@misc{oai:ir.soken.ac.jp:00001343,
 author = {谷口, 弘樹 and タニグチ, ヒロキ and TANIGUCHI, Hiroki},
 month = {2016-02-17, 2016-02-17},
 note = {One of the essential events during the formation of the nervous system is the wiring of neural circuits, which largely consists of two steps, axon pathfinding and target recognition. During the first process, neuronal growth cones traverse long distances along stereotyped pathways to their appropriate target regions. Then during the latter process, growth cones find and synapse with their specific target(s), by searching over many neighboring cells in the target region.<br />　　　Neuronal growth cones are guided by a variety of different environmental cues expressed on their pathway and in the target region, that act either as contact-mediated signals or as diffusible factors. These cues have been shown to have attractive or repulsive effects on the growth cones mediated by their corresponding receptors. However, how these molecules orchestrate to generate the precise pattern of neural connectivity in vivo remains largely unknown.<br />　　　Capricious (CAPS) is a cell-surface protein with leucine-rich repeat (LRR) motifs which was identified as a candidate target recognition molecule in Drosophila neuromuscular system. During the formation of neuromuscular connectivity, CAPS is expressed on small subsets of motoneurons and muscles, including muscle 12 and the motoneurons that innervate it (muscle 12 MNs). Loss of function of the capricious gene (caps) alters the target specificity of muscle 12 MNs; the MNs often form synaptic endings on a neighboring nontarget muscle, muscle 13, in addition to its normal target. A similar and more robust phenotype was observed when CAPS is ectopically expressed on all muscles. Although these results clearly showed that CAPS on muscles can function in guiding specific motor axons, the role played by neurally expressed CAPS remained obscure. Since CAPS is expressed not only on muscles but also on the motoneurons during the targeting of muscle 12 MNs, neurally expressed CAPS is also likely to play a role in this process. However, low penetrance of the loss-of-function phenotype makes it difficult to directly address this possibility. Neurally expressed CAPS may also play a redundant role in earlier events of motoneuronal pathfinding, that was not revealed by the analysis of the loss-of-function mutants.<br />　　　To assess the possible function of neurally expressed CAPS, in Chapter I, he induced ectopic and increased expression of CAPS in all neurons using the GAL4-UAS system. As expected, CAPS was ectopically expressed on all neurons, starting from embryonic stage 12, in embyos. CAPS protein was detected in all major axon tracts in the CNS and in the periphery, suggesting that ectopically expressed CAPS was properly transported to axons.<br />　　　To analyze the effect of pan-neural CAPS expression on the formation of the nervous system, he first examined motoneuronal circuits in the third instar larvae by mAb 1D4 (anti-Fasciclin II) and mAb 22C10 staining. No gross morphological defects were seen in the CNS and musculature, suggesting that their overall development proceeded normally. However, he detected a highly specific change in the trajectory of motoneurons that innervate muscle 12 (muscle 12 MNs). In wild-type, axons of muscle 12 MNs, that fasciculate to form the terminal branch of the intersegmental nerve b (ISNb), project along the internal surface of muscle 13 before reaching their final target, muscle 12. In contrast, when CAPS was overexpressed on all neurons, they passed along the exterior of muscle 13. Such a phenotype was not observed in control larvae. This finding in the larvae led us to analyze the developmental processes of axon extension of muscle 12 MNs in the embryos. In embryos that pan-neurally express CAPS, axons of muscle 12 MNs appeared to extend normally until mid-stage 16. However, from late stage 16 to early stage 17, striking defects were seen in the trajectory of the most distal part of ISNb. In addition to the misrouting phenotype as seen in the larvae, a stall phenotype, in which the terminal branch of ISNb stopped prematurely near muscle 30 was observed. These results strongly suggest that ectopic pan-neuronal expression of CAPS affects the behavior of muscle 12 MNs at a specific choice point along their pathway to the target muscle.<br />　　　CAPS is a transmembrane protein with 14 leucine-rich repeat motifs in its extracellular domain. Although its intracellular domain contains no known motif, the first 28 amino acids are highly homologous to the corresponding region of Tartan, another LRR protein in Drosophila. To study the function of the intracellular domain of CAPS and its possible link to the cytoskeltal and/or signal transduction machineries, he performed a deletion analysis of CAPS and tried to identify molecules that interact with the intracellular domain of CAPS by using the yeast two hybrid system in Chapter II. He ectopically expressed CAPS lacking the intracellular domain in neurons and muscles, and examined if the modified CAPS could induce the pathfinding and targeting phenotypes described above. He found that the function of muscularly expressed CAPS in target recognition is intracellular domain dependent whereas that of neurally expressed CAPS in pathfinding is not, suggesting that CAPS may function in neurons and muscles in a different manner. The requirement of the intracellular domain for the function of muscularly expressed CAPS suggests the presence of a signaling event in muscles that is essential for selective synapse formation., application/pdf, 総研大乙第79号},
 title = {Functional Dissection ofDrosophila Capricious:its Novel Roles in Neuronal Pathfinding and Selective Synapse Formation},
 year = {}
}