Identification and sexually dimorphic expression of vasa isoforms in Dabry′s sturgeon (Acipenser dabryanus), and functional analysis of vasa 3′-untranslated region

The Effects of Dietary n-3 Highly Unsaturated Fatty Acids on Growth, Antioxidant Capacity, Immunity, and Oxylipin Profiles in Acipenser dabryanus

Currently, the effects of dietary levels of n-3 highly unsaturated fatty acids (HUFAs) on the growth performance, antioxidant capacity, immunity, and serum oxylipin profiles of female F2-generation Yangtze sturgeon remain unknown. A total of 75 Yangtze sturgeons, an endangered freshwater fish species, with an average body weight of 3.60 ± 0.83 kg, were randomly allocated to 15 concrete pools, with each dietary group represented by 5 fish per pool. The fish were fed five different experimental diets containing various levels of n-3 HUFAs (0.5%, 1.0%, 1.5%, 2.0%, and 2.4%). After a feeding period of 5 months, no significant differences in the growth performances of the fish were observed among the five dietary groups (p > 0.05). However, we did note that the serum levels of low-density lipoprotein cholesterol (LDL-C), triglycerides (TGs), and total cholesterol (TCHO) exhibited a marked increase in the fish that consumed higher dietary n-3 HUFA levels (p < 0.05). Conversely, alkaline phosphatase (ALP) activities showed a notable decrease as dietary n-3 HUFA levels increased (p < 0.05). Serum antioxidant indices, such as the activity levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), were significantly higher in the 2.4% HUFA group compared to the 0.5% HUFA group. Additionally, muscle antioxidant indices, including total antioxidant capacity (T-AOC), catalase (CAT), and SOD activity, exhibited notable increases as dietary n-3 HUFA levels increased (p < 0.05). Furthermore, there was a decrease in malondialdehyde (MDA) levels as dietary n-3 HUFA levels increased (p < 0.05). In relation to immune indices, only serum immunoglobulin M (IgM) and muscle complement 3 (C3) were found to be influenced by dietary n-3 HUFA levels (p < 0.05). A total of 80 oxylipins were quantified, and our subsequent K-means cluster analysis resulted in the classification of 62 oxylipins into 10 subclasses. Among the different n-3 HUFA diets, a total of 14 differential oxylipins were identified in the sera. These findings demonstrate that dietary supplementation with n-3 HUFAs exceeding a 1.0% level can enhance antioxidant capacity and regulate serum lipid metabolism, potentially through modulation of oxylipins derived from ARA, DHA, and EPA. These insights provide novel perspectives on the mechanisms underlying these observations.

Vasa Is a Potential Germ Cell Marker in Leopard Coral Grouper (Plectropomus leopardus)

Vasa (Ddx4, DEAD box polypeptide 4), an extremely specific marker of germ cells in vivo, is an ATP-dependent RNA helicase that plays an essential role in germ cell development and gametogenesis. However, the expression and function information about this gene in groupers remains lacking. Here, vasa homolog termed Plvasa was isolated and identified Plvasa as a putative germ cell marker in the leopard coral grouper, (Plectropomus leopardus). Results indicated that Plvasa contained 17 exons in the genomic sequence and 9 conserved motifs of the DEAD-box protein by sequence analysis. The sequence comparison, phylogenetic analyses and synteny analyses showed that Plvasa was homologous with other teleosts. Additionally, the expression of Plvasa was significantly higher in gonads than in other tissues in adult individuals (p < 0.05). Further, the distribution of Plvasa revealed that it was only expressed in the germ cells, such as spermatids, germline stem cells and oocytes at different stages, and could not be detected in the somatic cells of gonads. The current study verified that the Plvasa gene is a valuable molecular marker of germ cells in leopard coral grouper, which potentially plays an important role in investigating the genesis and development of teleost germ cells.

