Production of quail-chick chimaeras by blastoderm cell transfer

Generation of transgenic chickens by the non-viral, cell-based method: effectiveness of some elements of this strategy

Transgenic chickens have, in general, been produced by two different procedures. The first procedure is based on viral transfection systems. The second procedure, the non-viral method, is based on genetically modified embryonic cells transferred directly into the recipient embryo. In this review, we analyzed the effectiveness of important elements of the non-viral, cell-based strategy of transgenic chicken production. The main elements of this strategy are: isolation and cultivation of donor embryonic cells; transgene construction; cell transfection in vitro; and chimera production: injection of cells into recipient embryos, raising and identification of germline chimeras, mating germline chimeras, transgene inheritance, and transgene expression. In this overview, recent progress and important limitations in the development of transgenic chickens are presented.

Production of chimeras between the Chinese soft-shelled turtle and Peking duck through transfer of early blastoderm cells

Chimeras are useful models for studies of developmental biology and cell differentiation. Intraspecies and interspecies germline chimeras have been produced in previous studies, but the feasibility of producing chimeras between animals of two different classes remains unclear. To address this issue, we attempted to produce chimeras between the Chinese soft-shelled turtle and the Peking duck by transferring stage X blastoderm cells to recipient embryos. We then examined the survival and development of the PKH26-labeled donor cells in the heterologous embryos. At early embryonic stages, both turtle and duck donor cells that were labeled with PKH26 were readily observed in the brain, neural tube, heart and gonads of the respective recipient embryos. Movement of turtle donor-derived cells was observed in the duck host embryos after 48 h of incubation. Although none of the hatchlings presented a chimeric phenotype, duck donor-derived cells were detected in a variety of organs in the hatchling turtles, particularly in the gonads. Moreover, in the hatched turtles, mRNA expression of tissue-specific duck genes MEF2a and MEF2c was detected in many tissues, including the muscle, heart, small and large intestines, stomach and kidney. Similarly, SPAG6 mRNA was detected in a subset of turtle tissues, including the gonad and the small and large intestines. These results suggest that duck donor-derived cells can survive and differentiate in recipient turtles; however, no turtle-derived cells were detected in the hatched ducks. Our findings indicate that chimeras can be produced between animals of two different classes.

Contribution of cells derived from the area pellucida to extraembryonic mesodermal cell lineages in heterospecific quail chick blastodermal chimeras

The current study has two main objectives: first, to determine if cells derived from the area pellucida are able to populate extraembryonic membranes, and second, to determine if donor cells have the potential to differentiate to endothelial (EC) and hematopoietic cells (HC) in the yolk sac and allantois, the two extraembryonic membranes functioning as hematopoietic organs in the avian embryo. To this end, quail chick chimeras were constructed by transferring dissociated cells from the areae pellucidae of the stage X-XII (EG&K) quail embryo into the subgerminal cavity of the unincubated chick blastoderm. The distribution of quail cells in the allantois, yolk sac, amnion, and chorion of resulting putative chimeras was examined using quail cell-specific antibody against a perinuclear antigen (QCPN) after 6 days of incubation. The presence of EC, HC, and smooth muscle cells among the QCPN(+) donor cells was examined using QH-1, a quail-specific marker identifying HC and EC and an anti-α-smooth muscle actin antibody. Evidence gathered in the present study demonstrates that quail cells derived from the areae pellucidae are able to populate all of the extraembryonic membranes of resulting heterospecific quail chick chimeras and, most importantly, give rise to HC, EC, and smooth muscle cells, all of the three main mesodermal lineages derived from the posterior mesoderm both in the yolk sac and allantois.

