Primordial germ cells (PGCs) as a tool for creating transgenic chickens

Establishment of the Primary Avian Gonadal Somatic Cell Lines for Cytogenetic Studies

Simple Summary

We developed a simple method for primary somatic cell culture establishment from the ovaries of the great tits and testes of ten Passerine species. The ovary-derived cell cultures were cultivated until the tenth passage without any noticeable decrease in their proliferative activity, while testis-derived cell cultures demonstrated a decreased proliferation potential. However, sufficient material was available from both cell cultures originating from the ovary and testis to make excellent mitotic metaphase chromosomal preparations. We demonstrated the high efficiency of electroporation for genetic modification of the ovary-derived cell line. Thus, the established ovary-derived cell line could be efficiently used in cytogenetic and genomic studies.

Abstract

The last decade was marked by a steep rise in avian studies at genomic and cellular levels. Cell lines are important tools for in vitro studies in cell biology and cytogenetics. We developed a simple method of primary somatic cell culture establishment from the ovaries of the great tits (Parus major) and testes of ten Passerine species, characterized the cellular composition of the ovary-derived lines using RT-PCR and immunolocalization of the tissue-specific markers and tested the efficiency of two methods of genetic transformation of the ovary-derived cell line. We found that the ovary-derived cell cultures of the great tit were composed of fibroblasts mainly, but also contained interstitial and granulosa cells. They were cultivated until the 10th passage without any noticeable decrease in their proliferative activity. The testis-derived cell cultures had lower proliferative potential. However, both ovary- and testis-derived cell cultures provided enough material for high quality mitotic metaphase chromosome preparations. The efficiency of its transduction with lentivirus containing a GFP reporter was very low, while electroporation with episomal vectors expressing GFP resulted in a high yield of GFP-positive cells. The proposed method could be used for the generation of high quality material for various cytogenetic and genomic studies.

Comparison of the Transcriptomic and Epigenetic Profiles of Gonadal Primordial Germ Cells of White Leghorn and Green-Legged Partridgelike Chicken Embryos

The Green-legged Partridgelike fowl is a native, dual-purpose Polish chicken. The White Leghorn has been intensively selected for several decades to mainly improve reproductive traits. Primordial germ cells (PGCs) represent the germline stem cells in chickens and are the only cells that can transfer the information stored in the genetic material from generation to generation. The aim of the study was to carry out a transcriptomic and an epigenetic comparison of the White Leghorn and Green-legged Partridgelike gonadal PGCs (gPGCs) at three developmental stages: days 4.5, 8, and 12 of the embryonic development. RNA and DNA were isolated from collected gPGCs. The RNA was further subjected to microarray analysis. An epigenetic analysis was performed based on the global methylation analysis and qMSP method for the particular silenced genes demonstrated in transcriptomic analysis. Statistically significant differences between the gPGCs from both breeds were detected on the day 8 of embryonic development. Global methylation analysis showed significant changes at the methylation level in the White Leghorn gPGCs on day 8 of embryonic development. The results suggest faster development of Green-legged Partridgelike embryos as compared to White Leghorn embryos. Changes in the levels of gene expression during embryonic development are determined by genetic and environmental factors, and this variability is influenced by breed and gender.

Concentration and total number of circulating primordial germ cells in Green-legged Partridgelike chicken embryos

The Green-legged Partridgelike fowl is an old Polish indigenous breed of chicken. Primordial germ cells (PGCs) are one of the best sources of precursor cells that can be used for the conservation and proliferation of the endangered breeds of bird. Initially, the chicken PGCs colonize at the anterior extraembryonic region called "germinal crescent," and after the establishment of blood vascular circulation, they temporally circulate via the embryonic blood vascular system along with embryonic blood cells. They further colonize at the microcapillary networks of both right and left future gonadal regions. Subsequently, they migrate interstitially to reach gonadal anlages, where they begin to differentiate and eventually develop into the future ova or sperm. The basic knowledge regarding the concentration and the total number of circulating PGCs (cPGCs) throughout their circulating phase in the early embryonic stages is crucial for providing an insight into the mechanisms by which they circulate and colonize at the capillary networks of left and right future gonadal regions in each developmental stage. The present study aims to determine the most efficient developmental stage that is suitable to collect cPGCs. The concentration of cPGCs was directly measured, and total volume of embryonic blood was calculated based on the concentration of PKH26-stained embryonic blood cells which were injected 10 min before the blood sampling process in the same embryo during each stage of embryonic development from stage 13 Hamburger and Hamilton (HH; Hamburger and Hamilton, 1951) to 16 HH. Analysis of whole embryonic bloodstream revealed that at stage 14 HH of embryonic development, peak total number of cPGCs (386.3 cells/μL) and peak concentration of cPGCs (18.6 cells/μL) were observed. Later, there was a decrease in concentration, suggesting that the cPGCs might be trapped gradually by the capillary networks at the future gonadal regions after stage 15 HH.