Vasa identifies germ cells in embryos and gonads of Oryzias celebensis

Vasa is the most studied germ cell marker that is indispensable for germ cell development in teleost fishes. Here, a vasa full-length cDNA from Oryzias celebensis was isolated. Analysis of gene expression by reversed transcription polymerase chain reaction and in situ hybridization showed the vasa transcript was maternally inherited and specifically expressed in germ cells during embryogenesis and in adult gonads. During embryogenesis, vasa mRNA was widely distributed in the embryos until the somitogenesis stage and then specifically expressed in primordial germ cells (PGCs). In the testis, vasa expression was highest in spermatogonia and gradually decreased during spermatogenesis. In ovary, vasa expression was present predominantly in immature oocytes and persisted throughout oogenesis. Constructs containing green or red fluorescence proteins and vasa 3' UTR or dnd 3' UTR, confirmed stable vasa expression in the PGCs of O. celebensis and co-expression of the two genes. In summary, the conservation of vasa expression in embryonic and adult germ cells of both sexes compared to other vertebrates suggests its function is also widely conserved.

Spermatogonia From Cryopreserved Testes of Critically Endangered Chinese Sturgeon Efficiently Colonized and Preferentially Proliferated in the Recipient Gonads of Yangtze Sturgeon

The critically endangered Chinese sturgeon, Acipenser sinensis, presents late sexual maturity and has a large body size. Germ cell transplantation is a powerful technique for the production of gametes from large-bodied species in closely related recipients with a smaller body size and shorter generation time. To accelerate reproduction of Chinese sturgeon, donor spermatogonia collected from the cryopreserved testes of 3-year-old Chinese sturgeon were intraperitoneally transplanted into 7-8 days post-hatch larvae of Yangtze sturgeon (Acipenser dabryanus) with shorter generation interval. At 2 months post-transplantation (mpt), donor spermatogonia had colonized in the 81.25% of recipient gonads, with average numbers about two times those of endogenous primordial germ cells. Within the next 2 months, the rate of endogenous germ cell division in females (2-3 times) was faster than that in males (once), whereas colonized donor-derived spermatogonia divided about 2-3 times and twice in recipient females and males, respectively. Furthermore, the expression of germ cell-related genes, dazl, dead end, and vasa, in transplanted fish was higher than that in non-transplanted fish, suggesting the incorporation and proliferation donor spermatogonia in recipient. At 18 mpt, donor-derived spermatogonia survived in the 75.00% of recipient gonads. These results showed that the somatic microenvironment of Yangtze sturgeon gonad can support the long-term colonization, proliferation, and survival of xenogeneic germ cells. Thus, this study suggested that small-bodied Yangtze sturgeon is promising recipient as surrogate for Chinese sturgeon gamete production.

Germline Specific Expression of a vasa Homologue Gene in the Viviparous Fish Black Rockfish (Sebastes schlegelii) and Functional Analysis of the vasa 3 Untranslated Region

Germ cells play a key role in gonad development. As precursors, primordial germ cells (PGCs) are particularly important for germline formation. However, the origination and migration patterns of PGCs are poorly studied in marine fish, especially for viviparous economic species. The vasa gene has been widely used as a germ cell marker to identify a germline because vasa RNA is a component of germ plasm. In this study, we described the expression pattern of black rockfish (Sebastes schlegelii) vasa (Ssvas) in gonadal formation and development by in situ hybridization. The results showed that Ssvas failed in localization at the cleavage furrows until the late gastrula stage, when PGCs appeared and migrated to the genital ridge and formed elongated gonadal primordia at 10 days after birth. This study firstly revealed the PGCs origination and migration characteristics in viviparous marine fish. Furthermore, we microinjected chimeric mRNA containing EGFP and the 3′untranslated region (3′UTR) of Ssvas into zebrafish (Danio rerio) and marine medaka (Oryzias melastigma) fertilized eggs for tracing PGCs. We found that, although Sebastes schlegelii lacked early localization, similar to red seabream (Pagrus major) and marine medaka, only the 3′UTR of Ssvas vasa 3′UTR of black rockfish was able to label both zebrafish and marine medaka PGCs. In comparison with other three Euteleostei species, besides some basal motifs, black rockfish had three specific motifs of M10, M12, and M19 just presented in zebrafish, which might play an important role in labeling zebrafish PGCs. These results will promote germ cell manipulation technology development and facilitate artificial reproduction regulation in aquaculture.

