Identification of a germ cell marker gene, the dead end homologue, in Chinese sturgeon Acipenser sinensis

Secondary growth ovarian follicles of the pigmented sterlet sturgeon Acipenser ruthenus L. 1758 (Acipenseriformes, Chondrostei, Actinopterygii, Osteichthyes) - Microscopic study of oocytes, egg envelope and diversification of follicular cells

The individual ovarian follicle of sturgeons (Acipenseriformes, Acipenseridae) contains an oocyte surrounded by follicular cells (FCs), basal lamina, and thecal cells. The late stages of the secondary growth of follicles (mid- and advanced vitellogenic) are not fully explained in Acipenseriformes. To explore and discuss the ultrastructure of oocytes, FCs, an egg envelope, and explain how micropylar cells differentiate and the canals of a multiple micropyle are formed, the samples of ovaries of the mature sterlet sturgeon Acipenser ruthenus were examined. The oocytes are polarized, the nucleus is located in the animal hemisphere, contains lampbrush chromosomes and multiple nucleoli. In the ooplasm three regions are present: a perinuclear (contains the mitochondria), an endoplasm (contains the lipid droplets and yolk platelets), and a periplasm (contains the cortical granules, melanosomes, endocytotic and exocytotic vesicles). The melanosomes in animal hemisphere form two concentric rings separated by a lighter region between them. The FCs are differentiated into bright and dark cells that are both translationally and secretory active. Diversification of FCs involves repeated and cytoskeleton-dependent change of shape. In the advanced follicles the FCs are diversified into micropylar, the animal and vegetal regions cells, and the cells that delaminated from the epithelium in the animal region. The egg envelope is present in the perioocytic space and consists of three layers: (1) an inner layer or vitelline envelope, (2) a middle layer, and (3) an outer layer. The inner layer consists of four sublayers: (a) a filamentous sublayer composed of filaments released from the oocytes, (b) a trabecular 1 sublayer and (c) a trabecular 2 sublayer named due to the sequence of the deposition, and composed of filaments, fibres and trabecules, (d) a homogeneous sublayer located between the trabecular 1 and trabecular 2 sublayers composed of filaments that adhere to each other closely. The middle layer contains two sublayers: a porous 1 and a porous 2 (composed of granular material) which are released by the oocyte and FCs. The outer layer consists of fibrillar material released by the FCs. The egg envelope is pierced by radial canals formed around the microvilli of the oocyte and the microvilli-like processes of FCs. A micropylar field in the egg envelope that covers the animal pole of the oocyte contains 1 - 4 micropylar canals. Micropylar cells are involved in their formation. The shape of these cells is icicle-like and the cytoplasm is differentiated into two regions (a basal and apical bearing a projection) equipped with different sets of organelles.

Characterization of potential spermatogonia biomarker genes in the European eel (Anguilla anguilla)

Identification of specific molecular markers for spermatogonial stem cells in teleost is crucial for enhancing the efficacy of reproductive biotechnologies in aquaculture, such as transplantation and surrogate production in fishes. Since it is not yet possible to distinguish spermatogonial stem cells of European eel (Anguilla anguilla) using specific molecular markers, we isolated spermatogonial cells from immature European eels to find these potential markers. We attempted this by studying three candidate genes: vasa, nanos2, and dnd1. Two vasa (vasa1 and vasa2) genes, nanos2, and dnd1 were identified, characterized, and studied in the muscle, testis, and isolated spermatogonia. Our results showed that vasa1 and vasa2 had the highest levels of expression when measured by qPCR. In situ hybridization and immunochemistry assays showed that the four genes were localized explicitly in type A spermatogonia. However, vasa1 and vasa2 exhibited stronger signals in the immature testicular tissue than the other two potential markers. According to this, vasa1 and vasa2 were found to be the most effective markers for spermatogonial cells in the European eel.

