Differentiation of female chicken primordial germ cells into spermatozoa in male gonads

Avian Primordial Germ Cells Are Bipotent for Male or Female Gametogenesis

In birds, males are the homogametic sex (ZZ) and females are the heterogametic sex (ZW). Here, we investigate the role of chromosomal sex and germ cell competition on avian germ cell differentiation. We recently developed genetically sterile layer cockerels and hens for use as surrogate hosts for primordial germ cell (PGC) transplantation. Using in vitro propagated and cryopreserved PGCs from a pedigree Silkie broiler breed, we now demonstrate that sterile surrogate layer hosts injected with same sex PGCs have normal fertility and produced pure breed Silkie broiler offspring when directly mated to each other in Sire Dam Surrogate mating. We found that female sterile hosts carrying chromosomally male (ZZ) PGCs formed functional oocytes and eggs, which gave rise to 100% male offspring after fertilization. Unexpectedly, we also observed that chromosomally female (ZW) PGCs carried by male sterile hosts formed functional spermatozoa and produced viable offspring. These findings demonstrate that avian PGCs are not sexually restricted for functional gamete formation and provide new insights for the cryopreservation of poultry and other bird species using diploid stage germ cells.

Two Homogametic Genotypes - One Crayfish: On the Consequences of Intersexuality

In the Australian redclaw crayfish, Cherax quadricarinatus (WZ/ZZ system), intersexuals, although exhibiting both male and female gonopores, are functional males bearing a female genotype (WZ males). Therefore, the occurrence of the unusual homogametic WW females in nature is plausible. We developed W/Z genomic sex markers and used them to investigate the genotypic structure of experimental and native C. quadricarinatus populations in Australia. We discovered, for the first time, the natural occurrence of WW females in crustacean populations. By modeling population dynamics, we found that intersexuals contribute to the growth rate of crayfish populations in the short term. Given the vastly fragmented C. quadricarinatus habitat, which is characterized by drought-flood cycles, we speculate that intersexuals contribute to the fitness of this species since they lead to occasional increment in the population growth rate which potentially supports crayfish population restoration and establishment under extinction threats or colonization events.

Reviving rare chicken breeds using genetically engineered sterility in surrogate host birds

In macrolecithal species, cryopreservation of the oocyte and zygote is not possible due to the large size and quantity of lipid deposited within the egg. For birds, this signifies that cryopreserving and regenerating a species from frozen cellular material are currently technically unfeasible. Diploid primordial germ cells (PGCs) are a potential means to freeze down the entire genome and reconstitute an avian species from frozen material. Here, we examine the use of genetically engineered (GE) sterile female layer chicken as surrogate hosts for the transplantation of cryopreserved avian PGCs from rare heritage breeds of chicken. We first amplified PGC numbers in culture before cryopreservation and subsequent transplantation into host GE embryos. We found that all hatched offspring from the chimera GE hens were derived from the donor rare heritage breed broiler PGCs, and using cryopreserved semen, we were able to produce pure offspring. Measurement of the mutation rate of PGCs in culture revealed that 2.7 × 10^-10 de novo single-nucleotide variants (SNVs) were generated per cell division, which is comparable with other stem cell lineages. We also found that endogenous avian leukosis virus (ALV) retroviral insertions were not mobilized during in vitro propagation. Taken together, these results show that mutation rates are no higher than normal stem cells, essential if we are to conserve avian breeds. Thus, GE sterile avian surrogate hosts provide a viable platform to conserve and regenerate avian species using cryopreserved PGCs.

