Syntheses of α(2,8) Sialosides Containing NeuAc and NeuGc by Using Double Carbonyl-Protected N-Acyl Sialyl Donors.

We report on the syntheses of NeuAc and NeuGc-containing glycosides via the use of double carbonyl-protected N-acetyl sialyl donors. The 7-O,9-O-carbonyl protection of an N-acyl-5-N,4-O-carbonyl-protected sialyl donor markedly increased the α-selectivity during glycosylation, particularly when glycosylating the C-8 hydroxyl group of sialic acids. The N-acyl carbamates were selectively opened with ethanethiol under basic conditions to provide N-acyl amines. It is noteworthy that N-glycolyl carbamate was more reactive to nucleophiles by comparison with the N-acetyl carbamate due to the electron-withdrawing oxygen in the N-acyl group and however, allowed selective opening of the carbamates without the loss of N-glycolyl groups. To demonstrate the utility of the approach, we began by synthesizing α(2,3) and α(2,6) sialyl galactosides. Glycosylation of the hydroxy groups of galactosides at the C-6 position with the NeuAc and NeuGc donors provided the corresponding sialyl galactoses in good yields with excellent α-selectivity. However, glycosylation of the 2,3-diol galactosyl acceptor selectively provided Siaα(2,2)Gal. Next, we prepared a series of α(2,8) disialosides composed of NeuAc and NeuGc. Glycosylation of NeuGc and NeuAc acceptors at the C-8 hydroxyl group with NeuGc and NeuAc sialyl donors provided the corresponding α(2,8) disialosides, and no significant differences were detected in the reactivities of these acceptors.

Stereoselective synthesis of D-glycero-D-manno-heptose-1ß,7-bisphosphate (HBP) from D-mannurono-2,6-lactone.

The synthesis of D-glycero-D-manno-heptose-1ß,7-bisphosphate (HBP) from D-mannose is described. This synthetic approach is notable for the elongation of the seventh carbon, employing mannurono-2,6-lactone, the substrate-controlled establishment of the C-6 configuration, and the nucleophilic introduction of phosphate at the C-1 position through the utilization of 4,6-O-benzylidene-α-triflate.

Production of functional sperm from cryopreserved testicular germ cells following intraperitoneal transplantation into allogeneic surrogate in yellowtail (Seriola quinqueradiata).

The aim of this study was to establish a method for the cryopreservation of spermatogonia of the yellowtail (Seriola quinqueradiata), which is the most commonly farmed fish in Japan. Testicular cells were prepared by enzymatic dissociation of testicular fragments containing an abundance of type A spermatogonia and were added to cryomedium containing dimethyl sulfoxide (DMSO), ethylene glycol, glycerol, or propylene glycol at concentrations of 0.5-2.5 M. The cells were then frozen and stored in liquid nitrogen for 3 days. After thawing, their survival and transplantability were evaluated. Testicular cells were most successfully cryopreserved in 1.0 M DMSO as indicated by survival of 34% of cells. Furthermore, in situ hybridization using the yellowtail vasa probe showed that these recovered cells contained a similar proportion of germ cells to fresh testicular cells before freezing. Transplantation of the recovered cells into the peritoneal cavities of allogeneic larvae resulted in 94% of surviving recipients having donor-derived germ cells in their gonads after 28 days. Sperm were then collected from seven randomly selected recipients once they reached 2 years of age and used to fertilize wild-type eggs, which led to an average of 26% of the first filial (F1) offspring being derived from donor fish, as confirmed through the use of microsatellite markers. Thus, we successfully cryopreserved yellowtail spermatogonia and produced functional sperm via intraperitoneal transplantation into allogeneic recipients.

Characterization of the sex differentiation and gonadal development in small yellow croaker (Larimichthys polyactis) and its hybrid (L. polyactis ♀ × L. crocea ♂).