Secreting oviduct epithelial cells of Coturnix coturnix japonica (QOEC) and changes to their proteome after nonviral transfection

The quail oviduct (Coturnix c. japonica) is a natural candidate avian bioreactor, while the secretive quail oviduct epithelial cells (QOECs) are potential in vitro producers of recombinant proteins and vaccines. In view of the need for highly performing and transformable cell lines, QOEC may potentially act as an alternative bioreactor platform to the existing ones, for example, to the Chinese hamster ovary. The aim of this work was to characterize QOECs and their response to nucleofection with a nonviral plasmid DNA carrying the human interferon-α 2a gene (hIFNλ2a), in vitro. Primary QOEC cultures from laying quails (10-15 weeks old) were characterized by their proliferation rate, doubling time, and multilineage differentiation. Electroporation to cell nuclei (nucleofection) was used to deliver nonviral plasmid DNA containing a reporter GFP and hIFN under the ovalbumin promoter. The posttransfection analysis included polymerase chain reaction, Western blot analysis, and liquid chromatography coupled to tandem mass spectrometry. QOEC showed a typical epithelial characteristic in a primary 2D monolayer culture system and retained secretive potential up to the first passage. QOEC showed differentiation into osteoblastic lineage after stimulation. The nucleofection mean efficiency was low (2.3%). Differences of up to 10% in the proteomic profiles between nontransfected and transfected QOEC were found, the most important of these were related to the absence of keratins and cell-adhesion proteins in the transfected QOEC. Concluding, with the practical information provided here, QOEC have the potential to serve as an avian secreting cellular platform. QOEC may be further transformed to cell lineage to meet the requirement for a stable, electrocompetent, and transfectable model. The first proteomic comparison of QOEC delivered in this study showed, in the majority, a stable proteome of the nontransfected vs transfected QOEC.

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.

Obtaining chicken primordial germ cells used for gene transfer: in vitro and in vivo results

Recently, several attempts have been made to create a generation of transgenic chickens via chimeric intermediates produced by primordial germ cells (PGCs) transfer. This study aimed to compare the influences of different chicken PGCs isolated from circulating blood (bPGCs) or gonads (gPGCs), purification (ACK, Percoll or trypsin) and transfection methods (electroporation or lipofection) on the expression of transgenes in vitro and the migration of modified donor cells to the recipient gonads. The highest average frequency of pEGFP-N1 plasmid-transfected bPGCs (75.8 %) was achieved with Percoll density gradient centrifugation and electroporation. After ammonium chloride-potassium (ACK) treatment and lipofection, in vitro transgene expression was only detected in 35.2 % of bPGCs. Chimeric chickens were produced from these purified, transfected and cultured cells, and the transgene was detected in the gonads of 44 and 42 % of the recipient embryos that had been injected with bPGCs and gPGCs, respectively. These data confirmed that the combination of PGC purification via Percoll centrifugation and electroporation was an effective method for producing transgenic chickens. Subsequently, we used this method with expression vectors for gene hIFNα 2a/hepatitis B virus surface antigen (HBsAg) under the control of the ovalbumin promoter to generate G0 transgenic chickens. Consequently, we observed that 4.9 % of the hens and 3.5 % of the roosters carried the hIFNα 2a gene, whereas 16.7 % of the hens and 2.4 % of the roosters carried the HBsAg gene, thus undisputedly confirming the exceptional effectiveness of the applied methods.