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.

The complete of mitochondrial genomes in two kinds of Corbicula fluminea, black and yellow, are 17,293 bp and 17,068 bp in length, respectively. Both of them contain 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes (tRNAs), and one control region (CRs). The proportion of base-pairs in two kinds of C. fluminea are different, with A þ T (68.78%) and G þ C (30.17%) in black one as well as A þ T (70.39%) and G þ C (29.61%) in yellow one. Besides, the secondary structures in two kinds of clam, including trnS2, trnD, trnE, trnI, trnL1 and trnT, are various. This paper demonstrates the range of variation in mtDNA which could explore the relationship between the C. fluminea and geographical distribution.

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