spacer gif spacer gif spacer gif spacer gif spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

First published online 12 November 2008
doi: 10.1242/dev.028209

Development 135, 4025-4035 (2008)
Published by The Company of Biologists 2008
This Article
Right arrow Summary Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplementary Material
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in Development
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Ng, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Ng, J.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

TGFβ signals regulate axonal development through distinct Smad-independent mechanisms

Julian Ng

MRC Centre for Developmental Neurobiology, New Hunt's House, Guy's Campus, King's College London, SE1 1UL, UK.


Figure 1
View larger version (46K):
[in this window]
[in a new window]

  		Fig. 1. Babo inactivation results in axon overextension. Babo regulates axon growth through Baboa and Babob isoforms. (A) Schematic of the adult Drosophila brain. The boxed region shows mushroom body (MB) neurons in the left hemisphere of the central brain (cb). Arrows show the MB axon trajectory extending from posterior dorsal cell bodies, projecting anteroventrally and then turning towards the midline. The MB images shown are either from the left hemisphere in this orientation, or of the central brain, showing both hemispheres. Dashed white lines indicate the midline. ol, optic lobe; D, dorsal; V, ventral; P, posterior; A, anterior; L, lateral; M, medial. (B) A wild-type MB neuroblast clone. Typical adult wild-type clones generated from newly hatched larvae have axonal projections that terminate either in the dorsal anterior cortex or just prior to the midline. Only {gamma}, {alpha} and β projections are indicated. (C-E) Representative images of babo52 (C), tkv4 (D) and sax4 (E) neuroblast clones. Note the β lobe overextensions (open red arrowhead) across the midline in babo clones. In these and subsequent figures, open white arrowheads indicate {gamma} axon pruning defects. (F,G) Representative images of babo52 neuroblast clones expressing either UAS-baboa (F), or UAS-babob (G). Many of the axons in the UAS-baboa rescue exhibited small protrusions that were not characteristic of any lobe (thin white arrow in F). These represent ectopic projections of a subclass of MB axons induced in the OK107>baboa genetic background. In these and subsequent figures, solid red or white arrowheads indicate normal {alpha} and β or {gamma} lobe termination points, as indicated. All images in this and subsequent figures are z-projections of confocal sections. Green, expression of the marker mCD8::GFP on all MB, neuroblast or single-cell MARCM clones (sometimes multiple single-cell clones); magenta, Fas2 staining of all MB {gamma} (weakly stained) and {alpha}β (strongly stained) axons (appearing white when overlapping with mCD8::GFP). Dashed white line, midline. Scale bar: 20 µm. (H) Quantification of axon overextension defects in the indicated genotypes. n, number of neuroblast clones examined.

 

Figure 2
View larger version (83K):
[in this window]
[in a new window]

  		Fig. 2. Babo regulates axon pruning and axon growth independently. Drosophila MB neurons misexpressing DN babo (A), DN babo plus EcR-B1 (B), or DN babo plus RhoGEF2 (C). Additional images (A',B',C') indicate the corresponding Fas2-positive (magenta in A,B,C) axon projections. Note the β lobe overextensions (open red arrowheads) present in A and B, but absent in C, and the axon pruning phenotypes (open white arrowheads highlight the aberrant {gamma}-dorsal and medial branches), which are visible in A' and C', but absent in B'. Cell body sections were removed from C to clearly show MB axons. Scale bar: 20 µm.

 

Figure 3
View larger version (52K):
[in this window]
[in a new window]

  		Fig. 3. Babo-regulated axon growth is Smad-independent. Drosophila Smad21 (A), Med13 (B) and double Smad21 Mad12 (C) neuroblast clones do not show β lobe overextensions. Scale bar: 20 µm.

