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

Major Histocompatibility Complex-B haplotype and ovarian graft response

Gonadal tissue transfer is considered one of the best methods to preserve genetic variability. Poultry hosts can receive a gonad from a donor of a different genetic background, sustain the growth of this graft, and produce gametes from it. Unfortunately, the host's strong immune response may significantly reduce the gonadal graft's ability to reach maturity. Our study aimed to evaluate the influence of MHC-B alleles in rejecting a gonadal graft of similar or different genetic backgrounds. In the first experiment, ovarian tissue was transplanted to chicks of similar genetic backgrounds, either Lohmann White (LW) with variable MHC-B or Barred Rock (BR) with fixed MHC-B. The sustained growth of donor ovarian tissues occurred in (4/7 hosts) BR (MHC-B matched) hosts only-one of these graft-positive-BR hens produced eggs derived from the donor ovary. No grafts were recovered when the host and the donor had an LW background (0/9; MHC-B mismatched). In the second experiment, ovarian transplantation was done between chicks of either similar or different genetic backgrounds (Brown Leghorn [BL], BR, and BL/BR F1). The 2 pure lines contained only one MHC-B allele, whereas the F1 heterozygotes had both. All host birds were given a daily dose of an immunosuppressant (mycophenolate mofetil) until maturity. The success rate was assessed by microsatellite genotype confirmation of donor-derived ovaries plus physiological and histological analyses of ovarian grafts. In this second experiment, 11 out of 43 ovarian hosts laid eggs. However, all fertilized eggs from these hens were derived from the remnant host ovarian tissue, not from the donor ovaries. A necropsy assessment was done on all 43 host birds. Ten donor grafts were recovered from hosts having matched (6 hosts) and mismatched (4 hosts) MHC-B, and none were functional. Interestingly, 6 of them were enclosed by a serous membrane capsule filled with fluid and had various tissue growth. In addition, clusters of immune cells were observed in all recovered donor grafts. Our results demonstrated that genetic background could greatly influence the success of gonadal transfer in chickens.

Male Gonads Transplantation from Kadaknath Chicken to Chicken and Duck Surrogates

Transplantation of the gonadal tissue of male and female avian species, such as chicken, onto suitable surrogates and production of live offspring has been successfully demonstrated as a strategy for the conservation and re-constitution of valuable chicken germplasm. The main objective of this study was to establish and develop the male gonadal tissue transplantation technology for the conservation of the indigenous chicken germplasm. The male gonads of the Indian native chicken breed, Kadaknath (KN), were transplanted from a day-old donor to a recipient white leghorn (WL) chicken, and Khaki Campbell (KC) ducks, as surrogates. All the surgical interventions were performed under permitted general anaesthesia, and the chicks, upon recovery, were reared with and without immunosuppressant. The recipient surrogates for the donor KN gonads were housed and reared for 10-14 weeks, and post-sacrifice, developed gonadal tissues were harvested to squeeze out the fluid to perform artificial insemination (AI). The AI-entailed fertility test using the recovered seminal extract from the transplanted KN testes from both surrogate species (KC ducks and WL males), used against KN purebred females, remained very close to the percent fertility realised from purebred KN chickens (controls). These initial results revealed from this trial study suggest definitively that, Kadaknath male gonads were readily accepted and grown inside the intra- and inter-species surrogate host, WL chicken and KC ducks, demonstrating a suitable intra- and inter-species donor-host system. Furthermore, the developed transplanted male gonads of KN chicken into the surrogates were found to have the potential to fertilise the egg and give rise to pure-line KN chicks.

Poultry genetic heritage cryopreservation and reconstruction: advancement and future challenges

Poultry genetics resources, including commercial selected lines, indigenous breeds, and experimental lines, are now being irreversibly lost at an alarming rate due to multiple reasons, which further threats the future livelihood and academic purpose. Collections of germplasm may reduce the risk of catastrophic loss of genetic diversity by guaranteeing that a pool of genetic variability is available to ensure the reintroduction and replenishment of the genetic stocks. The setting up of biobanks for poultry is challenging because the high sensitiveness of spermatozoa to freezing–thawing process, inability to cryopreserve the egg or embryo, coupled with the females being heterogametic sex. The progress in cryobiology and biotechnologies have made possible the extension of the range of germplasm for poultry species available in cryobanks, including semen, primordial germ cells, somatic cells and gonads. In this review, we introduce the state-of-the-art technologies for avian genetic resource conservation and breed reconstruction, and discuss the potential challenges for future study and further extending of these technologies to ongoing and future conservation efforts.

