PT  - JOURNAL ARTICLE
AU  - Weiling Hong
AU  - Haiyang Dong
AU  - Jian Zhang
AU  - Fengyan Zhou
AU  - Yandan Wu
AU  - Yang Shi
AU  - Shuo Chen
AU  - Bingbing Xu
AU  - Wendong You
AU  - Feng Shi
AU  - Xiaofeng Yang
AU  - Zhefeng Gong
AU  - Jianhua Huang
AU  - Yongfeng Jin
TI  - Intron-targeted mutagenesis reveals roles for <em>Dscam1</em> RNA pairing-mediated splicing bias in neuronal wiring
AID  - 10.1101/622217
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 622217
4099  - http://biorxiv.org/content/early/2019/04/29/622217.short
4100  - http://biorxiv.org/content/early/2019/04/29/622217.full
AB  - Drosophila melanogaster Down syndrome cell adhesion molecule (Dscam1) can potentially generate 38,016 different isoforms through stochastic, yet highly biased, alternative splicing. Genetic studies demonstrated that stochastic expression of multiple Dscam1 isoforms provides each neuron with a unique identity for self/non-self-discrimination. However, due to technical obstacles, the functional significance of the highly specific bias in isoform expression remains entirely unknown. Here, we provide conclusive evidence that Dscam1 splicing bias is required for precise mushroom body (MB) axonal wiring in flies in a variable exon-specific manner. We showed that targeted deletion of the intronic docking site perturbed base pairing-mediated regulation of inclusion of variable exons. Unexpectedly, we generated mutant flies with normal overall Dscam1 protein levels and an identical number but global changes in exon 4 and exon 9 isoform bias (DscamΔ4D−/− and DscamΔ9D−/−), respectively. DscamΔ9D−/− mutant exhibited remarkable mushroom body defects, which were correlated with the extent of the disrupted isoform bias. By contrast, the DscamΔ4D−/− animals exhibited a much less severe defective phenotype than DscamΔ9D−/− animals, suggestive of a variable domain-specific requirement for isoform bias. Importantly, mosaic analysis revealed that changes in isoform bias caused axonal defects but did not influence the self-avoidance of axonal branches. We concluded that, in contrast to the Dscam1 isoform number that provides the molecular basis for neurite self-avoidance, isoform bias may play a non-repulsive role in mushroom body axonal wiring.