Characterization and expression pattern of r-spondin1 in Cynoglossus semilaevis

Identification and Functional Analysis of Ras-Related Associated with Diabetes Gene (rrad) in Edwardsiella piscicida-Resistant Individuals of Japanese Flounder (Paralichthys olivaceus)

Ras-related associated with diabetes (RRAD) is a member of the Ras GTPase superfamily that plays a role in several cellular functions, such as cell proliferation and differentiation. In particular, the superfamily acts as an NF-κB signaling pathway inhibitor and calcium regulator to participate in the immune response pathway. A recent transcriptome study revealed that rrad was expressed in the spleen of disease-resistant Japanese flounder (Paralichthys olivaceus) individuals compared with disease-susceptible individuals, and the results were also verified by qPCR. Thus, the present study aimed to explore how rrad regulates antimicrobial immunity via the NF-κB pathway. First, the coding sequence of P. olivaceus rrad was identified. The sequence was 1092 bp in length, encoding 364 amino acids. Based on phylogenetic and structural relationship analyses, P. olivaceus rrad appeared to be more closely related to teleosts. Next, rrad expression differences between disease-resistant and disease-susceptible individuals in immune-related tissues were evaluated, and the results revealed that rrad was expressed preferentially in the spleen of disease-resistant individuals. In response to Edwardsiella piscicida infection, rrad expression in the spleen changed. In vitro, co-culture was carried out to assess the hypo-methylated levels of the rrad promoter in the disease-resistant spleen, which was consistent with the high mRNA expression. The siRNA-mediated knockdown of rrad performed with the gill cell line of P. olivaceus affected many rrad-network-related genes, i.e., dcp1b, amagt, rus1, rapgef1, ralbp1, plce1, rasal1, nckipsd, prkab2, cytbc-1, sh3, and others, as well as some inflammation-related genes, such as bal2 and Il-1β. In addition, flow cytometry analysis showed that rrad overexpression was more likely to induce cell apoptosis, with establishing a link between rrad's function and its potential roles in regulating the NF-κB pathway. Thus,. the current study provided some clarity in terms of understanding the immune response about rrad gene differences between disease-resistant and disease-susceptible P. olivaceus individuals. This study provides a molecular basis for fish rrad gene functional analysis and may serve as a reference for in-depth of bacterial disease resistance of teleost.

pitpβ_w Encoding Phosphatidylinositol Transfer Protein Is Involved in Female Differentiation of Chinese Tongue Sole, Cynoglossus semilaevis

Phosphatidylinositol transfer protein (pitp) plays an important role in phospholipid transfer in animals. A pitp variant (pitpβ_w) in Chinese tongue sole was identified by transcriptomic analysis for its female-biased expression. The coding sequence of pitpβ_w was 816 bp, encoding a 371-amino-acid protein. pitpβ_w showed female-biased expression and was relatively high in brain, muscle, and ovary tissues. In different developmental stages of the ovary, pitpβ_w could be detected from 40 days until 3 years post hatching, and the highest expression was observed at 90 days. In situ hybridization revealed that pitpβ_w was predominantly localized in early-stage oocytes (I-III stages). After siRNA-mediated knockdown of pitpβ_w in an ovarian cell line, the expression of sox9a was reduced, while that of figla_tv1 and sox9b was significantly increased. Our findings suggest that pitpβ_w might be involved in female differentiation and early oogenesis.

A Z-Linked E3 Ubiquitin Ligase Cs-rchy1 Is Involved in Gametogenesis in Chinese Tongue Sole, Cynoglossus semilaevis

Simple Summary

The sexual growth dimorphism prevails in animals and this phenomenon is even more obvious in marine fish, so understanding the mechanism of gonadal development and gametogenesis is of great importance for sex control, thus increased productivity in aquaculture. In mammal, ubiquitin ligase plays a versatile role in gonadal development and spermatogenesis, whereas its function in fish is little reported. Using Cynoglossus semilaevis (one-year-old female individual usually grows 2–4 times bigger than male) as the fish model, a Z-chromosome linked ubiquitin ligase neurl3 was previously identified and characterized, which suggested its involvement in spermatogenesis. However, in this study, characterization of another Z-chromosome linked ubiquitin ligase Cs-rchy1 suggested it might function both in spermatogenesis and oogenesis, as well as the potential role in growth. These data may provide the genetic resource for gene editing or marker exploration in future.

