Production of germline chimeric chickens following the administration of a busulfan emulsion

Innovations in poultry reproduction using cryopreserved avian germ cells

Meat and eggs from chicken are the major source of animal protein for the human population. The cryopreservation of poultry species is needed to guarantee sustainable production. Here, we describe the existing cryopreservation technologies for avian reproductive cells using embryonic germ cells, spermatozoa and ovarian tissues. We outline strategies to reconstitute chicken breeds from their cryopreserved embryonic germ cells using surrogate hosts and discuss the perspectives for genetic conservation and reconstitution of chicken and wild avian species using surrogate host animals.

Successful xenotransplantation of testicular cells following fractionated chemotherapy of recipient birds

An essential step in the success of germ cell transplantation is the preparation of the recipient's testicular environment to increase the availability of stem cell niches. However, most methods for this purpose in birds face serious limitations such as partial germ cell depletion, high toxicity and mortality, or the need to use expensive technologies. Here, we validated a simple and practical technique of transferring quail testicular cells into chicken testes depleted of endogenous spermatozoa by fractioned chemotherapy (20 mg/kg/week busulfan for 5 weeks). This protocol resulted in a very low mortality of the treated day-old chicks and, despite maintenance of androgenic activity, sperm production was decreased by 84.3% at 25 weeks of age. NANOG immunostaining revealed that very few to no germ cells were present following treatment with 20 and 40 mg/kg, respectively. RT-qPCR data also showed that c-MYC and NANOG expression declined in these treatments, but GRFα1 and BID expressions remained unaltered among groups. After xenotransplantation, quail germ cells were immunodetected in chicken testes using a species-specific antibody (QCPN), and quail ovalbumin DNA was found in seminal samples collected from chicken recipients. Together, these data confirm that fractionated administration of busulfan in hatchlings is a practical, effective, and safe protocol to prepare recipient male birds capable of supporting xenogeneic spermatogenesis.

In vivo enrichment of busulfan-resistant germ cells for efficient production of transgenic avian models

Most transgenic animals are generated using a genome-modified stem cell system and genome modification directly in embryos. Although this system is well-established in the development of transgenic animals, donor cell-derived transgenic animal production is inefficient in some cases. Especially in avian models such as chickens, the efficiency of transgenic animal production through primordial germ cells (PGCs) is highly variable compared with embryonic manipulation of mammalian species. Because germ cell and germline-competent stem cell-mediated systems that contain the transgene are enriched only at the upstream level during cell cultivation, the efficiency of transgenic animal production is unreliable. Therefore, we developed an in vivo selection model to enhance the efficiency of transgenic chicken production using microsomal glutathione-S-transferase II (MGSTII)-overexpressing PGCs that are resistant to the alkylating agent busulfan, which induces germ cell-specific cytotoxicity. Under in vitro conditions, MGSTII-tg PGCs were resistant to 1 μM busulfan, which was highly toxic to wild-type PGCs. In germline chimeric roosters, transgene-expressing germ cells were dominantly colonized in the recipient testes after busulfan exposure compared with non-treated germline chimera. In validation of germline transmission, donor PGC-derived progeny production efficiency was 94.68%, and the transgene production rate of heterozygous transgenic chickens was significantly increased in chickens that received 40 mg/kg busulfan (80.33–95.23%) compared with that of non-treated germline chimeras (51.18%). This system is expected to significantly improve the efficiency of generating transgenic chickens and other animal species by increasing the distribution of donor cells in adult testes.

Aldehyde dehydrogenase in fresh primordial germ cells as a marker of cell 'stemness'

SummaryChicken primordial germ cells (PGCs) are the primary pluripotent stem cell types that will differentiate towards germ cells. High aldehyde dehydrogenase (ALDH) activity is considered as a functional marker for the detection of cell 'stemness'. In our study the ALDEFLUOR™ kit was used for determination of ALDH activity in PGCs. PGCs were co-stained with diethylaminobenzaldehyde (DEAB) and ALDH and analyzed by flow cytometry. Our results showed a small cell population (8.0 ± 3.3%) upon preincubation of the cells with the specific inhibitor DEAB, however cells without inhibitor staining showed a fluorescence shift as an ALDH-positive population (70.5 ± 1.6%). These findings indicate higher expression of ALDH in PGCs and ALDH activity can therefore be used as a new functional marker for the detection of cell 'stemness' in chicken PGCs. These results may have importance for characterization of PGCs as a potential genetic resource in poultry. Further research is necessary to elucidate the role of this functional marker in these cells.