Effects of CRISPR/Cas9-mediated dnd1 knockout impairs gonadal development in striped catfish

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology allows for the generation of loss-of-function mutations to enable efficient gene targeting to produce desired phenotypes, such as the production of germ cell-free fish. This technology could provide several applications for aquaculture and conservation of fisheries resources, such as the prevention of overpopulation in fish culture and gene flow from escaped farmed fish into wild populations and the production of germ cell-free recipient larvae for germ cell transplantation. This study aimed to develop CRISPR/Cas9 mediated dead-end 1 (dnd1) knockout techniques for striped catfish (Pangasianodon hypophthalmus). To optimise CRISPR/Cas9-induced dnd1 knockout, three single-guide RNAs (sgRNAs) were designed to target upstream sequences of start codon of the dnd1 gene. A combination of two concentrations of each sgRNA (100 and 200 ng/µl) and three concentrations of Cas9 (100, 250, and 500 ng/µl) was microinjected into fertilised striped catfish eggs. These sgRNAs/Cas9 could induce indel mutations and lower the primordial germ cell (PGC) numbers. Histological analyses indicated that sgRNA3 targeting upstream and nearest to the start codon at 200 ng/µL and Cas9 at 500 ng/µL showed the lowest PGC number. The reduction in PGC number was confirmed by in situ hybridisation using antisense dnd1 and vasa probes. All sgRNA/Cas9 combinations reduced the expression of dnd1, cxcr4b, dazl, nanos1, nanos2, and vasa, and the lowest expression levels were observed in gonads obtained from fish injected with 200 ng/µL sgRNA3 and 500 ng/µL Cas9 (P < 0.05). In addition, at 1 year of age, a significantly lower gonadosomatic index was observed in fish injected with all sgRNA and Cas9 at 500 ng/µL. Moreover, compared to the control fish, the ovaries and testes presented different morphologies in the sgRNA/Cas9-injected fish, that is, few previtellogenic oocytes in the ovary and spermatogonial cell-less testes. In conclusion, CRISPR/Cas 9 targeting dnd1 knockout at the upstream sequences of start codon was achieved, which resulted in the downregulation of dnd1 and lowered PGC number.

Spinyhead Croaker Germ Cells Gene dnd Visualizes Primordial Germ Cells in Medaka

Spinyhead croaker (Collichthys lucidus) is an economically important fish suffering from population decline caused by overfishing and habitat destruction. Researches on the development of primordial germ cell (PGC) and reproduction biology were an emergency for the long-term conservation of the involved species. Dead end (dnd) gene plays an indispensable role in PGC specification, maintenance, and development. In the current study, we report the cloning and expression patterns of dnd in C. lucidus (Cldnd). RT-PCR analysis revealed that Cldnd was specifically expressed in both sexual gonads. In the ovary, Cldnd RNA was uniformly distributed in the oocytes and abundant in oogonia, and gradually decreased with oogenesis. A similar expression pattern was also detected in testis. Dual fluorescent in situ hybridization of Cldnd and Clvasa demonstrated that they almost had the same distribution except in oocytes at stage I, in which the vasa RNA aggregated into some particles. Furthermore, Cldnd 3' UTR was sufficient to guide the Green Fluorescent Protein (GFP) specifically and stably expressed in the PGCs of medaka. These findings offer insight into that Cldnd is an evolutionarily conserved germline-specific gene and even a potential candidate for PGC manipulation in C. lucidus.

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.

Isolation and Characterization of Highly Pure Type A Spermatogonia From Sterlet (Acipenser ruthenus) Using Flow-Cytometric Cell Sorting

