Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2008 Sep 25;59(6):972-85.
doi: 10.1016/j.neuron.2008.07.037.

A screen of cell-surface molecules identifies leucine-rich repeat proteins as key mediators of synaptic target selection

Mitsuhiko Kurusu  1 , Amy Cording, Misako Taniguchi, Kaushiki Menon, Emiko Suzuki, Kai Zinn
Affiliations

A screen of cell-surface molecules identifies leucine-rich repeat proteins as key mediators of synaptic target selection

Mitsuhiko Kurusu et al. Neuron. .

Abstract

In Drosophila embryos and larvae, a small number of identified motor neurons innervate body wall muscles in a highly stereotyped pattern. Although genetic screens have identified many proteins that are required for axon guidance and synaptogenesis in this system, little is known about the mechanisms by which muscle fibers are defined as targets for specific motor axons. To identify potential target labels, we screened 410 genes encoding cell-surface and secreted proteins, searching for those whose overexpression on all muscle fibers causes motor axons to make targeting errors. Thirty such genes were identified, and a number of these were members of a large gene family encoding proteins whose extracellular domains contain leucine-rich repeat (LRR) sequences, which are protein interaction modules. By manipulating gene expression in muscle 12, we showed that four LRR proteins participate in the selection of this muscle as the appropriate synaptic target for the RP5 motor neuron.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Flowchart of the screen
(A) Outline of the steps in the screen. (B) Diagram of the pathways taken by ISNb axons within the VLM field. Left, face-on view of the VLMs. The LBD (triangle shape) is indicated. Underlying muscles 14 and 30 are shaded. Right, side view, with the interior of the embryo to the left. EJ, exit junction. The seven VLM fibers are shaded.
Figure 2
Figure 2. Examples of mistargeting phenotypes
Confocal z-stack images of 3rd instar F1 larvae stained with 1D4 (green) and Alexa-488-phalloidin or anti-GFP (gray). (A) Control (UAS-GFP, 24B-GAL4×w). The NMJs on muscle (m) 6/7, 13, and 12 are evident. (B) NetB. Top arrowhead, an NMJ from an unidentified neuron grows onto m12 from below (Type 3 phenotype; see Figure 4A for phenotypic diagrams). Bottom arrowhead, truncated normal m12 NMJ. (C) caps. (D) trn. Arrowheads in (C) and (D), 12→13 loopback phenotype (Type 1). (E) CG2901. Arrowhead, the entire NMJ remains at the 12/13 junction and does not grow onto m12 (Type 2). (F) pot/CG2467. Arrowheads, ectopic NMJs (probably from m13) innervating m6 (Type 7). (G) 18w. Arrowheads, Type 3 (top) and Type 7 (bottom) ectopic NMJs. (H) CG7291/NPC2. Arrowhead, Type 3 ectopic NMJ. (I) CG5758. Arrowhead, 12→13 loopback phenotype (Type 1); note the complex multilooped structure of this NMJ. Bar in (A), 50µm; applies to all panels.
Figure 3
Figure 3. Looped ISNb nerves in trn caps mutants
(A–C) ISNbs in early stage 17 embryos stained with mAb 1D4 using HRP immunohistochemistry; these are brightfield images, as the loops are too faint to see with DIC optics. (A) is a control hemisegment. Loops indicated by arrows in (B–D); note that all are at the 12/13 border or on m13. The 12/13 border is indicated by a line in each panel. NMJs at the 6/7 cleft indicated by asterisks (*). (E–G) Loops visualized by confocal microscopy. 1D4 is green, Alexa-phalloidin is magenta. (E) is a control hemisegment, and (F) and (G) are trn caps. The control hemisegment was stretched more during dissection so the muscles are wider. The hemisegment in (F) is an A7, so the ventral muscles have a different morphology from (E) and (G). Arrow in (E), muscle 12 NMJ. Arrows in (F) and (G), terminal loops. Stars (*), muscle 6/7 NMJs. ISNd is indicated in (E) and (F). (H) Bar graph of total phenotypic penetrances (% defects) for ISNb and SNa in control (TM3-GFP/+; n=468 hemisegments for ISNb, n=432 for SNa), caps65.2 (n=202 for ISNb, n=152 for SNa), trns064117 (labeled as trn-hyp; n=197 for ISNb, n=143 for SNa), trn28.4 (labeled as trn-null; n=216 for ISNb, n=160 for SNa), trns064117 caps65.2(labeled as trn-hyp caps; n=196 for ISNb, n=140 for SNa), and Elav-GAL4, UAS-Trn, trns064117 caps65.2 (rescue of trn-hyp caps by neuronal Trn; labeled as "Rescue"; n=202 for ISNb, n=170 for SNa). p<.001 (Chi-square test) for differences between trn-hyp and trn-hyp caps, and between trn-hyp caps and Rescue. Bar in (A), 10 µm for (A–D), 5 µm for (E–G).