Uniparental chicken offsprings derived from oogenesis of chicken primordial germ cells (ZZ)

Cloning (somatic cell nuclear transfer) in avian species has proven unachievable due to the physical structure of the avian oocyte. Here, the sexual differentiation of primordial germ cells with genetic sex ZZ (ZZ PGCs) was investigated in female germline chimeric chicken hosts with the aim to produce uniparental offspring. ZZ PGCs were expanded in culture and transplanted into the same and opposite sex chicken embryos which were partially sterilized using irradiation. All tested chimeric roosters (ZZ/ZZ) showed germline transmission with transmission rates of 3.2%-91.4%. Unexpectedly, functional oogenesis of chicken ZZ PGCs was found in three chimeric hens, resulting in a transmission rate of 2.3%-27.8%. Matings were conducted between the germline chimeras (ZZ/ZZ and ZZ/ZW) which derived from the same ZZ PGCs line. Paternal uniparental chicken offspring were obtained with a transmission rate up to 28.4% and as expected, all uniparental offspring were phenotypic male (ZZ). Genotype analysis of uniparental offsprings was performed using 13 microsatellite markers. The genotype profile showed that uniparental offspring were 100% genetically identical to the donor ZZ PGC line, shared 69.2%-88.5% identity with the donor bird. Homozygosity of the tested birds varied from 61.5% to 84.6%, which was higher than the donor bird (38.5%). These results demonstrate that male avian ZZ PGCs can differentiate into functional ova in an ovary, and uniparental avian clones are possible. This technology suggests novel approaches for generating genetically similar flocks of birds and for the conservation of avian genetic resources.

Different approaches to establish infertile rooster

Several methods have been developed to suppress spermatogenesis in recipient males before spermatogonial stem cells (SSCs) transplantation. The aim of this study was to compare two different methods of depleting endogenous spermatogenesis in recipient ROSS 308 strain adult roosters. Gamma-radiation and alkylating agent busulfan were utilized to infertilize adult roosters (ROSS 308 strain). Two radiation therapy regimes (based on ⁶⁰co isotope) were conducted locally to testes using 40Gy (5×8Gy with three-day intervals) and 30Gy (3×10Gy with three-day intervals). And two different levels of busulfan 60mg(40+20) and 50mg(30+20) with 10-day intervals were injected intraperitoneally. The results showed that both radiation therapy regimes and both busulfan levels reduced sperm motility and sperm concentration significantly compared with control group. Moreover, there were no significant differences between gamma radiation and busulfan treatments in progressive and total motility of sperm reduction. Sperm concentration reached to zero at the end of the 4th week of experiment in all treatment groups. Also histological examinations revealed that both treatments could significantly reduce the diameter of seminiferous tubules and thickness of epithelium. None of the treatments had significant effect on body weight in comparison with control group and the health status of experimental roosters remained good throughout the study. Given that, the risk probability of high doses of radiation exposure and busulfan, it can be concluded that the 30Gy (3×10Gy) and 50mg (30+20) are appropriate for suppression of endogenous spermatogenesis in mature roosters.

Perspectives on avian stem cells for poultry breeding

Stem cells have prulipotency to differentiate into many types of cell lineages. Recent progress of avian biotechnology enabled us to analyze the developmental fate of the stem cells: embryonic stem cells / primordial germ cells (PGCs). The stem cells were identified in the central area of the area pellucida of the stage X blastoderms. These cells could be applied for production of germline chimeras and organ regeneration. Generation of medical substrate in transgenic chickens has considerable interests in pharmaceuticals. Sex alteration of the offspring should be enormously beneficial to the poultry industry. Fertilization of the sex-reversed sperm could lead to sexual alteration of the offspring. These strategies using stem cells / PGCs should be one of the most powerful tools for future poultry breeding.