Sturgeons are among the most ancient linages of actinopterygians. At present, many sturgeon species are critically endangered. Surrogate production could be used as an affordable and a time-efficient method for endangered sturgeons. Our study established a method for identifying and isolating type A spermatogonia from different developmental stages of testes using flow cytometric cell sorting (FCM). Flow cytometric analysis of a whole testicular cell suspension showed several well-distinguished cell populations formed according to different values of light scatter parameters. FCM of these different cell populations was performed directly on glass slides for further immunocytochemistry to identify germ cells. Results showed that the cell population in gate P1 on a flow cytometry plot (with high forward scatter and high side scatter parameter values) contains the highest amount of type A spermatogonia. The sorted cell populations were characterized by expression profiles of 10 germ cell specific genes. The result confirmed that setting up for the P1 gate could precisely sort type A spermatogonia in all tested testicular developmental stages. The P2 gate, which was with lower forward scatter and side scatter values mostly, contained type B spermatogonia at a later maturing stage. Moreover, expressions of plzf, dnd, boule, and kitr were significantly higher in type A spermatogonia than in later developed germ cells. In addition, plzf was firstly found as a reliable marker to identify type A spermatogonia, which filled the gap of identification of spermatogonial stem cells in sterlet. It is expected to increase the efficiency of germ stem cell culture and transplantation with plzf identification. Our study thus first addressed a phenotypic characterization of a pure type A spermatogonia population in sterlet. FCM strategy can improve the production of sturgeons with surrogate broodstock and further the analysis of the cellular and molecular mechanisms of sturgeon germ cell development.

Dead-end (dnd) protein in fish-a review

Dead end (dnd) is a germ plasm-specific maternal RNA discovered in zebrafish and then in other vertebrates. Dnd protein is essential for migration and motility of primordial germ cells (PGCs), only cells destined to transfer genetic information to offspring. PGCs arise far from somatic cells of developing gonads and they must migrate to their site of function. Migration of PGCs follows complex path by various developing tissues as their disruption impacts on the fertility. Recently, it has been found that dnd is not required for survival of PGCs and dnd-deficient zebrafish PGCs transdifferentiate into the somatic cells. In fish, targeting dnd causes removal of PGCs that ultimately affects sex differentiation. Sterility in various fish species can be achieved by knockdown or knockout of dnd. In our review, we have discussed dnd as a germ cell-specific molecular marker in fish, its interaction with miRNAs, and its use in aquaculture and fish conservation.

Bucky ball induces primordial germ cell increase in medaka

Balbaini body (Bb) plays a vital role in germ plasm (GP) assembly and dorsoventral pattern, which is of critical important in germline specification and development. Bucky ball (buc) is reported to be essential for boosting primordial germ cell (PGC) through Bb in previous research. In the present study, a buc homolog (Olbuc) was identified in medaka (Oryzias latipes), and the roles of Olbuc on PGC development were further elucidated. The full length of Olbuc was 2148 bp, which contains a 1724 bp CDS (Coding sequence), a 167 bp 5' UTR (Untranslated region), and a 257 bp 3' UTR. By RT-PCR, the Olbuc RNA expression was maternally provided during embryogenesis and was restricted in the ovary of adult tissues. By in situ hybridization, Olbuc RNA was abundant in oocyte of meiotic stage, but gradually decreased as the oogenesis proceeded. Surprisingly, Olbuc was not co-localized with dazl, the marker gene of Bb. Interestingly, GFP can be specifically and stably expressed through the induction of Olbuc 3'UTR in PGCs. Furthermore, overexpression of Olbuc mRNA could increase PGC number and generate ectopic PGC in medaka and zebrafish embryos. In summary, our results showed that Olbuc performs a conserved function in PGC development in medaka.

Rescue of germ cells in dnd crispant embryos opens the possibility to produce inherited sterility in Atlantic salmon

Genetic introgression of escaped farmed Atlantic salmon (Salmo salar) into wild populations is a major environmental concern for the salmon aquaculture industry. Using sterile fish in commercial aquaculture operations is, therefore, a sustainable strategy for bio-containment. So far, the only commercially used methodology for producing sterile fish is triploidization. However, triploid fish are less robust. A novel approach in which to achieve sterility is to produce germ cell-free salmon, which can be accomplished by knocking out the dead-end (dnd) gene using CRISPR-Cas9. The lack of germ cells in the resulting dnd crispants, thus, prevents reproduction and inhibits subsequent large-scale production of sterile fish. Here, we report a rescue approach for producing germ cells in Atlantic salmon dnd crispants. To achieve this, we co-injected the wild-type (wt) variant of salmon dnd mRNA together with CRISPR-Cas9 constructs targeting dnd into 1-cell stage embryos. We found that rescued one-year-old fish contained germ cells, type A spermatogonia in males and previtellogenic primary oocytes in females. The method presented here opens a possibility for large-scale production of germ-cell free Atlantic salmon offspring through the genetically sterile broodstock which can pass the sterility trait on the next generation.

