Screening of sex-special genes in common long-arm octopus <i>Octopus minor</i> based on gonadal transcriptome sequencing

The common long-arm octopus ( Octopus minor ) is a commercially important aquaculture species in East Asia, and the male octopus grows faster than the female ones, while the information about sex-regulating mechanisms in octopuses is limited. Therefore, gonadal transcriptome sequencing was performed in O. minor to reveal the molecular mechanisms of sex regulation in cephalopods. Based on the sexuality and gonad development stage, 4 groups of 12 gonad tissues were sampled, and 11 libraries were retained for bioinformatics analysis. A total of 263,749,727 clean reads were obtained. The percentage of clean reads mapped to the O. minor reference genome ranged from 77.20% to 90.59%. A total of 3936 differentially expressed genes (DEGs) were obtained between ovarian and testicular libraries by Venn diagram analysis, including 855 ovarian up-regulated and 3081 testicular up-regulated genes. Four unigenes (transcription factor Sox-8, fermentation-1, forkhead box protein L2, and ribosomal protein large 24) and one pathway (ECM-receptor interaction) were screened to be candidate molecular markers for sex determination. The reliability and accuracy of our analysis were validated via quantitative real-time PCR in 10 randomly selected DEGs. The results of our study enhanced our understanding of the molecular mechanism underlying sex determination and potentially helped to screen the bio-markers for O. minor in different sexes.