Effective accumulative temperature affects gonadal maturation by controlling expression of GnRH, GnRH receptor, serotonin receptor and APGWamide gene in Pacific abalone, Haliotis discus hannai during broodstock conditioning in hatcheries

Structural and functional characterization of Hdh-HSBP1 and its involvement in heat stress and early development in Pacific abalone, Haliotis discus hannai

Heat shock factor binding protein 1 (HSBP1) is known to regulate the activity of heat shock factor 1 (HSF1) and the early development of organisms. To understand the involvement of HSBP1 in the heat shock response and embryonic and larval development of Pacific abalone (Haliotis discus hannai), the Hdh-HSBP1 gene was sequenced from the digestive gland (DG) tissue. The full-length sequence of Hdh-HSBP1 encompassed 738 nucleotides, encoding an 8.42 kDa protein consisting of 75 deduced amino acids. The protein contains an HSBP1 domain and a coiled-coil domain, which are conserved features in the HSBP1 protein family. Protein-protein molecular docking revealed that the coiled-coil region of Hdh-HSBP1 binds to the coiled-coil region of Hdh-HSF1. Tissue expression analysis demonstrated that the highest Hdh-HSBP1 expression occurred in the DG, whereas seasonal expression analysis revealed that this gene was most highly expressed in summer. In heat-stressed abalone, the highest expression of Hdh-HSBP1 occurred at 30 °C. Moreover, time-series analysis revealed that the expression of this gene began to increase significantly at 6 h post-heat stress, with higher expression observed at 12 h and 24 h post-heat stress. Furthermore, Hdh-HSBP1 mRNA expression showed a link to ROS production. Additionally, the expression of Hdh-HSBP1 showed significantly higher expression in the early stages of embryonic development in Pacific abalone. These results suggest that Hdh-HSBP1 plays a crucial role in the stress physiology of Pacific abalone by interacting with Hdh-HSF1, as well as its embryonic development.

Molecular and structural analysis of Hdh-MIRP3 and its impact on reproductive regulation in female Pacific abalone, Haliotis discus hannai

Molluscan insulin-related peptides (MIRP) play a crucial role in various biological processes, including reproduction and larval development in mollusk species. To investigate the involvement of MIRP in the ovarian development of Pacific abalone (Haliotis discus hannai), the Hdh-MIRP3 was cloned from cerebral ganglion (CG). Hdh-MIRP3 cDNA was 993 bp long, encoded a 13.22 kDa peptide, comprising 118 amino acids. Fluorescence in situ hybridization confirmed the localization of Hdh-MIRP3 in the CG and ovary. Molecular docking revealed that Hdh-MIRP3 binds to the N-terminal region of Hdh-IRP-R. Tissue expression analysis showed the highest Hdh-MIRP3 expression in the CG, followed by ovarian tissue. Hdh-MIRP3 expression was significantly upregulated in the CG and ovary during the ripe stage of seasonal ovarian development and in effective accumulative temperature conditioned abalone. Furthermore, siRNA silencing of Hdh-MIRP3 significantly downregulated the expression of four reproduction-related genes, including Hdh-GnRH, Hdh-GnRH-R, Hdh-IRP-R, and Hdh-VTG in both the CG and ovary, and Hdh-MIRP3 as well. These results indicate that Hdh-MIRP3 acts as a regulator of ovarian development in Pacific abalone. Additionally, expression analysis indicated that Hdh-MIRP3 plays a role in embryonic and larval development. Overall, the present findings elucidate the role of Hdh-MIRP3 in reproductive development in female Pacific abalone.