Transcriptome analysis of ovarian maturation in a chondrostei Chinese sturgeon Acipenser sinensis

Chinese sturgeon (Acipenser sinensis) with an evolutionary history of over 200 million years, has a long lifespan, and an extremely late and asynchronous sexual maturation (8-18 years for males and 14-26 years for females), resulting in the difficulty of mature adult culture. However, little is known about the regulatory mechanisms of the transition among ovarian maturation stages in the Chinese sturgeon. We performed de novo transcriptome sequencing of the Chinese sturgeon at different ovarian maturation stages (FII, FIII, and FIV). The number of differentially expressed genes (DEGs) between FII and FIII/FIV (33,517/34,217) was more than that between FIII and FIV (22,123), suggesting that the transition from FII to FIII/FIV is more important than that from FIII to FIV for ovarian maturation. The number of upregulated genes was more than that of the downregulated genes, suggesting that increased gene expression was involved in the transition from FII to FIII/FIV. The representative pathways of DEGs were steroid biosynthesis, fatty acid biosynthesis, fatty acid elongation, glycerolipid metabolism, biosynthesis of unsaturated fatty acid, and α-linolenic acid metabolism. The differential expressions from the transcriptome sequencing were validated with real-time reverse-transcription polymerase chain reaction. We also found 13 genes in sexual development, female sex determination, gonadal development, ovarian maturation, ovarian follicle development, and oocyte development pathways, which were differently expressed among fish at FII, FIII, and FIV. We suggest that enhanced synthesis of steroid, unsaturated fatty acid, and α-linolenic acid may contribute to ovarian maturation of the Chinese sturgeon. These potential determinants provide a glimpse of the molecular architecture of ovary development in sturgeons.

Germline cysts and asymmetry in early previtellogenic ovarian follicles in cultured albino females of sterlet Acipenser ruthenus L. 1758 (Chondrostei, Acipenseriformes)

It is a first report on the structure of germline cells in ovaries of albino sterlet Acipenser ruthenus L. 1758. Ovarian nests, follicles, and germinal epithelium have been examined in gynogenetic and control specimens of this species. The structure of oogonia (named the cystoblasts) and of germline cysts in the nests has been described in detail. Also, the asymmetry in the cytoplasm and early growth of cystocytes in the cysts and of early previtellogenic oocytes has been described. In the cytoplasm of cystoblasts and in all cystocytes, a precursor of granular cytoplasm (Balbiani cytoplasm) is present and defines future vegetal region in the oocytes. Interestingly, the nuclei in cystoblasts comprise a large dense body that contains deoxyribonucleic acid (DNA). The role of this body in formation of multiple nucleoli has been explained. During the zygotene and pachytene stages, massive extrachromosomal amplification of DNA begins in the nucleoplasm of all cystocytes. As a result of the accumulation of extra DNA, an irregularly shaped DNA-body is formed. Multiple nucleoli arise in this DNA-body and around fragments of dense bodies. The asymmetry of the early previtellogenic oocyte cytoplasm is well marked by the presence of the granular cytoplasm. Moreover, the cisternae of the rough endoplasmic reticulum, dictyosomes, mitochondria, complexes of mitochondria with cement, nuage accumulations, and lipid droplets are located in specific zones in the granular cytoplasm. The follicular epithelium is composed of two subpopulations of somatic follicular cells (FCs): the main body cells and future micropylar cells.

