Tae Sub Park

Derivation and characterization of pluripotent embryonic germ cells in chicken.

Embryonic germ (EG) cell lines established from primordial germ cells (PGCs) are undifferentiated and pluripotent stem cells. To date, EG cells with proven germ‐line transmission have been completely established only in the mouse with embryonic stem (ES) cells. We isolated PGCs from 5.5‐day‐old (stage 28) chicken embryonic gonads and established a putative chicken EG cell line with EG culture medium supplemented with stem cell factor (SCF), leukemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF), interleukin‐11 (IL‐11), and insulin‐like growth factor‐I (IGF‐I). These cells grew continuously for ten passages (4 months) on a feeder layer of mitotically active chicken embryonic fibroblasts. After several passages, these cells were characterized by screening with the periodic acid‐Schiff reaction, anti‐SSEA‐1 antibody, and a proliferation assay. The chicken EG cells maintained characteristics of gonadal PGCs and undifferentiated stem cells. When cultured in suspension, the chicken EG cells successfully formed an embryoid body and differentiated into a variety of cell types. The chicken EG cells were injected into stage X blastodermal layer and produced chimeric chickens with various differentiated tissues derived from the EG cells. Chicken EG cells will be useful for the production of transgenic chickens and for studies of germ cell differentiation and genomic imprinting. Mol. Reprod. Dev. 56:475–482, 2000.

PRODUCTION OF GERMLINE CHIMERIC CHICKENS BY TRANSFER OF CULTURED PRIMORDIAL GERM CELLS

Primordial germ cells (PGCs) from stage 27 (5.5‐day‐old) Korean native ogol chicken embryonic germinal ridges were cultured in vitro for 5 days. As in in vivo culture, these cultured PGCs were expected to have already passed beyond the migration stage. Approximately 200 of these PGCs were transferred into 2.5‐day‐old white leghorn embryonic blood stream, and then the recipient embryos were incubated until hatching. The rate of hatching was 58.8% in the manipulated eggs. Six out of 60 recipients were identified as germline chimeric chickens by their feather colour. The frequency of germline transmission of donor PGCs was 1.3–3.1% regardless of sex. The stage 27 PGCs will be very useful for collecting large numbers of PGCs, handling of exogenous DNA transfection during culture, and for the production of desired transgenic chickens.

Improved Germline Transmission in Chicken Chimeras Produced by Transplantation of Gonadal Primordial Germ Cells into Recipient Embryos

Abstract 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.

Production of germline chimeras by transfer of chicken gonadal primordial germ cells maintained in vitro for an extended period

We previously reported that germline chimeras could be produced by transfer of chicken gonadal primordial germ cells (gPGCs) cultured for a short term (5 days). This study was subsequently undertaken to examine whether gPGCs maintained in vitro for an extended period could retain their specific characteristics to induce germline transmission. Chicken (White Leghorn, WL) gPGCs were retrieved from embryos at stage 28 (5.5 days of incubation) and continuously cultured for 2 months in modified Dulbeccos minimal essential medium without subpassage and changing of the feeder cell layer. After the identification of gPGC characteristics using Periodic acid-Shiffs (PAS) reaction and anti stage-specific embryonic antigen-1 (SSEA-1) antibody staining at the end of the culture, cultured gPGCs were injected into the dorsal aorta of Korean Ogol Chicken (KOC) recipient embryos at stage 17 (2.5 days of incubation). Nineteen chickens (13 males and 6 females) were hatched, grown to sexual maturity, and subsequently subjected to testcross analysis employing artificial insemination with adult KOC. Of these, four (three males and one female) hatched chickens with white coat color. The percentage of germline chimerism was 21% (4/19). The results of this study demonstrated that gPGCs could maintain their specific characteristics for up to 2 months in vitro, resulting in the birth of germline chimeras following transfer to recipient embryos.

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 Dulbeccos 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 α6 and β1, 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 α6, or integrin β1 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 α6, and integrin β1. The control mouse ES cells reacted with PAS, anti‐SSEA‐1, and anti‐EMA‐1 antibodies, as well as with antibodies to integrins α6 and β1, 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 inte‐grins α6 and β1. Double staining using these newly developed markers might be the method of choice for rapid characterization of chicken PGCs.

Targeted gene knockout in chickens mediated by TALENs

Significance Targeted gene knockout by editing specific loci in genome has revolutionized the field of functional genomics. Transcription activator-like effector nucleases (TALENs) are representative next-generation platforms for customized genomic editing in transgenic animals, as well as cultured cells in vitro. In this study, in combination with chicken primordial germ cell line with germ-line transmission capacity, we generated the ovalbumin gene knockout chickens by TALEN-mediated gene targeting. Our results extended the application of state-of-the-art TALEN technology from experimental animals to farm animals. As TALEN-mediated knockout chickens are genetically modified but nontransgenic, without genomic integration of any exogenous transgenes, specific genomic editing with TALENs could expedite the generation of genetically engineered chickens for agriculturally practical applications as well as for model animals. Genetically modified animals are used for industrial applications as well as scientific research, and studies on these animals contribute to a better understanding of biological mechanisms. Gene targeting techniques have been developed to edit specific gene loci in the genome, but the conventional strategy of homologous recombination with a gene-targeted vector has low efficiency and many technical complications. Here, we generated specific gene knockout chickens through the use of transcription activator-like effector nuclease (TALEN)-mediated gene targeting. In this study, we accomplished targeted knockout of the ovalbumin (OV) gene in the chicken primordial germ cells, and OV gene mutant offspring were generated through test-cross analysis. TALENs successfully induced nucleotide deletion mutations of ORF shifts, resulting in loss of chicken OV gene function. Our results demonstrate that the TALEN technique used in the chicken primordial germ cell line is a powerful strategy to create specific genome-edited chickens safely for practical applications.