Cryopreservation of specialized chicken lines using cultured primordial germ cells

Biosecurity and sustainability in poultry production requires reliable germplasm conservation. Germplasm conservation in poultry is more challenging in comparison to other livestock species. Embryo cryopreservation is not feasible for egg-laying animals, and chicken semen conservation has variable success for different chicken breeds. A potential solution is the cryopreservation of the committed diploid stem cell precursors to the gametes, the primordial germ cells ( PGCS: ). Primordial germ cells are the lineage-restricted cells found at early embryonic stages in birds and form the sperm and eggs. We demonstrate here, using flocks of partially inbred, lower-fertility, major histocompatibility complex- ( MHC-: ) restricted lines of chicken, that we can easily derive and cryopreserve a sufficient number of independent lines of male and female PGCs that would be sufficient to reconstitute a poultry breed. We demonstrate that germ-line transmission can be attained from these PGCs using a commercial layer line of chickens as a surrogate host. This research is a major step in developing and demonstrating that cryopreserved PGCs could be used for the biobanking of specialized flocks of birds used in research settings. The prospective application of this technology to poultry production will further increase sustainability to meet current and future production needs.

Nonviral minicircle generation of induced pluripotent stem cells compatible with production of chimeric chickens

Chickens are vitally important in numerous countries as a primary food source and a major component of economic development. Efforts have been made to produce transgenic birds through pluripotent stem cell [primordial germ cells and embryonic stem cells (ESCs)] approaches to create animals with improved traits, such as meat and egg production or even disease resistance. However, these cell types have significant limitations because they are hard to culture long term while maintaining developmental plasticity. Induced pluripotent stem cells (iPSCs) are a novel class of stem cells that have proven to be robust, leading to the successful development of transgenic mice, rats, quail, and pigs and may potentially overcome the limitations of previous pluripotent stem cell systems in chickens. In this study we generated chicken (c) iPSCs from fibroblast cells for the first time using a nonviral minicircle reprogramming approach. ciPSCs demonstrated stem cell morphology and expressed key stem cell markers, including alkaline phosphatase, POU5F1, SOX2, NANOG, and SSEA-1. These cells were capable of rapid growth and expressed high levels of telomerase. Late-passage ciPSCs transplanted into stage X embryos were successfully incorporated into tissues of all three germ layers, and the gonads demonstrated significant cellular plasticity. These cells provide an exciting new tool to create transgenic chickens with broad implications for agricultural and transgenic animal fields at large.

Compensatory proliferation of endogenous chicken primordial germ cells after elimination by busulfan treatment

Introduction

Primordial germ cells (PGCs) are the major population of cells in the developing bilateral embryonic gonads. Little is known about the cellular responses of PGCs after treatment with toxic chemicals such as busulfan during embryo development. In this study, we investigated the elimination, restorative ability, and cell cycle status of endogenous chicken PGCs after busulfan treatment.

Methods

Busulfan was emulsified in sesame oil by a dispersion-emulsifying system and injected into the chick blastoderm (embryonic stage X). Subsequently, we conducted flow cytometry analysis to evaluate changes in the PGC population and cell cycle status, and immunohistochemistry to examine the germ cell proliferation.

Results

Results of flow cytometry and immunohistochemistry analyses after busulfan treatment showed that the proportion of male PGCs at embryonic day 9 and female PGCs at embryonic day 7 were increased by approximately 60% when compared with embryonic day 5.5. This result suggests the existence of a compensatory mechanism in PGCs in response to the cytotoxic effects of busulfan. Results of cell cycling analysis showed that the germ cells in the G₀/G₁ phase were significantly decreased, while S/G₂/M-phase germ cells were significantly increased in the treatment group compared with the untreated control group in both 9-day-old male and female embryos. In addition, in the proliferation analysis with 5-ethynyl-2′-deoxyuridine (EdU) incorporation, we found that the proportion of EdU-positive cells among VASA homolog-positive cells in the 9-day embryonic gonads of the busulfan-treated group was significantly higher than in the control group.