Interspecific hybridization has been considered as a possible approach to improve biological traits and has been applied in aquaculture practices. In the present study, artificial hybridization was carried out in the small yellow croaker (SYC; Larimichthys polyactis) ♀ × large yellow croaker (LYC; L. crocea) ♂ by artificial insemination, and the processes of sex differentiation and gonadal development in SYC and its hybrid were investigated under controlled conditions. Histological analysis of SYC larvae showed that migrating primordial germ cells (PGCs) were observed at 4 days post-hatching (dph), a genital ridge was formed on the dorsal side of the peritoneum at 6 dph, and a pair of primary gonads was first observed at 10 dph. Signs of the differentiated ovary and ovarian cavity were observed at 45 dph. However, some presumptive testes showed alterations in morphology, including an increase in the number of oocytes and an enhanced basophilia at 50 dph. These presumptive testes seemed to alter again, and numerous gonial cells were arranged in cyst-like groups with several degenerating oocytes that developed into residual body-like structures during 60-90 dph. Compared with SYC, the hybrid had a lower number of PGCs and showed retarded gonadal development at the early stage. Ovarian differentiation in the hybrid was observed at 50 dph, while testicular differentiation occurred at 60 dph. The presence of vitellogenic oocytes and spermatozoa at 360 dph in the hybrids suggested that hybrid individuals can undergo successful gametogenesis in females and males, respectively. Overall, the present results suggest that morphological sex differentiation occurred at 40 and 50 dph in SYC and its hybrid, respectively, both of which have normal gametogenesis. Moreover, some level of heterosis (hybrid vigor) occurred in the growth of the hybrid (total length and body weight) compared with that in the growth of SCY over time. Gonadal development of the hybrid was also found to be advanced at 360 dph. The present information will contribute to the potential use and management of these fish for aquaculture.

Production of donor-derived eggs after ovarian germ cell transplantation into the gonads of adult, germ cell-less, triploid hybrid fish†.

In animals, spermatogonial transplantation in sterile adult males is widely developed; however, despite its utility, ovarian germ cell transplantation is not well developed. We previously showed that the interspecific hybrid offspring of sciaenid was a suitable model for germ cell transplantation studies as they have germ cell-less gonads. However, all these gonads have testis-like characteristics. Here, we tested whether triploidization in hybrid embryos could result in germ cell-less ovary development. Gonadal structure dimorphism and sex-specific gene expression patterns were examined in 6-month-old triploid hybrids (3nHybs). Thirty-one percent of 3nHybs had germ cell-less gonads with an ovarian cavity. cyp19a1a and foxl2, ovarian differentiation-related genes, were expressed in these gonads, whereas dmrt1 and vasa were not expressed, suggesting ovary-like germ cell-less gonad development. Some (26%) 3nHybs had testis-like germ cell-less gonads. Ovarian germ cells collected from homozygous green fluorescent protein (GFP) transgenic blue drum (BD) (Nibea mitsukurii) were transplanted into 6-month-old 3nHybs gonads via the urogenital papilla or oviduct. After 9 months, the recipients were crossed with wild type BD. Among the six 3nHyb recipients that survived, one female and one male produced fertile eggs and motile sperm carrying gfp-specific DNA sequences. Progeny tests revealed that all F1 offspring possessed gfp-specific DNA sequences, suggesting that these recipients produced only donor-derived eggs or sperm. Histological observation confirmed donor-derived gametogenesis in the 3nHyb recipients' gonads. Overall, triploidization reduces male-biased sex differentiation in germ cell-less gonads. We report, for the first time, donor-derived egg production in an animal via direct ovarian germ cell transplantation into a germ cell-less ovary.

Suitability of hybrid mackerel (Scomber australasicus × S. japonicus) with germ cell-less sterile gonads as a recipient for transplantation of bluefin tuna germ cells.

