Abstract
Transformer-2 (Tra-2) is an upstream regulatory element of the sex regulation mechanism in insects and plays a critical role in sex formation. To understand the role of tra-2 in Hyriopsis cumingii, the full-length Hctra-2 (1867 bp) was obtained from the gonads, and sequence alignment with other species showed that HCTRA-2 protein had a highly conserved RRM domain. Phylogenetic analysis showed that the HCTRA-2 protein was a close relative to of the mollusks TRA-2 protein. The qRT-PCR of tissue-specific expression pattern showed that the Hctra-2 was abundant in gonads, and the expression in testes was higher than that in ovaries (p < 0.01). It suggests that Hctra-2 may play a potential regulatory role in gonadal development of H. cumingii. In the early gonadal development, the Hctra-2 expression was the highest on the third day after fertilization and increased slightly from 4 months to 5 months, which may be related to the embryonic sex determination and early gonadal development. In situ hybridization showed that Hctra-2 mRNA signals were present in both male and female gonads. After silencing Hctra-2 by RNAi, the expression levels of Hcfem-1b and Hcdmrt were changed. It is speculated that there may be a certain relationship between them, which plays an important role in the sex regulation of H. cumingii. Our research will help to deepen our understanding of the shellfish sex determination mechanisms.
Highlights
Hyriopsis cumingii is a pearl-cultured species unique to China
The results showed that the silencing efficiency of the dsHctra-2 was 70.6% in males and 55.8% in females (Figures 7A,B), which indicated that the Double-stranded RNA (dsRNA)-mediated gene silencing was effective
The expression position of Hctra-2 signals is similar to that of tra-2 in M. nipponense (Wang et al, 2019). These results showed that Hctra-2 was closely related to spermatogonia proliferation, meiosis of spermatocytes and oocytes, and ova maturation, further confirming that Hctra-2 was involved in the gonadal development of H. cumingii
Summary
Hyriopsis cumingii is a pearl-cultured species unique to China. The pearl cultivated by it has smooth and delicate nacre quality and bright color, which is the best one among freshwater mussels (Wang et al, 2007). Male and female mussels showed different traits in the culture, and the quality of pearl produced by males was better than that of females (Zhao et al, 2013). It is of great significance to raise the pearl yield and quality by using sex control technology. The research on the regulation mechanism of H. cumingii sex determination is limited, which hinders the development of sex control breeding technology
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