Tissue distribution of cells derived from the area opaca in heterospecific quail-chick blastodermal chimeras

The objective of the current study was to determine the tissue distribution of cells derived from the area opaca in heterospecific quail-chick blastodermal chimeras. Quail-chick chimeras were constructed by transferring dissociated cells from the area opaca of the stage X-XII (EG&K) quail embryo into the subgerminal cavity of the unincubated chick blastoderm. The distribution of quail cells in embryonic as well as extra-embryonic tissues of the recipient embryo were examined using the QCPN monoclonal antibody after 6 days of incubation in serial sections taken at 100-mum intervals. Data gathered in the present study demonstrated that, when introduced into the subgerminal cavity of a recipient embryo, cells of the area opaca are able to populate not only extra-embryonic structures such as the amnion and the yolk sac, but also various embryonic tissues derived from the ectoderm and less frequently the mesoderm. Ectodermal chimerism was confined mainly to the head region and was observed in tissues derived from the neural ectoderm and the surface ectoderm, including the optic cup, diencephalon and lens. Although the possibility of random incorporation of transplanted cells into these embryonic structures cannot be excluded, these results would suggest that area opaca, a peripheral ring of cells in the avian embryo destined to form the extra-embryonic ectoderm and endoderm of the yolk sac, might harbor cells that have the potential to give rise to various cell types in the recipient chick embryo, including those derived from the surface ectoderm and neural ectoderm.

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 duck-chicken chimeras by transferring early blastodermal cells

Duck blastodermal cells isolated from Stage X embryos of Maya ducks were injected into subgerminal cavity of recipient Stage X chicken embryos treated with gamma-irradiation or untreated. Eleven somatic chimeras were obtained based on plumage color and were raised to sexual maturity. To test for germline chimerism, progeny tests were performed by mating the chimeras with Maya ducks. A total of 622 eggs was collected and incubated. Fertility rate and hatchability were 2.9% (18/622) and 1.0% (6/622), respectively. The six duck hatchlings were from Chimera 9801 and were considered to be derived from the germ cells developed from the donor Maya blastodermal cells, indicating that Chimera 9801 is a germline chimera.

Reconstitution of a chicken breed by inter se mating of germline chimeric birds

Blastoderm cells from chicken embryos of a donor breed (Green-legged Partridgelike; GP) were transferred to embryos of a recipient breed (White Leghorn; WL) to form chimeric progeny that, after inter se mating, permitted successful reconstitution of the donor breed. Among 23 chimeric chicks hatched from WL embryos injected with GP cells, 20 (87%) were raised until maturity, and progeny were tested by mating with GP birds to determine the ability of blastodermal cells to form germline chimeras. Six of the tested birds (30%) produced recipient-derived and donor-derived offspring, indicating that they were germline chimeras. The mean percentages of donor-derived germ cells in these birds were 21.1 (17.6 to 50.0%) and 16.9 (5.3 to 23.1%) in males and females, respectively. Among 477 chicks, resulting from mating the germline chimeric male with four germline chimeric females, 10 chicks (2.1%) exhibited a GP phenotype, indicating that the original donor stock had been reconstituted. Only one germline chimeric hen produced GP offspring, but the expected and calculated percentages of GP offspring were similar (2.99 and 2.08, respectively). Two methods of DNA analyses (RFLP and PCR amplification of polymorphic microsatellite loci) of chimeras and their offspring indicated that through mating of a relatively small number of chimeras it is possible to reconstitute a highly diverse population.

Improvement of hatchability of chicken eggs injected by blastoderm cells

In our first experiment, we studied the effect of injection method of blastoderm cells (BC) into the subgerminal cavity of White Leghorn embryos on hatchability of chicken chimeras. Freshly laid eggs were injected through a hole made in the equatorial plane of the eggshell (Method A). In Method B, eggs were stored pointed end down for 5 to 7 d prior to injection, and a hole was cut in the blunt end of the eggshell. An advantage of Method B was that the early embryonic mortality was reduced (P < or = 0.01) and resulted in higher hatchability (41.0%; 43/105) than Method A (9.8%; 14/143). In the second experiment, we studied chicken hatchabililty as influenced by windowing (no hole, Group 1; hole in the equatorial plane, Group 2; hole in the blunt end of egg, Groups 3 and 4) and egg turning (Groups 1 and 4) or not (Groups 2 and 3) during incubation. The hatchability percentages were as follows: 67.9 (Group 1) 0.0, (Group 2) 23.3, (Group 3), and 56.8 (Group 4). A statistically significant difference (P < or = 0.05) was noted between Group 1 or 4 and the other groups. We found no statistically significant differences in the weight changes (g) but did note certain differences in the egg weight loss (%) among different egg treatments. In the third experiment, we investigated the influence of origins of BC donors: Rhode Island Red (RIR), Barred Plymouth Rock (BPR), and Green-legged Partridgelike (GP) on hatchability of putative and somatic chimera chickens. The hatchability of chimeras was dependent on the adequate assortment of BC of the donor and ranged from 7.4% (RIR) to 56.1% (GP). In the case of BC injection of the GP breed, good hatchability was accompanied by very high percentage (86.9; 20/23) of somatic chimeras.