Both of marine fish species Oryzias melastigma and Pagrus major all failing in early localization at embryo stage by vasa RNA

Germ cells are essential for gonadal development. As precursors of germ cells, primordial germ cells (PGCs) are particularly important for germline formation. However, the research on distribution patterns of PGCs in marine fish is very limited, especially for economic species. The vasa gene has been widely used as marker to identify PGCs origination and migration because of vasa RNA is a component of germ plasm. In this study, we isolated full-length vasa cDNA (Omvas and Pmvas) from marine medaka (Oryzias melastigma) and red seabream (Pagrus major), detected vasa transcripts in different tissues by RT-PCR and described vasa expression patterns during embryogenesis and gametogenesis by in situ hybridization. At the same time, we also explored the relationship between early distribution of germ plasm components and species evolution. The results demonstrated that deduced amino acid sequence of Omvas and Pmvas shared several conserved motifs of Vasa homologues and high identity with other teleost, and vasa transcripts were exclusively detected in early germ cells of gonad. During embryogenesis, vasa RNA of both fishes, like medaka (Oryzias latipes), failed to localize at cleavage furrows and distributed uniformly throughout each blastomere. This study firstly discovered that the marine economic fish, red seabream, lost vasa RNA early specific localization at cleavage furrows and distinctive distribution in germ cells. In addition, compared with other teleost, we found that early distribution of germ plasm might not relate to species evolution. This will improve our understanding of vasa localization modes in teleost, and facilitate fish germ cell manipulation.

Assessment of Yangtze sturgeon as recipient for the production of American paddlefish gametes through spermatogonia transplantation

The Chinese paddlefish (Psephurus gladius), one of the world's largest freshwater fish, was last seen alive in 2003; they are presumed now to be extinct. In fish, germ cell transplantation is currently known as one of the most powerful assisted reproductive technologies for the conservation of endangered species. In the event that a Chinese paddlefish is unexpectedly caught in the near future, we aimed to develop an experimental strategy to produce paddlefish gametes in the gonads of surrogate sturgeon. Spermatogonia were collected from the testes of 2.5-year-old immature male American paddlefish (Polyodon spathula), the species most closely related to the Chinese paddlefish, by Percoll gradient centrifugation, and transplanted into the peritoneal cavity of Yangtze sturgeon (Acipenser dabryanus) larvae at 7-8 days post-hatch. At two months post-transplantation, donor-derived spermatogonia had efficiently colonized in the recipient gonads and proliferated. A PCR analysis developed to detect xenogenic donor-derived mtDNA sequences in recipient gonads revealed that American paddlefish germ cells survived for at least seven months after transplantation in the gonads of Yangtze sturgeon recipients. These results show that the somatic microenvironment of Yangtze sturgeon gonads was able to support the colonization, proliferation, and survival of xenogeneic germ cells from a different taxonomic family. This study provides key information that could lead to future restoration of Chinese paddlefish using germ cell transplantation.

Identifying difference in primordial germ cells between XX female and XY male yellow catfish embryos

Primordial germ cells (PGCs) are singled out from somatic cells very early during embryogenesis, then they migrate towards the genital ridge and differentiate into gametes through oogenesis or spermatogenesis. Labeling PGCs with Localized RNAexpression (LRE) technique by fluorescent proteins has been widely applied among teleost species to study the germ cell development and gonad differentiation. In this study, we first cloned and characterized the 3' untranslated regions (3'UTRs) of nanos homolog 1-like (nos1l), dead end (dnd), and vasa in yellow catfish (Pelteobagrus fulvidraco), and then synthesized the GFP-nos1l/dnd/vasa 3'UTR mRNAs. Each of these three 3'UTRs could label PGCs in yellow catfish embryos, of which, vasa 3'UTR exhibited the highest labeling efficiency. To identify the differences in PGCs at embryonic stage, XX all-female and XY all-male yellow catfish embryos were produced and injected with GFP-vasa 3'UTR mRNA. We observed the PGC migration route in these two monosex embryos from 24 hpf to 7 dpf, and found there was no difference between them. Besides, the PGC number was counted at 48 hpf, and the result showed that the average PGC number in XX females (11.3) was significantly larger than that in XY males (8.1).These findings provide an insight into the development of PGCs in yellow catfish embryos and the relationship between embryonicPGCnumberand thelatergonaddifferentiation.

