RNA-seq analysis of zebrafish foxc1a mutant For RNA-seq, mRNA was extracted from 38-40 hpf old embryos. We isolated wild type and foxc1a mutant samples by dissecting the entire first 6 anterior somitic segments (AS) through which the fin nerves migrate, and the adjacent posterior segments (PS; segments 7 through ~12) devoid of fin innervating nerves. Heads and yolks were excluded from all samples. Tissues were stored in RNAlater solution (Life Technologies) for up to 2 days at 4 degree before RNA was extracted using the RNAeasy kit (Qiagen) according to the manufacture’s protocol. RNA was tested for integrity using a Bioanalyzer (Agilent technologies). RNA samples showing RIN value of 8 or higher were used for generating cDNA libraries as described in the TruSeq® Stranded mRNA sample preparation guide. At the final stage, 15 cycles of PCR amplifications was performed. Barcoded libraries representing duplicates of AS and PS samples of wild type and mutants were validated using Bionalyzer (Agilent Technology) and finally sequenced in Illumina HiSeq 2500 yielding paired end reads of 100bp. The RNA-seq Unified Mapper (RUM) (Grant et al., 2011) was used to align the reads to the Zv9/danRer7 reference genome and to assign each read uniquely to a transcript. We investigated transcripts that showed the highest fold changes of expression between the different groups. For Gene Ontology annotations, genes tagged by the GO term “axon guidance” were obtained from the gene ontology database (http://www.geneontology.org/). Next we filtered this list for the “Danio rerio” taxon (resulting in 116 unique genes) and used them to annotate our RNA-seq results.