Animal board invited review: Germplasm technologies for use with poultry

Over the last century, several reproductive biotechnologies beyond the artificial incubation of eggs were developed to improve poultry breeding stocks and conserve their genetic diversity. These include artificial insemination (AI), semen storage, diploid primordial germ cell (PGC) methodologies, and gonad tissue storage and transplantation. Currently, AI is widely used for selection purposes in the poultry industry, in the breeding of turkeys and guinea fowl, and to solve fertility problems in duck interspecies crosses for the production of mule ducklings. The decline in some wild game species has also raised interest in reproductive technologies as a means of increasing the production of fertile eggs, and ultimately the number of birds that can be raised. AI requires viable sperm to be preserved in vitro for either short (fresh) or longer periods (chilling or freezing). Since spermatozoa are the most easily accessed sex cells, they are the cell type most commonly preserved by genetic resource banks. However, the cryopreservation of sperm only preserves half of the genome, and it cannot preserve the W chromosome. For avian species, the problem of preserving oocytes and zygotes may be solved via the cryopreservation and transplantation of PGCs and gonad tissue. The present review describes all these procedures and discusses how combining these different technologies allows poultry populations to be conserved and even rapidly reconstituted.

Improvement of the application of gonadal tissue allotransplantation in the in vitro conservation of chicken genetic lines

In avian species, the surgical technique for ovarian allotransplantation has been developed for domestic chickens; however, not all genotypes can be effectively used as recipients. The aims of the present study were to ascertain donor/recipient combinations for production of offspring from frozen/thawed ovarian tissues. The development of the technique is important because domestic chicken offspring have only been produced from fresh (never frozen) ovarian and from frozen-thawed testicular tissues. Information obtained from evaluating genetic differences of intensively selected lines in which there was successful pairing was compared in the indigenous breeds. Results indicate donor/recipient combinations were created which could be effectively used for gonadal tissue allotransplantations. Gonadal tissues of Yellow, Speckled and Partridge-color Hungarian, Black and Speckled Transylvanian Naked Neck chicken breeds were allotransplanted into White Leghorn or Novogen White breeds for offspring production. The gonadal tissues of these indigenous breeds were cryopreserved using vitrification procedures. There was successful allografting of frozen/thawed gonadal tissues at a rate between 20 % and 100 % depending on the genotype and sex, and histological examination and microsatellite marker analysis provided evidence that the donor ovarian and testicular tissues had the capacity for producing gametes. The hens of Speckled Transylvanian Naked Neck/White Leghorn combination using frozen/thawed ovarian tissues were produced for progeny tests. Of these, 58 % produced eggs and 9.1 % produced donor-derived offspring, based on data for both feather color markers and genetic analysis.

Biobanking Genetic Material for Agricultural Animal Species

Biobanking animal germplasm and tissues is a major component of conserving genetic resources. Effectively constructing such gene banks requires an understanding and evaluation of genetic resources, the ability to conserve various tissues through cryopreservation, and a robust information technology infrastructure to allow managers and potential users to fully understand and make use of the collection. Progress has been made internationally in developing national genetic resource collections. As these collections have been developed, it has become apparent that gene banks can serve a multitude of roles, thereby serving short- and long-term needs of research communities and industry. This article documents the development of gene banks and provides examples of how they have been used to date and the extent to which they have captured genetic diversity for future use.

Characterization of the testicular regeneration potential in premature cockerels

Previous studies have shown that grafted neonatal chicken testicular tissue can develop and produce functional sperm; however, it was unclear whether regenerative processes or proportional growth caused the re-appearance of spermatogenic tissue. We dissociated testicular tissues, performed subcutaneous auto-transplantation of the re-aggregated cells to castrated cockerels, and monitored the post-surgery development of these transplanted aggregates. We found that these transplanted cell aggregates experienced compensatory growth in the form of a 300-fold increase in size, rather than the 30-fold increase observed in normal testis development. Further, these dissociated testicular cell aggregates restored seminiferous tubule structure and were able to produce testosterone and motile sperm. Therefore, we concluded that the dissociated testicular cells from 11-week-old cockerels retained a strong regenerative potential, as they exhibited compensatory growth, restored destroyed structure, and sustained spermatogenesis.

Development of heterotopic transplantation of the testis with the epididymis to evaluate an aspect of testicular immunology in rats

Transplantation of testicular cells and tissues has been studied for the investigation of immunology of the testis, which is an immunologically privileged organ. However, reports of transplant of the testis at organ level have been extremely limited because of technical difficulties of the orthotopic testis transplantation (OTT) in experimental animals. In the present study, we developed a new and simple model of the heterotopic testis transplantation (HTT), which is donor testis transplantation into the cervical region of recipients, in a syngeneic model in rats [donor Lewis (LEW) graft to LEW recipient]. The duration of HTT was significantly shorter and success rate higher than that of OTT. To histologically evaluate HTT, the local immune responses were compared among the syngeneic model, an acute rejection allogeneic model [donor Augustus Copenhagen Irish (ACI) graft to LEW recipient] and a chronic rejection allogeneic model (donor F344 graft to LEW recipient) at postoperative day 3. We found that allogeneic ACI grafts resulted in mild and not severe orchitic lesions, whereas immune responses of allogeneic F344 grafts seemed intact and were not significantly different from those of syngeneic LEW grafts. These results suggest that our new operative procedure will be useful in future for the investigation of the testicular immunology.