Age-Dependent Growth-Related QTL Variations in Pacific Abalone, Haliotis discus hannai

Pacific abalone is a high-value, commercially important marine invertebrate. It shows low growth as well as individual and yearly growth variation in aquaculture. Marker-assisted selection breeding could potentially resolve the problem of low and variable growth and increase genetic gain. Expression of quantitative trait loci (QTLs) for growth-related traits, viz., body weight, shell length, and shell width were analyzed at the first, second, and third year of age using an F1 cross population. A total of 37 chromosome-wide QTLs were identified in linkage groups 01, 02, 03, 04, 06, 07, 08, 10, 11, 12, and 13 at different ages. None of the QTLs detected at any one age were expressed in all three age groups. This result suggests that growth-related traits at different ages are influenced by different QTLs in each year. However, multiple-trait QTLs (where one QTL affects all three traits) were detected each year that are also age-specific. Eleven multiple-trait QTLs were detected at different ages: two QTLs in the first year; two QTLs in the second year; and seven QTLs in the third year. As abalone hatcheries use three-year-old abalone for breeding, QTL-linked markers that were detected at the third year of age could potentially be used in marker-assisted selection breeding programs.

A PITX2-HTR1B pathway regulates the asymmetric development of female gonads in chickens

All female vertebrates develop a pair of ovaries except for birds, in which only the left gonad develops into an ovary, whereas the right gonad regresses. Previous studies found that the transcription factor Paired-Like Homeodomain 2 (PITX2), a key mediator for left/right morphogenesis in vertebrates, was also implicated in asymmetric gonadal development in chickens. In this study, we systematically screened and validated the signaling pathways that could be targeted by Pitx2 to control unilateral gonad development. Integrated chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) analyses indicated that Pitx2 directly binds to the promoters of genes encoding neurotransmitter receptors and leads to left-biased expression of both serotonin and dopamine receptors. Forcibly activating serotonin receptor 5-Hydroxytryptamine Receptor 1B (HTR1B) signaling could induce ovarian gene expression and cell proliferation to partially rescue the degeneration of the right gonad. In contrast, inhibiting serotonin signaling could block the development of the left gonad. These findings reveal a PITX2-HTR1B genetic pathway that guides the left-specific ovarian growth in chickens. We also provided new evidence showing neurotransmitters stimulate the growth of nonneuronal cells during the early development of reproductive organs well before innervation.

Identification and characterization of gonadotropin-releasing hormone (GnRH) in Zhikong scallop Chlamys farreri during gonadal development

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on neuroendocrine control of gonadal function, such as the function of GnRH during gonadal development is limited. In this study, we investigated the morphology and structure of the nerve ganglia of Zhikong scallop Chlamys farreri by physiological and histological observations. We also cloned the ORF and studied the expression patterns of GnRH in the scallop. Tissue expression analysis showed that GnRH was highly expressed in parietovisceral ganglion (PVG). The in situ hybridization result further confirmed that GnRH mRNA only distributed in some good-sized neurons in the posterior lobe (PL) and some pint-sized neurons in the lateral lobe (LL). In addition, by examining the expression of GnRH during gonadal development in ganglia, we found GnRH displayed higher expression in the female scallops, and showed significant high expression at the growing stage of female scallops in PVG. This study would contribute to gaining insight into the mechanism underlying reproduction regulation by GnRH in the scallop and help to provide a better understanding of reproductive neuroendocrine in mollusks.

Gonadotropins and Sex Steroid Hormones in Captive-Reared Small Yellow Croaker (Larimichthys polyactis) and Their Role in Female Reproductive Dysfunction

The seed production of small yellow croaker (SYC) is constrained by reproductive dysfunction in captive-reared females. Reproductive dysfunction is closely linked to endocrine reproductive mechanisms. To better understand the reproductive dysfunction in captive broodstock, functional characterization of gonadotropins (GtHs: follicle stimulating hormone β subunit, fshβ; luteinizing hormone β subunit, lhβ; and glycoprotein α subunit, gpα) and sex steroids (17β-estradiol, E2; testosterone, T; progesterone; P) was performed using qRT-PCR, ELISA, in vivo, and in-vitro assay. The pituitary GtHs and gonadal steroids levels were significantly higher in ripen fish of both sexes. However, changes in lhβ and E2 levels in females were not significant in the developing and ripen stages. Furthermore, GtHs and steroids levels were lower in females compared to males throughout the reproductive cycle. In vivo administration of gonadotropin releasing hormone analogue (GnRHa) significantly increased the expression of GtHs in both dose- and time-related manners. The lower and higher doses of GnRHa led to successful spawning in male and female SYC, respectively. Sex steroids in vitro significantly inhibited the expression of lhβ in female SYC. Overall, GtHs were shown to play a vital role in final gonadal maturation, while steroids promoted negative feedback in the regulation of pituitary GtHs. Lower levels of GtHs and steroids might be key components in the reproductive dysfunction of captive-reared female SYC.