Conclusions

We conclude that PGCs enter a restoration pathway by promoting their cell cycle after experiencing a cytotoxic effect.

Production of functional gametes from cryopreserved primordial germ cells of the Japanese quail

The Japanese quail (Coturnix japonica) is a valuable bird as both an experimental animal, for a wide range of scientific disciplines, and an agricultural animal, for the production of eggs and meat. Cryopreservation of PGCs would be a feasible strategy for the conservation of both male and female fertility cells in Japanese quail. However, the effects of freeze-thaw treatment on viability, migration ability and germline transmission ability of quail PGCs still remain unclear. In the present study, male and female PGCs were isolated from the blood of 2-day-old embryos, which were cooled by slow freezing and then cryopreserved at –196 C for 77–185 days, respectively. The average recovery rate of PGCs after freeze-thawing was 47.0%. The viability of PGCs in the frozen group was significantly lower than that of the control group (P<0.05) (85.5% vs. 95.1%). Both fresh and Frozen-thawed PGCs that were intravascularly transplanted into recipient embryos migrated toward and were incorporated into recipient gonads, although the number of PGCs settled in the gonads was 48.5% lower in the frozen group than in the unfrozen control group (P<0.05). Genetic cross analysis revealed that one female and two male recipients produced live progeny derived from the frozen-thawed PGCs. The frequency of donor-derived offspring was slightly lower than that of unfrozen controls, but the difference was not significant (4.0 vs. 14.0%). These results revealed that freeze-thaw treatment causes a decrease in viability, migration ability and germline transmission ability of PGCs in quail.

Comparative costs of programmes to conserve chicken genetic variation based on maintaining living populations or storing cryopreserved material

1. There have been substantial losses of chicken lines kept for research in recent years and the objective of this research was to critically review alternative methods of preserving genetic resources. 2. The costs of programmes using living populations, semen cryopreservation and reconstitution, and ovary and semen cryopreservation and reconstitution were evaluated over 20 years using biological parameters of cryopreservation and population reconstitution that were derived from the literature. 3. Keeping live populations was most cost effective for periods of up to three years, but keeping live populations is increasingly difficult to justify with longer periods and any research population that will not be used within five years should be cryoconserved and in situ maintenance discontinued. 4. The rapid reconstitution possible using ovaries and semen would allow the inclusion of cryopreserved material in a short-term research project with the cost of recovery included in the budget. The low cost of cryoconservation suggests that all avian material should be conserved and reconstituted when needed for research.

The effect of busulfan treatment on endogenous spermatogonial stem cells in immature roosters

Several methods have been developed for suppression of endogenous spermatogenesis in recipient males before spermatogonial stem cells transfer. Currently the chemical treatment with alkylating agent busulfan is the method of choice in mammals. Still, in different mammalian species wide variability in optimal doses of busulfan has been demonstrated, whereas in birds, the dosage has not yet been optimized. We tested the sterilizing effect of several busulfan doses: 20, 40, and 60 mg/kg of BW as a single or double intraperitonial injections in pubertal-age roosters. It was found that the 20 to 40 mg/kg of BW doses effective in mice did not lead to suppression of spermatogenesis in birds. A single high dose of busulfan (60 mg/kg of BW) resulted in the death of all treated chickens, whereas the same amount of busulfan applied in 2 doses resulted in considerable suppression of spermatogenesis in majority of treated birds. Application of busulfan in several doses also caused less physiological stress than single-dose application.