Improved hatching for in vitro quail embryo culture using surrogate eggshell and artificial vessel

The establishment of avian embryonic culture is important both for the analysis of the developmental process and the establishment of transgenic chickens that produce useful biological materials in eggs. However, the hatchability of cultured embryos has been approximately 50%. We identified that the low rate of hatchability of cultured embryos was caused by limited oxygen and calcium availability. In quail embryo culture using chicken eggshell as a culture vessel, viability in the middle stage of culture was improved and 30% of embryos were hatched by oxygen enrichment. Furthermore, hatchability increased to 80% by supplementation with calcium lactate in addition to oxygen aeration. In the present study, a fully artificial vessel for quail embryo culture was designed using a gas-permeable Teflon membrane. By the addition of fine eggshell powder and calcium lactate, quail embryos grew and developed normally, and 43% of embryos hatched. Although the hatchability was lower than that of cultures using a surrogate eggshell, we achieved in hatching an avian embryo using a fully artificial vessel.

Improved transfection efficiency of chicken gonadal primordial germ cells for the production of transgenic poultry

Electroporation is a common method of DNA transfection for many types of eukaryotic cells, but has not been attempted in avian primordial germ cells (PGCs). DNA uptake in chicken primordial germ cells (PGCs) was tested using electroporation with and without dimethyl sulfoxide (DMSO). Gonadal tissue and chicken embryonic fibroblasts (CEFs) were isolated from 6-day-old embryos (stage 29), transfected with pCMV beta carrying the bacterial lacZ gene, and cultured for 24 h. Gonadal primordial germ cells (gPGCs) were purified from culture using a Ficoll gradient. The addition of DMSO significantly increased the transfection efficiency of gPGCs but had no effect on chicken embryonic fibroblasts. Electroporation of gPGCs resulted in an 80% transfection efficiency compared with about 17% observed with liposomes. Approximately 200 transfected gPGCs were injected into 2.5-day-old (stage 17) recipient embryos and the eggs were incubated for an additional 3.5 days, 7.5 days or to hatching. The exogenous gene was detectable in 100%, 67% and 41% of the 6-day-old (stage 29), 10-day-old (stage 36) recipient embryos and hatched chicks gonads, respectively. PCR analysis of DNA from the hatched chicks showed that exogenous lacZ DNA was detected only in the gonad and not the liver and heart. These results indicated that electroporation was a suitable means of transfecting avian gPCGs for the goal of producing transgenic poultry.

Donor primordial germ cell-derived offspring from recipient germline chimaeric chickens: absence of long-term immune rejection and effects on sex ratios

1. Germline chimaeric chickens were produced by the transfer of primordial germ cells, and the generation of donor-derived offspring was examined for a maximum of 146 weeks. 2. The frequencies of donor-derived offspring from the chimaeras were 47% to 97%, and no apparent changes in frequency were observed with increasing age during the test period. 3. Differentiation of donor primordial germ cells into functional gametes appeared to be restricted to a degree at some developmental stage in the gonads of chimaeric chickens of the opposite sex.