Identification and Characterization of Hdh-FMRF2 Gene in Pacific Abalone and Its Possible Role in Reproduction and Larva Development

FMRFamide-related peptides are neuropeptides involved in a wide range of biological processes, including reproduction and larval development. To characterize the involvement of FMRFamide in the reproduction and larval development of Pacific abalone Haliotis discus hannai, an FMRFamide cDNA (Hdh-FMRF2) was cloned from the cerebral ganglion (CG). Fluorescence in situ hybridization and qRT-PCR were performed for functional characterization. The Hdh-FMRF2 cDNA encoded 204 deduced amino acids that contained a putative signal peptide and four FaRP domains. The major population of Hdh-FMRF2 neuronal cell bodies was localized in the cortex of CG. Hdh-FMRF2 mRNA expression was significantly upregulated in CG during the mature stage of gonadal development and effective accumulative temperature (EAT) exposed abalone in both sexes. In the induced spawning event, Hdh-FMRF2 expression was significantly upregulated during spawning in males. However, no upregulation was observed in females, suggesting Hdh-FMRF2 might inhibit gamete release in female abalone. These results revealed Hdh-FMRF2 as a reproduction related peptide. Furthermore, mRNA expression in larval development suggested that this peptide was also involved in larval development during development of Pacific abalone. Collectively, this study provides evidence of possible involvement of an FMRFamide neuropeptide in the reproduction and larval development of Pacific abalone.

Molecular Cloning and Functional Characterization of Catalase in Stress Physiology, Innate Immunity, Testicular Development, Metamorphosis, and Cryopreserved Sperm of Pacific Abalone

Catalase is a crucial enzyme of the antioxidant defense system responsible for the maintenance of cellular redox homeostasis. The aim of the present study was to evaluate the molecular regulation of catalase (Hdh-CAT) in stress physiology, innate immunity, testicular development, metamorphosis, and cryopreserved sperm of Pacific abalone. Hdh-CAT gene was cloned from the digestive gland (DG) of Pacific abalone. The 2894 bp sequence of Hdh-CAT had an open reading frame of 1506 bp encoding 501 deduced amino acids. Fluorescence in situ hybridization confirmed Hdh-CAT localization in the digestive tubules of the DG. Hdh-CAT was induced by different types of stress including thermal stress, H₂O₂ induction, and starvation. Immune challenges with Vibrio, lipopolysaccharides, and polyinosinic-polycytidylic acid sodium salt also upregulated Hdh-CAT mRNA expression and catalase activity. Hdh-CAT responded to cadmium induced-toxicity by increasing mRNA expression and catalase activity. Elevated seasonal temperature also altered Hdh-CAT mRNA expression. Hdh-CAT mRNA expression was relatively higher at the trochophore larvae stage of metamorphosis. Cryopreserved sperm showed significantly lower Hdh-CAT mRNA expression levels compared with fresh sperm. Hdh-CAT mRNA expression showed a relationship with the production of ROS. These results suggest that Hdh-CAT might play a role in stress physiology, innate immunity, testicular development, metamorphosis, and sperm cryo-tolerance of Pacific abalone.