Avian Biotechnology

Primordial germ cells (PGCs) generate new individuals through differentiation, maturation and fertilization. This means that the manipulation of PGCs is directly linked to the manipulation of individuals, making PGCs attractive target cells in the animal biotechnology field. A unique biological property of avian PGCs is that they circulate temporarily in the vasculature during early development, and this allows us to access and manipulate avian germ lines. Following the development of a technique for transplantation, PGCs have become central to avian biotechnology, in contrast to the use of embryo manipulation and subsequent transfer to foster mothers, as in mammalian biotechnology. Today, avian PGC transplantation combined with recent advanced manipulation techniques, including cell purification, cryopreservation, depletion, and long-term culture in vitro, have enabled the establishment of genetically modified poultry lines and ex-situ conservation of poultry genetic resources. This chapter introduces the principles, history, and procedures of producing avian germline chimeras by transplantation of PGCs, and the current status of avian germline modification as well as germplasm cryopreservation. Other fundamental avian reproductive technologies are described, including artificial insemination and embryo culture, and perspectives of industrial applications in agriculture and pharmacy are considered, including poultry productivity improvement, egg modification, disease resistance impairment and poultry gene "pharming" as well as gene banking.

Cryopreservation and other assisted reproductive technologies for the conservation of threatened amphibians and reptiles: bringing the ARTs up to speed

Amphibians and reptiles are experiencing serious declines, with the number of threatened species and extinctions growing rapidly as the modern biodiversity crisis unfolds. For amphibians, the panzootic of chytridiomycosis is a major driver. For reptiles, habitat loss and harvesting from the wild are key threats. Cryopreservation and other assisted reproductive technologies (ARTs) could play a role in slowing the loss of amphibian and reptile biodiversity and managing threatened populations through genome storage and the production of live animals from stored material. These vertebrate classes are at different stages of development in cryopreservation and other ARTs, and each class faces different technical challenges arising from the separate evolutionary end-points of their reproductive biology. For amphibians, the generation of live offspring from cryopreserved spermatozoa has been achieved, but the cryopreservation of oocytes and embryos remains elusive. With reptiles, spermatozoa have been cryopreserved in a few species, but no offspring from cryopreserved spermatozoa have been reported, and the generation of live young from AI has only occurred in a small number of species. Cryopreservation and ARTs are more developed and advanced for amphibians than reptiles. Future work on both groups needs to concentrate on achieving proof of concept examples that demonstrate the use of genome storage and ARTs in successfully recovering threatened species to increase awareness and support for this approach to conservation.

Growth of subcutaneous chicken testicular transplants

Avian genetic resources have declined dramatically over the past half century, partly because the poultry community has been slow to adopt cryoconservation of avian germplasm. Techniques for gonadal cryopreservation and functional recovery have recently been developed but only some have been optimized. Chicks were castrated at 2 or 6 d and testicles were autotransplanted subcutaneously in one piece after disruption of the tunica membranes to optimize transplantation procedures without the complication of tissue rejection or immunosuppression. At 22 wk of age, the roosters were euthanized and growth of the testicular tissue was evaluated. Mortality with castration at 2 d was high but was much reduced with castration at 6 d. Transplantation of whole testicles subcutaneously on the back of chicks, without complete removal of the tunica membranes, yielded good growth of tissue with transplantation at 2 or 6 d of age. These results will contribute to the use of testicular cryopreservation and transplantation as an effective conservation strategy for avian germplasm. Further definition of the age of treatment will improve the overall efficiency.

Preliminary results of the application of gonadal tissue transfer in various chicken breeds in the poultry gene conservation

The aim of the study was to devise a technique to allow transfer of ovarian and testicular tissues obtained from one day old chicks to recipient animals. The following combinations of chicken breeds were used: Tetra SL/Tetra SL, Tetra SL/Harco, Tetra SL/Black Transylvanian Naked Neck, Godollo New Hampshire/Speckled Transylvanian Naked Neck (recipient/donor), respectively. Only animals less than 24h old from hatching were used as either recipient or donor. Eggs yielding recipients were treated with busulfan to hinder the development of the recipient's own gonads. Gonads were transferred surgically to the new host which was then immunosuppressed for two months. The animals were checked at 8 or 16 weeks for the existence of implanted gonads, and if found, the gonads were removed for histology examination. Tetra SL/Tetra SL pairing resulted in successfully adhered and functioning gonads in most cases. In other combinations, no gonads originating from the donors were found in the recipients. We conclude that not all breeds seem to be suitable recipients; some breeds or individuals may show incompatibility to each other and further examination is needed to find the cause of incompatibility and to establish a suitable breed combination, which can be used for gonad transfer.