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.

Dnd is required for primordial germ cell specification in Oryzias celebensis

Dead end (dnd) is a germ plasm component that plays an essential role for primordial germ cell (PGC) development in vertebrates. Previously, we have found that dnd is the first fish PGC specifier in medaka. Here, we present an additional evidence that dnd is the determinant for PGC specification in Oryzias celebensis. In adult tissues, the O. celebensis dnd (Ocdnd) RNA shows germ cells specific expression in gonads. In the testis, Ocdnd RNA is strongly detected in spermatogonia and meiotic cells and gradually decreases during the spermatogenesis. In the ovary, Ocdnd RNA is present throughout oogenesis. In the embryos, Ocdnd RNA is maternally provided and asymmetrically localized to prominent particles of presumptive PGCs before gastrulation stage and restricted to PGCs subsequently. In addition, Ocdnd 3' UTR can induce specific and stabilized GFP reporter expression in PGCs. Furthermore, knockdown of Ocdnd by morpholino (MO) injection abolishes the PGCs formation and this can be rescued by co-injection of medaka dnd (Oldnd) mRNA. More importantly, overexpression of Oldnd mRNA surprisingly boosts PGCs number. These results provide insights into function of dnd as a conserved specifier of PGCs in the genus Oryzias.

Diet simplification selects for high gut microbial diversity and strong fermenting ability in high-altitude pikas

The gut microbiota in mammals plays a key role in host metabolism and adaptation. However, relatively little is known regarding to how the animals adapts to extreme environments through regulating gut microbial diversity and function. Here, we investigated the diet, gut microbiota, short-chain fatty acid (SCFA) profiles, and cellulolytic activity from two common pika (Ochotona spp.) species in China, including Plateau pika (Ochotona curzoniae) from the Qinghai-Tibet Plateau and Daurian pika (Ochotona daurica) from the Inner Mongolia Grassland. Despite a partial diet overlap, Plateau pikas harbored lower diet diversity than Daurian pikas. Some bacteria (e.g., Prevotella and Ruminococcus) associated with fiber degradation were enriched in Plateau pikas. They harbored higher gut microbial diversity, total SCFA concentration, and cellulolytic activity than Daurian pikas. Interestingly, cellulolytic activity was positively correlated with the gut microbial diversity and SCFAs. Gut microbial communities and SCFA profiles were segregated structurally between host species. PICRUSt metagenome predictions demonstrated that microbial genes involved in carbohydrate metabolism and energy metabolism were overrepresented in the gut microbiota of Plateau pikas. Our results demonstrate that Plateau pikas harbor a stronger fermenting ability for the plant-based diet than Daurian pikas via gut microbial fermentation. The enhanced ability for utilization of plant-based diets in Plateau pikas may be partly a kind of microbiota adaptation for more energy requirements in cold and hypoxic high-altitude environments.

Sex steroid production associated with puberty is absent in germ cell-free salmon

In all vertebrates studied so far, germ cells are not required for pubertal maturation of the gonadal steroidogenic system, subsequent development of secondary sex characteristics and reproductive behavior. To explore if the absence of germ cells affects puberty or growth in Atlantic salmon, germ cell-free (GCF), dnd knockout and wild type (WT) postsmolts were stimulated to enter puberty. No GCF fish entered puberty, whereas 66.7% (males) and 30% (females) WT fish completed or entered puberty, respectively. Expression of genes related to steroidogenesis (star, cyp17a1, cyp11β, cyp19a1a), gonadal somatic cells (insl3, amh, igf3), oocytes (bmp15), gonadotropin receptors (fshr, lhcgr), and pituitary gonadotropic cells (fshb, lhb, gnrhr4) showed an immature status and failure to up-regulate gonadal sex steroid production in male and female GCF fish was also reflected in low or undetectable plasma sex steroids (11-ketotestosterone, estradiol-17β and testosterone). A gender difference (high in females, low in males) was found in the expression of star and cyp17a1 in GCF fish. No clear difference in growth was detected between GCF and immature WT fish, while growth was compromised in maturing WT males. We demonstrate for the first time in a vertebrate that germ cells are required for pubertal activation of the somatic steroidogenic cells.