Full-length transcriptome sequencing and comparative transcriptomic analysis to uncover genes involved in early gametogenesis in the gonads of Amur sturgeon (Acipenser schrenckii)

BACKGROUND

Sturgeons (Acipenseriformes) are polyploid chondrostean fish that constitute an important model species for studying development and evolution in vertebrates. To better understand the mechanisms of reproduction regulation in sturgeon, this study combined PacBio isoform sequencing (Iso-Seq) with Illumina short-read RNA-seq methods to discover full-length genes involved in early gametogenesis of the Amur sturgeon, Acipenser schrenckii.

RESULTS

A total of 50.04 G subread bases were generated from two SMRT cells, and herein 164,618 nonredundant full-length transcripts (unigenes) were produced with an average length of 2782 bp from gonad tissues (three testes and four ovaries) from seven 3-year-old A. schrenckii individuals. The number of ovary-specific expressed unigenes was greater than those of testis (19,716 vs. 3028), and completely different KEGG pathways were significantly enriched between the ovary-biased and testis-biased DEUs. Importantly, 60 early gametogenesis-related genes (involving 755 unigenes) were successfully identified, and exactly 50% (30/60) genes of those showed significantly differential expression in testes and ovaries. Among these, the Amh and Gsdf with testis-biased expression, and the Foxl2 and Cyp19a with ovary-biased expression strongly suggested the important regulatory roles in spermatogenesis and oogenesis of A. schrenckii, respectively. We also found the four novel Sox9 transcript variants, which increase the numbers of regulatory genes and imply function complexity in early gametogenesis. Finally, a total of 236,672 AS events (involving 36,522 unigenes) were detected, and 10,556 putative long noncoding RNAs (lncRNAs) and 4339 predicted transcript factors (TFs) were also respectively identified, which were all significantly associated with the early gametogenesis of A. schrenckii.

CONCLUSIONS

Overall, our results provide new genetic resources of full-length transcription data and information as a genomic-level reference for sturgeon. Crucially, we explored the comprehensive genetic characteristics that differ between the testes and ovaries of A. schrenckii in the early gametogenesis stage, which could provide candidate genes and theoretical basis for further the mechanisms of reproduction regulation of sturgeon.

Visualization of Turbot (Scophthalmus maximus) Primordial Germ Cells in vivo Using Fluorescent Protein Mediated by the 3' Untranslated Region of nanos3 or vasa Gene

Primordial germ cells (PGCs) as the precursors of germ cells are responsible for transmitting genetic information to the next generation. Visualization of teleost PGCs in vivo is essential to research the origination and development of germ cells and facilitate further manipulation on PGCs isolation, cryopreservation, and surrogate breeding. In this study, artificially synthesized mRNAs constructed by fusing fluorescent protein coding region to the 3' untranslated region (3'UTR) of nanos3 or vasa (mCherry-Smnanos3 3'UTR or mCherry-Smvasa 3'UTR mRNA) were injected into turbot (Scophthalmus maximus) fertilized eggs for tracing PGCs. The results demonstrated that the fluorescent PGCs differentiated from somatic cells and aligned on both sides of the trunk at the early segmentation period, then migrated and located at the dorsal part of the gut where the gonad would form. In the same way, we also found that the zebrafish (Danio rerio) vasa 3'UTR could trace turbot PGCs, while the vasa 3'UTR s of marine medaka (Oryzias melastigma) and red seabream (Pagrus major) failed, although they could label the marine medaka PGCs. In addition, through comparative analysis, we discovered that some potential sequence elements in the3 'UTRs of nanos3 and vasa, such as GCACs, 62-bp U-rich regions and nucleotide 187-218 regions might be involved in PGCs stabilization. The results of this study provided an efficient, rapid, and specific non-transgenic approach for visualizing PGCs of economical marine fish in vivo.

