clone, Tau∷GFP marking MTs. (G) APC2d40 APC1Q8, Tau∷GFP. Time is given in minutes:seconds. Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2568018&req=5

fig1: CB NBs do not require APCs for asymmetric cell division. (A) Larval brain. (B) CB NB, GMCs, neurons, and their fasciculated axons and target. (C) Asymmetric APC2 localization in CB NB (arrow). (D–G) Time-lapse images, wild-type, or double mutant NBs from nuclear envelope breakdown through next interphase. In all panels, NB divides asymmetrically (fourth column, brackets). White arrows, contractile ring; yellow arrows, new GMC. (D) Wild-type control clone. CD8∷GFP marks cell membrane, nuclei, and spindle. (inset) Different plane of focus showing nuclear envelope. (E) APC2g10 APC1Q8, CD8∷GFP. (F) Control clone, Tau∷GFP marking MTs. (G) APC2d40 APC1Q8, Tau∷GFP. Time is given in minutes:seconds. Bars, 10 μm.
Mentions: APC2 is asymmetrically localized in larval CB NBs (Fig. 1, A–C; Akong et al., 2002). These neural progenitors undergo a series of asymmetric divisions, giving rise to ganglion mother cells (GMCs) that remain associated with the NB (Fig. 1 B). Progeny of GMCs remain associated as a cluster and differentiate as neurons. CB NB asymmetric divisions occur with a persistent spindle orientation with each new daughter born next to the previous daughter (Akong et al., 2002). This persistent orientation is thought to involve a series of cues, including a fixed centrosome, cortical cues, and cortical interactions of astral MTs (Siller et al., 2005, 2006; Rebollo et al., 2007; Rusan and Peifer, 2007). APC2's striking asymmetric localization suggested it helps orient spindles as it does in the Drosophila male germline (Yamashita et al., 2003).

Bottom Line: Experimental data based on dominant-negative approaches suggest that the tumor suppressor adenomatous polyposis coli (APC), a regulator of Wnt signaling and the cytoskeleton, regulates polarity of neuroectodermal precursors and neurons, helping specify one neurite as the axon, promoting its outgrowth, and guiding axon pathfinding.However, such dominant-negative approaches might affect processes in which APC is not essential.Likewise, CB, lobular plug, and mushroom body neurons do not require APCs for polarization, axon outgrowth, or, in the latter two cases, axon targeting.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
The highly polarized architecture of neurons is important for their function. Experimental data based on dominant-negative approaches suggest that the tumor suppressor adenomatous polyposis coli (APC), a regulator of Wnt signaling and the cytoskeleton, regulates polarity of neuroectodermal precursors and neurons, helping specify one neurite as the axon, promoting its outgrowth, and guiding axon pathfinding. However, such dominant-negative approaches might affect processes in which APC is not essential. We completely removed both APCs from Drosophila melanogaster larval neural precursors and neurons, testing whether APCs play universal roles in neuronal polarity. Surprisingly, APCs are not essential for asymmetric cell division or the stereotyped division axis of central brain (CB) neuroblasts, although they do affect cell cycle progression and spindle architecture. Likewise, CB, lobular plug, and mushroom body neurons do not require APCs for polarization, axon outgrowth, or, in the latter two cases, axon targeting. These data suggest that proposed cytoskeletal roles for APCs in mammals should be reassessed using loss of function tools.

Show MeSH
Related in: MedlinePlus