Estrogens and androgens that coexist in the aquatic environment could potentially affect shellfish, however, endocrine disrupting effects of them in shellfish are significant. As an important aquaculture shellfish in China, Hyriopsis cumingii has remarkable economic benefits. In this study, the effects of endocrine disrupting chemicals on the steroid synthase Hc-Cyp17a in the male and female gonads of the H. cumingii were assessed by exposing juvenile mussels to cultured waters containing 17β-Estradiol (E2) and 17α-Methyltestosterone (MT) for 28 days. At the same time, the E2 content in the four stages of gonadal development, the expression changes of Hc-Cyp17a in gonadal development and its localization in the mature gonad were measured to explore the relationship between genes and hormones. The results showed that both E2 and MT at 50 ng/L and 200 ng/L could affect the transcription level of Hc-Cyp17a, which was inhibited initially and promoted in post-development. E2 content was positively correlated with gonadal development stage, which was in mussel. By tracing the expression of Hc-Cyp17a, difference was found during different developmental periods. The expression level in ovary was higher than that in testis during gonadal development of 1/ 2/ 3-year-old mussels and showed an increasing trend with age. Furthermore, the expression levels in 6 tissues of mature individuals were measured and it showed that there was a significant difference between male and female in the gonads (p < 0.01). In situ hybridization, it suggested that Hc-Cyp17a was significantly signaled in the follicular wall and oocyte of female and in the follicular membrane of testis, respectively. These results could play a vital role in assessing and understanding the effects of aquatic environment on the endocrine system of H. cumingii.

MK2 is a gene involved in the regulation of meiotic gametogenesis and plays a vital role not only in spermatogenesis, but also in regulating chromosome arrangement in oocytes. In addition, MK2 also resists pathogenic bacterial infestation and takes part in inflammatory responses triggered by pathogen-derived substances. Studies are mostly about mammals, but less as for bivalves. Hyriopsis cumingii is a significant mussel resource in China, and a good material for pearl breeding, meanwhile. MK2 was cloned to explore its function in H. cumingii. The full length of MK2 cDNA in H. cumingii was 1531bp, including 87 bp in 5 'UTR, 923 bp in 3' UTR and 1083 (88-1170) bp in ORF region, encoding 360 amino acids in this study. High expression of MK2 in gonads and gills implied its important physiological functions. MK2 gene expression was significantly higher at the age of 4 to 5 months old, when primordial germ cells began to appear in juveniles (one to eight-month-old), than that in other months. In situ hybridization (ISH) results showed that there was a obvious blue-purple hybridization signal in the oocytes and egg membranes of the female gonads, but partially in the spermatogonia, spermatocytes and follicle walls of the male gonads. After Aeromonas hydrophila infestation, transcript levels of the MK2 was up-regulated in gills, consistent with Lipopolysaccharide injection. To sum up, it was suggested that MK2 might not only participate in immune regulation, but was also sex-dependent in H. cumingii.

MAPKAPK2 (MK2) is an important regulator of the p38 mitogen-activated protein kinase (p38 MAPK) pathway, which is involved in a plethora of cellular processes concluding the development of gamete cells in meiosis and resisting pathogenic bacterial infestation. Hyriopsis cumingii is a significant mussel resource in China and a good material for pearl breeding. To explore the role of MK2 in H. cumingii, MK2 was identified and cloned, whose full-length cDNA was 1568 bp, including 87 bp in 5 ' UTR, 398 bp in 3 ' UTR, and 1083 bp in the open reading frame (ORF) region, encoding 360 amino acids. The expression of MK2 was the highest in the gills. Meanwhile, there was a significant difference in the gonads. After Aeromonas hydrophila and Lipopolysaccharide (LPS) infestation, the transcript level of the MK2 was upregulated in the gills. It indicated that MK2 might be involved in the innate immune response of H. cumingii after a pathogenic attack. After quantifying H. cumingii of different ages, it was found that the expression of MK2 was highest at 1 year old. In situ hybridization (ISH) results showed that the blue-purple hybridization signal was very significant in the oocytes and egg membranes of the female gonads of H. cumingii. The expression of MK2 increased gradually at the age of 1 to 5 months and showed a downward trend at the age of 5 to 8 months. It was suggested that MK2 might play an important role in the formation of primitive germ cells in H. cumingii. To sum up, MK2 might not only be involved in the immune response against pathogenic bacterial infection but also might play an important role in the development of the gonads in H. cumingii.