X-irradiation removes endogenous primordial germ cells (PGCs) and increases germline transmission of donor PGCs in chimeric chickens

Primordial germ cells (PGCs) are embryonic precursors of germline cells with potential applications in genetic conservation, transgenic animal production and germline stem cell research. These lines of research would benefit from improved germline transmission of transplanted PGCs in chimeric chickens. We therefore evaluated the effects of pretransplant X-irradiation of recipient embryos on the efficacy of germline transmission of donor PGCs in chimeric chickens. Intact chicken eggs were exposed to X-ray doses of 3, 6 and 9 Gy (dose rate = 0.12 Gy/min) after 52 h of incubation. There was no significant difference in hatching rate between the 3-Gy-irradiated group and the nonirradiated control group (40.0 vs. 69.6%), but the hatching rate in the 6-Gy-irradiated group (28.6%) was significantly lower than in the control group (P<0.05). No embryos irradiated with 9 Gy of X-rays survived to hatching. X-irradiation significantly reduced the number of endogenous PGCs in the embryonic gonads at stage 27 in a dose-dependent manner compared with nonirradiated controls. The numbers of endogenous PGCs in the 3-, 6- and 9-Gy-irradiated groups were 21.0, 9.6 and 4.6% of the nonirradiated control numbers, respectively. Sets of 100 donor PGCs were subsequently transferred intravascularly into embryos irradiated with 3 Gy X-rays and nonirradiated control embryos. Genetic cross-test analysis revealed that the germline transmission rate in the 3-Gy-irradiated group was significantly higher than in the control group (27.5 vs. 5.6%; P<0.05). In conclusion, X-irradiation reduced the number of endogenous PGCs and increased the germline transmission of transferred PGCs in chimeric chickens.

Pure line laying chickens at the Agassiz Research Centre

Six lines of laying chickens representing high-producing non-industrial lines chosen or produced with consideration for characters of production are being kept at the Agassiz Research Centre. The collection includes one Barred Plymouth Rock (Line 60), one Columbian Plymouth Rock, one Rhode Island Red (Line 50), and three White Leghorn lines (Blue, Black, and Burgundy). Before coming to the Agassiz Research Centre these pure lines were subjected to mild selection for egg production and their egg production approaches that of commercial hybrids. The lines are currently maintained as a genetic resource as live populations without selection and with populations large enough to minimize inbreeding. In addition, samples of DNA from these lines have been conserved for genetic studies, and samples of embryonic cells are being kept cryogenically to allow the possibility of reconstitution of the lines through the production of germline chimeras. Techniques of ovarian transplantation are being developed which will allow more efficient cryogenic conservation and recuperation of the genetic material into live populations.

Gamma-irradiation depletes endogenous germ cells and increases donor cell distribution in chimeric chickens

The production of chimeric birds is an important tool for the investigation of vertebrate development, the conservation of endangered birds, and the development of various biotechnological applications. This study examined whether gamma (γ)-irradiation depletes endogenous primordial germ cells and enhances the efficiency of somatic chimerism in chickens. An optimal irradiation protocol for stage X embryos was determined after irradiation at various doses (0, 100, 300, 500, 600, 700, and 2,000 rad). Exposure to 500 rad of γ-irradiation for 73 s significantly decreased the number of primordial germ cells (P < 0.0001). Somatic chimera hatchlings were then produced by transferring blastodermal cells from a Korean Oge into either an irradiated (at 500 rad) or intact stage X White Leghorn embryo. An analysis of feather color pattern and polymerase chain reaction-based species-specific amplification of various tissues of the hatchlings confirmed chimerism in most organs of the chick produced from the irradiated recipient; a lesser degree of chimerism was observed in the non-irradiated control recipient. In conclusion, the exposure of chick embryos to an optimized dose of γ-irradiation effectively depleted germ cells and yielded greater somatic chimerism than non-irradiated control embryos. This technique can be applied to interspecies reproduction or the production of transgenic birds.

Germline replacement by transfer of primordial germ cells into partially sterilized embryos in the chicken

We report a novel technique for almost complete replacement of the recipient germline with donor germ cells in the chicken. Busulfan solubilized in a sustained-release emulsion was injected into the yolk of fertile eggs before incubation. A dose of 100 microg was found to provide the best outcome in terms of reducing the number of endogenous primordial germ cells (PGCs) in embryonic gonads (0.6% of control numbers) and hatchability (36.4%). This was applied for preparing partially sterilized embryos to serve as recipients for the transfer of exogenous PGCs. Immunohistochemical analysis showed that the proportion of donor PGCs in busulfan-treated embryos was significantly higher than in controls (98.6% vs. 6.4%). Genetic cross-test analysis revealed that the germline transmission rate in busulfan-treated chickens was significantly higher than in controls (99.5% vs. 6.0%). Of 11 chimeras, 7 produced only donor-derived progenies, suggesting that these produced only donor-derived gametes in the recipient's gonads. This novel germline replacement technique provides a powerful tool for studying germline differentiation, for generating transgenic individuals, and for conserving genetic resources in birds.