Figure 4
Figure 4. Trn overexpression in muscle subsets causes mistargeting
(A) Classification of observed mistargeting phenotypes. Green lines indicate normally patterned NMJs on muscles 6,7, 12, and 13. The TN is indicated at the left. Red lines indicate ectopic (mistargeted) NMJs. (B–G) Confocal z-stack images of the VLM regions of 3rd instar F1 larvae stained with 1D4 (anti-FasII; green). Muscles (gray) were visualized by UAS-GFP driven by 24B-GAL4 (B,C) or by phalloidin staining (D–G). (B) Control (UAS-GFP, 24B-GAL4 × w). (C) Overexpression of intact Trn (in GS10885 × UAS-GFP, 24B-GAL4). Arrow in (C), ectopic NMJ wrapping over the dorsal edge of m12 (Type 3). Arrowheads in (C), ectopic NMJ on m12/13, presumably split off from the normal NMJ. (D–E) Trn overexpression on muscles 13 and 6 (in GS10885 × H94-GAL4). Arrow in (D), ectopic innervation of m6 (Type 7); arrow in (E) indicates the absence of innervation on m13 (only an axon traversing m13 is observed; Type 8). (F–G) Trn overexpression on m12 only (in GS10885 × 5053A-GAL4). Arrow in (F), a branch of the m13 NMJ extends dorsally but there is no innervation of m12 (Type 2); arrow in (G), the NMJ on m12 emerges from under m13, and there is no axon crossing over m13 (Type 5). (H) Bar graph of total phenotypic percentages. Numbers of A2 hemisegments examined indicated on bars. (I) Bar graph showing the distribution of phenotypes among the categories illustrated in (A). Bar in (B), 50µm: applies also to (C–G).
Figure 5
Figure 5. haf (CG14351) mutant and RNAi phenotypes in embryos
(A–J) ISNb nerves (brown) in late stage 16/early stage 17 embryos stained with mAb 1D4, visualized with HRP immunohistochemistry and DIC optics. m12 is labeled for reference in many panels; arrows indicate m6/7 NMJs, triangles indicate LBD cells (part of the TN), and double arrowheads indicate the SNa. Single arrowheads in (A–C): ISN. The allele in all images of mutants is LL01240. (A) Early stage 17 control. (B,C) Bypass phenotypes, in the haf mutant. In the left hemisegment in (B) the ISNb extends along the SNa, while in the right hemisegment in (B) and the left hemisegment in (C) it extends along the ISN. In the right hemisegment in (C) the ISNb appears to initially follow the SNa, then leave it and extend onto the VLMs. (D–F) Various kinds of stall phenotypes. (D,E) VDRC2 haf RNAi × 24B-GAL4. The ISNb is truncated and curled, ending at the 6/7 cleft in (D); in (E) the ISNb is split at the exit junction; one part stops at the 6/7 cleft, and the other forms an abnormal branch to m14 (asterisk). (F) VDRC2 haf RNAi × G14-GAL4. The ISNb stops at the 6/7 cleft and forms a forked NMJ. (G–J) "Other" phenotypes. (G) VDRC2 haf RNAi × 24B-GAL4. The ISNb emerges into focus, grows across the internal surfaces of the VLMs, and joins the TN at the point marked by the arrowhead. (H) VDRC2 haf RNAi × G14-GAL4. The ISNb splits, forming a short ventral branch (*); the remainder of the nerve grows over the VLMs, forming NMJs at m6/7 and m12/13, then joins the TN (arrowhead), which has abnormally crossed over the ISN. (I,J) haf mutant. In (I) the ISNb grows underneath the VLMs, splits at the dorsal edge of m12, and sends one branch to the LBD, while the other branch (arrowhead) contacts the lateral muscle m5. In (J) the ISNb grows on top of the VLMs and splits (arrowhead) at the dorsal edge of m12. One branch extends along the muscle edge, while the other follows the ISN pathway. (K) Bar graph of phenotypic penetrances for the mutant and RNAi lines. n=135 hemisegments for the RBe04649 mutant, n=203 for RBe02960, n=418 for LL01240, n=226 for VDRC2 RNAi × 24B-GAL4, n=243 for VDRC2 RNAi × G14-GAL4, n=193 for NIG RNAi × 24B-GAL4, n=231 for 24B-GAL4 × w control, n=129 for G14-GAL4 × w control. Penetrances of other genotypes not indicated on bar graph: LL01240/Df(2L) dp-79b, 51% (n=218), LL01240/Df (2L) ast2, 57% (n=267), LL01240/RBe02960, 32% (n=264). Differences between mutants/RNAi and controls are significant (p<.001, Chi-square test). (L) Distribution of phenotypes in selected haf mutant and RNAi genotypes. Bar in (A), 20 µm; applies to all panels.
