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Bimodal control of dendritic and axonal growth by the dual leucine zipper kinase pathway.

Wang X, Kim JH, Bazzi M, Robinson S, Collins CA, Ye B - PLoS Biol. (2013)

Bottom Line: Highwire, an evolutionarily conserved E3 ubiquitin ligase, restrains axonal growth but acts as a positive regulator for dendritic growth in class IV dendritic arborization neurons in the larva.While both the axonal and dendritic functions of highwire require the DLK kinase Wallenda, these two functions diverge through two downstream transcription factors, Fos and Knot, which mediate the axonal and dendritic regulation, respectively.This study not only reveals a previously unknown function of the conserved DLK pathway in controlling dendrite development, but also provides a novel paradigm for understanding how neuronal compartmentalization and the diversity of neuronal morphology are achieved.

View Article: PubMed Central - PubMed

Affiliation: Life Sciences Institute and Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Knowledge of the molecular and genetic mechanisms underlying the separation of dendritic and axonal compartments is not only crucial for understanding the assembly of neural circuits, but also for developing strategies to correct defective dendrites or axons in diseases with subcellular precision. Previous studies have uncovered regulators dedicated to either dendritic or axonal growth. Here we investigate a novel regulatory mechanism that differentially directs dendritic and axonal growth within the same neuron in vivo. We find that the dual leucine zipper kinase (DLK) signaling pathway in Drosophila, which consists of Highwire and Wallenda and controls axonal growth, regeneration, and degeneration, is also involved in dendritic growth in vivo. Highwire, an evolutionarily conserved E3 ubiquitin ligase, restrains axonal growth but acts as a positive regulator for dendritic growth in class IV dendritic arborization neurons in the larva. While both the axonal and dendritic functions of highwire require the DLK kinase Wallenda, these two functions diverge through two downstream transcription factors, Fos and Knot, which mediate the axonal and dendritic regulation, respectively. This study not only reveals a previously unknown function of the conserved DLK pathway in controlling dendrite development, but also provides a novel paradigm for understanding how neuronal compartmentalization and the diversity of neuronal morphology are achieved.

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Related in: MedlinePlus

Hiw-Wnd pathway regulates the expression and transcriptional activity of the C4da-specific transcription factor Kn.(A) Overexpressing Wnd attenuates the nuclear Kn expression levels. Representative immunofluorescence images of wt and Wnd-overexpressing (OE Wnd) ddaC neurons labeled with antibodies against Kn (top) and Elav (bottom). Scale bar, 5 µm. (B) Quantification of the immunofluorescence intensity of nuclear Kn normalized to that of nuclear Elav in wt, hiwΔN, and OE Wnd neurons. (C) Wnd overexpression down-regulates the promoter activity of the ENaC ion channel pickpocket (ppk), a known target of Kn. Representative ddaC neurons labeled with ppk-eGFP in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) OE Kn; (5) hiwΔN+OE Kn; (6) OE Kn+OE Wnd. Scale bar, 5 µm. (D) Quantification of ppk-eGFP fluorescent intensity in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) knKN1/KN4; (5) OE Kn; (6) hiwΔN+OE Kn; (7) OE mCD8RFP+OE Kn; (8) OE Kn+OE Wnd.
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pbio-1001572-g004: Hiw-Wnd pathway regulates the expression and transcriptional activity of the C4da-specific transcription factor Kn.(A) Overexpressing Wnd attenuates the nuclear Kn expression levels. Representative immunofluorescence images of wt and Wnd-overexpressing (OE Wnd) ddaC neurons labeled with antibodies against Kn (top) and Elav (bottom). Scale bar, 5 µm. (B) Quantification of the immunofluorescence intensity of nuclear Kn normalized to that of nuclear Elav in wt, hiwΔN, and OE Wnd neurons. (C) Wnd overexpression down-regulates the promoter activity of the ENaC ion channel pickpocket (ppk), a known target of Kn. Representative ddaC neurons labeled with ppk-eGFP in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) OE Kn; (5) hiwΔN+OE Kn; (6) OE Kn+OE Wnd. Scale bar, 5 µm. (D) Quantification of ppk-eGFP fluorescent intensity in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) knKN1/KN4; (5) OE Kn; (6) hiwΔN+OE Kn; (7) OE mCD8RFP+OE Kn; (8) OE Kn+OE Wnd.

Mentions: In order to understand how the function of DLK pathway diverges into dendritic and axonal regulations, we hypothesized that the divergence occurred at the transcriptional level, and therefore tested the transcription factors that are known to regulate dendritic growth in da neurons. Among them, the Krüppel-like factor Dar1, the homeodomain transcription factor Cut (Ct), and zinc-finger transcription factor Knot (Kn, as known as Collier) have been shown to be essential for dendritic growth in C4da neurons. Loss-of-function mutations in each of these transcription factors severely reduce dendritic growth in C4da neurons [6],[45]–[48]. We first tested whether expression levels of these transcription factors in C4da neuron nucleus were altered in hiw loss-of-function mutants. No significant difference in the levels of Dar1 [6] or Cut [45] was observed between wild-type and hiw mutant C4da neurons (Figure S5A–C). In contrast, the nuclear levels of Kn, which belongs to the evolutionarily conserved Collier/Olf1/EBF (COE) family, were significantly reduced in both hiw mutant neurons and Wnd-overexpressing neurons (Figure 4A and B)


Bimodal control of dendritic and axonal growth by the dual leucine zipper kinase pathway.