Increased proportion of donor primordial germ cells in chimeric gonads by sterilisation of recipient embryos using busulfan sustained-release emulsion in chickens

The aim of the present study was to improve the efficiency of endogenous primordial germ cell (PGC) depletion and to increase the ratio of donor PGCs in the gonads of recipient chicken embryos. A sustained-release emulsion was prepared by emulsifying equal amounts of Ca(2+)- and Mg(2+)-free phosphate-buffered saline containing 10% busulfan solubilised in N,N-dimethylformamide and sesame oil, using a filter. Then, 75 microg per 50 microL busulfan sustained-release emulsion was injected into the yolk. To determine the depletion and repopulation of PGCs in the gonads after 6 days incubation, whole-mount immunostaining was performed. The busulfan sustained-release emulsion significantly reduced the number of endogenous PGCs compared with control (P < 0.05). Moreover, the busulfan sustained-release emulsion significantly depleted endogenous PGCs compared with other previously reported busulfan delivery systems (P < 0.05), but with less variation, suggesting that the sustained-release emulsion delivered a consistent amount of busulfan to the developing chicken embryos. The PGC transfer study showed that the proportion of donor PGCs in the gonads of busulfan sustained-release emulsion-treated embryos after 6 days incubation increased 28-fold compared with control. In conclusion, the results demonstrate that exogenous PGCs are capable of migrating and settling in gonads from which endogenous PGCs have been removed using a busulfan sustained-release emulsion.

Absence of donor-derived zona pellucida protein C homolog in the inner perivitelline layer of Peking duck (Anas platyrhynchos)-Japanese quail (Coturnix coturnix japonica) chimeras (Duails)

Avian blastodermal cells at stage X are used to produce interspecies chimeras for heterogenous poultry reproduction. However, recipient-derived inner perivitelline layer (IPVL)-enclosed donor-derived ova may affect the efficiency of germline transmission via chimera. Among the proteins in the IPVL, zona pellucida protein C (ZPC) plays an important role in sperm-egg binding and inducing the acrosome reaction. In the present study, Peking duck blastodermal cells at stage X were transferred into subgerminal cavities of Japanese quail embryos at the same stage. Fourteen female duck-quail chimeras (duails) were hatched and raised to sexual maturity. After being screened by PCR, 3 duails were selected for examination of donor-derived ZPC. A total of 152 IPVL protein samples from the individual eggs laid by the 3 duails then underwent a preliminary examination for the presence of donor-derived ZPC by means of SDS-PAGE, periodic acid-Schiff staining, and Western blotting. A novel 35-kDa ZPC, not observed in quail but in duck, was found in the IPVL of the duails. Further analysis of peptide mass fingerprinting of Peking duck ZPC, Japanese quail ZPC, and the 35-kDa duail ZPC by matrix-assisted laser desorption-ionization reflectron time-of-flight mass spectrometry revealed that the novel ZPC was an isoform of quail ZPC. Moreover, comparison of N-terminal amino acid sequences of these 3 ZPC confirmed that the 35-kDa quail ZPC had more amino acids at the N terminus than did native quail ZPC, and none of the donor-derived ZPC was found in the duails. These findings suggest that it would be difficult to obtain donor-derived offspring by natural mating of interspecies chimeras.

Production of offspring from cryopreserved chicken testicular tissue

Cryopreservation of avian germplasm provides a means of genetic banking for future needs in biological research and animal production. The sperm of birds can be cryopreserved and used to fertilize eggs. However, the fertility of frozen-thawed avian semen is generally much lower than that of mammalian semen and varies among species or among lines, reducing the value of semen for the preservation of genetic resources. In the present study, a simple freezing protocol was used to cryopreserve testicular tissue of day-old chicks, and after subsequent transplantation, the frozen-thawed testicular tissue developed functional seminiferous tubules that produced sufficient sperm to fertilize eggs, resulting in donor-derived offspring. This study provides an alternative to semen cryopreservation for storage of the male germline in birds.