MicroRNA-mediated posttranscriptional regulation is required for maintaining undifferentiated properties of blastoderm and primordial germ cells in chickens

MicroRNAs (miRNAs) play a critical role in determining the differentiation fate of pluripotent stem cells and germ cells in mammals. However, the mechanism(s) of miRNA-mediated posttranscriptional regulation with regard to lineage specification and differentiation in chick development require further investigation. Therefore, we conducted miRNA expression profiling to explore specific miRNA signatures in undifferentiated blastoderm and primordial germ cells (PGCs). We identified seven miRNAs that are highly expressed in blastoderm and 10 that are highly expressed in PGCs. In this study, miR-302a and miR-456 for blastoderm and miR-181a* for PGCs were analyzed further for their target transcripts and regulatory pathways. Both miR-302a and miR-456 bound directly to the sex-determining region Y box 11 transcript and could act as posttranscriptional coregulators to maintain the undifferentiated state of the chicken blastoderm through the suppression of somatic gene expression and differentiation. Moreover, miR-181a* showed a bifunctional role in PGCs by binding to two different transcripts. miR-181a* inhibited the somatic differentiation of PGCs by silencing homeobox A1 expression. Additionally, miR-181a* prevented PGCs from entering meiosis through the repression of the nuclear receptor subfamily 6, group A, member 1 transcript. Collectively, our data demonstrate that in chickens miRNAs intrinsically regulate the differentiation fate of blastoderms and PGCs and that the specific timing of germ cell meiosis is controlled through miRNA expression.

A Testis-Mediated Germline Chimera Production Based on Transfer of Chicken Testicular Cells Directly into Heterologous Testes

Abstract In this study, we proposed a testis-mediated germline chimera production system based on the transplantation of testicular cells directly into heterologous testes. The testicular cells of juvenile (4-wk-old) or adult (24-wk-old) Korean Ogol chickens with a recessive pigmentation inhibitory gene, with or without prior culture, were injected (2 × 107 cells/head) into the seminiferous tubules of juvenile or adult recipients with White Leghorn with a dominant pigmentation inhibitory gene in a 2 × 2 factorial arrangement. The localization of transplanted cells into the inner space of the seminiferous tubules was confirmed within 24 h after injection. Subsequent testcross analyses showed that 7.8% (5/64) of the recipients had chimeric status in their testes. The periods of time from transfer to hatching of the first progeny with black feathers were 38 and 45 days for adult cells transplanted into an adult recipient, 188 days for adult cells into a juvenile recipient, and 137 days for juvenile cells into a juvenile recipient. Culture of the testicular cells derived both colony-forming and monolayer-forming cells. The colony-forming cells were stained positively for periodic acid Schiff solution, and further reacted with anti-SSEA-1, anti-SSEA-3, and anti-SSEA-4 antibodies both before and after culture for 15 days. In conclusion, it may be possible to develop the testis-mediated germline chimera production technique, which extends the feasibility of genetic manipulations in avian species.

Production of Biofunctional Recombinant Human Interleukin 1 Receptor Antagonist (rhIL1RN) from Transgenic Quail Egg White

Oviduct-specific expression of heterologous recombinant proteins in transgenic birds is a promising technology for the large-scale production of therapeutic proteins in eggs. We describe the production of recombinant human interleukin 1 receptor antagonist (rhIL1RN) in the eggs of transgenic quails. To drive tissue-specific expression of rhIL1RN, a 1.35-kb fragment of the chicken ovalbumin promoter, which contains both the steroid-dependent regulatory element and the negative regulatory element, was used. A transgenic quail was generated by microinjection of a concentrated stock of lentivirus into stage X blastodermal cells. A single copy of the transgene was integrated into the seventh intron of the gene for conserved oligomeric golgi complex protein 5 (COG5) on chromosome 1. As expected, rhIL1RN expression was restricted to oviductal tissue, and the amount of protein deposited in the eggs of homozygous transgenic quails ranged from 88.7 to 233.8 ng/ml. Transgene expression was conserved from the G1 generation to the G4 generation, and there was no evidence of transgene silencing. In a bioassay using the EL4.NOB-1/CTLL-2 coculture system, no significant difference was observed between the egg-produced rhIL1RN and a commercially available rhIL1RN (anakinra).

Migration and Proliferation of Intact and Genetically Modified Primordial Germ Cells and the Generation of a Transgenic Chicken

Abstract This study evaluated gonadal migration and postmigratory proliferation of intact and genetically modified chicken primordial germ cells (PGCs). A randomized, controlled trial was conducted with the gonadal population of PGCs and transgenic chicken production as major parameters. PGCs (0, 90, 900, 1800, or 3000 cells) were transferred into 53-h-old embryos. The percentage of PGCs migrating on Day 6 of development was highest (35.8%) following the transfer of 900 PGCs and did not change with increases in transferred PGCs. The number of migrating PGCs gradually increased (P = 0.0001) as the number of transferred PGCs was increased. Gonadal migration was detected after the transfer of intact and genetically modified PGCs, but prominent decreases in PGC migration (from 21.9% to 0.38%) and chimera ratio (from 0.4 to 0.007) occurred with genetically modified PGCs. However, subsequent vigorous proliferation of the modified PGCs (3.67-fold increase from transferred number) led to the derivation of a germline chimera and produced a transgenic hatchling. In conclusion, the number of migrating PGCs increased as the number of transferred cells increased. Vigorous proliferation after transfer compensated for the decreased migration capacity of genetically modified PGCs and resulted in the production of a transgenic chicken.