Avian Primordial Germ Cells

Germ cells transmit genetic information to the next generation through gametogenesis. Primordial germ cells (PGCs) are the first germ-cell population established during development, and are the common origins of both oocytes and spermatogonia. Unlike in other species, PGCs in birds undergo blood circulation to migrate toward the genital ridge, and are one of the major biological properties of avian PGCs. Germ cells enter meiosis and arrest at prophase I during embryogenesis in females, whereas in males they enter mitotic arrest during embryogenesis and enter meiosis only after birth. In chicken, gonadal sex differentiation occurs as early as embryonic day 6, but meiotic initiation of female germ cells starts from a relatively late stage (embryonic day 15.5). Retinoic acid controls meiotic entry in developing chicken gonads through the expressions of retinaldehyde dehydrogenase 2, a major retinoic acid synthesizing enzyme, and cytochrome P450 family 26, subfamily B member 1, a major retinoic acid-degrading enzyme. The other major biological property of avian PGCs is that they can be propagated in vitro for the long term, and this technique is useful for investigating proliferation mechanisms. The main factor involved in chicken PGC proliferation is fibroblast growth factor 2, which activates the signaling of MEK/ERK and thus promotes the cell cycle and anti-apoptosis. Furthermore, the activation of PI3K/Akt signaling is indispensable for the proliferation and survival of chicken PGCs.

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.

Poultry genetic resource conservation using primordial germ cells

The majority of poultry genetic resources are maintained in situ in living populations. However, in situ conservation of poultry genetic resources always carries the risk of loss owing to pathogen outbreaks, genetic problems, breeding cessation, or natural disasters. Cryobanking of germplasm in birds has been limited to the use of semen, preventing conservation of the W chromosome and mitochondrial DNA. A further challenge is posed by the structure of avian eggs, which restricts the cryopreservation of ova and fertilized embryos, a technique widely used for mammalian species. By using a unique biological property and accessibility of avian primordial germ cells (PGCs), precursor cells for gametes, which temporally circulate in the vasculature during early development, an avian PGC transplantation technique has been established. To date, several techniques for PGC manipulation including purification, cryopreservation, depletion, and long-term culture have been developed in chickens. PGC transplantation combined with recent advanced PGC manipulation techniques have enabled ex situ conservation of poultry genetic resources in their complete form. Here, the updated technologies for avian PGC manipulation are introduced, and then the concept of a poultry PGC-bank is proposed by considering the biological properties of avian PGCs.

Chicken stem cell factor enhances primordial germ cell proliferation cooperatively with fibroblast growth factor 2

An in vitro culture system of chicken primordial germ cells (PGCs) has been recently developed, but the growth factor involved in the proliferation of PGCs is largely unknown. In the present study, we investigated the growth effects of chicken stem cell factor (chSCF) on the in vitro proliferation of chicken PGCs. We established two feeder cell lines (buffalo rat liver cells; BRL cells) that stably express the putative secreted form of chSCF (chSCF1-BRL) and membrane bound form of chSCF (chSCF2-BRL). Cultured PGC lines were incubated on chSCF1 or chSCF2-BRL feeder cells with fibroblast growth factor 2 (FGF2), and growth effects of each chSCF isoform were investigated. The in vitro proliferation rate of the PGCs cultured on chSCF2-BRL at 20 days of culture was more than threefold higher than those cultured on chSCF1-BRL cells and more than fivefold higher than those cultured on normal BRL cells. Thus, use of chSCF2-BRL feeder layer was effective for in vitro proliferation of chicken PGCs. However, the acceleration of PGC proliferation on chSCF2-BRL was not observed without FGF2, suggesting that chSCF2 would act as a proliferation co-factor of FGF2. We transferred the PGCs cultured on chSCF2-BRL cells to recipient embryos, generated germline chimeric chickens and assessed the germline competency of cultured PGCs by progeny test. Donor-derived progenies were obtained, and the frequency of germline transmission was 3.39%. The results of this study demonstrate that chSCF2 induces hyperproliferation of chicken PGCs retaining germline competency in vitro in cooperation with FGF2.