Ovarian nests in cultured females of the Siberian sturgeon Acipenser baerii (Chondrostei, Acipenseriformes)

Ovaries of Acipenser baerii are of an alimentary type and probably are meroistic. They contain ovarian nests, individual follicles, inner germinal ovarian epithelium, and fat tissue. Nests comprise cystoblasts, germline cysts, numerous early previtellogenic oocytes, and somatic cells. Cysts are composed of cystocytes, which are connected by intercellular bridges and are in the pachytene stage of the first meiotic prophase. They contain bivalents, finely granular, medium electron dense material, and nucleoli in the nucleoplasm. Many cystocytes degenerate. Oocytes differ in size and structure. Most oocytes are in the pachytene and early diplotene stages and are referred to as the PACH oocytes. Oocytes in more advanced diplotene stage are referred to as the DIP oocytes. Nuclei in the PACH oocytes contain bivalents and irregularly shaped accumulation of DNA (DNA-body), most probably corresponding to the rDNA-body. The DNA-body is composed of loose, fine granular material, and comprises multiple nucleoli. At peripheries, it is fragmented into blocks that remain in contact with the inner nuclear membrane. In the ooplasm, there is the rough endoplasmic reticulum, Golgi complexes, free ribosomes, complexes of mitochondria with cement, fine fibrillar material containing granules, and lipid droplets. The organelles and material of nuclear origin form a distinct accumulation (a granular ooplasm) in the vicinity of the nucleus. Some of the PACH oocytes are surrounded by flat somatic cells. There are lampbrush chromosomes and multiple nucleoli present (early diplotene stage) in the nucleoplasm. These PACH oocytes and neighboring somatic cells have initiated the formation of ovarian follicles. The remaining PACH oocytes transform to the DIP oocytes. The DIP oocytes contain lampbrush chromosomes and a DNA-body is absent in nuclei. Multiple nucleoli are numerous in the nucleoplasm and granular ooplasm is present at the vegetal region of the oocyte.

Previtellogenic and vitellogenic oocytes in ovarian follicles of cultured siberian sturgeon Acipenser baerii (Chondrostei, Acipenseriformes)

Previtellogenic and vitellogenic oocytes in ovarian follicles from cultured Siberian sturgeon Acipenser baerii were examined. In previtellogenic oocytes, granular and homogeneous zones in the cytoplasm (the ooplasm) are distinguished. Material of nuclear origin, rough endoplasmic reticulum, Golgi complexes, complexes of mitochondria with cement and round bodies are numerous in the granular ooplasm. In vitellogenic oocytes, the ooplasm comprises three zones: perinuclear area, endoplasm and periplasm. The endoplasm contains yolk platelets, lipid droplets, and aggregations of mitochondria and granules immersed in amorphous material. In the nucleoplasm, lampbrush chromosomes, nucleoli, and two types of nuclear bodies are present. The first type of nuclear bodies is initially composed of fibrillar threads only. Their ultrastructure subsequently changes and they contain threads and medium electron dense material. The second type of nuclear bodies is only composed of electron dense particles. All nuclear bodies impregnate with silver, stain with propidium iodide, and are DAPI-negative. Their possible role is discussed. All oocytes are surrounded by follicular cells and a basal lamina which is covered by thecal cells. Egg envelopes are not present in previtellogenic oocytes. In vitellogenic oocytes, the plasma membrane (the oolemma) is covered by three envelopes: vitelline envelope, chorion, and extrachorion. Vitelline envelope comprises four sublayers: filamentous layer, trabecular layer 2 (t2), homogeneous layer, and trabecular layer 1 (t1). In the chorion, porous layer 1 and porous layer 2 are distinguished in most voluminous examined oocytes. Three micropylar cells that are necessary for the formation of micropyles are present between follicular cells at the animal hemisphere. J. Morphol. 278:50-61, 2017. ©© 2016 Wiley Periodicals,Inc.