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.

Production of live offspring from testicular tissue cryopreserved by vitrification procedures in Japanese quail (Coturnix japonica)

Cryopreservation of testicular tissue can be used for ex situ conservation of male germplasm of avian species. The possibility of using vitrification and transplantation of testicular tissue for fertility preservation and recovery was tested in Japanese quail. Testes were removed from 1-wk-old Japanese quail; transfixed on acupuncture needles; equilibrated with dimethyl sulphoxide, ethylene glycol, and sucrose; plunged into liquid nitrogen; and stored in 2-ml straws. Cryopreserved tissue was warmed in sucrose solution at room temperature or at 40°C. Fresh and cryopreserved tissue were transplanted subcutaneously into castrated, 1-wk-old recipients. Twenty of 21 recipients survived the surgery, and 18 had viable transplants at maturity, with no difference in transplantation success between fresh and cryopreserved tissue. Fluid extrusion from 11 of the transplants was collected and inseminated surgically into the magnum of 22 quail hens, and 10 inseminations included foam from the proctodeal gland of the same recipients. Egg production in the 2 wk after insemination was reduced, and none of the hens inseminated with foam produced fertile eggs. Five hens inseminated without foam produced a total of eight live offspring; four of these hens had been inseminated with fluid extrusion from cryopreserved tissue. Histological examination showed spermatogenesis in the transplants, and the tubules, lumens, and epithelium of the seminiferous tubules were of comparable size to those of testicular tissue from intact males. These results demonstrate that testicular tissue of Japanese quail can be preserved using vitrification procedures and recovered through transplantation.

Efficient system for preservation and regeneration of genetic resources in chicken: concurrent storage of primordial germ cells and live animals from early embryos of a rare indigenous fowl (Gifujidori)

The unique accessibility of chicken primordial germ cells (PGCs) during early development provides the opportunity to combine the reproduction of live animals with genetic conservation. Male and female Gifujidori fowl (GJ) PGCs were collected from the blood of early embryos, and cryopreserved in liquid nitrogen for >6 months until transfer. Manipulated GJ embryos were cultured until hatching; fertility tests indicated that they had normal reproductive abilities. Embryos from two lines of White Leghorn (24HS, ST) were used as recipients for chimera production following blood removal. The concentration of PGCs in the early embryonic blood of 24HS was significantly higher than in ST (P < 0.05). Frozen–thawed GJ PGCs were microinjected into the bloodstream of same-sex recipients. Offspring originating from GJ PGCs in ST recipients were obtained with a higher efficiency than those originating from GJ PGCs in 24HS recipients (23.3% v. 3.1%). Additionally, GJ progeny were successfully regenerated by crossing germline chimeras of the ST group. In conclusion, the cryogenic preservation of PGCs from early chicken embryos was combined with the conservation of live animals.

Inseminating fresh or cryopreserved semen for maximum efficiency: implications for gene banks and industry

Developing gene bank germplasm collections for animal genetic resources requires establishing germplasm collection goals, that consider capturing the genetic diversity of the population in question and the amount of germplasm required for its reconstitution or other purposes, or both. Computing collection goals for chickens is complicated, compared with mammalian species, due to the multiple chances a single insemination of semen has to fertilize an egg. To address this issue, fertility data were used in conjunction with econometric procedures for determining production efficiency and diminishing returns. Experimental treatments consisted of inseminating fresh semen intravaginally (FIV), frozen-thawed semen inseminated intramagnally (FTIM), and frozen-thawed semen inseminated intravaginally (FTIV). Analysis revealed that the maximum efficiency for a single insemination was at postinsemination d 6, 8, and 3 for FIV, FTIM, and FTIV, respectively. But, additional benefit from a single insemination can be garnered by continuing to collect and incubate eggs to d 11, 17, and 11 for FIV, FTIM, and FTIV, respectively. By extending the insemination interval, the number of fertile eggs can be increased by 62 (FIV), 62 (FTIM), and 48% (FTIV). The ramifications of these results are profound when placed in the context of germplasm collection for gene banks. By using the FTIM treatment, the number of germplasm samples needed to secure a chicken breed, at the 150% level, can be reduced from the FAO projection of 2,454 to 386 straws (0.5 mL). Such a change represents a substantial reduction in collection, processing, and storage costs for gene banks. For industry, the results suggest that extending the time interval between inseminations will yield more fertile eggs and create opportunities to increase the number of hens mated to a rooster.

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.