Transfer and detection of freshly isolated or cultured chicken (Gallus gallus) and exotic species' embryonic gonadal germ stem cells in host embryos

The management of captive avian breeding programs increasingly utilizes various artificial reproductive technologies, including in ovo sexing of embryos to adjust population sex ratios. Currently, however, no attention has been given to the loss of genetic diversity following sex-selective incubation, even with respect to individuals from critically endangered species. This project evaluated the possibility of using xenotransfer of embryonic gonadal germline stem cells (GGCs) for future reintroduction of their germplasm into the gene pool. We examined and compared the host gonad colonization of freshly isolated and 3 day (3d) cultured donor GGCs from chicken and 13 species of exotic embryos. Following 3d-culture of GGCs, there was a significant increase in the percentage of stem cell marker (SSEA-1, -3, -4) positive cells. However, the percentage of positive host gonads with chicken donor-derived cells decreased from 68% (fresh) to 22% (3d), while the percentage of exotic species donor-cells positive host gonads decreased from 61% (fresh) to 49% (3d-cultured). Donor GGCs from both chicken and exotic species were localized within the caudal endoderm, including the region encompassing the gonadal ridge by 16 hours post-injection. Furthermore, donor-derived cells isolated from stage 36 host embryos were antigenic for anti SSEA-1, VASA/DDX4 and EMA-1 antibodies, presumably indicating maintenance of stem cell identity. This study demonstrates that GGCs from multiple species can migrate to the gonadal region and maintain presumed stemness following xenotransfer into a chicken host embryo, suggesting that germline stem cell migration is highly conserved in birds.

Transfer of blood containing primordial germ cells between chicken eggs development of embryonic reproductive tract

The present study was carried out to investigate development of recipient chicken embryonic reproductive tracts which are transferred chicken primordial germ cells (PGCs). It is thought that differentiation of PGCs is affected by the gonadal somatic cells. When female PGCs are transferred to male embryos, it is possible that they differentiate to W-spermatogonia. However, the relationship development between PGCs and gonads has not been investigated. At stage 12-15 of incubation of fertilized eggs, donor PGCs, which were taken from the blood vessels of donor embryos, were injected into the blood vessels of recipient embryos. The gonads were removed from embryos that died after 16 days of incubation and from newly hatched chickens and organs were examined for morphological and histological features. The survival rate of the treated embryos was 13.6% for homo-sexual transfer of PGCs (male PGCs to male embryo or female PGCs to female embryo) and 28.9% for hetero-sexual transfer PGCs (male PGCs to female embryo or female PGCs to male embryo) when determined at 15 days of incubation. The gonads of embryos arising from homo-sexual transfer appeared to develop normally. In contrast, embryos derived from hetero-sexual transfer of PGCs had abnormal gonads as assessed by histological observation. These results suggest that hetero-sexual transfer of PGCs may influence gonadal development early-stage embryos.

Potential application of sperm bearing female-specific chromosome in chickens

This paper reviews studies on sex reversal experiments in chickens, production of sperm bearing a female-specific chromosome, its application for poultry resources and finally a mechanism of sex differentiation of gonads in the chicken.

Differentiation of female primordial germ cells in the male testes of chicken (Gallus gallus domesticus)

In our previous studies, we demonstrated that female primordial germ cells (PGCs) have the ability to differentiate into W chromosome-bearing (W-bearing) spermatozoa in male gonads of germline chimeric chickens. In this study, to investigate the differentiation pattern of female PGCs in male gonads in chickens, three germline chimeric chickens were generated by injecting female PGCs into the male recipient embryos. After these male chimeras reached sexual maturity, the semen samples were analyzed for detecting W-bearing cells by PCR and in situ hybridization analyses. The results indicated that the female PGCs had settled and differentiated in their testes. A histological analysis of the seminiferous tubule in those chimeras demonstrated that the W-bearing spermatogonia, spermatocytes, and round spermatids accounted for 30.8%, 32.7%, and 28.4%, respectively. However, the W-bearing elongating spermatid was markedly lower (7.7%) as compared to the W-bearing round spermatid. The W-bearing spermatozoa were hardly ever observed (0.2%). We concluded that although female PGCs in male gonads are capable of passing through the first and second meiotic division in adapting themselves to a male environment, they are hardly complete spermiogenesis.