Visualizing primordial germ cell migration in embryos of rice field eel (Monopterus albus) using fluorescent protein tagged 3' untranslated regions of nanos3, dead end and vasa

In rice field eel (Monopterus albus), germ cell development in the developing gonad has been revealed in detail. However, it is unclear how primordial germ cells (PGCs) migrate to the somatic part of the gonad (genital ridge). This study visualized PGC migration by injecting a chimeric mRNA containing a fluorescent protein fused to the 3' untranslated region (3'UTR) of three different genes, nanos3 of zebrafish (Danio rerio) and dead end (dnd) and vasa of rice field eel. The mRNAs were injected either alone or in pairs into embryos at the one-cell stage. The results showed that mRNAs containing nanos3 and dnd 3'UTRs labeled PGCs over a wider time frame than those containing vasa 3'UTR, suggesting that nanos3 and dnd 3'UTRs are suitable for visualizing PGCs in rice field eel. Using this direct visualization method, the normal migration route of PGCs was observed from the 50%-epiboly stage to hatching stage for the first time, and the ectopic PGCs were also visualized during this period in rice field eel. These findings extend our knowledge of germ cell development, and lay a foundation for further research on the relationship between PGCs and sex differentiation, and on incubation conditions for embryos in rice field eel.

Evolutionarily conserved vasa identifies embryonic and gonadal germ cells in spinyhead croaker Collichthys lucidus

In this study, a 2198 bp full-length cDNA of spinyhead croaker Collichthys lucidus vasa gene encoding 616 amino-acid residues was obtained. Multiple alignment revealed that C. lucidus vasa has eight conserved characteristic motifs of the DEAD box protein family and has the highest identity to large yellow croaker Larimichthys croceas. Reverse-transcription (RT)-PCR and Western blot analyses indicated that the vasa messenger (m)RNA and Vasa protein are specifically expressed in the gonads in both sexes. In situ hybridisation (ISH) demonstrated that vasa RNA is exclusively detected in the germ cells in C. lucidus gonads and its temporospatial expression reveals a dynamic pattern during oogenesis. Surprisingly, C. lucidus vasa 3'UTR can direct stable and specific GFP expression in the primordial germ cells (PGC) of medaka Oryzias latipes embryos. Taken together, these results suggest that because C. lucidus vasa expression delineates critical stages of oogenesis, it may be a useful molecular marker for the identification of gonadal germ cells, facilitating the isolation and utilization of germ cells in future study.

Optimization of In Vitro Culture Conditions of Sturgeon Germ Cells for Purpose of Surrogate Production

Simple Summary

The sturgeon is among the most ancient of actinopterygian fishes. Most species of sturgeon are listed as critically endangered due to habitat alteration caused by damming of rivers, pollution and overharvesting. Germ cell transplant is a useful tool to save these endangered species. To expand germ cell populations and sustain the supply for long periods for transplant, we established basal culture conditions for sturgeon germ cells. Germ cell mitotic activity has been enhanced by eliminating gonad somatic cells, supplementing with growth factor and using an alternative to fetal bovine serum. The optimal condition identified was purified germ cells cultured in serum-free medium supplemented with leukemia inhibitory factor (LIF) and glial cell line-derived neurotrophic factor (GDNF) at 21 °C. Cultured sterlet germ cells showed development after transplant into Russian sturgeon. The study provided useful information for sturgeon germ cell culture.