The origin of the avian germ line and transgenesis in birds

The origin of the germ cell lineage in vertebrates is a fundamental question that has preoccupied developmental biologists. Recent work on the origin of the avian germ line has extended and clarified our understanding of the temporal and spatial segregation of primordial germ cells (PGC) during prestreak stages of development. The germ cells first appear at Stage X (Eyal-Giladi and Kochav, 1976) in the ventral surface of the area pellucida in a scattered pattern among polyingressing cells. Subsequently, the PGC gradually translocate from the epiblast to the hypoblast. The entire process appears to be dependent upon the maintenance of an organized area pellucida. Little is known about the regulatory events governing germ cell emergence during this period; however, the culture of dispersed blastodermal cells on a mouse fibroblast feeder layer can compensate for a disorganized area pellucida and offers an in vitro system to examine the molecular basis of germ cell development. Such basic information is valuable for current approaches towards the production of transgenic poultry with targeted changes to the genome through the use of avian embryonic stem cells or primordial germ cells. Refinement of the culture of primordial germ cells or their precursors should allow academic and industrial research laboratories to answer significant biological questions and to improve the genetic potential of commercial poultry stocks. A better understanding of the biology of avian primordial germ cells during early embryo development can only enhance this process.

Somatic and germline chicken chimeras obtained from brown and white Leghorns by transfer of early blastodermal cells

Stage X blastodermal cells were isolated from freshly laid unincubated Brown Leghorn chicken eggs. Five hundred cells from Stage X Brown Leghorn embryos were injected into the subgerminal cavity of White Leghorn unincubated embryos exposed to 550 rad of gamma irradiation from a cesium-137 source. Of 712 White Leghorn embryos that were irradiated and injected with Brown Leghorn blastodermal cells, 52 (7.3%) survived to hatching. Somatic chimerism was examined in the melanocyte population and erythroid lineage. The presence of brown feathers indicating donor cell contribution to melanocyte pigmentation was observed in 23 (44%) out of the 52 hatched chicks. Analysis of blood DNA was performed using a probe that revealed an endogenous retroviral gag fragment specific for the donor genome. Three out of these 23 chimeric chickens exhibited the gag-specific fragment. To test germline chimerism, chickens that reached sexual maturity were mated with Brown Leghorns. Three somatically chimeric hens produced Brown Leghorn progeny at a rate of 30.7, 9.2, and 2.9% respectively, thus proving donor cell contribution to the germline differentiation. Chimeric chickens obtained after injection of nonirradiated embryos exhibited a lower extent of chimerism at the feather level and did not show any chimerism in the erythroid lineage and the germline, thus demonstrating the value of the use of compromised recipient embryos to produce chimeras in chickens. Nevertheless, the extent of somatic chimerism could not be used to predict the germline chimerism.

Production of germline chimeric chickens, with high transmission rate of donor-derived gametes, produced by transfer of primordial germ cells

Germline chimeric chickens were produced by transfer of primordial germ cells from White Leghorn to Barred Plymouth Rock, and vice versa. Blood was collected from stage 13-15 embryos and primordial germ cells were concentrated by Ficoll density gradient centrifugation. Approximately 200 primordial germ cells were injected into the bloodstream through the dorsal aorta of stage 14-15 recipient embryos from which blood had been drawn via the dorsal aorta prior to the injection. Intact embryos were also prepared as recipients for White Leghorns only. The manipulated embryos were cultured in recipient eggshells until hatching. Germline chimerism of the chickens reaching maturity was examined by mating them with Barred Plymouth Rocks and donor-derived offspring were identified based on their feather color. The efficiency of production of germline chimeras was 95% (19/20). When primordial germ cells were transferred from White Leghorn to Barred Plymouth Rock, the average frequency of donor-derived offspring was 81% for three male chimeras (96% for one female chimera), and it was approximately 3.5 times higher for transfer in the opposite direction (23% for 6 male chimeras). Removing blood from recipient embryos prior to primordial germ cell injection enhanced the frequency of donor-derived offspring by 10% in resulting male chimeras. Male chimeras produced donor-derived offspring more frequently (approximately 3.8 times) than female chimeras. Increases, decreases, or no changes were observed in the frequency of donor-derived offspring from the germline chimeras with increasing age.(ABSTRACT TRUNCATED AT 250 WORDS)

Transgenesis in chickens

The application of transgenic technology to domestic poultry offers an alternative means to conventional practice for improvement of this highly productive agricultural species. The hen's reproductive system has unique characteristics which have imposed limitations on the use of established methods for artificial gene transfer. In this article, we review the various strategies that have been adopted to overcome the problem. Target sites for gene insertion include the fertilized ovum, the blastodermal embryo in the unincubated egg, and the primordial germ cells. Notable success in obtaining somatic and germline transformation has been achieved with the use of retroviral vectors to infect the blastodermal embryo. Current attempts to introduce DNA directly into the genome, without resort to pathogen-derived vectors, are discussed.