Development of Novel Markers for the Characterization of Chicken Primordial Germ Cells

This study was undertaken to develop novel markers for chicken primordial germ cells (PGCs), which are of potentially enormous value in transgenic research. Gonadal cells collected from 5.5-day-old chicken embryos were cultured in a Dulbecco's minimal essential medium and the PGC colonies formed during the primary culture period were subcultured three times. Characterization of the PGCs with the candidate marker reagents was performed on the mixed cell population 2 hours after seeding, after the primary culture period (day 10), and after the third passage (day 40). Mouse embryonic stem (ES) cells were used as controls. The cytochemical reagents investigated included periodic acid-Schiff (PAS) stain, antibodies to stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), antibody to epithelial membrane antigen (EMA)-1, antibodies to integrins alpha6 and beta1, several lectins (Solanum tuberosum agglutinin [STA], Dolichos biflorus agglutinin [DBA], concanavalin A agglutinin [ConA], and wheat germ agglutinin [WGA]), and double staining with antibodies to SSEA-1, SSEA-3, SSEA-4, integrin alpha6, or integrin beta1 and then with the lectin STA. Densitometric quantification was used to identify PGC-specific markers. The results showed that chicken PGCs were stained selectively by PAS and by antibodies to SSEA-1, SSEA-3, SSEA-4, EMA-1, integrin alpha6, and integrin beta1. The control mouse ES cells reacted with PAS, anti-SSEA-1, and anti-EMA-1 antibodies, as well as with antibodies to integrins alpha6 and beta1, but not with antibodies to SSEA-3 and SSEA-4. Chicken PGCs reacted with the lectins STA and DBA, but mouse ES cells reacted with STA and WGA. The results of double staining of PGC colonies subcultured three times showed that the intensity of staining was not altered by concomitant use of the marker reagents. This study demonstrated that, in addition to PAS and antibodies to SSEA-1 and EMA-1, new specific markers of chicken PGCs are recognized by the lectins STA and DBA and by antibodies to SSEA-3 and SSEA-4 and integrins alpha6 and beta1. Double staining using these newly developed markers might be the method of choice for rapid characterization of chicken PGCs.

Improved germline transmission in chicken chimeras produced by transplantation of gonadal primordial germ cells into recipient embryos

In the avian species, germline chimera production could be possible by transfer of donor germ cells into the blood vessel of recipient embryos. This study was conducted to establish an efficient transfer system of chicken gonadal primordial germ cells (gPGCs) for producing the chimeras having a high capacity of germline transmission. Gonadal PGCs retrieved from 5.5-day-old embryos (stage 28) of Korean Ogol chicken (KOC with i/i gene) were transferred into the dorsal aorta of 2.5-day-old embryos (stage 17) of White Leghorn chicken (WL with I/I gene). Prospective evaluations of whether culture duration (0, 5, or 10 days) and subsequent Ficoll separation of gPGCs before transfer affected chimera production and germline transmission in the chimeras were made while retrospective analysis was conducted for examining the effect of chimera sexuality. A testcross analysis by artificial insemination of presumptive chimeras with adult KOC was performed for evaluating each treatment effect. First, comparison was made for evaluating whether experimental treatments could improve chimera production, but none of the treatments were significantly (P = 0.6831) influenced (5.1%-14.4%). Second, it was determined whether each treatment could enhance germline transmission in produced chimeras. More (P < 0.0001) progenies with black feathers (i/i) were produced in the germline chimeras derived from the transfer of 10-day-cultured gPGCs than from the transfer of 0- or 5-day-cultured gPGCs (0.6%-7.8% vs. 10.7%-49.7%). Ficoll separation was negatively affected (P < 0.0001), whereas there was no effect in chimera sexuality (P = 0.6011). In conclusion, improved germline transmission of more than a 45% transmission rate was found in chicken chimeras produced by transfer of 10-day-cultured gPGCs being separated without Ficoll treatment.

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.

