4.1 Whole-genome resequencing reads predicted a potentially sex-determining region
Based on the whole-genome resequencing, we predicted a sex-determining region (approximately 10 Mb) in chromosome 37 of C. japonica . Interestingly, we found some genes in this region that seem to be involved in sex differentiation in C. japonica , namely, theF-box gene and WD repeat domain (WDR ) gene. A previous study considered that the F-box protein encoded by recombinant FBXW gene (containingF-box gene and WDR gene) is specific for substrate recognition in ubiquitin-mediated proteolysis (Risseeuw et al., 2003). It can bind S-phase kinase-associated protein 1 (SKP1) and Cullin to form an evolutionary conserved Skp–Cullin–F-box (SCF) ubiquitin ligase complex (Figure 10) (Zhang et al., 2002; Welcker and Clurman, 2008; Roberts et al., 2020), which can selectively bind to degraded proteins and participate in the ubiquitin–proteasome pathway (UPP) (Li et al., 2010). The UPP system in plants causes functional loss of male germ cells by regulating the conversion of functional proteins (Kipreos and Pagano, 2000). The sex-determining mechanism of crustaceans living in the open environment is still in the early stage of evolution, and the intensity of genetic factors in determining the gender of crustaceans is lower than that of the external environment (Lou et al., 2004; Wu et al., 2002). Therefore, we have every reason to infer that the UPP system regulated by recombinant FBXW gene may potentially limit the testis development of male C. japonica , reduce sperm production, and even promote vitellus formation. However, this mechanism is still speculative and needs further verification.