Abstract

Ubiquitin ligase (E3) plays a versatile role in gonadal development and spermatogenesis in mammals, while its function in fish is little reported. In this study, a Z-chromosome linked ubiquitin ligase rchy1 in C. semilaevis (Cs-rchy1) was cloned and characterized. The full-length cDNA was composed of 1962 bp, including 551 bp 5′UTR, 736 bp 3′UTR, and 675 bp ORF encoding a 224-amino-acid (aa) protein. Cs-rchy1 was examined among seven different tissues and found to be predominantly expressed in gonads. In testis, Cs-rchy1 could be detected from 40 days post hatching (dph) until 3 years post hatching (yph), but there was a significant increase at 6 months post hatching (mph). In comparison, the expression levels in ovary were rather stable among different developmental stages. In situ hybridization showed that Cs-rchy1 was mainly localized in germ cells, that is, spermatid and spermatozoa in testis and stage I, II and III oocytes in ovary. In vitro RNA interference found that Cs-rchy1 knockdown resulted in the decline of sox9 and igf1 in ovarian cell line and down-regulation of cyp19a in the testicular cell line. These data suggested that Cs-rchy1 might participate in gonadal differentiation and gametogenesis, via regulating steroid hormone synthesis.

Knockdown of R-spondin1 leads to partial sex reversal in genetic female Chinese soft-shelled turtle Pelodiscus sinensis

Chinese soft-shelled turtle Pelodiscus sinensis is an important aquaculture species in China, the male individual being more valuable in aquaculture because of its larger body size, higher growth rate and less fat compared with females. Understanding the mechanism of ovarian differentiation and development is crucial for the production of mono-sex male offspring. However, little is known about the molecular mechanism underlying turtle ovarian differentiation. Here, we characterized the Rspo1 gene, an upstream regulator of vertebrate female sexual differentiation, in P. sinensis. The messenger RNA of Rspo1 was initially expressed at stage 14, preceding gonadal sex differentiation, and exhibited a sexually dimorphic expression pattern throughout the sex determination and gonadal differentiation periods. Rspo1 was rapidly downregulated during aromatase inhibitor-induced female-to-male sex reversal, which occurred prior to gonadal differentiation. Rspo1 loss of function by RNA interference led to partial female-to-male sex reversal, with masculinized changes in the phenotype of gonads, the distribution of germ cells and the expression of testicular regulators. Collectively, these findings suggest that Rspo1 is necessary for primary female sexual differentiation in P. sinensis. This study demonstrates for the first time the functional role of Rspo1 in reptilian sex determination, and is of fundamental significance for the production of fertile pseudo-female parents and mono-sex male offspring of P.sinensis.

The autosomal Gsdf gene plays a role in male gonad development in Chinese tongue sole (Cynoglossus semilaevis)

Gsdf is a key gene for testicular differentiation in teleost. However, little is known about the function of Gsdf in Chinese tongue sole (Cynoglossus semilaevis). In this study, we obtained the full-length Gsdf gene (CS-Gsdf), and functional characterization revealed its potential participation during germ cell differentiation in testes. CS-Gsdf transcription was predominantly detected in gonads, while the levels in testes were significantly higher than those in ovaries. During the different developmental stages in male gonads, the mRNA level was significantly upregulated at 86 dph, and a peak appeared at 120 dph; then, the level decreased at 1 and 2 yph. In situ hybridization revealed that CS-Gsdf mRNA was mainly localized in the Sertoli cells, spermatogonia, and spermatids in mature testes. After CS-Gsdf knockdown in the male testes cell line by RNA interference, a series of sex-related genes was influenced, including several sex differentiation genes, CS-Wnt4a, CS-Cyp19a1a and CS-Star. Based on these data, we speculated that CS-Gsdf may play a positive role in germ differentiation and proliferation via influencing genes related to sex differentiation.