Heterotopic Transplantation of Testes in Newly Hatched Chickens and Subsequent Production of Offspring via Intramagnal Insemination1

Transplantation of testicular tissue onto the back of immunodeficient nude mice provides a tool to examine testicular development and preserve fertility in mammals. There is no immunodeficient model in birds, but we recently transplanted ovarian tissue between newly hatched chicks from two lines of chickens and produced donor-derived offspring, showing that experimental transplantation is possible in newly hatched chicks. In the present study testicular tissue from newly hatched Barred Plymouth Rock (BPR) chicks was transplanted under the skin of the back, under the skin of the abdomen, or in the abdomen of White Leghorn chicks that had been surgically castrated and immunocompromised. Recipient birds were killed at 10 mo of age. Transplanted tissue was observed in one of five hosts receiving tissue under the skin of the back, two of five hosts receiving tissue under the skin of the abdomen, and three of five chicks with grafts inside the abdominal cavity. In recipients with no regeneration of host testes, testicular transplants grew to the size of normal testes, and histologic analysis showed active spermatogenesis. Subsequent collection of sperm from two successful transplants and surgical insemination of the sperm into the magna of the oviducts of BPR hens resulted in the production of 24 donor-derived chicks. These results demonstrate that the combination of testicular tissue transplantation with intramagnal insemination can produce viable, normal chicks, which could provide a simple approach for the recuperation of live offspring in avian species.

Production of Chick Germline Chimeras from Fluorescence-Activated Cell-Sorted Gonocytes

Modification of the chicken germline has been difficult, because it has been challenging to fractionate sufficient numbers of primordial germ cells for manipulation and implantation into developing embryos. A technique to enrich cell suspensions for primordial germ cells, using fluorescence-activated cell sorting (FACS), has recently been developed. The objective of the current study was to demonstrate that the FACS-enriched early embryonic gonocytes could fully participate in development of the germline. Therefore, cells were disassociated from stage 27 gonads, incubated with mouse anti-stage-specific embryonic antigen-1, which was detected with goat-antimouse IgM-fluorescein isothiocyanate, and the fluorescently labeled cells were sorted from the unlabeled cells using FACS. The isolated gonocyte population was injected into the blastoderm of unincubated stage X embryos, the germinal crescent of 3-d embryos, and into the circulation of stage 17 embryos that were pretreated with busulfan. Barred Plymouth Rock gonocytes were implanted exclusively into recipient White Leghorn embryos, and White Leghorn gonocytes were implanted exclusively into Barred Plymouth Rock recipient embryos. Embryos were cultured until hatch, and male putative chimeras were reared to sexual maturity. Germline chimerism was evaluated by observing feather color of the progeny. All injection methods resulted in germline chimeras demonstrating that FACS-sorted gonocytes can fully participate in development. Moreover, it was demonstrated that gonocytes isolated from stage 27 embryonic gonads can be introduced into embryos at an earlier stage of development, and the introduced gonocytes can fully participate in germline development.

Restoration of spermatogenesis and male fertility by transplantation of dispersed testicular cells in the chicken

Transplantation of male germ cells into sterilized recipients has been widely used in mammals for conventional breeding and transgenesis purposes. This study presents a workable approach for germ cell transplantation between male chickens. Testicular cells from adult and prepubertal donors were dispersed and transplanted by injection directly into the testes of recipient males sterilized by repeated gamma irradiation. We describe the repopulation of the recipient seminiferous epithelium up to the production of heterologous sperm in about 50% of transplanted males. In comparison to males transplanted with testicular cell preparations from adult donors, in which the first ejaculates with sperm were recovered about 5 wk after transfer, a substantial interval (about 10 wk) was necessary to obtain ejaculates after the transfer of testicular cells from prepubertal donors. However, in both cases, recipient males produced ejaculates capable of fertilizing ova and producing progeny expressing donor genes.