Characterization and Expression Analysis of Mollusk-like Growth Factor: A Secreted Protein Involved in Pacific Abalone Embryonic and Larval Development

Growth factors are mostly secreted proteins that play key roles in an organism's biophysical processes through binding to specific receptors on the cell surface. The mollusk-like growth factor (MLGF) is a novel cell signaling protein in the adenosine deaminase-related growth factor (ADGF) subfamily. In this study, the MLGF gene was cloned and characterized from the digestive gland tissue of Pacific abalone and designated as Hdh-MLGF. The transcribed full-length sequence of Hdh-MLGF was 1829 bp long with a 1566 bp open reading frame (ORF) encoding 521 amino acids. The deduced amino acid sequence contained a putative signal peptide and two conserved adenosine deaminase domains responsible for regulating molecular function. Fluorescence in situ hybridization localized Hdh-MLGF in the submucosa layer of digestive tubules in the digestive gland. The mRNA expression analysis indicated that Hdh-MLGF expression was restricted to the digestive gland in the adult Pacific abalone. However, Hdh-MLGF mRNA expressions were observed in all stages of embryonic and larval development, suggesting Hdh-MLGF might be involved in the Pacific abalone embryonic and larval development. This is the first study describing Hdh-MLGF and its involvement in the Pacific abalone embryonic and larval development.

Expression and Characterization of the Spats1 Gene and Its Response to E2/MT Treatment in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

Spats1 (spermatogenesis-associated, serinerich 1) has been characterized as a male-biased gene which acts an important role in the germ cell differentiation of mammals. Nevertheless, the function of Spats1 in the Chinese soft-shelled turtle (P. sinensis) has not yet been reported. To initially explore the expression of Spats1 in P. sinensis and its response to sex steroid treatment, we cloned the CDS of Spats1 for the first time and analyzed its expression profile in different tissues, including the testes in different seasons. The Spats1 cDNA fragment is 1201 base pairs (bp) in length and contains an open reading frame (ORF) of 849 bp, which codes for 283 amino acids. Spats1 mRNA was highly expressed in the testes (p < 0.01) and barely detectable in other tissues. In P. sinensis, the relative expression of Spats1 also responsive to seasonal changes in testis development. In summer (July) and autumn (October), Spats1 gene expression was significantly higher in the testes than in other seasons (p < 0.05). Spats1 mRNA was found to be specifically expressed in germ cells by chemical in situ hybridization (CISH), and it was mainly located in primary spermatocytes (Sc1), secondary spermatocytes (Sc2) and spermatozoa (St). Spats1 expression in embryos was not significantly changed after 17α-methyltestosterone (MT)and 17β-estradiol (E2) treatment. In adults, MT significantly induced Spats1 expression in male P. sinensis. However, the expression of Spats1 in testes was not responsive to E2 treatment. In addition, the expression of Spats1 in females was not affected by either MT or E2 treatment. These results imply that Spats1 is a male-specific expressed gene that is mainly regulated by MT and is closely linked to spermatogenesis and release in P. sinensis.

Hdh-Tektin-4 Regulates Motility of Fresh and Cryopreserved Sperm in Pacific Abalone, Haliotis discus hannai

As structural components of sperm, tektins are thought to play a fundamental role in sperm flagellar motility. In this study, Tektin-4 (Hdh-TEKT4) gene was successfully cloned and characterized from the testis tissue in Pacific abalone, Haliotis discus hannai. The full-length cDNA of Hdh-TEKT4 was 1,983 bp, with a coding region of 1,350 bp encoding 51.83 kDa putative protein of 449 deduced amino acids. Hdh-TEKT4 contains a tektin domain including a nonapeptide signature motif (RPGVDLCRD). Fluorescence in situ hybridization revealed that Hdh-TEKT4 localized in the spermatids of Pacific abalone testis. qRT-PCR analysis showed that Hdh-TEKT4 was predominantly expressed in testis tissues. Hdh-TEKT4 mRNA expression was upregulated during the fully mature testicular developmental stage in both seasonal development and EAT exposed abalone. Furthermore, mRNA expression of Hdh-TEKT4 was significantly higher in sperm with higher motility than in sperm with lower motility during peak breeding season, induced spawning activity stages, and after cryopreservation in different cryoprotectants. Taken together, these results indicate that the expression of Hdh-TEKT4 in Pacific abalone sperm might have a positive correlation with sperm motility.