Strain preference in donor and recipient for production of W-bearing sperm in mixed-sex germline chimeric chickens

To elucidate the strain preference in donor and recipient for the production of W-bearing sperm, mixed-sex germline chimeric chickens were produced. The combination of donor and recipient was White Leghorn (WL) and Barred Plymouth Rock (BPR), and vice versa. Four sets of mixed-sex chimeras that had the male phenotype at sexual maturity were subjected to analysis: group 1, a female WL donor and a male BPR recipient; group 2, a male WL donor and a female BPR recipient; group 3, a female BPR donor and a male WL recipient; group 4, a male BPR donor and a female WL recipient. The mean number of W-bearing sperm detected by in situ hybridization among 10000 sperm observed was 135, 158, 26 and 71 in groups 1, 2, 3 and 4, respectively. The number in group 1 was significantly higher than that of group 3 (P<0.05). And the number in group 2 was significantly higher than those of groups 3 and 4 (P<0.05). It is suggested that the combination of a WL donor and a BPR recipient produced W-bearing sperm more efficiently than the reverse combination.

Sex reversal of germ cell gametogenesis in chimeras of Pleurodeles waltl (urodele amphibian): genetic and immunogenetic demonstration using tolerance or rejection of skin grafts

Viable chimeras were constituted with two cranial and caudal complementary pieces of embryos derived from two distinct histocompatible AA and BB strains, which were incompatible with each other. The embryonic gonads of the resulting chimeras constituted two homo- or heterosexual territories. In most heterosexual chimeras, the testicular territory sex reversed the ovarian territory. The offspring analysis of a male chimera conclusively proved that ZW germ cells derived from the posterior female piece differentiated into spermatozoa. Nevertheless, the opposite situation was also demonstrated with a female chimera in which ZZ germ cells derived from the anterior male piece differentiated into oocytes. These gametogenesis reversions were tested by genetic and immunogenetic analyses of chimera offspring. The phenomenon of tolerance or rejection of skin allo- and autograft was used as a marker of origin of the chimera germ cells, which had produced the offspring. Moreover, in the first stage of the study, the origin of the pieces of adult chimeras was determined using skin grafts. During this stage, the embryonic tolerance was confirmed by the acquisition of four pieces of pairs of chimeras, and by the preservation of skin immunogenicity that was derived from each piece of the chimeras.

Spermiogenesis in commercial poultry species: anatomy and control

Spermatogenesis is a complicated process dependent upon several factors. Formation of a testis requires the interaction of gene-products and hormones (androgens) on pluripotent tissue. In birds, the female is the heterogametic (ZW) sex, but W chromosomal genes do not influence gonadal development in a way similar to the SRY gene on the mammalian Y chromosome. However, autosomal genes such as SRY-like HMG box gene 9 (SOX9) may influence gonadal development. Hormones affect development; male gonads subjected to estrogen form an ovotestis, whereas ovaries exposed to aromatase inhibitors form an atypical testis. Sertoli cell numbers are set early in spermiogenesis, possibly under the influence of follicle-stimulating hormone and thyroid hormone, and this may determine the number of gonial cells that can be supported. Sertoli cells make a number of substances that affect testicular development and function, particularly anti-Müllerian hormone, which inhibits female oviduct formation from the Müllerian anlage, inhibits aromatase activity to stop estrogen production, and possibly stimulates androgen production by Leydig cells. Undifferentiated primordial germ cells (PGC) migrate to the testis and are converted to spermatogonia by factors from gonadal ridge tissue and androgens. The PGC of males in the ovary form oocytes of Z genotype, whereas the female PGC in males form mostly Z sperm (with a few of W genotype). Transmission electron microscopy micrographs of turkey testis are presented, and control of spermatogenesis by hormones and cytokines is discussed. This discussion includes follicle-stimulating hormone, luteinizing hormone, inhibin, activin, follistatin, tumor necrosis factor-alpha, growth factors such as transforming growth factor-beta, interleukins, and interferon. Although information concerning paracrine and autocrine regulation of the avian testis by these substances is sparse, much can be learned from mammalian studies, in which putative roles of each of these substances have been established. How Sertoli cells cause directed apoptosis of spermatogonia using the Fas-ligand, Fas-receptor pathway is reviewed, as well as ways to circumvent this process. A possible role for ubiquitin concerning prevention of heat-induced damage to the testis is presented.

