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.

Production of chicken progeny (Gallus gallus domesticus) from interspecies germline chimeric duck (Anas domesticus) by primordial germ cell transfer.

The present study aimed to investigate the differentiation of chicken (Gallus gallus domesticus) primordial germ cells (PGCs) in duck (Anas domesticus) gonads. Chimeric ducks were produced by transferring chicken PGCs into duck embryos. Transfer of 200 and 400 PGCs resulted in the detection of a total number of 63.0 ± 54.3 and 116.8 ± 47.1 chicken PGCs in the gonads of 7-day-old duck embryos, respectively. The chimeric rate of ducks prior to hatching was 52.9% and 90.9%, respectively. Chicken germ cells were assessed in the gonad of chimeric ducks with chicken-specific DNA probes. Chicken spermatogonia were detected in the seminiferous tubules of duck testis. Chicken oogonia, primitive and primary follicles, and chicken-derived oocytes were also found in the ovaries of chimeric ducks, indicating that chicken PGCs are able to migrate, proliferate, and differentiate in duck ovaries and participate in the progression of duck ovarian folliculogenesis. Chicken DNA was detected using PCR from the semen of chimeric ducks. A total number of 1057 chicken eggs were laid by Barred Rock hens after they were inseminated with chimeric duck semen, of which four chicken offspring hatched and one chicken embryo did not hatch. Female chimeric ducks were inseminated with chicken semen; however, no fertile eggs were obtained. In conclusion, these results demonstrated that chicken PGCs could interact with duck germinal epithelium and complete spermatogenesis and eventually give rise to functional sperm. The PGC-mediated germline chimera technology may provide a novel system for conserving endangered avian species.

Primordial germ cell-mediated chimera technology produces viable pure-line Houbara bustard offspring: potential for repopulating an endangered species.

BACKGROUND: The Houbara bustard (Chlamydotis undulata) is a wild seasonal breeding bird populating arid sandy semi-desert habitats in North Africa and the Middle East. Its population has declined drastically during the last two decades and it is classified as vulnerable. Captive breeding programmes have, hitherto, been unsuccessful in reviving population numbers and thus radical technological solutions are essential for the long term survival of this species. The purpose of this study was to investigate the use of primordial germ cell-mediated chimera technology to produce viable Houbara bustard offspring. METHODOLOGY/PRINCIPAL FINDINGS: Embryonic gonadal tissue was dissected from Houbara bustard embryos at eight days post-incubation. Subsequently, Houbara tissue containing gonadal primordial germ cells (gPGCs) was injected into White Leghorn chicken (Gallus gallus domesticus) embryos, producing 83/138 surviving male chimeric embryos, of which 35 chimeric roosters reached sexual maturity after 5 months. The incorporation and differentiation of Houbara gPGCs in chimeric chicken testis were assessed by PCR with Houbara-specific primers and 31.3% (5/16) gonads collected from the injected chicken embryos showed the presence of donor Houbara cells. A total of 302 semen samples from 34 chimeric roosters were analyzed and eight were confirmed as germline chimeras. Semen samples from these eight roosters were used to artificially inseminate three female Houbara bustards. Subsequently, 45 Houbara eggs were obtained and incubated, two of which were fertile. One egg hatched as a male live born Houbara; the other was female but died before hatching. Genotyping confirmed that the male chick was a pure-line Houbara derived from a chimeric rooster. CONCLUSION: This study demonstrates for the first time that Houbara gPGCs can migrate, differentiate and eventually give rise to functional sperm in the chimeric chicken testis. This approach may provide a promising tool for propagation and conservation of endangered avian species that cannot breed in captivity.