 

Figure 4
View larger version (48K):
[in this window]
[in a new window]

  		Fig. 4. CA babo misexpression results in MB axon truncation. babo and wit genetically interact with LIMK1. (A-D) Drosophila MB neurons misexpressing CA babo (A,A'), CA tkv (B), CA sax (C) or LIMK1 (D). Solid red or white arrowheads indicate normal {alpha} and β or {gamma} lobe termination points, as indicated. Open red or white arrows indicate axon truncations in {alpha} and β lobes, or in {gamma} lobes, respectively. In D, the cell body section was removed to clearly reveal axon phenotypes. Scale bar: 20 µm. (E) Quantification of axon growth defects in LIMK1-overexpressing neurons (using intermediate expression line F4) in the presence of control (y, w), or one copy of each TGFβ receptor mutant. Phenotypic quantifications were carried out as described previously (Ng and Luo, 2004Go), and are briefly summarised in the key. n, number of hemispheres examined.

 

Figure 5
View larger version (31K):
[in this window]
[in a new window]

  		Fig. 5 CA babo genetically interacts with the components of the Rho GTPase pathway. (A) Quantification of CA Babo defects in the presence of control (w1118) or one mutant copy of Rho or Smad, as indicated. CA Babo phenotypes were classed according to the loss or truncation of dorsal (D-M+), medial (D+M-) or both (D-M-) lobes. Axon fasciculation defects were also observed (classed as misguidance, MG; see Fig. S1 in the supplementary material). Based on the level of Babo expression (see Materials and methods), misguidance represents the strongest phenotype and loss of dorsal lobes the weakest phenotype (MG > D+M- > D-M- > D-M+). The asterisk denotes CA Babo-induced β lobe overextension upon the loss of one copy of LIMK1. (B) Quantification of CA Babo defects in control (UAS-mCD8::GFP), or with one copy of the indicated transgene. n, number of hemispheres examined.

 

Figure 6
View larger version (93K):
[in this window]
[in a new window]

  		Fig. 6. The type 2 receptors Wit and Put regulate axon growth and can function interchangeably. (A,B) witA12 (A) and put135 (B) Drosophila neuroblast clones show β lobe overextensions (open red arrowheads). (C) DN put-expressing neurons show similar overextensions. (D-F) wit clones expressing UAS-put (D), or put clones expressing either UAS-wit (E) or UAS-wit{Delta}C (F). (G) Quantification of these defects. n, number of neuroblast clones examined. Scale bars: 20 µm.

 

Figure 7
View larger version (29K):
[in this window]
[in a new window]

  		Fig. 7. Wit and Put act downstream of Babo. (A) Quantification of CA Babo defects in control (w1118), or with one mutant copy of wit, put, UAS-wit{Delta}I or UAS-put{Delta}I, as indicated. n, number of hemispheres examined. (B,C) babo-null clones expressing either UAS-wit (B) or UAS-put (C). Wit or Put expression suppresses the babo axon overextension but not the axon pruning phenotype. Scale bar: 20 µm. (D) Quantification of babo axon growth phenotypes in the presence of one copy of UAS-wit, or UAS-put, as indicated. (E) A model of Babo-regulated axon growth derived from data in this study.

 

Figure 8
View larger version (27K):
[in this window]
[in a new window]

  		Fig. 8. Babo regulates extension and targeting of AL and OL axons independently of Smads. (A) Schematic of the adult Drosophila brain. Shown from the left hemisphere, antennal lobe (AL) contralateral projection neurons elaborate dendrites (green) ipsilaterally to one AL, but project axons contralaterally to the opposite AL. The blue boxed region indicates the location of all represented AL images. Also, from the left hemisphere, optic lobe (OL) contralateral projection neurons elaborate dendrites (green) ipsilaterally to one OL, but project axons contralaterally to the opposite OL. The red boxed region indicates the orientation of all represented OL axons. Green circles indicate cell bodies. (B-I) Wild-type (B,F), babo52 (C,G), Smad21 (D,H) and Med13 (E,I) AL (B-E) and OL (F-I) contralateral projecting neurons. White arrows indicate a wild-type number of axons that reach the target zone. Open white arrows indicate axon extension defects. Blue arrowheads indicate wild-type axon termination zones. Open blue arrowheads indicate targeting defects (`gaps'). Scale bar: 20 µm. See also Fig. S5 in the supplementary material. (J) Quantification of these OL (grey bars) and AL (black bars) phenotypes. n, number of clones analysed.

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



© The Company of Biologists Ltd 2008