Figure 6
Figure 6. Expressing haf (CG14351) RNAi in muscle subsets causes mistargeting
(A–I) Confocal z-stack images of 3rd instar F1 larvae stained with 1D4 (green) and Alexa-phalloidin or UAS-GFP expression (gray). (A) Control (UAS-GFP, 24B-GAL4 × w). (B,C) Haf muscle overexpression (in EY11244 × UAS-GFP, 24B-GAL4). Arrow in (B), loopback collateral from m12 onto m13 (Type 1). Arrow in (C), ectopic innervation of m6 (Type 7). (D, E) VDRC3 haf RNAi × UAS-GFP, 24B- GAL4. Arrow in (D), 12→13 loopback (Type 1). Arrow in (E), ectopic m6 innervation (Type 7). (F) NIG2 haf RNAi × UAS-GFP, 24B-GAL4. Arrow, a long loopback collateral from m12 to m6. (G, H) VDRC3 haf RNAi × 5053A-GAL4 (muscle 12 only). Arrows, axons not only make normal NMJs on m12, but also arborize on m5 (arrow in G) or m8 (arrows in H). (I) VDRC3 haf RNAi × H94-GAL4 (muscles 13, 6). Arrows, ectopic NMJ wrapping over the dorsal edge of m12 (Type 3); arrowhead, abnormal ending on m13 (extreme Type 2). Asterisk, normal NMJ on m30/14. (J) Bar graph of mistargeting penetrances in control, overexpression, and RNAi larvae with pan-muscle or muscle subset drivers. Number of A2 hemisegments examined indicated on bars. (K) Bar graph showing the distribution of mistargeting phenotypes among the categories illustrated in Figure 4A. Bar in (A), 50µm: applies also to (B–I).
Figure 7
Figure 7. Expressing CG8561 RNAi in muscles causes mistargeting and synaptic phenotypes
(A)–(C) Confocal z-stack images of 3rd instar F1 larvae stained with 1D4 (green) and Alexa-phalloidin or UAS-GFP expression (gray). (A) Control (UAS-GFP, 24B-GAL4 × w). (B) CG8561 muscle overexpression (in GS10548 × UAS-GFP, 24B-GAL4). Arrow, long loopback collateral from m12 to m6 (Type 1). (C) CG8561 RNAi × 24B-GAL4. Arrow, m12→m13 loopback (Type 1). Arrowhead, tangled NMJ arbor. (D) CG8561 RNAi × H94-GAL4 (muscles 13, 6). Arrow, abnormal NMJ on m12 emerging from under m13 (Type 5). Asterisk, normal NMJ on m30/14. (E, F) CG8561 RNAi × 5053A-GAL4 (muscle 12 only). Arrow in (E), ectopic innervation of m6 (Type 7); arrow in (F), m12→m13 loopback (Type 1). (G–I) Confocal z-stacks showing higher-magnification views of the 6/7 NMJ in the indicated genotypes. In (H), boutons are fused. In (H) and (I), the arbor is tangled. (J) Bar graph of penetrances for mistargeting and synaptic bouton phenotypes in control, overexpression, and RNAi larvae. Numbers of A2 hemisegments examined indicated on bars. (K) Bar graph showing the distribution of mistargeting phenotypes among the categories illustrated in Figure 4A. Bar in (A), 50µm; applies also to (B–F); in (G), 20µm; applies also to (H–I).
Figure 8
Figure 8. Effects of muscle 12-specific overexpression and knockdown of LRR genes
Representative phenotypes caused by m12-specific perturbations (genes or RNAi driven by 5053A-GAL4) are illustrated. Dotted lines indicate that axons travel under (external to) m13, m6, and m7. OE, overexpression.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abrell S, Jackle H. Axon guidance of Drosophila SNb motoneurons depends on the cooperative action of muscular Kruppel and neuronal capricious activities. Mech Dev. 2001;109:3–12. - PubMed
    1. Artero R, Furlong EE, Beckett K, Scott MP, Baylies M. Notch and Ras signaling pathway effector genes expressed in fusion competent and founder cells during Drosophila myogenesis. Development. 2003;130:6257–6272. - PubMed
    1. Brand AH, Perrimon N. Targeted gene expression as a means of altering cell fates and generating dominant phenotypes. Development. 1993;118:401–415. - PubMed
    1. Chang Z, Price BD, Bockheim S, Boedigheimer MJ, Smith R, Laughon A. Molecular and genetic characterization of the Drosophila tartan gene. Dev Biol. 1993;160:315–332. - PubMed
    1. Chiba A, Snow P, Keshishian H, Hotta Y. Fasciclin III as a synaptic target recognition molecule in Drosophila. Nature. 1995;374:166–168. - PubMed

Publication types

MeSH terms

LinkOut - more resources