Genome and transcriptome of freshwater leech Whitmania pigra reveal key genes related to morphogenesis, signal pathways and neurogenesis during embryonic development

Abstract

Whitmania pigra Whitman (phylum Annelida) is a widely distributed freshwater leech in East Asia, with an annual consumption of nearly 1,000 tons dry bodies for curing blood stasis syndrome. W. Pigra has be seen as a representative model organism of neurodevelopmental studies. Here, we sequenced a Chinese individual by sin-gle-molecule real-time (SMRT) long-read sequencing, and generated a de novo as-sembly of 178.87 Mb with contig N50 2.0 Mb. In addition, we obtained a total of 239.64 Gb transcriptome data of eight representative developmental phases of embryos (from blastocyst stage to maturity). Totally, 21482 genes were annotated, among these, 3114 genes were differentially expressed with phase-specific expression pattern, and mainly in the middle and late development (G, H, I, J phase). Using a comprehensive transcriptome dataset, we demonstrated that 57, 49 and 77 DEGs were respectively related to morphogenesis, signal pathways and neurogenesis. 49 DEGs related to signal pathways included 30 wnt genes, 14 notch genes, and 5 hedgehog genes. In par-ticular, we found a cluster consisting of 7 genes related to signal pathways as well as synapses, which were essential for regulating embryonic development. To some ex-tent, our results are helpful to reveal the whole picture of development mechanism from the perspective of transcriptome and also provide new clues for organogenesis and neurodevelopmental studies of Annelida species.