Animal Genetic Resources Conservation in the Netherlands and Europe: Poultry Perspective

Increased global use of highly productive breeds of farm animals has been coupled to loss of genetic diversity in most species. In European countries, various governmental, non-governmental, and private organizations try to preserve genetic diversity of livestock in situ (e.g., by stimulating the use of indigenous, rare breeds by farmers; in nature reserves; or in noncommercial farms). In the case of poultry, maintaining in situ populations of the noncommercial (fancy) breeds largely relies on hobby farmers. In addition to in situ conservation, gene banks are being established for ex situ conservation. In at least 2 countries, France and The Netherlands, there are limited collections of frozen semen of rare poultry breeds. Since 2003, the CGN has started with a more systematic effort to collect, freeze, and store semen of indigenous Dutch poultry breeds. At present, the CGN gene bank contains semen of 11 Dutch rare poultry breeds. Also, CGN has performed research on the methodology for cryopreservation of fowl semen. This recent work was focused on finding a suitable replacement for glycerol, which is contraceptive in the hen, as a cryoprotectant. For reasons of hygiene and sample identification, we favored straw freezing, as opposed to the highly effective pellet freezing method. A significant interaction was found between cooling rate and cryoprotectant concentration. Best post-thaw sperm quality was obtained when combining 0.6 mol of dimethylacetamide/L with a cooling rate of +/- 200 degrees C/min. Inseminations twice per week with 0.3 billion sperm per insemination resulted in 97 and 88% fertilized eggs with fresh and frozen semen, respectively. In 2005, CGN has used this straw freezing method to extend the collection of poultry semen in the Dutch gene bank.

Avian Germplasm Preservation: Embryonic Stem Cells or Primordial Germ Cells?

Presently, avian genetic resources are best maintained as living collections of birds. Unfortunately, these stocks have been under constant pressure to be destroyed because of the decline in the number of Poultry Science Departments and pressures to cut costs at land grant institutions. Cryopreservation of semen is often suggested as a means to bank avian germplasm. However, this is only applicable for single-gene traits and does not allow for full reconstitution of the genetics of the original line. Over the last 15 yr, advances in the manipulation of the early chick embryo, manipulation of primordial germ cells (PGC), and the culture of embryonic stem cells (ESC) suggests that cryopreservation of blastodermal cells, ESC, or PGC might offer a means to preserve the entire genome of highly selected, specialized stocks of poultry. Freezing each of these cell types is possible with varying degrees of efficiency. Similarly, the effectiveness of generating germ line chimeras using blastodermal cells, ESC, or PGC also varies greatly. Other factors that must be considered include the choice of the recipient lines to develop the germ line chimeras and the number of individuals needed to reconstitute the line. Finally, the low efficiency rate of reconstitution and the high cost associated with current technologies makes these approaches prohibitive. Significant challenges remain to be overcome before the entire genome of poultry stocks can be routinely cryoperserved and reconstituted.

Effects of 2,2',5,5'-tetrachlorobiphenyl (PCB52) on migration of chicken primordial germ cells

Polychlorinated biphenyls cause developmental and physiological anomalies in the reproductive system. This study investigated the effects of 2,22,5,52-tetrachlorobiphenyl (PCB52), which can produce oestrogenic effects on the homeostasis of chicken primordial germ cells from the initial stage until completion of their settlement in the gonadal primordium. The blastoderm of chicken embryos was injected with 1 (1/4)L PCB52 (10 micromol/L) and oestradiol (100 micromol/L) before incubation, and the number of primordial germ cells was determined during their migration and development. The number of primordial germ cells in germinal crescents in PCB52-treated groups was slightly decreased (P = 0.068), but it was reduced significantly at stages 13-15 and 28-30 (P < 0.01, respectively) compared with controls. No obvious effects on primordial germ cell migration were observed with oestradiol treatments. The present results suggest that the influence of PCB52 on chicken primordial germ cell migration and proliferation may be via its toxic effect, not its oestrogen-mimicking effect, and provide information on the sensitivity of primordial germ cells to the direct action of PCB52.