We aim to establish a small-bodied surrogate broodstock, such as mackerel, which produces functional bluefin tuna gametes by spermatogonial transplantation. When reproductively fertile fish are used as recipients, endogenous gametogenesis outcompetes donor-derived gametogenesis, and recipient fish predominantly produce their gametes. In this study, we assessed fertility of hybrid mackerel, Scomber australasicus × S. japonicus, and its suitability as a recipient for transplantation of bluefin tuna germ cells. Hybrid mackerel were produced by artificially inseminating S. australasicus eggs with S. japonicus spermatozoa. Cellular DNA content and PCR analyses revealed that F1 offspring were diploid carrying both paternal and maternal genomes. Surprisingly, histological observations found no germ cells in hybrid mackerel gonads at 120 days post-hatch (dph), although they were present in the gonad of 30- and 60-dph hybrid mackerel. The frequency of germ cell-less fish was 100% at 120-dph, 63.1% at 1-year-old, and 81.8% at 2-year-old. We also confirmed a lack of expression of germ cell marker (DEAD-box helicase 4, ddx4) in the germ cell-less gonads of hybrid mackerel. By contrast, expression of Sertoli cell marker (gonadal soma-derived growth factor, gsdf) and of Leydig cell marker (steroid 11-beta-hydroxlase, cyp11b1) were clearly detected in hybrid mackerel gonads. Together these results showed that most of the hybrid gonads were germ cell-less sterile, but still possessed supporting cells and steroidogenic cells, both of which are indispensable for nursing donor-derived germ cells. To determine whether hybrid gonads could attract and incorporate donor bluefin tuna germ cells, testicular cells labeled with PKH26 fluorescent dye were intraperitoneally transplanted. Fluorescence observation of hybrid recipients at 14 days post-transplantation revealed that donor cells had been incorporated into the recipient's gonads. This suggests that hybrid mackerel show significant promise for use as a recipient to produce bluefin tuna gametes.

Germ cell-less hybrid fish: ideal recipient for spermatogonial transplantation for the rapid production of donor-derived sperm†.

An interspecific hybrid marine fish that developed a testis-like gonad without any germ cells, i.e., a germ cell-less gonad, was produced by hybridizing a female blue drum Nibea mitsukurii with a male white croaker Pennahia argentata. In this study, we evaluated the suitability of the germ cell-less fish as a recipient by transplanting donor testicular cells directly into the gonads through the urogenital papilla. The donor testicular cells were collected from hemizygous transgenic, green fluorescent protein (gfp) (+/-) blue drum, and transplanted into the germ cell-less gonads of the 6-month-old adult hybrid croakers. Fluorescent and histological observations showed the colonization, proliferation, and differentiation of transplanted spermatogonial cells in the gonads of hybrid croakers. The earliest production of spermatozoa in a hybrid recipient was observed at 7 weeks post-transplantation (pt), and 10% of the transplanted recipients produced donor-derived gfp-positive spermatozoa by 25 weeks pt. Sperm from the hybrid recipients were used to fertilize eggs from wild-type blue drums, and approximately 50% of the resulting offspring were gfp-positive, suggesting that all offspring originated from donor-derived sperm that were produced in the transplanted gfp (+/-) germ cells. To the best of our knowledge, this is the first report of successful spermatogonial transplantation using a germ cell-less adult fish as a recipient. This transplantation system has considerable advantages, such as the use of comparatively simple equipment and procedures, and rapid generation of donor-derived spermatogenesis and offspring, and presents numerous applications in commercial aquaculture.

Adjuvant effect of recombinant interleukin-12 in the Nocardiosis formalin-killed vaccine of the amberjack Seriola dumerili.

