Transcriptome analysis of metamorphosis stage of Holothuria leucospilota

Development of sea cucumber larvae needs to go through stages of auricularia, doliolaria, pentactula and juvenile. High mortality rate from metamorphosis and development of planktonic larvae to attachment stage of seedlings is a common problem in tropical sea cucumbers breeding. However, the gene regulation mechanism underlying the metamorphosis development of tropical sea cucumber is still unclear. In this study, we chose larval Holothuria leucospilota from four periods of early auricularia (A), mid auricularia (B), late auricularia (C) and doliolaria (D) as samples for high-throughput transcriptome sequencing to investigate the molecular mechanism underlying its metamorphosis development. The results show that a total of 83.6 GB Raw reads were generated, and 93 528 Unigenes were obtained by splicing. Pairwise comparisons between adjacent groups of the four sequencing libraries show that the number of genes with significant differential expression in A_vs_B, B_vs_C and C_vs_D were 17 732, 11 757 and 11 319, respectively. GO function enrichment shows that differential genes were mainly enriched in GO functions related to cell growth, such as molecular function and catalytic activity. In addition, KEGG pathways were analyzed, and the results show that the differential genes were significantly enriched in pathways related to cell differentiation, proliferation and apoptosis, such as PI3K-Akt, cell cycle and cancer pathways. Among them, the enrichment frequency of the pathway in cancer significantly increased during the metamorphosis process, which indicates a key role in the transformation of larval growth and development mode. The screened differentially expressed genes and predicted functional information can lay a foundation for the research on the regulatory mechanism of growth and development, artificial breeding and molecular improvement application of H. leucospilota.