23Scalable production of avian suspension cell exhibits a valuable potential on 24 therapeutic application by producing recombinant protein and as the substrate for virus 25 growth. This study sought to establish a system with chemically defined components 26 for three-dimensional (3D) culture of chicken primordial germ cells (cPGCs), a 27 pluripotent avian cell type. cPGCs were cultured in medium supplemented with the 28 functional polymer FP003. Viscoelasticity was low in this medium, and cPGCs did not 29 sediment, and consequently their expansion was improved. The total number of cPGCs 30 increased by 17-fold after 1 week of culture in 3D-FAot medium, an aseric chemically 31 defined medium containing FP003, indicating that this medium enhances the expansion 32 of cPGCs. Moreover, cPGC cell lines stably expressed the germline-specific reporter 33 VASA:tdTOMATO, as well as other markers of cPGCs, for more than 1 month upon 34 culture in 3D-FAot medium, indicating that the characteristics of these cells are 35 maintained. cPGCs harboring both PGK:EGFP and VASA:tdTOMATO robustly 36 expressed both fluorescent proteins upon culture in 3D-FAot, suggesting that this 37 approach is perspective for recombinant protein production. In summary, this novel 3D38 culture system can be used to efficiently expand cPGCs in suspension without 4 39 mechanical stirring or loss of cellular properties. This system provides a platform for 40 large-scale culture of cPGCs in industry. 41 42 Keywords: chicken; primordial germ cell; 3D culture; FP003; chemically defined 43 medium 44 45 Introduction 46 A three-dimensional (3D) sphere cell culture system that does not require 47 mechanical stirring or agitation was established using the properties of a polysaccharide 48 polymer [1]. Moreover, 3D culture systems enable mammalian and human embryonic 49 stem cells, induced pluripotent stem cells, and hepatocytes derived from these cells to 50 float in the culture medium [2-4]. In traditional medium, cells eventually settle on the 51 bottom of the culture dish due to the effect of gravity and may subsequently lose critical 52 properties. Preventing cells attaching to the surface of the dish would help to overcome 53 such problems and enable efficient utilization of culture space and resources. In 54 addition, cells can be cultured on a large scale using 3D systems. Suspension cells could 55 be potentially cultured in large-volume bioreactors using 3D culture medium to produce 5 56 a large number of cells for industrial manufacture of recombinant proteins.
57Recombinant proteins have many therapeutic purposes, and consequently several 58 systems have been established for their industrial production. Escherichia coli has been 59 used to produce recombinant proteins because it can be easily cultured and is amenable 60 to genetic modification. However, the production of recombinant proteins using this 61 system is hampered by a lack of post-translational modifications (PTMs) and the risk 62 of endotoxin contamination [5]. Recombinant proteins are a...