Nocardiosis causes serious economic damage in the fish farming of Japanese yellowtail fish. Nocardia seriolae identified as pathogenic bacterium is an intracellular-pathogen. In general, induction of cell-mediated immunity (CMI) is effective in infection defense against intracellular-pathogen. However, the conventional formalin-killed N. seriolae (FKC) vaccine induces humoral immunity. Interleukin-12 (IL-12) is Th1 type heterodimeric cytokine and induces cell differentiation in mammals. Our previous study showed that recombinant amberjack IL-12 has a role in CMI induction in vitro and could be a possible CMI inducing adjuvant. However, its adjuvant effect of fish IL-12 was not studied. In the present study, six types of amberjack recombinant IL-12 (rIL-12) were mixed and injected into amberjack with FKC. Firstly, we analyzed Th1- and Th2- related gene expression and monitored Th1/Th2 status followed by investigation of antibody titer. As a result, Th1-type immunity was induced in FKC + rIL-12 vaccinated fish. Secondly, we checked Th1/Th2 status of vaccinated fish after 10 days of N. seriolae infection using the expression of related genes. High T-bet/GATA-3 ratio was observed in FKC + rIL-12 vaccinated fish, suggesting that Th1 cells possesing antigen memory were induced against N. seriolae infection. Finally, the survival rate in challenge test showed that 88% of FKC + rIL-12 vaccinated fish was survived at 34 days after N. seriolae injection whereas PBS (control) and FKC only were exterminated. These result suggest that i) rIL-12 is viable CMI inducible adjuvant and ii) production of Th1 cells having antigen memory resulting from activation of IL-12 signaling pathway is important for defense against N. seriolae infection.

Assessment of yellowtail kingfish (Seriola lalandi) as a surrogate host for the production of southern bluefin tuna (Thunnus maccoyii) seed via spermatogonial germ cell transplantation.

Germ cell transplantation is an innovative technology for the production of interspecies surrogates, capable of facilitating easier and more economical management of large-bodied broodstock, such as the bluefin tuna. The present study explored the suitability of yellowtail kingfish (Seriola lalandi) as a surrogate host for transplanted southern bluefin tuna (Thunnus maccoyii) spermatogonial cells to produce tuna donor-derived gametes upon sexual maturity. Germ cell populations in testes of donor T. maccoyii males were described using basic histology and the molecular markers vasa and dead-end genes. The peripheral area of the testis was found to contain the highest proportions of dead-end-expressing transplantable Type A spermatogonia. T. maccoyii Type A spermatogonia-enriched preparations were transplanted into the coelomic cavity of 6-10-day-old post-hatch S. lalandi larvae. Fluorescence microscopy and polymerase chain reaction analysis detected the presence of tuna cells in the gonads of the transplanted kingfish fingerlings at 18, 28, 39 and 75 days after transplantation, indicating that the transplanted cells migrated to the genital ridge and had colonised the developing gonad. T. maccoyii germ cell-derived DNA or RNA was not detected at later stages, suggesting that the donor cells were not maintained in the hosts' gonads.

A phase I study of farletuzumab, a humanized anti-folate receptor α monoclonal antibody, in patients with solid tumors.

Farletuzumab is a humanized monoclonal antibody against folate receptor α (FRA). The purpose of the study is to assess safety and tolerability, the pharmacokinetic (PK) profile, and preliminary antitumor effect. Patients with ovarian cancer (OC) or FRA-expressing solid tumors who are resistant to standard treatments were eligible for the study. After single-dose administration for PK assessment, farletuzumab was administered by intravenous injection, repeating every week until disease progression. Dose-limiting toxicities (DLTs) were defined as grade 4 hematological and grade 3/4 nonhematological toxicities. Dose escalation was planned in 4 cohorts (50, 100, 200, and 400 mg/m(2)). Fourteen patients with OC and two patients with gastric cancer (GC) received farletuzumab infusion. Neither DLTs nor grade 3/4 toxicities were reported in all cohorts. Major adverse events, including grade 1/2 infusion related reaction (15 patients, 93.8%), headache (seven patients, 43.8%), and nausea and decreased appetite (five patients each, 31.3%), were observed and medically managed. AUC and Cmax increased dose-dependently and linear PK profiles were observed. No tumor shrinkage was recorded, but long-term disease stabilization for 25 and 20 months was observed in one patient with clear cell OC (100 mg/m(2)) and one patient with GC (400 mg/m(2)), respectively. No cumulative toxicity occurred in any patient. Farletuzumab was well tolerated in Japanese patients with a similar PK profile as compared with the US population. Long-term disease stabilization was observed in a subpopulation of clear cell OC and GC; both of them were resistant and progressive after standard chemotherapies (ClinicalTrials.gov Identifier: NCT01049061).