Abstract

To expand germ cell populations and provide a consistent supply for transplantation, we established basal culture conditions for sturgeon germ cells and subsequently increased their mitotic activity by eliminating gonad somatic cells, supplementing with growth factor, and replacing fetal bovine serum (FBS). The initial basal culture conditions were Leibovitz’s L-15 medium (pH 8.0) supplemented with 5% FBS (p < 0.001) at 21 °C. Proliferation of germ cells was significantly enhanced and maintained for longer periods by elimination of gonad somatic cells and culture under feeder-cell free conditions, with addition of leukemia inhibitory factor and glial-cell-derived neurotrophic factor (p < 0.001). A serum-free culture medium improved germ cell proliferation compared to the L-15 with FBS (p < 0.05). Morphology remained similar to that of fresh germ cells for at least 40 d culture. Germline-specific gene expression analysis revealed no significant changes to germ cells before and after culture. Sterlet Acipenser ruthenus germ cells cultured more than 40 days showed development after transplant into Russian sturgeon Acipenser gueldenstaedtii. Polymerase chain reaction showed 33.3% of recipient gonads to contain sterlet cells after four months. This study developed optimal culture condition for sturgeon germ cells. Germ cells after 40 d culture developed in recipient gonads. This study provided useful information for culture of sturgeon germ cells.

Feedback regulation of 17β-estradiol on two kisspeptin genes in the Dabry's sturgeon (Acipenser dabryanus)

In tetrapods, kisspeptins are a group of peptides that play essential roles in the regulation of the Gonadotropin-releasing hormone secretion, and may participate in the feedback regulation of sex steroids as well. In this study, two kiss paralogs, designated as dskiss1 and dskiss2 were identified in Acipenser dabryanus. The full-length cDNA sequences of dskiss1 and dskiss2 are 1265 and 744 base pairs (bp), encoding 130 and 146 amino acids, respectively. Multiple sequence alignment indicated that both Kiss1 and Kiss2 decapeptides were highly conserved among vertebrates. Besides, Kiss1 of Dabry's sturgeon shared closer evolutionary relationship with the holostean species spotted gar (Lepisosteus oculatus), while Kiss2 of Acipenser dabryanus was conservatively grouped with the early sarcopterygian coelacanth (Latimeria chalumnae) in the phylogenetic analysis. Tissue distribution analysis showed that dskiss1 transcribed exclusively in the brain, whereas dskiss2 exhibited wider tissue distribution including brain, testis and ovary. Furthermore, male Dabry's sturgeons were intraperitoneally injected with 17β-estradiol (E2) and the effect of E2 on hypothalamus kiss and its receptors kissr mRNA levels was evaluated by relative real-time PCR. The transcription levels of dskiss2 and dskissr1 were significantly increased by E2 injection (P < .05). However, the mRNA levels of dskiss1 and dskissr2 were not changed in E2-treated group compared to the control group. These results indicate that E2 exerts positive feedback effects through dskiss2/dskissr1 in male Dabry's sturgeon.

Molecular characterization of three toll-like receptors (TLR21, TLR22, and TLR25) from a primitive ray-finned fish Dabry's sturgeon (Acipenser dabryanus)

Dabry's sturgeon (Acipenser dabryanus) is a useful model for the study of fish evolution, as it is one of the most primitive actinopterygian species. However, studies of the immune system of this fish are limited. Here, we identified three toll-like receptors (adaTLR21, adaTLR22, and adaTLR25) from Dabry's sturgeon. The three sturgeon TLRs had characteristic TLR features, including a signal peptide, several leucine rich repeat (LRR) domains, a transmembrane domain, and a Toll/interleukin-1 receptor (TIR) domain. Although the predicted amino acid sequences encoded by the sturgeon adaTLR21, adaTLR22, and adaTLR25 had somewhat low levels of sequence identity and similarity with TLRs from other fish species, the three sturgeon TLRs fell in well-supported clades with other teleost TLRs in our neighbor-joining phylogenetic tree. Real-time quantitative PCR showed that the three sturgeon TLRs were ubiquitously expressed in all examined tissues from healthy adult sturgeon, but that their expression patterns varied greatly among the different tissues. The three sturgeon TLRs were also expressed across all embryonic developmental stages that were examined, but their expression levels differed between developmental stages. All three TLRs were upregulated in head-kidney primary leucocytes following lipopolysaccharide (LPS) and polyinosinic: polycytidylic acid (polyI:C) stimulation. To the best of our knowledge, this is the first characterization of these three TLRs in Darby's sturgeon. Our results provide a framework for further studies of TLR ligand specificity and signaling pathways in sturgeon, and increase our understanding of the functional evolution of TLRs in vertebrates.