De novo annotation of the immune-enriched transcriptome provides insights into immune system genes of Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon (Acipenser sinensis), one of the oldest extant actinopterygian fishes with very high evolutionary, economical and conservation interest, is considered to be one of the critically endangered aquatic animals in China. Up to date, the immune system of this species remains largely undetermined with little sequence information publicly available. Herein, the first comprehensive transcriptome of immune tissues for Chinese sturgeon was characterized using Illumina deep sequencing. Over 67 million high-quality reads were generated and de novo assembled into the final set of 91,739 unique sequences. The annotation pipeline revealed that 25,871 unigenes were successfully annotated in the public databases, of which only 2002 had significant match to the existing sequences for the genus Acipenser. Overall 22,827 unigenes were categorized into 52 GO terms, 12,742 were classified into 26 KOG categories, and 4968 were assigned to 339 KEGG pathways. A more detailed annotation search showed the presence of a notable representation of immune-related genes, which suggests that this non-teleost actinopterygian fish harbors the same intermediates as in the well known immune pathways from mammals and teleosts, such as pattern recognition receptor (PRR) signaling pathway, JAK-STAT signaling pathway, complement and coagulation pathway, T-cell receptor (TCR) and B-cell receptor (BCR) signaling pathways. Additional genetic marker discovery led to the retrieval of 20,056 simple sequence repeats (SSRs) and 327,140 single nucleotide polymorphisms (SNPs). This immune-enriched transcriptome of Chinese sturgeon represents a rich resource that adds to the currently nascent field of chondrostean fish immunogenetics and furthers the conservation and management of this valuable fish.

Sterilization of sterlet Acipenser ruthenus by using knockdown agent, antisense morpholino oligonucleotide, against dead end gene

Sturgeons (chondrostean, acipenseridae) are ancient fish species, widely known for their caviar. Nowadays, most of them are critically endangered. The sterlet (Acipenser ruthenus) is a common Eurasian sturgeon species with a small body size and the fastest reproductive cycle among sturgeons. Such species can be used as a host for surrogate production; application is of value for recovery of critically endangered and huge sturgeon species with an extremely long reproductive cycle. One prerequisite for production of the donor's gametes only is to have a sterile host. Commonly used sterilization techniques in fishes such as triploidization or hybridization do not guarantee sterility in sturgeon. Alternatively, sterilization can be achieved by using a temporary germ cell exclusion-specific gene by a knockdown agent, the antisense morpholino oligonucleotide (MO). The targeted gene for the MO is the dead end gene (dnd) which is a vertebrate-specific gene encoding a RNA-binding protein which is crucial for migration and survival of primordial germ cells (PGCs). For this purpose, a dnd homologue of Russian sturgeon (Agdnd), resulting in the same sequence in the start codon region with isolated fragments of sterlet dnd (Ardnd), was used. Reverse transcription polymerase chain reaction confirmed tissue-specific expression of Ardnd only in the gonads of both sexes. Dnd-MO for depletion of PGCs together with fluorescein isothiocyanate (FITC)-biotin-dextran for PGCs labeling was injected into the vegetal region of one- to four-cell-stage sterlet embryos. In the control groups, only FITC was injected to validate the injection method and labeling of PGCs. After optimization of MO concentration together with volume injection, 250-μM MO was applied for sterilization of sturgeon embryos. Primordial germ cells were detected under a fluorescent stereomicroscope in the genital ridge of the FITC-labeled control group only, whereas no PGCs were present in the body cavities of morphants at 21 days after fertilization. Moreover, the body cavities of MO-treated and nontreated fish were examined by histology and in situ hybridization, showing gonads which had no germ cells in morphants at various stages (60, 150, and 210 days after fertilization). Taken together, these results report the first known and functional method of sturgeon sterilization.