Reproductive Characteristics and Suitability of Sterile dead end Knockout Nibe Croaker as a Recipient for Intraperitoneal Germ Cell Transplantation.

The use of sterile recipients is crucial for efficiently producing donor-derived offspring through surrogate broodstock technology for practical aquaculture applications. Although knockout (KO) of the dead end (dnd) gene has been used in previous studies as a sterilization method, it has not been reported in marine fish. In this study, nibe croaker was utilized as a model for marine teleosts that produce small pelagic eggs, and the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system was utilized to produce dnd KO fish. The F1 generation, which carried a nonsense mutation in the dnd gene, was produced by mating founder individuals with wild-type counterparts. Subsequently, the F2 generation was produced by mating the resulting males and females. Among the F2 generations, 24.0% consisted of homozygous KO individuals. Histological analysis revealed that primordial germ cells (PGCs) were present in homozygous KO individuals at 10 days post-hatching (dph), similar to wild-type individuals. However, by 20 dph, PGCs were absent in KO individuals. Furthermore, no germ cells were observed in the gonads of both sexes of homozygous KO individuals at 6 months old, which is the typical maturity age for wild-type individuals of both sexes. In addition, when cryopreserved donor nibe croaker testicular cells were transplanted, only donor-derived offspring were successfully obtained through the spontaneous mating of homozygous KO recipient parents. Results indicate that dnd KO nibe croaker lacks germ cells and can serve as promising recipients, producing only donor-derived gametes as surrogate broodstock.

The Pacific bluefin tuna (Thunnus orientalis) dead end gene is suitable as a specific molecular marker of type A spermatogonia.

We developed a spermatogonial transplantation technique to produce donor-derived gametes in surrogate fish. Our ultimate aim is to establish surrogate broodstock that can produce bluefin tuna. We previously determined that only type A spermatogonia (ASG) could colonize recipient gonads in salmonids. Therefore, it is necessary to develop a precise molecular marker that can distinguish ASG in order to develop efficient spermatogonial transplantation methods. In this study, the Pacific bluefin tuna (Thunnus orientalis) dead end (BFTdnd) gene was identified as a specific marker for ASG. In situ hybridization and RT-PCR analysis with various types of spermatogenic cell populations captured by laser microdissection revealed that localization of BFTdnd mRNA was restricted to ASG, and not detected in other differentiated spermatogenic cells. In order to determine if BFTdnd can be used as a molecular marker to identify germ cells with high transplantability, transplantation of dissociated testicular cells isolated from juvenile, immature, and mature Pacific bluefin tuna, which have different proportions of dnd-positive ASG, were performed using chub mackerel as the surrogate recipient species. Colonization of transplanted donor germ cells was only successful with testicular cells from immature Pacific Bluefin tuna, which contained higher proportions of dnd-positive ASG than juvenile and mature fish. Thus, BFTdnd is a useful tool for identifying highly transplantable ASG for spermatogonial transplantation.

Reproductive characteristics of the hermaphroditic four-finger threadfin, Eleutheronema tetradactylum (Shaw, 1804), in tropical coastal waters.

This study investigated the reproductive traits of the hermaphroditic four-finger threadfin, Eleutheronema tetradactylum, along the coasts of Thailand during January to December 2021. Fish samples were collected from Pattani Bay, Thailand to assess the sex ratio, gonadosomatic index (GSI), maturity stage and fecundity. Additional fish samples were also collected from other areas to evaluate the length and weight at first sex change (Ls50 and Ws50) and length at first maturity (Lm50). The overall sex ratio for male and female was 1:0.69 with male being predominant throughout the year. Threadfin fish spawn the whole year round with peaks during moderate rainy and heavy rainy seasons. Histological examination confirmed its protandrous hermaphrodite posing multiple spawning habits. The average fecundity was 1.85 × 105 ± 1.05 × 105 eggs and positively related with standard length, body weight, gonad weight, and egg diameter (p < 0.05). The Ls50 and Ws50 were 27.58 cm and 419.39 g, and 29.71 cm and 457.28 g, for fish from Pattani Bay and Samut Prakan province, respectively. The Lm50 of male from Pattani Bay and Samut Prakan province were 25.78 cm and 25.56 cm, respectively, which were larger than those from Satun and Nakhon Sri Thammarat provinces. The Lm50 of females from Pattani Bay was smaller than that from Samut Prakan province. This study provided fundamental information on the reproductive characteristics of E. tetradactylum, which can be implemented to support management of natural fish stock and aquaculture development.