Wang X, Kim JH, Bazzi M, Robinson S, Collins CA, Ye B - PLoS Biol. (2013)

Hiw-Wnd pathway regulates the expression and transcriptional activity of the C4da-specific transcription factor Kn.(A) Overexpressing Wnd attenuates the nuclear Kn expression levels. Representative immunofluorescence images of wt and Wnd-overexpressing (OE Wnd) ddaC neurons labeled with antibodies against Kn (top) and Elav (bottom). Scale bar, 5 µm. (B) Quantification of the immunofluorescence intensity of nuclear Kn normalized to that of nuclear Elav in wt, hiwΔN, and OE Wnd neurons. (C) Wnd overexpression down-regulates the promoter activity of the ENaC ion channel pickpocket (ppk), a known target of Kn. Representative ddaC neurons labeled with ppk-eGFP in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) OE Kn; (5) hiwΔN+OE Kn; (6) OE Kn+OE Wnd. Scale bar, 5 µm. (D) Quantification of ppk-eGFP fluorescent intensity in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) knKN1/KN4; (5) OE Kn; (6) hiwΔN+OE Kn; (7) OE mCD8RFP+OE Kn; (8) OE Kn+OE Wnd.
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pbio-1001572-g004: Hiw-Wnd pathway regulates the expression and transcriptional activity of the C4da-specific transcription factor Kn.(A) Overexpressing Wnd attenuates the nuclear Kn expression levels. Representative immunofluorescence images of wt and Wnd-overexpressing (OE Wnd) ddaC neurons labeled with antibodies against Kn (top) and Elav (bottom). Scale bar, 5 µm. (B) Quantification of the immunofluorescence intensity of nuclear Kn normalized to that of nuclear Elav in wt, hiwΔN, and OE Wnd neurons. (C) Wnd overexpression down-regulates the promoter activity of the ENaC ion channel pickpocket (ppk), a known target of Kn. Representative ddaC neurons labeled with ppk-eGFP in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) OE Kn; (5) hiwΔN+OE Kn; (6) OE Kn+OE Wnd. Scale bar, 5 µm. (D) Quantification of ppk-eGFP fluorescent intensity in neurons of the following genotypes: (1) wt; (2) hiwΔN; (3) OE Wnd; (4) knKN1/KN4; (5) OE Kn; (6) hiwΔN+OE Kn; (7) OE mCD8RFP+OE Kn; (8) OE Kn+OE Wnd.
Mentions: In order to understand how the function of DLK pathway diverges into dendritic and axonal regulations, we hypothesized that the divergence occurred at the transcriptional level, and therefore tested the transcription factors that are known to regulate dendritic growth in da neurons. Among them, the Krüppel-like factor Dar1, the homeodomain transcription factor Cut (Ct), and zinc-finger transcription factor Knot (Kn, as known as Collier) have been shown to be essential for dendritic growth in C4da neurons. Loss-of-function mutations in each of these transcription factors severely reduce dendritic growth in C4da neurons [6],[45]–[48]. We first tested whether expression levels of these transcription factors in C4da neuron nucleus were altered in hiw loss-of-function mutants. No significant difference in the levels of Dar1 [6] or Cut [45] was observed between wild-type and hiw mutant C4da neurons (Figure S5A–C). In contrast, the nuclear levels of Kn, which belongs to the evolutionarily conserved Collier/Olf1/EBF (COE) family, were significantly reduced in both hiw mutant neurons and Wnd-overexpressing neurons (Figure 4A and B)

Bottom Line: Highwire, an evolutionarily conserved E3 ubiquitin ligase, restrains axonal growth but acts as a positive regulator for dendritic growth in class IV dendritic arborization neurons in the larva.While both the axonal and dendritic functions of highwire require the DLK kinase Wallenda, these two functions diverge through two downstream transcription factors, Fos and Knot, which mediate the axonal and dendritic regulation, respectively.This study not only reveals a previously unknown function of the conserved DLK pathway in controlling dendrite development, but also provides a novel paradigm for understanding how neuronal compartmentalization and the diversity of neuronal morphology are achieved.

View Article: PubMed Central - PubMed

Affiliation: Life Sciences Institute and Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Knowledge of the molecular and genetic mechanisms underlying the separation of dendritic and axonal compartments is not only crucial for understanding the assembly of neural circuits, but also for developing strategies to correct defective dendrites or axons in diseases with subcellular precision. Previous studies have uncovered regulators dedicated to either dendritic or axonal growth. Here we investigate a novel regulatory mechanism that differentially directs dendritic and axonal growth within the same neuron in vivo. We find that the dual leucine zipper kinase (DLK) signaling pathway in Drosophila, which consists of Highwire and Wallenda and controls axonal growth, regeneration, and degeneration, is also involved in dendritic growth in vivo. Highwire, an evolutionarily conserved E3 ubiquitin ligase, restrains axonal growth but acts as a positive regulator for dendritic growth in class IV dendritic arborization neurons in the larva. While both the axonal and dendritic functions of highwire require the DLK kinase Wallenda, these two functions diverge through two downstream transcription factors, Fos and Knot, which mediate the axonal and dendritic regulation, respectively. This study not only reveals a previously unknown function of the conserved DLK pathway in controlling dendrite development, but also provides a novel paradigm for understanding how neuronal compartmentalization and the diversity of neuronal morphology are achieved.

Show MeSH
Related in: MedlinePlus