Inter embryonic (homo- or hetero-sexual) transfer of primordial germ cells between chicken embryos

Chicken primordial germ cells (PGCs) collected from thecirculating blood in embryonic vessels at stage 13-15 were inter-embryonically, homo- or hetero-sexually,transferred to the blood vessels of recipient embryosat the same stage of development. Approximately 30%of the embryos treated with hetero-sexual transfer of PGCs had abnormal gonads, showing ovotestis likeorgans. In this case, some of these reversed gonadswere considered to be dependent upon the ratio of thenumber of PGCs from donor to recipient embryos. Oneof the treated embryos possessed completely reversedorgans. Therefore, the introduction of exogenousembryonic vessels was thought to be also useful forproducing transgened gonads.

Production of donor-derived offspring by transfer of primordial germ cells in Japanese quail

We transfused concentrated primordial germ cells (PGCs) of the black strain (D: homozygous for the autosomal incomplete dominant gene, D) of quail into the embryos of the wild-type plumage strain (WP: d+/d+) of quail. The recipient quail were raised until sexual maturity and a progeny test of the putative germline chimeras was performed to examine the donor gamete-derived offspring (D/d+). Thirty-one percent (36/115) of the transfused quail hatched and 21 (13 females and 8 males) of them reached maturity. Five females and 2 males were germline chimeras producing donor gamete-derived offspring. Transmission rates of the donor derived gametes in the chimeric females and males were 1.8-8.3% and 2.6-63.0%, respectively. Germline chimeric and the other putative chimeric males were also test-mated with females from the sex-linked imperfect albino strain (AL: d+/d+, al/W, where al indicates the sex-linked imperfect albino gene on the Z chromosome, and W indicates the W chromosome) for autosexing of W-bearing spermatozoa: No albino offspring were born.

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 developmental origin of primordial germ cells and the transmission of the donor-derived gametes in mixed-sex germline chimeras to the offspring in the chicken

A novel system has been developed to determine the origin and development of primordial germ cells (PGCs) in avian embryos directly. Approximately 700 cells were removed from the center of the area pellucida, the outer of the area pellucida, and the area opaca of the stage X blastoderm (Eyal-Giladi and Kochav, 1976; Dev Biol 49:321-337). When the cells were removed from the center of the area pellucida, the mean number of circulating PGCs per 1 microliter of blood was significantly decreased to 13 (P < 0.05) in the embryo at stage 15 (Hamburger and Hamilton, 1951: J Morphol 88:49-92) as compared to intact embryos of 51. When the removed recipient cells from the center of the area pellucida were replenished with 500 donor cells, no reduction in the PGC number was observed. The removal of cells from the outer of area pellucida or from the area opaca had no effect on the number of PGCs. When another set of the manipulated embryos were cultured ex vivo to hatching and reared to sexual maturity, the absence of germ cells and the degeneration of seminiferous tubules were observed in resulting chickens derived from the blastoderm from which the cells were removed from the center of the area pellucida. Chimeric embryos produced by the male donor cells and the female recipient contained the female-derived cells at 97.2% in the whole embryo and 94.3% in the erythrocytes at 5 days of incubation. At 5-7 days of incubation, masculinization was observed in about one half of the mixed-sex embryos. The proportions of the female-derived cells in the whole embryo and in the erythrocytes were 76.5% and 80.2% at 7 days to 55.7% and 62.5% at 10 days of incubation, respectively. When the chimeras reached their sexual maturity, they were test mated to assess donor contribution to their germline. Five of six male chimeras (83%) and three of five female chimeras (60%) from male donor cells and a female recipient embryo from which 700 cells at the center of area pellucida were removed were germline chimeras. Three of the five male germline chimeras (60%) and one of the three female germline chimeras (33%) transmitted exclusively (100%) donor-derived gametes into the offspring. When embryonic cells were removed from the outer of area pellucida or area opaca, regardless of the sex combination of the donor and the recipient, the transmission of the donor-derived gametes was essentially null. The findings in the present studies demonstrated, both in vivo and in vitro, that the PGCs originate in the central part of the area pellucida and that the developmental fate to germ cell (PGCs) had been destined at stage X blastoderm in chickens.