Effect of degree of substitution on the microphase separation and mechanical properties of cellooligosaccharide acetate-based elastomers.

Thermoplastic elastomers (TPEs) have long been used in a wide range of industries. However, most existing TPEs are petroleum-derived polymers. To realize environmentally benign alternatives to conventional TPEs, cellulose acetate is a promising TPE hard segment because of its sufficient mechanical properties, availability from renewable sources, and biodegradability in natural environments. Because the degree of substitution (DS) of cellulose acetate governs a range of physical properties, it is a useful parameter for designing novel cellulose acetate-based TPEs. In this study, we synthesized cellulose acetate-based ABA-type triblock copolymers (AcCelx-b-PDL-b-AcCelx) containing a celloologosaccharide acetate hard A segment (AcCelx, where x is the DS; x = 3.0, 2.6, and 2.3) and a poly(δ-decanolactone) (PDL) soft B segment. Small-angle X-ray scattering showed that decreasing the DS of AcCelx-b-PDL-b-AcCelx resulted in the formation of a more ordered microphase-separated structure. Owing to the microphase separation of the hard cellulosic and soft PDL segments, all the AcCelx-b-PDL-b-AcCelx samples exhibited elastomer-like properties. Moreover, the decrease in DS improved toughness and suppressed stress relaxation. Furthermore, preliminary biodegradation tests in an aqueous environment revealed that the decrease in DS endowed AcCelx-b-PDL-b-AcCelx with greater biodegradability potential. This work demonstrates the usefulness of cellulose acetate-based TPEs as next-generation sustainable materials.

Flow-cytometric isolation and enrichment of teleost type A spermatogonia based on light-scattering properties.

The transplantation of germ cells is a powerful tool both for studying their development and for reproductive biotechnology. An intraperitoneal germ cell transplantation system was recently developed for use in several teleost species. Donor germ cells transplanted into the peritoneal cavity of hatchlings migrated toward and were incorporated into the recipient's genital ridges, where they underwent gametogenesis. Among male germ cells, only type A spermatogonia were capable of colonizing the recipient gonads, unlike those at more advanced stages. The enrichment of type A spermatogonia is therefore important to achieve efficient donor-cell incorporation and subsequent donor-derived gametogenesis. Here we established a simple and rapid system of isolation and enrichment for fish type A spermatogonia, using flow cytometry. Type A spermatogonia were found to have distinctive forward and side light scatter properties compared to that with other types of testicular cell. Based on these characteristics, we were able to isolate and enrich type A spermatogonia by using flow cytometry. After intraperitoneal transplantation, the enriched type A spermatogonia could be successfully incorporated into the recipient genital ridges. This flow cytometry approach using forward and side light scatter was also found to be applicable to other salmonid and sciaenid species, suggesting that it could be a powerful tool for isolating and enriching transplantable type A spermatogonia in a wide range of teleosts. We expect this method to contribute significantly to germ cell biology and biotechnology.

Production of donor-derived offspring by allogeneic transplantation of spermatogonia in the yellowtail (Seriola quinqueradiata).