Molecular characterization and expression analysis of TLR1 and TLR4 from the endangered fish Dabry's sturgeon (Acipenser dabryanus)

Toll-like receptors (TLRs) are important pattern recognition receptors (PRRs) of teleost innate immune system. However, information about TLRs is absent in Dabry's sturgeon (Acipenser dabryanus), one of the most primitive actinopterygii species. In the present study, the full lengths of adaTLR1 and adaTLR4 were cloned from Dabry's sturgeon using RT-PCR and RACE-PCR. The obtained adaTLR1 was 2957 bp in length, encoding a putative protein of 767 amino acids and adaTLR4 cDNA was 2902 bp in length, encoding a putative protein of 830 aa. Both adaTLR1 and adaTLR4 possessed several typical TLRs motifs, including signal peptides, leucine-rich repeat (LRR) motifs, a transmembrane domain and a TIR motifs. In addition, adaTLR4 contained three conserved boxes in its TIR motif, involving in TLRs signal transduction. A proline, important for LPS recognition of mammalian TLR4, was also found in adaTLR4. Physicochemical features of adaTLR1 and adaTRL4 were also analyzed. Quantitative realtime PCR showed that both transcripts were ubiquitously expressed in all 11 normal tissues selected, but they exhibited different expression patterns, with adaTLR1 highly expression in heart and adaTLR4 highly in skin. Further, adaTLR1 and adaTLR4 were up-regulated in the primary head-kidney leucocytes following LPS and polyI:C stimulation, indicating that both genes involved in the sturgeon immune response to LPS and polyI:C. To our best knowledge, this was the first report of these genes in sturgeon and these results provided the basis for further elucidating the ligand specificity and signaling pathway of fish TLRs.

Establishment of intraperitoneal germ cell transplantation for critically endangered Chinese sturgeon Acipenser sinensis

Recent progress in germ cell transplantation techniques in fish has paved the way for the conservation of endangered species. Here, we developed an intraperitoneal germ cell transplantation procedure using Chinese and Dabry's sturgeon as donor and recipient species, respectively. Histological analysis revealed that primordial germ cells migrated on the peritoneal wall at 16 days post-hatch (dph) in Dabry's sturgeon. The genital ridges of Dabry's sturgeon (recipient) first formed at 28 dph, suggesting that for successful colonization of donor germ cells in the recipient gonads, the transplantation should be performed earlier than this age. Sexual dimorphism of gonadal structure was first observed at 78 dph. Gonadal germ cell proliferation was not seen in either sex during this period. Immunohistochemistry using the anti-Vasa antibody found that donor testes from 2-year-old Dabry's sturgeon mainly consisted of single- or paired-type A spermatogonia, while donor ovaries from 11.5-year-old Chinese sturgeon had perinucleolus stage oocytes and clusters of oogonia. Donor cells isolated from Dabry's sturgeon testes or Chinese sturgeon ovary labeled with PKH26 fluorescent dye were transplanted into the peritoneal cavity of the 7- or 8-dph Dabry's sturgeon larvae. More than 90% and 70% of transplanted larvae survived after 2 days post-transplantation (dpt) and 51 dpt, respectively. At 51 dpt, PKH26-labeled cells exhibiting germ cell-specific nuclear morphology and diameter were observed in excised recipient gonads by fluorescent and confocal microscopy. The colonization rate of allogeneic testicular germ cell transplantation (Group 1) was 70%, while that of two batches of xenogeneic ovarian germ cell transplantation (Group 2 and Group 3) were 6.7% and 40%, respectively. The ratio of colonized germ cells to endogenous germ cells was 11.96%, 5.35% and 3.56% for Group 1, Group 2 and Group 3, respectively. Thus, we established a germ cell transplantation technique for the critically endangered Chinese sturgeon using the most closely related species as a recipient and demonstrated the successful preparation of transplantable female germ cells from aged adult Chinese sturgeon.