Early development of the chick embryo

The ultrastructure of the early chick embryo was investigated, using scanning (SEM) and transmission electron microscopy (TEM). Eggs were obtained from the shell gland by injecting hens intravenously with a synthetic prostaglandin or arginine vasopressin. Embryos were examined during late cleavage (stages IV-VI, Eyal-Giladi and Kochav, '76), formation of the area pellucida (stages VII-XI), and formation of the hypoblast (stages X-XIV). SEM highlighted the reduction in cell number at the underside of the embryo during formation of the area pellucida although it became apparent that the thickness of the embryo is not reduced to a single layer of cells at stage X. In addition, blastomeres at the perimeter of embryos (stages V-VI) project filopodial extensions onto a smooth membrane that separates the sub-embryonic cavity from the yolk. During hypoblast formation, epiblast cells generate stellate projections at their basal aspect, thus providing a meshwork for the advancing secondary hypoblast cells. By stage XII the epiblast was one cell thick and reminiscent of a columnar epithelium when viewed transversely. Cells of the deep portion of the posterior marginal zone were distinguished morphologically in the stage XII embryo by their many cell surface projections and ruffled appearance. Blastomeres at the perimeter of stage V-VI embryos projected filopodial extensions onto a smooth membrane which separates the sub-embryonic cavity from the yolk. This membrane is presumed to be confluent with the cytolemma. Evidence is presented demonstrating the presence of intracellular membrane-bound droplets which are hypothesised to contain sub-embryonic fluid.

Germline chimeric chickens from dispersed donor blastodermal cells and compromised recipient embryos

Stage-X blastoderms, within intact eggs from White Leghorn hens, were exposed to 500–700 rads of gamma radiation from a 60Co source prior to injection, into the subgerminal cavity, of approximately 100 or 200–400 dispersed cells from stage-X blastoderms isolated from eggs laid by Barred Plymouth Rock hens. Embryos developing past day 14 of incubation and hatched chicks were assessed for donor and recipient cell contribution to the melanocyte population through examination of black and yellow down pigmentation, respectively (Barred Plymouth Rocks have a recessive allele at the I locus while the White Leghorns have a dominant allele at the I locus). Of the 809 embryos injected with approximately 100 cells, 192 developed past day 14 and black pigmentation, indicating somatic chimerism, was observed on 118 of the 192 (58%) embryos and chicks. Of the 296 embryos injected with 200–400 donor cells, 86 developed past day 14 of incubation. Somatic chimerism was observed on 55 of the 86 (64%) embryos and chicks. To test for germline chimerism, birds surviving to maturity were mated to Barred Plymouth Rocks. Five somatically chimeric females were produced when approximately 100 cells were injected, and one was a germline chimera. Six somatic female chimeras were produced following the injection of 200–400 cells, three of which proved to be germline chimeras by the presence of Barred Rock chicks among their offspring. Two of the nine males produced by injecting approximately 100 cells were germline chimeras.(ABSTRACT TRUNCATED AT 250 WORDS)

Preservation of quail blastoderm cells in liquid nitrogen

1. Quail blastoderm cells isolated from the yolk were preserved in liquid nitrogen. 2. Frozen-thawed blastoderm cells of the quail were viable and survived in vitro. By injecting the frozen-thawed cells into chick embryos, quail-chick chimaeras were produced.

Developmental ability of twin embryos produced by microinjection treatment into chick blastoderm

Twins and triplets of chick embryos were produced by microinjection treatment of cell suspension into the blastoderm. One pair of the twin embryos had an ability to develop normally and survived up to Day 21 of incubation, but did not hatch. The other twins and triplets died within 7 days.