Although the yellowtail (Seriola quinqueradiata) is the fish most commonly farmed in Japan, breeding of this species has not yet started. This is primarily due to the lack of sufficiently sophisticated methods for manipulating gametogenesis, which makes it difficult to collect gametes from specific dams and sires. If it were possible to produce large numbers of surrogate fish by transplanting germ cells isolated from donor individuals harboring desirable genetic traits, then the probability of acquiring gametes carrying the donor-derived haplotype would increase, and breeding programs involving this species might increase as a result. As a first step, we established a method for the allogeneic transplantation of yellowtail spermatogonia and the production of donor-derived offspring. Donor cells were collected from immature (10-month-old) yellowtail males with testes containing abundant type A spermatogonia, labeled with PKH26 fluorescent dye, and transferred into the peritoneal cavities of 8-day-old larvae. Fluorescence observation at 28 days post-transplantation revealed that PKH26-labeled cells were incorporated into recipients' gonads. To assess whether donor-derived spermatogonia could differentiate into functional gametes in the allogeneic recipient gonads, gametes collected from nine male and four female adult recipients were fertilized with wild-type eggs and milt. Analysis of microsatellite DNA markers confirmed that some of the first filial (F(1)) offspring were derived from donor fish, with the average contribution of donor-derived F(1) offspring being 66% and the maximum reaching 99%. These findings confirmed that our method was effective for transplanting yellowtail spermatogonia into allogeneic larvae to produce donor-derived offspring.

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.

Lymphocyte antigen 75 (Ly75/CD205) is a surface marker on mitotic germ cells in rainbow trout.

In mammals, several cell surface molecular markers have been characterized in order to identify the mitotic germ cells. However, little is known in fish about their cell surface antigen. In this study, we identified lymphocyte antigen 75 (Ly75/CD205) as a germ cell-specific cell surface marker by combination expressed sequence tag analysis of purified type A spermatogonia (A-SG) from immature testis, in silico prediction of membrane proteins, and expression studies. The ly75 transcripts were abundant in the testis and gills, and weak signals were detected in the head kidney and brain. In addition, ly75 mRNA was predominantly localized in the primordial germ cells of newly hatched embryos, A-SG in testis, oogonia, and chromatin nucleolus-stage oocytes in the ovary. In contrast, ly75 mRNA was not detected in spermatocytes, spermatids, spermatozoa, vitellogenic oocytes, or gonadal somatic cells from either males or females. The expression profile of Ly75 protein was similar to that of the mRNA. Furthermore, identification of various fish homologs of ly75 confirmed that their amino acid sequences are well conserved. Therefore, Ly75 may be appropriate for use as a versatile cell surface marker for mitotic germ cells in fish.

Chub mackerel gonads support colonization, survival, and proliferation of intraperitoneally transplanted xenogenic germ cells.

The production of xenogenic gametes from large-bodied, commercially important marine fish species in closely related smaller host fish species with short generation times may enable rapid and simple seed production of the target species. As a first step toward this goal, we assessed the suitability of chub mackerel, Scomber japonicus, as a small-bodied recipient species for xenogenic spermatogonial transplantation. Histological observation of the early gonadal development of chub mackerel larvae and transplantation of fluorescent-labeled spermatogonia from Nibe croaker, Nibea mitsukurii, revealed that 5.3-mm chub mackerel larvae were suitable recipients for successful transplantation. Intraperitoneally transplanted xenogenic spermatogonia efficiently colonized the gonads of these recipient larvae, and donor-derived Nibe croaker germ cells proliferated rapidly soon after colonization. Moreover, gonadal soma-derived growth factor (gsdf) mRNA, a gonadal somatic cell marker, was expressed in recipient-derived cells surrounding the incorporated donor-derived germ cells, suggesting that donor-derived germ cells had settled at an appropriate location in the recipient gonad. Our data show that xenogenic spermatogonial transplantation was successful in chub mackerel and that the somatic microenvironment of the chub mackerel gonad can support the colonization, survival, and proliferation of intraperitoneally transplanted xenogenic germ cells derived from a donor species of a different taxonomic family.

Biotechnology: surrogate broodstock produces salmonids.

A worldwide decline in the number of wild salmonids calls for strategies to restore endangered populations. Here we show that germ cells can be transplanted between two different salmonid species, with the subsequent production of xenogenic, donor-derived offspring. This pioneering xenotransplantation technology may eventually find applications in facilitating the production of commercially valuable fish, as well as in species conservation.